Radioactive Waste in Geologic Storage 9780841204980, 9780841206472, 0-8412-0498-5

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Radioactive Waste in Geologic Storage Sherman Fried,

EDITOR

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.fw001

Argonne National Laboratory

Based on a symposium sponsored by the Division of Nuclear Chemistry and Technology at the 176th Meeting of the American Chemical Society, Miami Beach, Florida, September 11-15, 1978.

100

ACS SYMPOSIUM SERIES

AMERICAN

CHEMICAL

WASHINGTON,

D. C .

SOCIETY 1979

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.fw001

L i b r a r y o f Congress CIP D a t a Radioactive waste i n geologic storage. ( A C S symposium series; 100 I S S N 0097-6156) Includes bibliographies and index. 1. Radioactive waste disposal in the g r o u n d — C o n gresses. I. Fried, Sherman Meyer, 1917. II. American Chemical Society. D i v i s i o n of Nuclear Chemistry and Technology. III. Series: American Chemical Society. A C S symposium series; 100. TD898.R333 ISBN 0-8412-0498-5

621.48'38 ACSMC8

79-9754 100 1-344 1979

Copyright © 1979 American Chemical Society All Rights Reserved. T h e appearance of the code at the bottom of the first page of each article i n this volume indicates the copyright owner's consent that reprographic copies of the article may be made for personal or internal use or for the personal or internal use of specific clients. T h i s consent is given o n the condition, however, that the copier pay the stated per copy fee through the Copyright Clearance Center, Inc. for copying beyond that permitted by Sections 107 or 108 of the U . S . Copyright Law. T h i s consent does not extend to copying or transmission by any means—graphic or electronic—for any other purpose, such as for general distribution, for advertising or promotional purposes, for creating new collective works, for resale, or for information storage and retrieval systems. T h e citation of trade names and/or names of manufacturers i n this publication is not to be construed as an endorsement or as approval by ACS of the commercial products or services referenced herein; nor should the mere reference herein to any drawing, specification, chemical process, or other data be regarded as a license or as a conveyance of any right or permission, to the holder, reader, or any other person or corporation, to manufacture, reproduce, use, or sell any patented invention or copyrighted work that may in any way be related thereto. PRINTED IN THE UNITED STATES OF AMERICA

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

ACS Symposium Series Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.fw001

Robert F . G o u l d , Editor

Advisory Board Kenneth B. Bischoff

James P. Lodge

Donald G . Crosby

John L. Margrave

Robert E. Feeney

Leon Petrakis

Jeremiah P. Freeman

F. Sherwood Rowland

E. Desmond Goddard

Alan C. Sartorelli

Jack Halpern

Raymond B. Seymour

Robert A. Hofstader

Aaron Wold

James D. Idol, Jr.

Gunter Zweig

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

FOREWORD

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.fw001

The ACS SYMPOSIUM SERIES was founded in 1974 to provide

a medium for publishing symposia quickly in book form. The format of the Series parallels that of the continuing ADVANCES IN CHEMISTRY SERIES except that in order to save time the papers are not typeset but are reproduced as they are submitted by the authors in camera-ready form. Papers are reviewed under the supervision of the Editors with the assistance of the Series Advisory Board and are selected to maintain the integrity of the symposia; however, verbatim reproductions of previously published papers are not accepted. Both reviews and reports of research are acceptable since symposia may embrace both types of presentation.

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.pr001

PREFACE T t is almost three years since the first American Chemical Society symposium on radioactive waste isolation and management was held in New York. The second symposium in Miami Beach marked an effort to draw attention to the rapidly growing accumulation of information in this field. Interest in the safe disposal of radioactive waste has deepened and strenuous efforts are being made to understand the processes by which radionuclides may migrate (into the biosphere) from a deep geologic repository. This understanding will ultimately make possible a credible safety assessment of any deep geologic storage proposal. Therefore, this symposium focused on the conceptual, chemical, and geological aspects of the radioactive waste isolation program. The work reported in this symposium on "Radioactive Waste in Geological Storage" covers the most recent radioactive waste disposal concepts and proposals as well as the experiments carried out to determine the most important parameters. The first four papers cover the general geologic and hydrologie considerations involved in a deep repository. The following four papers examine the leaching characteristics of the source terms. The remainder of the volume consists of papers on the sorption behavior of various nuclides on minerals, rocks, and clays as it relates to migration and the possible entrance into the biosphere. The work presented here enables us to get a clearer picture of the problems involved in permanent isolation of radioactive wastes from the environment. Chemistry Division

SHERMAN FRIED

Argonne National Laboratory Argonne, IL 60439 January 16, 1978

vii

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

1 The Department of Energy Program for Long-Term Isolation of Radioactive Waste C O L I N A.

HEATH

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch001

Division of Waste Isolation, B-107, U.S. Department of Energy, Washington, DC 20545

I wish to thank the American Chemical Society and its members f o r the opportunity to d i s c u s s with you today the Department of Energy (DOE) program i n r a d i o a c t i v e waste management. This program, which is of vital concern to our country's energy and defense programs, has r e c e n t l y become the t o p i c of newspaper articles, TV shows and much p u b l i c d i s c u s s i o n . I welcome t h i s chance to describe to you some of the activities underway to move the program forward and perhaps answer questions that may have been r a i s e d during all t h i s p u b l i c d i s c u s s i o n . The Department of Energy is charged by the Congress with the r e s p o n s i b i l i t y f o r accepting h i g h - l e v e l r a d i o a c t i v e waste from commercial uses of nuclear power and p r o v i d i n g f o r t h e i r management l e a d i n g to final d i s p o s a l . This final d i s p o s a l must provide i s o l a t i o n of these wastes from the human environment f o r as long as they remain hazardous. At the present time, there is some u n c e r t a i n t y as to what form the r a d i o a c t i v e wastes from the commercial nuclear f u e l c y c l e will take. E a r l y development of the f u e l c y c l e and the power r e a c t o r s now p r o v i d i n g electricity i n s e v e r a l regions of the count r y was undertaken w i t h the assumption that f u e l elements would be p e r i o d i c a l l y removed from operating r e a c t o r s and subjected to r e processing and r e c y c l e whereby unburned uranium and generated plutonium would be recovered from the f u e l elements f o r r e f a b r i c a t i o n and r e c y c l e d back i n t o operating r e a c t o r s . The e f f l u e n t by­products stream from t h i s chemical processing was then to become a h i g h - l e v e l waste which must be processed f o r permanent d i s p o s a l . Within the l a s t two years, major concerns over the p r o l i f e r a t i o n problems a s s o c i a t e d with the r e c y c l e of uranium and plutonium have l e a d the President of the United States to call f o r an indefinite delay i n f u t u r e plans f o r reprocessing pending an e v a l u a t i o n Paper presented at the American Chemical Society Meeting i n Miami Beach, F l o r i d a on September 13, 1978.

This chapter not subject to U.S. copyright. Published 1979 American Chemical Society

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch001

2

RADIOACTIVE WASTE IN GEOLOGIC

STORAGE

of a l t e r n a t i v e s to provide p r o l i f e r a t i o n r e s i s t a n t f u e l c y c l e s . The waste management program i s t h e r e f o r e faced with the p o t e n t i a l that the r a d i o a c t i v e waste from the commercial f u e l c y c l e could be i n the form of spent f u e l elements which have been d e c l a r e d to be waste or i n the form of s o l i d i f i e d h i g h - l e v e l waste produced from the byproducts stream of the r e p r o c e s s i n g p l a n t . The issues surrounding the use or nonuse of r e c y c l e d r e a c t o r f u e l and plutonium are exceedingly complex and w i l l r e q u i r e a cons i d e r a b l e amount of time b e f o r e our s o c i e t y and the i n t e r n a t i o n a l community can reach a d e c i s i o n as to whether or not the r i s k s of p r o l i f e r a t i o n are appropriate to the b e n e f i t s that might be r e ceived from the r e c y c l e of these m a t e r i a l s . In the meantime, the Department of Energy's waste management program needs to get on with the long-neglected job of i d e n t i f y i n g the technology, systems, and f a c i l i t i e s f o r p r o v i d i n g f o r the permanent i s o l a t i o n of these wastes from the human environment. In order not to get bogged down i n the dispute over p r o l i f e r a t i o n , t h e r e f o r e , the program i s proceeding on the b a s i s that the waste could take e i t h e r form. P r e l i m i n a r y e v a l u a t i o n i n d i c a t e s that, even though d i s p o s a l of spent f u e l w i l l r e s u l t i n l a r g e r q u a n t i t i e s of plutonium being placed i n permanent i s o l a t i o n , there i s no o v e r r i d i n g s a f e t y r e a son which suggests that d i s p o s a l of spent f u e l w i l l not be able to be accomplished with any more d i f f i c u l t y than d i s p o s a l of s o l i d i f i e d r a d i o a c t i v e waste i n which the plutonium content has been reduced by r e p r o c e s s i n g . Over the l a s t twenty years, s i g n i f i c a n t research and development has been performed concerning the u l t i m a t e d i s p o s a l mechanism for r a d i o a c t i v e waste. In 1957, the N a t i o n a l Academy of Sciences recommended that deep beds of bedded s a l t be considered as potent i a l l o c a t i o n s f o r the d i s p o s a l of r a d i o a c t i v e waste m a t e r i a l s . Following t h i s recommendation a program of research and development was undertaken by the Atomic Energy Commission (AEC) to exp l o r e t h i s approach. The high point of t h i s program was the opera t i o n of P r o j e c t S a l t Vault i n an abandoned s a l t mine i n Lyons, Kansas. T h i s p r o j e c t placed encapsulated spent f u e l elements from an experimental AEC r e a c t o r i n t o storage holes d r i l l e d i n t o the f l o o r of the mine l o c a t e d i n a s a l t bed. Valuable experimental informat i o n was obtained about the i n t e r a c t i o n between the waste form and the s a l t i n which the waste was emplaced. I t was i n f a c t t h i s experiment, conducted i n 1968, which revealed that i n c l u s i o n s of moisture, or b r i n e , i n the s a l t beds have a tendency to migrate up a thermal gradient towards a heat source placed i n the s a l t . Q u a n t i t i e s of b r i n e were measured as migrating to the deposited waste c a n i s t e r s and the i n t e r a c t i o n of t h i s b r i n e with the c a n i s tered m a t e r i a l was observed. The i n i t i a l experiments conducted i n P r o j e c t S a l t Vault were not extended to provide more d e t a i l e d work. I f i t had been poss i b l e f o r t h i s experiment to have continued to operate s i n c e 1970, we would d e f i n i t e l y have a c o n s i d e r a b l y greater amount of informa-

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch001

1.

HEATH

DOE Isolation

of Radioactive

Waste

3

t i o n concerning the a c t u a l i n t e r a c t i o n s between waste and the bedded s a l t than we p r e s e n t l y have today. U n f o r t u n a t e l y , a dispute between the AEC and the State of Kansas over p o t e n t i a l use of t h i s s i t e as a permanent r e p o s i t o r y l e d the AEC to withdraw from f u r ther operations i n Kansas. In r e t r o s p e c t , one can only r e g r e t that an arrangement was not made whereby the experimental f a c i l i t y would have been permitted to remain i n o p e r a t i o n with a c l e a r understanding that the F e d e r a l Government would make no f u r t h e r a t tempt to q u a l i f y the s i t e as a permanent r e p o s i t o r y . F o l l o w i n g the abandonment of P r o j e c t S a l t V a u l t , a t t e n t i o n of the AEC turned towards the p o s s i b i l i t y o f using a r e t r i e v a b l e surface storage concept f o r temporary storage o f r a d i o a c t i v e waste u n t i l such time as a permanent i s o l a t i o n f a c i l i t y could be d e v e l oped. At the time, t h i s seemed to provide a reasonable and perf e c t l y adequate plan to handle the waste from the commercial i n dustry p a r t i c u l a r l y s i n c e the l a r g e - s c a l e r e p r o c e s s i n g o f commerc i a l nuclear f u e l hadn't s t a r t e d e i t h e r . Since t e n years was env i s i o n e d between s e p a r a t i o n of waste i n a r e p r o c e s s i n g p l a n t and d e l i v e r y f o r u l t i m a t e d i s p o s a l to the F e d e r a l Government, there appeared to be p l e n t y of time. The r e j e c t i o n by the C o u n c i l of Environmental Q u a l i t y and the Environmental P r o t e c t i o n Agency of the impact statement concerning the proposed R e t r i e v a b l e Surface Storage F a c i l i t y (RSSF) made everybody r e a l i z e that a s s e r t i n g the t e c h n i c a l f e a s i b i l i t y of u l timate g e o l o g i c d i s p o s a l was i n s u f f i c i e n t . These agencies took the p o s i t i o n that the RSSF merely put o f f p r o v i d i n g f a c i l i t i e s f o r permanent d i s p o s a l and d i v e r t e d the e f f o r t to another i n t e r i m measure. Dr. Seamans i n one of h i s f i r s t a c t s as the new a d m i n i s t r a tor o f the Energy Research and Development A d m i n i s t r a t i o n (ERDA) decided to withdraw the Environmental Impact Statement (EIS) assoc i a t e d with the RSSF and that establishment of a permanent waste r e p o s i t o r y should be given much greater budget p r i o r i t y . A new l a r g e - s c a l e program was i n i t i a t e d by ERDA i n 1976 with an announcement that each o f 36 s t a t e s contained g e o l o g i c format i o n s which might be s u i t a b l e f o r establishment of permanent waste repositories. ERDA e s t a b l i s h e d an O f f i c e of Waste I s o l a t i o n managed by Union Carbide Corporation i n Oak Ridge, Tennessee, to d i r e c t the program t o e s t a b l i s h the s u i t a b i l i t y of l o c a t i o n s f o r r e p o s i t o r y s i t e s and to develop the necessary technology to design, b u i l d and o b t a i n l i c e n s i n g approval of these permanent geologic f a c i l i t i e s . Two years a f t e r the i n i t i a t i o n of t h i s f u l l s c a l e program, a number of changes have taken place both i n the s i t e s e l e c t i o n and t e c h n i c a l areas, and a t t h i s p o i n t approximatel y two years l a t e r , i t i s a p p r o p r i a t e to provide a s t a t u s r e p o r t of where things stand today. 1

Organization o f DOE s Waste Management Program In May 1978 Secretary S c h l e s i n g e r approved a r e o r g a n i z a t i o n w i t h i n the Department of Energy which e s t a b l i s h e d an O f f i c e of

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch001

4

RADIOACTIVE WASTE IN GEOLOGIC STORAGE

Nuclear Waste Management r e p o r t i n g d i r e c t l y t o the A s s i s t a n t Secr e t a r y f o r Energy Technology. Within the waste i s o l a t i o n program, the major t e c h n i c a l a c t i v i t i e s are c a r r i e d on a t three f i e l d o f f i c e l o c a t i o n s . These l o c a t i o n s and the supporting c o n t r a c t o r s are summarized i n Table I . A c t u a l d i r e c t i o n o f the t e c h n i c a l a c t i v i t i e s w i t h i n the program i s the r e s p o n s i b i l i t y o f f i e l d o f f i c e s . The primary f i e l d o f f i c e i n the waste i s o l a t i o n program i s l o c a t e d i n Columbus, Ohio as a s a t e l l i t e t o the Richland Operations O f f i c e . Co-located with t h i s o f f i c e i s the O f f i c e of Nuclear Waste I s o l a t i o n (ONWI) r e c e n t l y e s t a b l i s h e d by B a t t e l l e Memorial I n s t i t u t e . T h i s o f f i c e d i r e c t s geologic e x p l o r a t i o n outside those areas occupied by e x i s t i n g Department o f Energy r e s e r v a t i o n s . Current ONWI i n v e s t i g a t i o n s are c o n c e n t r a t i n g on v a r i o u s s a l t formations around the country. ONWI w i l l a l s o develop the supporting data base and technology and coordinate the development of waste i s o l a t i o n technology as i t a p p l i e s to a number of p o t e n t i a l l y p o s s i b l e geologic media. The other three major a c t i v i t i e s w i t h i n the waste i s o l a t i o n program are s p e c i f i c t o p a r t i c u l a r s i t e s . We are c u r r e n t l y e v a l u a t i n g the p o t e n t i a l o f deep b a s a l t flows below the Hanford r e s e r v a t i o n i n the State o f Washington. T h i s work i s managed by the Richland Operations O f f i c e and i s being conducted by the Rockwell Hanford Company. An e v a l u a t i o n of a p o t e n t i a l s i t e i s underway i n southeast New Mexico f o r the l o c a t i o n of the Waste I s o l a t i o n P i l o t Plant (WIPP) which i s p r i m a r i l y a f a c i l i t y f o r the placement of transuranium contaminated wastes (TRU) from the defense program. F i n a l l y , a study i s underway to determine the s u i t a b i l i t y o f the Nevada Test S i t e i n southern Nevada which has been used i n the past f o r both surface and underground t e s t i n g o f nuclear weapons, to see i f i t may p o s s i b l y be s u i t a b l e as a p o t e n t i a l permanent r a d i o a c t i v e waste r e p o s i t o r y s i t e . T e c h n i c a l Issues and the DOE T e c h n i c a l Program T e c h n i c a l i s s u e s concerning the placement and d i s p o s a l o f r a d i o a c t i v e waste can be broken i n t o two c a t e g o r i e s . The f i r s t i s sue i s whether o r not we have a v a i l a b l e t o us the technology to provide f o r the safe encapsulation, t r a n s p o r t a t i o n , handling and placement o f r a d i o a c t i v e m a t e r i a l s i n an o p e r a t i n g g e o l o g i c f a c i l ity. The second i s s u e i s , when the f a c i l i t y has been f i l l e d with these m a t e r i a l s and subsequently decommissioned, w i l l the p l a c e ment of these m a t e r i a l s i n geologic formations provide the permanent i s o l a t i o n from the human environment that i s sought. There has been a past p e r c e p t i o n , p a r t i c u l a r l y i n the nuclear community, that the i s s u e s of waste i s o l a t i o n l i e p r i m a r i l y i n the p o l i t i c a l and socio-economic arena and that no r e a l t e c h n i c a l problems remain. I b e l i e v e that t h i s i s c o r r e c t with respect t o the f i r s t category o f i s s u e s , namely, there i s no question that we understand how t o encapsulate, t r a n s p o r t and s a f e l y handle r a d i o -

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch001

1.

HEATH

DOE

Isohtion

of

Radioactive

Waste

5

a c t i v e m a t e r i a l s and the placement of those i n an operating mine i s a technology a v a i l a b l e today. However, I must disagree somewhat with t h i s view of the status of technology when i t comes to the second category, namely, to prove that we can provide f o r permanent i s o l a t i o n of these m a t e r i a l s from the human environment to the s a t i s f a c t i o n of an independent l i c e n s i n g a u t h o r i t y , and the general p u b l i c . We must understand a l l of the processes i n v o l v e d to be a b l e to guarantee to a reasonable degree that these wastes w i l l indeed be permanently i s o l a t e d . Over the l a s t year or so, s e v e r a l papers have been published which have been concerned with the adequacy of the technology f o r p r o v i d i n g f o r permanent i s o l a t i o n of r a d i o a c t i v e wastes. In a l l cases the concerns that have been r a i s e d have focused on the second set of i s s u e s , r a t h e r than the f i r s t , so that the apparent d i s p u t e between those who say that there are no t e c h n i c a l problems and those who say that there are s t i l l some to be solved i s perhaps more a dispute as to what p a r t i c u l a r set of problems are being d e s c r i b e d . These papers have provided a v a l u a b l e mechanism f o r independent peer review from t e c h n i c a l experts not n e c e s s a r i l y a s s o c i a t e d with the waste management program. These review papers have i n c l u d e d the c i r c u l a r by the U.S. G e o l o g i c a l Survey, C i r c u l a r 779, "Geologic D i s p o s a l of High-Level Radioactive Wastes - Earth-Science P e r s p e c t i v e s " ; the review by the Ad-Hoc Committee of Earth S c i e n t i s t s f o r the EPA; reviews by the O f f i c e of Science and Technology P o l i c y and f i n a l l y a review prepared by an Interagency Committee chaired by the O f f i c e of Science and Technology P o l i c y whose paper was r e l e a s e d f o r p u b l i c comment on J u l y 3, 1978. Without going i n t o great d e t a i l about the i s s u e s described i n these papers, I would l i k e to make the p o i n t that the response of the waste i s o l a t i o n program to these papers w i l l be to use them to help us to design a t e c h n i c a l program p l a n to ensure that these i s s u e s are adequately addressed, as indeed they must be, before we can commit r a d i o a c t i v e waste to i r r e t r i e v a b l e permanent d i s p o s a l . I would l i k e , however, to spend a few minutes b r i e f l y summarizing the questions that have been r a i s e d and d e s c r i b e the v a r i o u s p a r t s of the DOE program which are addressing them. In the c o n s t r u c t i o n of a f a c i l i t y c o n t a i n i n g hazardous mat e r i a l s , m u l t i p l e b a r r i e r s are provided between the m a t e r i a l and the human environment. F i g u r e 1 i l l u s t r a t e s s c h e m a t i c a l l y what these b a r r i e r s might be. T h i s f i g u r e i l l u s t r a t e s that by supplying a number of m u l t i p l e and redundant b a r r i e r s , one gains a d d i t i o n a l assurance that true i s o l a t i o n can be maintained f o r very long periods of time. Although i t i s impossible to guarantee abs o l u t e l y f u t u r e events, one does not need absolute c e r t a i n t y that any s i n g l e b a r r i e r w i l l provide r e q u i r e d i s o l a t i o n . The redundancy of b a r r i e r s provides greater assurance that the r e q u i r e d permanent i s o l a t i o n can be achieved. The f i n a l design of a geologic r e p o s i t o r y w i l l employ m u l t i -

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

6

RADIOACTIVE WASTE IN GEOLOGIC STORAGE

Table I ELEMENTS OF DOE'S WASTE ISOLATION

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch001

Lead Contractor

Corresponding Projects

Field Office

PROGRAM

Richland

B a s a l t Program

Rockwell Hanford

Richland-Columbus

ONWI

B a t t e l l e Mem. I n s t . ONWI

Albuquerque

WIPP

Sandia/Westinghouse

Nevada

NTS I n v e s t i g a t i o n s

Sandia/LASL/LLL/USGS

WASTE FORM (P„J

Figure 1.

CONTAINER (P > P

OVERPACK (P ) ft

BUFFER

ROCK

(p )

(ρ*)

n

ISOLATION (p > T

Barriers between waste and biosphere. Protection of biosphere = PWF + ρ + ρ + ρ + ρ + Ρj. ο

0

Β

η

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

1.

HEATH

DOE

Isolation

of Radioactive

Waste

7

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch001

pie b a r r i e r s but the exact form that each might take w i l l depend on the s p e c i f i c c o n d i t i o n s i n the g e o l o g i c a l system that i s f i n a l l y chosen f o r the s i t e . Let me now t u r n to some of the s p e c i f i c areas of concern i d e n t i f i e d i n the v a r i o u s reviews r e f e r r e d to and t r y to i n d i c a t e e x a c t l y how we are addressing these i s s u e s . Waste Form and I n t e r a c t i o n s . Several reviewers have expressed concern over the waste form and the p o t e n t i a l f o r i n t e r a c t i o n s between waste and surrounding m i n e r a l s . Chemical and r a d i o l o g i c a l i n t e r a c t i o n s between the host rock with i t s contained water and e i t h e r the waste form or the c o n t a i n e r might lead to d i s i n t e g r a t i o n of the packaging and p a r t i a l d i s s o l u t i o n i n g of the waste. E a r l y experiments with some of the proposed waste forms have i n d i cated a high r e s i s t a n c e to l e a c h i n g by groundwaters, however, the environment to which these waste forms w i l l be exposed w i l l i n clude a number of f a c t o r s . F i r s t of a l l , the pressure which e x i s t s at the depths at which we are c o n s i d e r i n g p l a c i n g t h i s mat e r i a l w i l l change the p h y s i c a l behavior of l i q u i d s which may e x i s t at those depths. Secondly, concern with the phenomena of b r i n e m i g r a t i o n has r e s u l t e d i n research which i n d i c a t e s that the s o l u t i o n s which might be formed i n the presence of m u l t i p l e ions may l e a d to a much higher degree of c o r r o s i o n than had p r e v i o u s l y been considered. T h e o r e t i c a l i n v e s t i g a t i o n s of these phenomena are c o n t i n u i n g i n a d d i t i o n to which a number of s p e c i f i c i n s i t u experiments are planned. We have over the l a s t s e v e r a l years been planning and conducting e l e c t r i c a l l y heated t e s t s i n both near-surface and deep f a c i l i t i e s i n order to simulate the r a d i o a c t i v e h e a t i n g that w i l l come from deposited waste forms and to l e a r n more about the e f f e c t s of t h i s heat upon the g e o l o g i c media. As more i n f o r m a t i o n i s being obtained about the p o t e n t i a l geochemical i n t e r a c t i o n s between the b r i n e s and these complex s o l u t i o n s , e f f o r t s w i l l be made to d u p l i c a t e s o l u t i o n s i n s i t u to see i f the mechanisms that are being p o s t u l a t e d f o r p o s s i b l e d i s s o l u t i o n and f a i l u r e of c o n t a i n ers w i l l indeed occur. At the present time we are conducting t e s t s with e l e c t r i c a l heaters i n a s a l e mine i n L o u i s i a n a , i n a g r a n i t e formation i n Sweden, i n a g r a n i t e formation i n Nevada and i n shale formations both i n Tennessee and Nevada. E a r l y information developing from these heater t e s t s w i l l be used i n the design of f u r t h e r , more s o p h i s t i c a t e d t e s t s i n which some of these geochemical i n t e r a c t i o n s w i l l be simulated. We are p r e s e n t l y c o n s t r u c t i n g a near-surface t e s t f a c i l i t y at the Hanford r e s e r v a t i o n which w i l l be l o c a t e d i n a b a s a l t i c flow i n the s i d e of a mountain t h e r e . T h i s f a c i l i t y w i l l have e l e c t r i c a l heaters emplaced i n i t i n 1979 and by 1980 we expect to emplace encapsulated c y l i n d e r s c o n t a i n i n g spent f u e l elements there. A second p r o j e c t under development w i l l provide placement of spent f u e l i n s i m i l a r c o n t a i n e r s i n a deep g r a n i t e f a c i l i t y at the

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

8

RADIOACTIVE WASTE IN GEOLOGIC

STORAGE

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch001

Nevada Test S i t e , h o p e f u l l y as e a r l y as 1979. Both of these experiments are s t r i c t l y to e s t a b l i s h a b e t t e r understanding of the i n t e r a c t i o n s between the waste form and the media. In n e i t h e r case i s the experimental l o c a t i o n considered as a permanent d i s posal l o c a t i o n . P r o p e r t i e s of the Host Rock and Rock Mechanics. Considerable information w i l l be needed about the p r o p e r t i e s of the host rock i n t o which m a t e r i a l w i l l be placed. The host rock provides the f i r s t n a t u r a l b a r r i e r to waste migration and s t r o n g l y i n f l u e n c e s the d e t a i l e d design of the engineered r e p o s i t o r y . Some media that e x h i b i t creep or p l a s t i c flow might be capable of s e a l i n g r e p o s i t o r y workings by flow without f r a c t u r e propagation or might s e l f heal i n the event of f a u l t - i n d u c e d f r a c t u r i n g . Creep i s observed i n rock s a l t and to a l e s s e r extent i n some s h a l e s . The creep p r o p e r t i e s of these m a t e r i a l s can be measured i n the l a b o r a t o r y but g e n e r a l l y these observations are not completely accurate because of the l a c k of the r e s t a i n i n g l i t h o s t a t i c pressure. The recent report by the N a t i o n a l Research C o u n c i l of the N a t i o n a l Academy of Sciences e n t i t l e d " L i m i t a t i o n s of Rock Mecha n i c s i n Energy Resource Recovery and Development", h i g h l i g h t e d some of the problems which must be addressed. The rock strength and other mechanical p r o p e r t i e s of the media must be understood both under the impact of the thermal pulse represented by the r e l e a s e of heat from decaying r a d i o a c t i v e waste m a t e r i a l s and the p e r t u r b a t i o n represented by c o n s t r u c t i o n of the mine. The r e s u l t ing thermal s t r e s s e s must be understood i n developing the layout and the allowable r a t e of heat generation from the i n d i v i d u a l canisters. C a l c u l a t i o n a l models are being developed to b e t t e r understand the p r o p e r t i e s and behavior of rock i n response to these s t i m u l i . Measurement of p r o p e r t i e s at depth w i l l probably be r e q u i r e d i n order to get a b e t t e r understanding of the behavior of these rocks. These i s s u e s are important because rock motion or f r a c t u r ing could r e s u l t i n changes to the o v e r l y i n g s t r a t a which might a f f e c t the flow of ground water i n a q u i f e r s o v e r l y i n g the r e p o s i tory. In order to understand t h i s p r o p e r l y , t h e r e f o r e , an extens i v e program of rock mechanics w i l l be conducted. Hydrogeologic Transport. A f t e r a r e p o s i t o r y i s f u l l y loaded and sealed, the most l i k e l y mechanism f o r the r e l e a s e of r a d i o n u c l i d e s to the biosphere would be by t h e i r d i s s o l u t i o n and t r a n s port i n ground water. R e p o s i t o r i e s l o c a t e d below the water t a b l e are expected to f i l l with ground water at some time a f t e r t h e i r s e a l i n g . The r a t e of ground water i n f l o w w i l l depend on the host rock p e r m e a b i l i t y , the depth of the r e p o s i t o r y beneath the water t a b l e , the design of the s h a f t s and bore holes, and the e f f e c t i v e ness of techniques f o r s e a l i n g the shaft and bore h o l e s . After the r e p o s i t o r y has been sealed and l a t e r has become saturated, ground water flow through the r e p o s i t o r y w i l l be i n f l u e n c e d by the

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch001

1.

HEATH

DOE

Isohtion

of

Radioactive

Waste

9

mechanical response of the host rock to the r e p o s i t o r y construct i o n and to the thermal pulse and by n a t u r a l h y d r a u l i c g r a d i e n t s . The c h a r a c t e r i z a t i o n of the hydrology of p o t e n t i a l s i t e s i s as the present time a major item i n our program. In most areas the capab i l i t y of the United Stated G e o l o g i c a l Survey i s being employed to assess the e x i s t i n g h y d r a u l i c gradients i n the areas being considered. The a b i l i t y of the ground water to d i s s o l v e wastes and t r a n s port them from the r e p o s i t o r y depends on the s o l u b i l i t y of the waste forms at the temperatures that the r e p o s i t o r y w i l l reach and the ion-exchange p r o p e r t i e s of the host rock and of a l l media between the r e p o s i t o r y and the p o t e n t i a l r e l e a s e point to the b i o sphere. Consequently, measurements are p r e s e n t l y being made on absorption c o e f f i c i e n t s of v a r i o u s r a d i o i s o t o p e s with the minerals that are expected to be encountered i n the g e o l o g i c a l environment. Measurements are being taken not only f o r s i n g l e species but a l s o f o r combinations of species with the range of pH values of the ground water that may be expected to be found. A number of models have been developed to estimate the p o t e n t i a l transport of r a d i o n u c l i d e s by ground water. By v a r y i n g boundary c o n d i t i o n s and generic input data such as p e r m e a b i l i t y , p o r o s i t y and a b s o r p t i o n c a p a c i t y of geologic media these models y i e l d the measure of r e l a t i v e importance of the flow path l i f e , the flow v e l o c i t y and a q u i f e r absorption c h a r a c t e r i s t i c s as b a r r i e r s to r a d i o n u c l i d e t r a n s p o r t . Results from c a l c u l a t i o n s with the model suggest that i f a r e p o s i t o r y i s s i t e d w i t h a flow path s u f f i c i e n t l y long, such as may be found i n r e g i o n a l a q u i f e r systems, the r e t e n t i o n of r a d i o n u c l i d e s i n the geology f o r periods of thousands of years w i l l be achieved. A major i s s u e that needs more work i n the area of hydrogeol o g i c t r a n s f e r has to do with flow of ground water through f r a c tured rock systems. There are a number of models that have been developed to date to t r y to o b t a i n a b e t t e r understanding of ground water flow through geologic media. But most of these assume the p r o p e r t i e s of porous or semi-porous media. Should the ground water flow be p r i m a r i l y through f r a c t u r e s , which of course i s v e r y s i t e s p e c i f i c , models are not yet a v a i l a b l e to represent t h i s flow a c c u r a t e l y . I t may very w e l l be that s i t e s p e c i f i c experiments w i l l be r e q u i r e d i n order to c h a r a c t e r i z e the flow through f r a c t u r e d media. A d d i t i o n a l work i n t h i s area w i l l be r e q u i r e d before we w i l l be i n a p o s i t i o n to i d e n t i f y the c h a r a c t e r i s t i c s of flow paths where considerable q u a n t i t i e s of f r a c t u r e d rock e x i s t . Risk Assessment. The o v e r a l l compilation and assessment of the f a c t o r s that must be considered i n designing and s i t i n g geol o g i c r e p o s i t o r i e s i s p u l l e d together i n a general d i s c i p l i n e of r i s k assessment. Risk assessment c a l c u l a t i o n s develop both generi c and site s p e c i f i c models and c a l c u l a t e the p o t e n t i a l t r a n s p o r t times as a r e s u l t of v a r i o u s phenomena. C a l c u l a t i o n s are being

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch001

10

RADIOACTIVE WASTE IN GEOLOGIC STORAGE

performed f o r those s i t u a t i o n s i n which the r e p o s i t o r y environment remains e s s e n t i a l l y unchanged and a l s o f o r those c o n d i t i o n s where s i g n i f i c a n t unplanned events such as earthquakes, climate change or other phenomena take p l a c e . As each of these s i t u a t i o n s are analyzed, an understanding i s gained of the importance of the v a r ious f a c t o r s and the m u l t i p l e b a r r i e r s which might be provided between the r a d i o a c t i v e m a t e r i a l s and the environment. An important element of r i s k a n a l y s i s i s a s s e s s i n g the importance of the u n c e r t a i n t i e s i n the data now being used to e v a l uate v a r i o u s s c e n a r i o s . By v a r y i n g the value of the parameters that are used i n the a n a l y s i s , one can understand the importance of present u n c e r t a i n t i e s i n s i g n i f i c a n t v a r i a b l e s by t h e i r impact on the c a l c u l a t e d r i s k from the r e p o s i t o r y . These r e s u l t s w i l l be used to d i r e c t the research program toward those elements which are most s i g n i f i c a n t . The o v e r a l l design of the program by e v a l u a t i n g f a c t o r s which could l e a d to r i s k of r e l e a s e to the environment i n v o l v e s the type of a n a l y s i s that w i l l be r e q u i r e d during a l i c e n s i n g process. A d e t a i l e d l i c e n s i n g plan i s being prepared and w i l l be published when a v a i l a b l e to d e s c r i b e those areas which w i l l be of concern to the l i c e n s i n g a u t h o r i t i e s , the methods a v a i l a b l e to us to analyze those areas and the data that w i l l be used i n performing the a n a l yses. The s e n s i t i v i t y a n a l y s i s j u s t described w i l l i n d i c a t e where a d d i t i o n a l data are r e q u i r e d i n order to gain more assurance i n p r e d i c t i n g p o t e n t i a l r i s k s that might occur from the placement of the r e p o s i t o r i e s . Conclusion I have t r i e d to present to you some of the c o n s i d e r a t i o n s that go i n t o designing the research and development programs which are and w i l l be undertaken under the sponsorship of the Department of Energy. The new O f f i c e of Nuclear Waste I s o l a t i o n has been charged with the task of compiling a l l of these v a r i o u s thoughts and c o n s i d e r a t i o n s i n t o a s i n g l e program plan document. T h i s document w i l l i n c o r p o r a t e the input of the l i c e n s i n g plan, the r i s k assessment and s e n s i t i v i t y analyses which have been performed and a l s o the independent review that has been s u p p l i e d by such groups as the USGS, the N a t i o n a l Academy of Sciences, EPA and others. T h i s program plan w i l l be published w i t h i n the next few months and w i l l be c i r c u l a t e d f o r p u b l i c review and comment. We hope that both the American Chemical Society and i t s i n d i v i d u a l members w i l l provide us feedback on t h i s p l a n . H o p e f u l l y , i n t h i s way a greater understanding of the t e c h n i c a l components of the program w i l l be achieved and we w i l l be able to demonstrate that we are addressing the concerns that have been r a i s e d i n a respons i b l e manner. I f I can supply an o v e r a l l assessment of where we stand i n the program today, I b e l i e v e that there i s a consensus i n the

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch001

1.

HEATH

DOE

Isolation

of Radioactive

11

Waste

s c i e n t i f i c community that a p p r o p r i a t e i s o l a t i o n of r a d i o a c t i v e wastes can be obtained by p l a c i n g them i n g e o l o g i c formations. There are s e v e r a l f a c t o r s that have to be considered before speci f i c s i t e s can be i d e n t i f i e d and many of the gaps i n our knowledge are indeed very s p e c i f i c to the s i t e s i n q u e s t i o n . P r i m a r i l y because of t h i s s i t e s p e c i f i c c h a r a c t e r i s t i c I b e l i e v e one can say that the concept of r a d i o a c t i v e waste i s o l a t i o n w i l l not be proven u n t i l we are i n a p o s i t i o n of being able to i d e n t i f y a s p e c i f i c s i t e with a l l of these m u l t i p l e c h a r a c t e r i s t i c s adequately chara c t e r i z e d so that we can o b t a i n a c l e a r e r understanding and app r o v a l by both the r e g u l a t o r y a u t h o r i t i e s and the general p u b l i c . The proposed f a c i l i t y i n southeast New Mexico i s the c l o s e s t to being completely c a t e g o r i z e d i n t h i s way. I t i s i n t h i s context that the Department of Energy has proposed that t h i s p r o j e c t be subjected to the l i c e n s i n g process by NRC even i f the m a t e r i a l to be placed there i s only defense r a d i o a c t i v e waste. Unfortuna t e l y , the sponsoring committees of the Congress who are concerned p r i m a r i l y with the i s s u e s of defense have taken the p o s i t i o n that f a c i l i t i e s r e l a t e d to the defense program should remain completely exempt from the l i c e n s i n g process. Opposition to work l e a d i n g to i d e n t i f i c a t i o n of s p e c i f i c s i t e s i s the g r e a t e s t problem f a c i n g the program today. It i s agreed i n the s c i e n t i f i c community that one cannot reach a f i n a l c o n c l u s i o n of the s u i t a b i l i t y of g e o l o g i c i s o l a t i o n without looking at s p e c i f i c s i t e s i n d e t a i l . This of course i s the one area to which there has been s i g n i f i c a n t o p p o s i t i o n . Members of the p u b l i c and s t a t e and l o c a l l e a d e r s have stated that more s p e c i f i c information i s needed as to the s a f e t y and p o t e n t i a l s u i t a b i l i t y of r a d i o a c t i v e waste d i s p o s a l before one can allow even the exami n a t i o n or d i s c u s s i o n of s p e c i f i c s i t e s . On the other hand, s c i e n t i f i c consensus i s that u n t i l one does evaluate s p e c i f i c s i t e s one i s not going to be a b l e to o b t a i n the r e q u i r e d information. In order to r e s o l v e t h i s dilemma, we are seeking to cons t r u c t a j o i n t c o n s u l t a t i o n process with s t a t e and l o c a l authori t i e s to allow the examination of s p e c i f i c s i t e s i n order that we can answer the s c i e n t i f i c questions that we must. The ongoing a c t i v i t i e s of the Interagency Review Group on Waste Management and i t s i n t e r a c t i o n w i t h s t a t e and l o c a l o f f i c i a l s and the p u b l i c i s the f i r s t step i n o b t a i n i n g the necessary consensus before proceeding . We have reached a c r i t i c a l t u r n i n g p o i n t i n the DOE s waste management program. The program i s now adequately funded, and with the a s s i s t a n c e of many q u a l i f i e d and experienced s c i e n t i s t s and engineers a comprehensive t e c h n i c a l program i s underway. A r e s o l u t i o n must now be reached to a l l o w us to extend our i n v e s t i gations i n t o s p e c i f i c s i t e l o c a t i o n s . With input and feedback from groups such as t h i s , and with cooperation at a l l l e v e l s of government, I am c o n f i d e n t that we can proceed to r e s o l v e t h i s very important n a t i o n a l problem. 1

RECEIVED January 16,

1979.

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

2 WIPP: A Bedded Salt Repository for Defense Radioactive Waste in Southeastern New Mexico W. D. WEART

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch002

Sandia Laboratories, Albuquerque, N M 87185

For twenty years the Department o f Energy (DOE) and its predecessor o r g a n i z a t i o n s , the Atomic Energy Commission and the Energy Research and Development A d m i n i s t r a t i o n , have pursued a research e f f o r t i n v e s t i g a t i n g the phenomena accompanying the emplacement o f r a d i o a c t i v e waste i n rock s a l t . This program, which has not revealed any e f f e c t s which would preclude the use of s a l t beds f o r geologic d i s p o s a l of r a d i o a c t i v e wastes, has led to the implementation o f the Waste I s o l a t i o n Pilot Plant (WIPP) p r o j e c t . The WIPP, as p r e s e n t l y conceived (Figure 1) will utilize the deep s a l t beds i n southeast New Mexico to provide geologic i s o l a t i o n for transuranic (TRU) contaminated waste generated by t h i s nation's defense programs. In a d d i t i o n , the WIPP will provide an underground " l a b o r a t o r y " where realistic and l a r g e - s c a l e t e s t s can be conducted using h i g h - l e v e l waste (HLW). While v a r i a t i o n s and a d d i t i o n s to t h i s WIPP mission have been proposed from time to time, (the charter f o r t h i s facility i s p r e s e n t l y under d i s c u s s i o n w i t h i n the DOE) these two c e n t r a l features have remained a fundamental part o f the WIPP. Sandia Laboratories began s i t e e v a l u a t i o n studies i n April, 1975 at a l o c a t i o n p r e v i o u s l y recommended by the United States G e o l o g i c a l Survey (USGS) and Oak Ridge N a t i o n a l Laboratory (ORNL). Subsequent e v a l u a t i o n revealed t h i s s p e c i f i c s i t e to be g e o l o g i c a l l y unacceptable and renewed site s e l e c t i o n i n v e s t i g a t i o n s r e s u l t e d i n the choice o f the "Los Medanos" area which i s now being thoroughly examined. The s i t e s e l e c t i o n phase i s now virtually complete and the area i s b e l i e v e d to be acceptable, i n a l l t e c h n i c a l respects, f o r continued development o f the WIPP. Non-technical aspects o f the s i t e which have been q u a n t i f i e d for c o n s i d e r a t i o n i n the Environmental Impact Statement (EIS) are the demographic and socio-economic f a c e t s , the ecologic and archaeologic features of the region and the p o t e n t i a l f o r n a t u r a l resources such as hydrocarbons and potash. 0-8412-0498-5/79/47-100-013$06.00/0 © 1979 A m e r i c a n C h e m i c a l Society

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Artist's concept of WIPP.

The WIPP will be constructed at two different levels.

HLW experiments and high gamma TRU will be placed in the lower horizon. The bulk of the TRU waste will be on the upper level. New waste disposal corridors will be mined as existing rooms are filled.

Figure 1.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch002

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>

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10" i n the e f f l u e n t from a t i t a n a t e column loaded t o s l i g h t l y more than 100$ o f the c a l c u l a t e d capacity. The use of the z e o l i t e does not e f f e c t the o v e r a l l process conditions since i t can be i n c o r p o r a t e d d i r e c t l y i n t o the sodium t i t a n a t e during p r e p a r a t i o n . A Dowex 1-X8 resin bed was used to remove the 9 9 j from the e f f l u e n t and a l s o served t o remove a d d i t i o n a l Ru, l e a v i n g 0.002$ of the o r i g i n a l Ru a c t i v i t y i n the e f f l u e n t . F i n a l l y , the e f f l u e n t was passed through a f e r r i c t i t a n a t e bed (13) which reduced the - ^ R u con­ c e n t r a t i o n by an a d d i t i o n a l f a c t o r of 120. A comparison of the a c t i v i t y i n the e f f l u e n t from the above process with the a c t i v i t y i n the "feed" s o l u t i o n i s shown i n Table I I I f o r an experiment i n which a t i t a n a t e column was used at approximately 100$ c a p a c i t y . Only Ru and a small amount o f r e s i d u a l alpha a c t i v i t y were detected i n the e f f l u e n t . A s i n g l e t e s t o f a batch procedure was done u s i n g magnesium t i t a n a t e i n s t e a d o f the sodium form. Since no sodium was present, a w a s h i n g / f i l t e r i n g step was not r e q u i r e d . A f t e r a d d i t i o n of the magnesium t i t a n a t e t o the l i q u i d waste, the s o l i d product was c a l c i n e d i n the r e a c t i o n v e s s e l at 650°C t o remove water and destroy n i t r a t e s , and the r e s u l t i n g m a t e r i a l was pressure s i n t e r e d under the same conditions used f o r column m a t e r i a l . The density and leaching c h a r a c t e r i s t i c s of the product were comparable t o or b e t t e r than those found i n the same q u a l i f y i n g t e s t s a p p l i e d to any o f the t i t a n a t e s produced by other methods. The advantage of the Mg(Ti 0^H)2 b a t c h e q u i l i b r a t i o n process would be i t s s i m p l i c i t y . Secondly, an o f f - g a s stream from t h i s process would be almost i d e n t i c a l w i t h t h a t produced i n e x i s t i n g flowsheets f o r d i r e c t c a l c i n a t i o n o f l i q u i d wastes. A p o t e n t i a l disadvantage would be the i n c l u s i o n o f anions such as phosphate, 1

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch008

2

c

2

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

138

RADIOACTIVE

WASTE

IN

GEOLOGIC

STORAGE

s u l f a t e , and f l u o r i d e i n the f i n a l waste form. The p r o j e c t ended before f u r t h e r i n v e s t i g a t i o n s i n t o the batch process and the e f f e c t s o f the anions on the p r o p e r t i e s o f the t i t a n a t e waste form c o u l d be i n i t i a t e d .

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch008

C o n s o l i d a t i o n and C h a r a c t e r i z a t i o n o f the Ceramic Waste Form The use o f i o n exchange r e s i n s and n a t u r a l or s y n t h e t i c i n o r g a n i c exchange m a t e r i a l s i n the nuclear i n d u s t r y i s w e l l documented ( l A ) . In the waste s o l i d i f i c a t i o n a p p l i c a t i o n , the t i t a n a t e s or niobates o f f e r no unique s o r p t i o n p r o p e r t i e s . They do, however, provide a r e l a t i v e l y high o v e r a l l s o r p t i o n c a p a c i t y f o r a v a r i e t y o f n u c l i d e s i n m a t e r i a l s which can be converted i n t o a s t a b l e ceramic host f o r the sorbed i o n s . A f t e r the sorpt i o n process, the column bed must be c o n s o l i d a t e d t o reduce surface area. The p r o j e c t emphasis was d i r e c t e d toward a s t a b l e waste form and a considerable e f f o r t was devoted t o producing and c h a r a c t e r i z i n g a h i g h l y dense form w i t h favorable p h y s i c a l , chemical and thermal p r o p e r t i e s (15). At temperatures o f 600°-650°C, the waste form dehydrates and c r y s t a l l i z e s t o form a mixture o f t i t a n a t e s (niobates, z i r c o n a t e s ) and t i t a n i a ( n i o b i a , z i r c o n i a ) as i l l u s t r a t e d f o r the case of Sr by Eq. k. + +

Sr(Ti 0 H) 2

5

2

4 SrTi0

3

+ 3Ti0

2

+ HgO

(Eq.

k)

Both c o l d p r e s s i n g / s i n t e r i n g and pressure s i n t e r i n g were s t u d i e d as c o n s o l i d a t i o n methods. R e s i d u a l p e l l e t p o r o s i t y c o u l d not be reduced, however, below 30 v o l $ by the former method at temperatures up t o 1000°C and with the a d d i t i o n o f up t o 30$ by weight o f a g l a s s binder. More favorable r e s u l t s were obtained by pressure s i n t e r i n g methods. This process was c a r r i e d out i n vacuum i n graphite dies where c o n d i t i o n s ranged from 900 t o 1100°C and 6.9 t o 13.8 MPa (1000 t o 2000 p s i ) . In general, the l a t t e r technique was h i g h l y s u c c e s s f u l f o r samples w i t h l e s s than 2$ r e s i d u a l p o r o s i t y were obtained r o u t i n e l y . A d d i t i o n o f a g l a s s c o n s o l i d a t i o n a i d t o the waste allowed f o r a s i g n i f i c a n t r e d u c t i o n i n the p r e s s i n g parameters. For example, t i t a n a t e waste forms w i t h 5, 15 and 30$ by weight o f g l a s s binder were s u c c e s s f u l l y c o n s o l i d a t e d t o near maximum density at temperatures o f 1000, 950 and 900°C, r e s p e c t i v e l y . C y l i n d r i c a l p e l l e t s up t o 5 em i n diameter were produced and the f e a s i b i l i t y o f a semi-continuous pressure s i n t e r i n g process was demonstrated. Wide v a r i a t i o n s i n Cs and Na l e a c h i n g observed i n some o f the f i r s t samples produced were found t o r e s u l t from the formation o f the corresponding molybdate compounds which are h i g h l y water s o l u b l e . T h i s problem was e l i m i n a t e d by the a d d i t i o n of 1-2$ by weight o f elemental s i l i c o n which served as a reducing agent and prevented molybdate formation. The s i l i c o n was added during the p r e p a r a t i o n o f the sodium t i t a n a t e m a t e r i a l .

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch008

8.

DOSCH

Ceramic

Forms for

Nuclear

Waste

139

During development, e v a l u a t i o n o f the c o n s o l i d a t e d m a t e r i a l s was based p r i m a r i l y on two c r i t e r i a , l e a c h a b i l i t y and the concen­ t r a t i o n f a c t o r , i . e . , the concentration of waste oxides on a v o l ­ ume b a s i s . The concentration f a c t o r i s d i r e c t l y a f f e c t e d by the r e s i d u a l p o r o s i t y i n a consolidated waste as w e l l as b y the d i l u ­ t i o n caused b y the a d d i t i o n of c o n s o l i d a t i o n a i d s . T h i s f a c t o r can be as high as 1 . 2 g/cm3 f o r a f u l l y dense (k.5 g/cm^) t i t a n a t e waste prepared from the p r o j e c t e d Barnwell plant s o l u t i o n compo­ s i t i o n . The f a c t o r i s s l i g h t l y lower f o r a t i t a n a t e waste con­ t a i n i n g s i l i c o n and z e o l i t e a d d i t i o n s , which has a t y p i c a l d e n s i t y of k.2 g/cnH. The l e a c h a b i l i t y was determined by an " i n s t a n t a ­ neous" l e a c h t e s t developed f o r f a s t , comparative e v a l u a t i o n s of m a t e r i a l s , the d e t a i l s of which are described elsewhere ( l 6 ) . The c o n s o l i d a t e d t i t a n a t e waste p e l l e t s are s i m i l a r i n appearance t o t h e i r g l a s s counterparts, i . e . , both are dense, b l a c k and apparently homogeneous. M i c r o s c o p i c analyses, however, r e v e a l important d i f f e r e n c e s between these two waste forms. While l i t t l e d e f i n i t i v e work has been done w i t h g l a s s y waste forms, i t i s apparent t h a t s e v e r a l r e a d i l y s o l u b l e oxide p a r t i c u l a t e s o f various n u c l i d e s are simply encapsulated i n the g l a s s matrix. The t i t a n a t e waste form has undergone extensive analyses which i n ­ cludes o p t i c a l microscopy, x-ray, scanning e l e c t r o n microscopy, microprobe, and t r a n s m i s s i o n e l e c t r o n microscopy ( 1 7 ) . The samples o f t i t a n a t e examined were prepared by pressure s i n t e r i n g and c o n s i s t e d o f m a t e r i a l from a f u l l y loaded t i t a n a t e column. Z e o l i t e and s i l i c o n a d d i t i o n s were a l s o present i n the samples. A s o l i d s o l u t i o n t i t a n a t e i s not produced by pressure s i n t e r ­ i n g , but r a t h e r a complex assemblage o f phases. O p t i c a l micros­ copy showed that a few percent o f c l o s e d p o r o s i t y remains i n the p e l l e t s , and on t h i s s c a l e no gross inhomogeneities are apparent. X-ray a n a l y s i s c l e a r l y showed t h a t the dominant phase i s r u t i l e ( T i 0 ) and t h a t s e v e r a l other background l i n e s are a l s o detectable. Scanning e l e c t r o n microscopy g e n e r a l l y confirmed the absence o f inhomogeneities, but the microprobe c l e a r l y i n d i c a t e d that some degree o f elemental segregation e x i s t s . Transmission e l e c t r o n microscopy provided a completely d i f ­ f e r e n t impression of the m a t e r i a l ( F i g . 2) and was used t o i d e n t i ­ f y e i g h t d i f f e r e n t phases i n the waste which are summarized i n Table IV. The major phase was r u t i l e , which made up approximately 50$ of the s o l i d , and to w i t h i n the l i m i t s on the x-ray d e t e c t o r (HL A t $ ) , no other elements were i n the s o l u t i o n i n the r u t i l e . The second most abundant c r y s t a l l i n e compound (estimated volume f r a c t i o n ~ 0 . l ) was gadolinium t i t a n a t e , ( Μ Τ ΐ 0 γ . There i s evidence t h a t U, Z r , Y, and p o s s i b l y Sm and Eu are i n s o l i d s o l u t i o n w i t h t h i s gadolinium phase. Elemental s i l i c o n c r y s t a l s remaining i n the waste were found t o be surrounded by S i 0 . Two types o f m e t a l l i c globules were observed i n the waste form. These were p r i n c i p a l l y elemental molybdenum w i t h t r a c e elements i n s o l u t i o n and elemental palladium w i t h other t r a c e elements i n s o l u t i o n . In the case of molybdenum, the s i l i c o n 2

2

2

2

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

RADIOACTIVE

WASTE

IN GEOLOGIC

STORAGE

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch008

140

Figure 2. Transmission electron photomicrograph of a ceramic titanate waste form. The sample was prepared by pressure sintering a titanate fully loaded with fission waste oxides and includes zeolite and silicon additions.

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Ceramic

DOSCH

Table I I I .

Waste

Comparison o f the Radionuclide A c t i v i t y i n E f f l u e n t from T i t a n a t e S o l i d i f i c a t i o n Process w i t h the A c t i v i t y i n the High L e v e l Waste Feed S o l u t i o n

10 6.6 χ 10"

9

°iSr 99UTc

Cs

137, Cs

h.8 χ 1 0

Gross Alpha

5 x 10

2

8 Λ χ 10*

5.7 χ 10

Ce

10

10 , and « 1 0 f o r S r , C s , and P u , r e s p e c t i v e l y . W a t e r was pumped f r o m e a c h zone u n t i l t h e Τ c o n c e n t r a t i o n was r e l a t i v e l y c o n s t a n t a s i l l u s t r a t e d i n F i g u r e 5 f o r Zone I I , the lower c a v i t y region. The pH a n d c o n d u c t i v i t y were measured i n t h e f i e l d a n d s t a n d a r d w a t e r a n a l y s e s were p e r f o r m e d l a t e r . A summary o f t h e s e d a t a i s g i v e n i n T a b l e I I I . R e p r e s e n t a t i v e a c t i v i t y l e v e l s o f t h e r a d i o n u c l i d e s d e t e c t e d i n water from each zone a r e g i v e n i n T a b l e I V . W a t e r f r o m t h e r e g i o n o f h i g h e s t r a d i o a c t i v i t y a t t h e b o t t o m o f t h e c a v i t y c o n t a i n s o n l y Τ and S r a t l e v e l s h i g h e r t h a n t h e recommended (2_) c o n c e n t r a t i o n g u i d e s (CG) f o r d r i n k i n g w a t e r i n u n c o n t r o l l e d a r e a s . 8 5

8 5

8 5

k

8

9 0

1 3 7

2 3 9

9 0

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

156

STORAGE

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch009

RADIOACTIVE W A S T E IN GEOLOGIC

160

140

120

100

80

60

HORIZONTAL DISTANCE SOUTH OF SURFACE SITE OF RNM-1 (m) Figure 4.

Construction details of RNM-1 (I)

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

40

Radionuclide

Migration

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch009

H O F F M A N

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

40

30

20

«

«

«

III

IV

V

4

30

so

65

18.6

45.7

« 110

«

18.9

23.7

« 53

GO

110

%

» 200

^

^ a t a from Reference 1, p. 66.

« 350

« 550

« 470

« 140

II

I

100

3

te

HC0

« 170

«

CI

20

Zone

Pumped

Volume

^

670

Ο Μ

Ο

ο Η

ε

M Ο

ο

Η M

>

0.4 « 50

>

δ M

7.4

01 00

« 1.5

« 90

7.1

« 1100

0.2 « 70 7.2

« 1100

0.4

« 50

8.3

« 1000

(ppm)

Li

< 0.05

(ppm)

Ca

« 15

8.1

PH

420

«

(umho/cm)

Conductivity

ANALYSES OF REPRESENTATIVE WATER SAMPLES PUMPED FROM RNM-1

TABLE I I I

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch009

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

CG « Recommended (Ref. 2) c o n c e n t r a t i o n u n c o n t r o l l e d areas.

• not detected.

1 2 5

b

n.d.

0.2

222

11.1

n.d.

0.8

n.d.

44.4

1 0 f o r P u and > 1 0 f o r ?m to 10 to 10* f o r S r , Ru, S b , and Cs. The v e r y h i g h v a l u e s f o r P u and P m may be r e l a t e d t o t h e i r l o w s o l u b i l i t y a t t h e s e p H s a s w e l l a s t o l o w l e a c h i n g r a t e s f r o m t h e f u s e d d e b r i s . The v a l u e s f o r S r and C s a p p e a r t o be s i g n i f i c a n t l y l o w e r i n t h e chimney t h a n i n t h e c a v i t y r e g i o n , p e r h a p s r e f l e c t i n g t h e i r movement f r o m t h e c a v i t y a s t h e g a s e o u s s p e c i e s K r and Xe and s u b s e q u e n t a d s o r p t i o n on t h e s u r f a c e o f t h e a l l u v i u m r a t h e r than i n the fused d e b r i s i n t h e c a v i t y region. 7

9 0

2 3 9

1 0 6

1 2 5

2 3 9

6

lh7

2

1 3 7

ltf7

f

9 0

1 3 7

9 0

1 3 7

S a t e l l i t e W e l l RNM-2S The s a t e l l i t e w e l l d e s i g n a t e d RNM-2S was d r i l l e d 91 m s o u t h o f RNM-1. A f t e r c o m p l e t i o n o f s a m p l i n g o p e r a t i o n s a t RNM-1, t h e p a c k e r b e t w e e n z o n e s I V a n d V was d r i l l e d o u t and pumping was begun a t RNM-2S i n O c t o b e r , 1975 a t a r a t e o f 250 t o 300 g a l l o n s (0.95 t o 1.14 m ) p e r m i n u t e . T h i s pumping was e x p e c t e d t o overcome any n a t u r a l g r a d i e n t and i n d u c e a s u f f i c i e n t a r t i f i c i a l g r a d i e n t t o draw w a t e r f r o m t h e C a m b r i c c a v i t y t o RNM-2S. De­ t e c t i o n o f Τ w o u l d s i g n a l t h e a r r i v a l o f w a t e r f r o m C a m b r i c . By A u g u s t 1977, more t h a n 1.14 m i l l i o n m o f w a t e r h a d been removed w i t h o u t d e t e c t i o n o f T. An e s t i m a t e b a s e d s t r i c t l y on t h e volume o f w a t e r i n a s p h e r e 91 m i n r a d i u s ( t h e d i s t a n c e between RNM-1 and 2S) u s i n g a p o r o s i t y o f ^ 0 . 3 f o r t h e a l l u v i u m and t h e a s ­ sumption o f equal t r a n s m i s s i v i t y i n a l l d i r e c t i o n s , i n d i c a t e s that « 1 0 m o f w a t e r must be pumped t o draw Τ t o RNM-2S. Pumping was s u s p e n d e d and RNM-1 was r e s a m p l e d t o s e e i f t h e r a d i o n u c l i d e l e v e l s h a d changed. P r e s s u r i z e d and pumped w a t e r 3

3

6

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

0

n.d.

5

n.d.*

2

2

Sb

n.d.

n.d.

3.6xl0

2.9xl0

Bg

1 2 5

2

2

a c t i v i t y d e t e c t a b l e above background l e v e l s ,

^n.d. = not detected.

n

2

Adjacent to Chimney

Bg

1

3.1xl0

3.9X10

Chimney

1.9xl0

3

1.6xl0

Upper C a v i t y

l.OxlO

Bg

p

106 Ru

3

2.1xl0

Lower C a v i t y

a

Sr

Bg

9 0

Below C a v i t y

Zone

1

Ε , s FROM WATER SAMPLES

TABLE V

C8

l.lxlO

6.6xl0

1.8xl0

2.5xl0

Bg

1 3 7

3

2

4

4

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch009

n.d.

n.d.

n.d.

n.d.

n.d.

>1.9xl0

>3.2xl0

>io

D

239 Pu

Bg 6

Pta

Bg

1 4 7

7

7

162

RADIOACTIVE W A S T E IN GEOLOGIC STORAGE

s a m p l e s were o b t a i n e d f r o m RNM-1 and a n a l y s e s showed t h a t t h e Τ l e v e l h a d d e c r e a s e d b y a f a c t o r o f 50 o r more ( s e e T a b l e V I ) r e l a t i v e t o t h e o r i g i n a l v a l u e s f o r Zone I V . ( A l t h o u g h w a t e r c a n e n t e r f r o m p e r f o r a t i o n s i n b o t h Zones I V a n d V, most o f t h e w a t e r p r o d u c t i o n i s b e l i e v e d t o be f r o m Zone I V ) . The S r and C s l e v e l s shown i n T a b l e V I I a r e n o t t o o d i f f e r e n t f r o m t h e o r i g i n a l values. T h i s seems t o i n d i c a t e t h a t t h e d i s t r i b u t i o n r a t i o s ( a c t i v i t y p e r gram s o l i d d i v i d e d by a c t i v i t y p e r m l w a t e r ) a r e r e l a t i v e l y h i g h (> 1 0 0 ) . The s o u r c e t e r m w i l l t h e n n o t be r a p i d l y d e p l e t e d and a more o r l e s s c o n s t a n t e q u i l i b r i u m v a l u e s h o u l d be m a i n t a i n e d i n t h e water. I n O c t o b e r , 1977 a h i g h e r c a p a c i t y pump was i n s t a l l e d i n RNM-2S and pumping was resumed a t a r a t e o f a b o u t 2.27 m p e r minute. S i g n i f i c a n t amounts o f t r i t i u m were f i n a l l y d e t e c t e d a f t e r a t o t a l o f a b o u t 1.44 m i l l i o n m o f w a t e r h a d been pumped. The c o n c e n t r a t i o n s a r e s t i l l r i s i n g r a p i d l y a s shown i n F i g u r e 6. A number o f p r e s s u r i z e d s a m p l e s h a v e been t a k e n and show K r a s w e l l a s HTO and HT. These d a t a a r e summarized i n T a b l e VIII. The o b s e r v e d K r / T atom r a t i o s a r e v e r y s i m i l a r t o t h a t o f 1.2 χ 10~ c a l c u l a t e d f o r t h e C a m b r i c s o u r c e t e r m , c o n s i s t e n t w i t h t h e h y p o t h e s i s t h a t t h e K r i s d i s s o l v e d i n t h e w a t e r and moves a l o n g w i t h t h e HTO. 9 0

1 3 7

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch009

3

3

8 5

8 5

k

8 5

TABLE V I REPRESENTATIVE ACTIVITY LEVELS I N RNM-1 WATER SAMPLES Activity at t 8 5

Atom R a t i o

Kr

( y C i / m l ) (dpm/ml)

85

Kr/T

Original: Zone I V (8-8-75)

0.15

70

1.8x10

Zone V

0.038

13

1.3x10

75

9.4x10

(8-14-75)

Re-entry: I

(10-4-77) 0.0032 6 3 (1.17x10 m pumped f r o m 2S)

II

(11-30-77) 0.0020 6 3 (1.34x10 m pumped f r o m 2S)

1.3x10

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch009

H O F F M A N

Figure 6.

Radionuclide

Migration

Tritium concentration as a function of volume of water pumped

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

RADIOACTIVE W A S T E IN GEOLOGIC STORAGE

164

TABLE V I I ACTIVITY LEVELS OF

9 0

S r AND

1 3 7

C s IN WATER

FROM RE-ENTRY OF RNM-1

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch009

A c t i v i t y at t 90

Atom R a t i o 137 90 Cs/T Sr/T

(dpm/ml) 137 Sr Cs

Original: Zone IV (8-8-75)

« 6

« 1

Zone V

«0.25

«0.2

« 1

«0.2

«0.6

«0.5

(8-14-75)

1.8x10" -6 2.3x10"

3.1x10 -6 1.8x10

1.4x10" -4 1.4x10

3.0x10Γ -4 1.2x10

Re-entry: 1(10-4-77) 11(11-30-77)

5

TABLE V I I I ANALYSES OF PRESSURIZED WATER SAMPLES FROM RNM-2S ( A l l a c t i v i t i e s c o r r e c t e d to zero time.) Volume Pumped

Τ

8 5

Atom Ratio

Kr

8 5

Kr/T

Sample

(m )

1

1.702x10

2

1.702xl0

6

1.62xl0"

5

1.06xl0"

2

2.58xl0*~

3

1.852xl0

6

3.64xl0"

5

1.15xl0~

2

1.24χ1θ""

4

1.852xl0

6

3.65xl0"

5

0.91xl0"

2

0.98xl0"

3

6

(yCi/ml)

(dpm/ml)

-5 1.69x10

0.48x10

D

-2

-4 1.11x10

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

4

4

4

9.

H O F F M A N

Radionuclide

Migration

165

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch009

Future Pumping a t RNM-2S w i l l c o n t i n u e and l a r g e v o l u m e s o f w a t e r w i l l be analyzed f o r o t h e r r a d i o n u c l i d e s . Simple c a l c u l a t i o n s (R. S t o n e , p r i v a t e c o m m u n i c a t i o n , 1978) show t h a t i t w i l l t a k e more t h a n 1500 y e a r s f o r n u c l i d e s f r o m RNM-1 h a v i n g d i s t r i b u t i o n r a t i o s o f 100 o r more t o r e a c h RNM-2S. L a b o r a t o r y e x p e r i m e n t s (3) i n d i c a t e t h a t t h e r a t i o s f o r S r , Ru, C s , Ce, Pm, and P u a r e l a r g e r t h a n 100. Those f o r Sb and U a r e much s m a l l e r and i s o ­ t o p e s o f t h e s e e l e m e n t s m i g h t be d e t e c t a b l e i n t h e w a t e r . N o n e q u i l i b r i u m e f f e c t s or the presence of c o l l o i d a l or non-sorbed s p e c i e s m i g h t a l l o w o t h e r n u c l i d e s t o move more r a p i d l y t h a n e x p e c t e d . Pumping and m o n i t o r i n g o f r a d i o n u c l i d e l e v e l s w i l l b e c o n t i n u e d a t l e a s t u n t i l a maximum i n t h e t r i t i u m c o n c e n t r a t i o n has b e e n r e a c h e d and t h e shape o f t h e Τ c o n c e n t r a t i o n c u r v e has been d e f i n e d . I t i s hoped t h a t s t u d i e s s i m i l a r t o t h o s e c o n d u c t e d a t Cambric can be c a r r i e d out f o r n u c l e a r d e v i c e s t e s t e d i n o t h e r m e d i a s u c h as t u f f . R e - e n t r y d r i l l b a c k and s a m p l i n g s o o n e r a f t e r d e t o n a t i o n would be d e s i r a b l e so t h a t the b e h a v i o r of s h o r t e r l i v e d s p e c i e s s u c h as Z r , M o - T c , Ru, I , N d , and U can be s t u d i e d . A l t h o u g h t h e s e n u c l i d e s have such s h o r t h a l f l i v e s t h a t they a r e n o t apt t o be t r a n s p o r t e d o f f - s i t e , they would p r o v i d e s e n s i t i v e m o n i t o r s o f the b e h a v i o r of l o n g e r - l i v e d a c t i v i t i e s o f t h e same e l e m e n t s , s u c h as 9.5 χ 1 0 - y e a r Zr, 2.1 χ 1 0 - y e a r T c , 1.6 χ 1 0 - y e a r I , and > u which are of i n t e r e s t o n a l o n g t i m e s c a l e . 9 5

9 9

9 9

1 0 3

1

3

1

l l f 7

2 3 7

5

5

9 9

7

1

2

9

2 3 5

9 3

2 3 8

Acknowledgments I wish t o acknowledge the many people from the Los Alamos S c i e n t i f i c Laboratory, the Lawrence Livermore Laboratory, the U. S. G e o l o g i c a l Survey, and the Desert Research I n s t i t u t e who have contributed to the studies which have been b r i e f l y reviewed here. R. W. Newman, NV, i s P r o j e c t Manager, and J . E. S a t t i z a h n (LASL), R. H. Ide (LLL), L. D. Ramspott (LLL), and D. C. Hoffman (LASL) have served as T e c h n i c a l D i r e c t o r s . Abstract The radionuclide distribution i n both the water and aggregate around a 0.75-kt nuclear test which was detonated below the water table at the Nevada Test Site has been investigated. An extensive suite of sidewall core samples was obtained from near the surface to below the o r i g i n a l cavity region. Representative water samples were pumped from five different zones i n the cavity and rubble r e ­ gions. Most of the radioactivity was found i n solid material con­ tained i n the lower cavity region. Water pumped from the region of highest radioactivity showed only tritium and strontium-90 at

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

166

RADIOACTIVE WASTE IN GEOLOGIC STORAGE

levels higher than the recommended concentration guides for drinking water. Water is being pumped from a s a t e l l i t e well some 90 m away to induce an artificial gradient and draw water from the test zone. Literature Cited 1.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch009

2.

3.

Hoffman, Darleane C., Stone, Randolph, and Dudley, Jr., William W., Los Alamos Scientific Laboratory Report LA-6877MS (1977), "Radioactivity in the Underground Environment of the Cambric Nuclear Explosion at the Nevada Test Site". ERDA-0524, Standards for Radiation Protection, April 8, 1975, Appendix A, Table II, p. 13; Code 10 Federal Regulations, January 1, 1975, Appendix B, Table II, p. 177. Wolfsberg, Kurt, Los Alamos Scientific Laboratory Report LA7216-MS (1978), "Sorption-Desorption Studies of Nevada Test Site Alluvium and Leaching Studies of Nuclear Test Debris".

RECEIVED January 16, 1979.

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

10 Nuclide Migration in Fractured or Porous Rock P. G. RICKERT, R. G. STRICKERT, and M. G. SEITZ 1

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch010

Argonne National Laboratory, Argonne, IL 60439

R e p o s i t o r i e s built i n geologic bodies are being considered f o r permanent d i s p o s a l of nuclear wastes. In the context o f deep geologic r e p o s i t o r i e s , the rock formation itself may be considered as part o f the mechanism r e t a i n i n g the wastes w i t h i n the immediate neighborhood of the r e p o s i t o r y . The i n t e r a c t i o n s of nuclear wastes with geologic m a t e r i a l s are being studied i n l a b o r a t o r y experiments to evaluate geologic media as b a r r i e r s to n u c l i d e migrat i o n . M i g r a t i o n caused by flowing water is considered the most c r e d i b l e mechanism f o r moving wastes from a r e p o s i t o r y i n a w e l l chosen site. The extent and r a t e of migration o f wastes under the i n f l u e n c e o f groundwater, o f course, depend on s e v e r a l parameters; i n c l u d i n g the type and extent of the chemical r e a c t i o n of the r a d i o n u c l i d e s with the geologic media. In previous work (1,2,3) it was found that the k i n e t i c s o f s o r p t i o n was an important parameter a f f e c t i n g the migration of nuc l i d e s i n geologic media. For example, i n experiments designed to measure the k i n e t i c s o f r e a c t i o n f o r r a d i o n u c l i d e s i n s o l u t i o n with t a b l e t s o f rock, it was found that periods from s e v e r a l minutes t o s e v e r a l hours were r e q u i r e d f o r the r a d i o n u c l i d e s to reach steady s t a t e concentrations on the rock t a b l e t s and in the s o l u t i o n s . Figure 1 shows the r e a c t i o n curves found f o r the s o r p t i o n of plutonium and americium from solution by a tablet of granite. The r e a c t i o n r a t e s f o r the s o r p t i o n o f plutonium and americium from s o l u t i o n are not the same, and both r e q u i r e a number of hours to reach steady s t a t e c o n c e n t r a t i o n s . The observation that the s o r p t i o n process progresses as a f u n c t i o n of time i m p l i e s that under c o n d i t i o n s of s o l u t i o n flow through geologic media, there may not be instantaneous o r local e q u i l i b r i u m between a n u c l i d e bearing s o l u t i o n and geologic media, but r a t h e r , the n u c l i d e would be sorbed from s o l u t i o n through a length o r zone of the media. Following adsorption, the n u c l i d e would desorb a f t e r an amount of water passed over the media. The n u c l i d e would again be readsorbed downstream a d i s t a n c e dependent 1

Current address: Battelle Pacific Northwest Laboratories, Richland, Washington 99352.

0-8412-0498-5/79/47-100-167$06.00/0 © 1979 American Chemical Society

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

RADIOACTIVE W A S T E IN

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch010

168

GEOLOGIC STORAGE

upon the r a t e of adsorption and the flow r a t e of the s o l u t i o n . Desorption and readsorption would continue i n t h i s manner and the migration of the n u c l i d e would be defined i n terms of the r a t e of adsorption, the r a t e of desorption, and the e q u i l i b r i u m d i s t r i b u ­ t i o n of the n u c l i d e between s o l u t i o n and geologic media. To quantify t h i s treatment of migration as i n f l u e n c e d by k i n e t i c s , a model has been developed i n which instantaneous or l o c a l e q u i l i b r i u m i s not assumed. The model i s c a l l e d the Argonne D i s p e r s i o n Code (ARDISC) (_4) . In the model, adsorption and de­ s o r p t i o n are treated independently and the r a t e s f o r adsorption and desorption are taken i n t o account. The model t r e a t s one d i ­ mensional flow and assumes a constant v e l o c i t y of s o l u t i o n through a uniform homogeneous media. This paper describes an experimental study of the a p p l i c a ­ b i l i t y of the ARDISC model to l a b o r a t o r y studies of n u c l i d e mi­ g r a t i o n i n geologic media. Basic D e s c r i p t i o n of Model The model assumes a one dimensional column d i v i d e d i n t o an a r b i t r a r y number (LEND) of u n i t s or zones. Each zone can sorb a given species such that at e q u i l i b r i u m the d i s t r i b u t i o n of the species between the surface of the zone and the volume of s o l u ­ t i o n ( i n i t i a l l y at u n i t concentration of the species) i s

α/3 where a = amount of species sorbed on the and

(1)

surface

3 = 1 - α If a f t e r t h i s d i s t r i b u t i o n i s e s t a b l i s h e d , a second c y c l e occurs i n which the s o l u t i o n from the i n i t i a l zone i s t r a n s f e r r e d to a second zone with the same c h a r a c t e r i s t i c s as the f i r s t zone and a f r e s h s o l u t i o n c o n t a i n i n g none of the species i s placed i n the f i r s t zone, another e q u i l i b r a t i o n , t h i s time i n both zones w i l l occur. This process i s continued by the model f o r a d d i t i o n a l c y c l e s and zones. The d e s c r i p t i o n of the model up to t h i s point i s analogous to a d e s c r i p t i o n of a chromatographic model which incorporates the concept of the t h e o r e t i c a l p l a t e (5). I f , however, the movement from zone to zone i s f a s t enough that e q u i l i b r i u m does not occur, the f r a c t i o n sorbed from s o l u ­ t i o n can be c a l c u l a t e d i f the r a t e of s o r p t i o n i s known (or can be estimated). A parameter, F, i s therefore defined p _ f r a c t i o n of species sorbed from s o i n , during one c y c l e time f r a c t i o n of species sorbed from s o i n , at e q u i l i b r i u m which can be r e l a t e d to the r a t e of adsorption

of the

species.

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

10.

RICKERT E T A L .

Nuclide

Migration

169

The parameter, F, gives d i r e c t l y the amount adsorbed i n a zone i n which the species i n i t i a l l y i s present only i n the s o l u t i o n . For any species adsorbed on the surface o f a zone, the f r a c ­ t i o n of the sorbed species which desorbs during the time of a c y c l e can be measured (or estimated). Another parameter, G, i s therefore defined

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch010

^ f r a c t i o n of species desorbed from surface during 1 c y c l e t i m e l y f r a c t i o n of species desorbed from surface at e q u i l i b r i u m to account f o r desorption under non-equilibrium c o n d i t i o n s . The parameter, G, gives d i r e c t l y the amount desorbed i n a zone where the species i s i n i t i a l l y present only on the s u r f a c e of a zone. Thus f o r each zone, during a given c y c l e , the adsorptiondesorption process i s separated i n t o two d i s t i n c t events with F or G d e s c r i b i n g the k i n e t i c s o f each event. Such an approach i s of course v a l i d only f o r f i r s t order r a t e r e a c t i o n s . In the l i m i t of low concentration, (such as that r e s u l t i n g from slow l e a c h i n g from a r e p o s i t o r y ) the r e a c t i o n s i t e s on the rock w i l l not approach s a t u r a t i o n and the number of r e a c t i o n s i t e s can be considered to remain constant during adsorption. Therefore, f o r a s i n g l e species i n s o l u t i o n at t r a c e r concentrations the reac­ t i o n should approximate a f i r s t order r e a c t i o n ( i . e . , where no complications such as concentration e f f e c t s , step-wise dehydra­ t i o n , d i s s o c i a t i o n , e t c . , are p r e s e n t ) . I f a c a l c u l a t e d c y c l e i s defined as a p a r t i a l e q u i l i b r a t i o n between the species on the surface of a zone and the species i n the s o l u t i o n of a zone, and i s followed by an instantaneous t r a n s f e r of the s o l u t i o n to the next zone, the f o l l o w i n g r e c u r ­ s i v e formulae apply: R(£,Z) = GaR(£-l,Z) + (1-G)R(£-1,Z) + FaS(£-l,Z)

(4)

S(£,Z+1) = FgS(£-l,Z) + (l-F)Sa-l,Z) + G3R(^-1,Z)

(5)

or rearranging R(£,Z) = [Ga+l-G]R(£-l,Z) + FaS(il-l,Z)

(6)

S(£,Z+1) = [Fg+l-F]S(£-l,Z) + GgR(£-l,Z)

(7)

where R(£,Z) = amount of species sorbed on the surface i n the Zth zone a f t e r the £th c y c l e . S(£,Z+1) = amount of species i n s o l u t i o n i n the (Z+l)th zone a f t e r the £th c y c l e . ( the s o l u t i o n i n the Zth zone i s t r a n s f e r r e d to the (Z+l)th zone at the end of the £th c y c l e . ) Thus i f a, F, and G are known and i f I and Ζ are s p e c i f i e d , the d i s t r i b u t i o n o f the species both i n s o l u t i o n and on the media can be c a l c u l a t e d by the model. For equations 6 and 7, one must have

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

170

RADIOACTIVE W A S T E IN

an i n i t i a l amount of species

GEOLOGIC STORAGE

present.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch010

Experimental I f the r a t e of adsorption, the r a t e of desorption, and the e q u i l i b r i u m p a r t i t i o n i n g of a n u c l i d e between a s o l i d medium and s o l u t i o n are known, then the r a t e of migration of a n u c l i d e through the medium can be p r e d i c t e d with the ARDISC model. The r a t e of a d s o r p t i o n and the r a t e of desorption are assumed to be dependent on the geometric r e l a t i o n s h i p of the rock and sol u t i o n ( i . e . , dependent upon the volume of s o l u t i o n and on the shape and area of the s o l i d medium i n contact with the s o l u t i o n ) . Because the dependence of s o r p t i o n k i n e t i c s on the geometric r e l a t i o n s h i p i s not known, the r a t e s f o r s o r p t i o n are determined by experiment f o r the p a r t i c u l a r geometry (surface area of rock to volume of s o l u t i o n ) f o r which the p r e d i c t i o n of n u c l i d e migration is desired. The a p p l i c a b i l i t y of the ARDISC model to l a b o r a t o r y migration experiments was studied i n two sets of experiments. In the f i r s t set of experiments, the r a t e of adsorption, the r a t e of desorpt i o n , and the e q u i l i b r i u m p a r t i t i o n i n g of americium I I I between s o l u t i o n and simulated f i s s u r e s were measured i n s t a t i c and batch experiments. The measured parameters were used i n the model to p r e d i c t the m i g r a t i o n of americium I I I through simulated f i s s u r e s . The p r e d i c t i o n s were compared with experimental r e s u l t s . In the second set of experiments, strontium was eluted through a column of g l a u c o n i t e at s i x s o l u t i o n flow r a t e s ranging from 14.4 to 721 centimeters per hour. To o b t a i n input data f o r the ARDISC model the e q u i l i b r i u m p a r t i t i o n i n g of strontium between s o l u t i o n and g l a u c o n i t e was determined from the r e s u l t i n g curves and the r a t e for adsorption and the r a t e f o r desorption were determined by curve f i t t i n g the r e s u l t s of one of the column i n f i l t r a t i o n experiments. The parameters that were determined i n t h i s way were used i n the model to p r e d i c t the migration of strontium through the column of g l a u c o n i t e f o r four of the s o l u t i o n flow r a t e s . The p r e d i c t i o n s were compared with experimental r e s u l t s . Fissures F i s s u r e s were f a b r i c a t e d by c u t t i n g slabs of rock from a core of gray hornblende s c h i s t . X-ray d i f f r a c t i o n a n a l y s i s of gray hornblende s c h i s t i d e n t i f i e d c h l o r i t e and an amphibole (hornblende) as the major mineral phases present and f e l d s p a r as a minor c o n s t i t u e n t . The s l a b s were cut i n t o r e c t a n g l e s approximately 2.54 cm wide by 5.08 cm long. Each piece was p o l i s h e d on one s i d e with s u c c e s s i v e l y f i n e r s i z e d abrasive with the f i n a l a b r a s i v e s i z e being 600 mesh. To form a f i s s u r e , two rectangular pieces were put together. Wax gaskets were placed along the long edges of the rectangular pieces to form a 0.027 cm gap between

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

10.

RiCKERT E T A L .

Nuclide

171

Migration

the two p i e c e s . The surface area to volume r a t i o produced was 74 cm to 1 mL and the surface area to volume r a t i o was constant f o r a l l the f i s s u r e s used.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch010

2

F i s s u r e Adsorption Experiments. To perform f i s s u r e s o r p t i o n experiments, one end of each f i s s u r e was connected v i a small bore tubing to a m i c r o l i t e r p i p e t t e r as i s shown i n Figure 2. Rocke q u i l i b r a t e d water, described below, was i n j e c t e d i n t o each f i s sure and the f i s s u r e w a l l s were allowed to e q u i l i b r a t e with the s o l u t i o n f o r a p e r i o d of two days before the a d s o r p t i o n e x p e r i ments were performed. Rock-équilibrated water was produced by a l l o w i n g d i s t i l l e d water to be i n contact w i t h granulated gray hornblende s c h i s t f o r a period of s e v e r a l days. The s o l u t i o n produced was f i l t e r e d through a 0.4 \im NUCLEPORE f i l t e r before use. A n a l y s i s of the r e s u l t i n g s o l u t i o n showed that rock e q u i l i b r a t e d - w a t e r contained 48 mg/L t o t a l s o l i d s (dried at 180°C). The E^ of the s o l u t i o n was measured to be 0.275 V. The pH of the gray hornblende s c h i s t e q u i l i b r a t e d water was measured to be 7.6 at the time of the f i r s t a d s o r p t i o n experiment. Thereafter the s o l u t i o n pH was maintained at 7.5-7.7. Adsorption experiments were performed by removing rocke q u i l i b r a t e d water from the f i s s u r e s and i n j e c t i n g stock s o l u t i o n which was made by d i s s o l v i n g t r a c e r amounts of americium-241 i n rock e q u i l i b r a t e d water. The stock s o l u t i o n was allowed to e q u i l i b r a t e w i t h i n the f i s s u r e s f o r d i f f e r e n t p e r i o d s of time and was then removed from each f i s s u r e . The stock s o l u t i o n was assayed before i n j e c t i o n and a f t e r removal from the f i s s u r e s so that the change i n americium c o n c e n t r a t i o n was determined f o r a d i f f e r e n t time i n each f i s s u r e . Ten a d s o r p t i o n experiments were performed i n t h i s manner and the r e s u l t s are presented i n t a b l e I . F i g u r e 3 i s a g r a p h i c a l r e p r e s e n t a t i o n of the i n i t i a l part of the adsorpt i o n curve. E q u i l i b r i u m P a r t i t i o n i n g Experiments. The e q u i l i b r i u m p a r t i t i o n i n g of americium-III between gray hornblende s c h i s t and rock e q u i l i b r a t e d water was determined i n batch p a r t i t i o n i n g e x p e r i ments w i t h r e c t a n g u l a r blocks of gray hornblende s c h i s t ( 5 ) . The surface area s o r p t i o n c o e f f i c i e n t , K , was determined to be 4.5 ± .5 mL/cm where g

2

Κ s α from tion 3 from tion

— volume of s o l u t i o n β surface area of sample

,gv

equation 1 i s the f r a c t i o n of n u c l i d e concentra­ adsorbed from s o l u t i o n . equation 1 i s the f r a c t i o n of n u c l i d e concentra­ remaining i n s o l u t i o n ; 1 - a.

Solving equation 8 f o r the geometric surface area to volume r a t i o

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch010

172

RADIOACTIVE W A S T E IN GEOLOGIC

STORAGE

ADSORPTION TIME, hr Figure 1. Sorption of plutonium IV and americium III from solution by a tablet of granite. Experiment No. 16; granite LI-6152; (•), Pu; (O), Am. 237

241

FISSURE WITH WAX GASKET -ROCK FISSURE

MICROLITER PIPETTE

-MICROBORE TUBING

Figure 2.

Apparatus used in static fissure adsorption experiments

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

10.

RICKERT

ET

AL.

Nuclide

Migration

173

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch010

found i n the f i s s u r e s , the f r a c t i o n of the n u c l i d e concentration p r e d i c t e d to be adsorbed by the f i s s u r e surfaces at e q u i l i b r i u m i n f i s s u r e s o r p t i o n experiments i s 0.997. F i s s u r e Desorption Experiments. Desorption experiments were performed w i t h two f i s s u r e s by i n j e c t i n g rock e q u i l i b r a t e d water i n t o the f i s s u r e s immediately a f t e r removing the americium-bearing s o l u t i o n from the f i s s u r e s i n adsorption experiments. A f t e r i n j e c t i o n , the r o c k - e q u i l i b r a t e d water was allowed to r e a c t w i t h i n the f i s s u r e s f o r a p e r i o d of time before removal. The rocke q u i l i b r a t e d water was assayed a f t e r removal from the two f i s s u r e s and the amount of n u c l i d e desorbed as a f u n c t i o n of contact time was determined. Between f i v e and seven desorption experiments were performed f o r each of s i x time p e r i o d s between ten seconds and s i x t y minutes f o r each of the two f i s s u r e s . The r e s u l t s of the desorption experiments are presented i n t a b l e 2 as the percent of 3 (at e q u i l i b r i u m ) that desorbed from the f i s s u r e s i n a period of time. Because most of the americium remains on the rock even a f t e r d e s o r p t i o n i s completed, the r a t i o of a c t i v i t y desorbed to that expected at e q u i l i b r i u m i s subject to l a r g e u n c e r t a i n t y . The r e s u l t s of the desorption experiments are so v a r i e d that no q u a n t i t a t i v e c o n c l u s i o n can be drawn about the r a t e f o r d e s o r p t i o n . However, the r e s u l t s do i n d i c a t e that desorption may occur with a r a t e equal to or l e s s than the r a t e f o r a d s o r p t i o n . F i s s u r e E l u t i o n Experiments. The m i g r a t i o n c h a r a c t e r i s t i c s of americium by water transport i n f i s s u r e s f a b r i c a t e d from gray hornblende s c h i s t were determined. F i s s u r e s not used i n the previous s o r p t i o n experiments were used f o r these e l u t i o n e x p e r i ments. A diagram of the experimental apparatus i s shown i n Figure 4. S o l u t i o n r e s e r v o i r s were attached above the f i s s u r e s and the small bore tubes a f f i x e d to the bottom o f the f i s s u r e s were connected to s o l u t i o n metering pumps. Before the e l u t i o n experiments were performed, the " s c h i s m e q u i l i b r a t e d water was pumped through the f i s s u r e s f o r two days to a l l o w the f i s s u r e w a l l s to i n t e r a c t w i t h the r o c k - e q u i l i b r a t e d water. Two sets of f i s s u r e e l u t i o n experiments were performed. In the f i r s t set of experiments, the rock e q u i l i b r a t e d water contained i n the r e s e r v o i r s above three f i s s u r e s was f i r s t replaced with americium b e a r i n g stock s o l u t i o n . The s o l u t i o n metering pumps were l e f t running i n order not to i n t e r r u p t the flow w h i l e the exchange was made. The flow was slow enough that a i r was not drawn i n t o the f i s s u r e s during the exchange. Flow was continued u n t i l an a r b i t r a r y volume, 0.67 f i s s u r e volumes, of stock s o l u t i o n were drawn i n t o each f i s s u r e and then the s o l u t i o n metering pumps were turned o f f . T h i s volume was chosen to permit the observance of a l e a d i n g edge of a c t i v i t y , i f i t e x i s t e d , moving w i t h the water f r o n t . Stock s o l u t i o n was drawn i n t o the f i s s u r e s at l i n e a r

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

RADIOACTIVE W A S T E

Table I .

241 Am Adsorption by Gray Hornblende S c h i s t : F i s s u r e Experiments ( s t a t i c )

Adsorption Time, Seconds

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch010

IN GEOLOGIC STORAGE

Fissure Number

15 54 150 300 600 3600 60120 60120 86400 250200

1 5 8 2 7 4 2* 8* 5* 6

Percent Remaining in Solution

Activity Applied i n 152 λ

84 .6 71 63 .1 50 .7 36 .3 32 .3 25 .0 17 .4 2.20 0. 05

65 n C i 0.98 n C i 0.97 n C i 1.1 n C i 1.7 n C i 56 n C i 173 n C i 184 n C i 111 n C i 0.84 n C i

± .1 + 1 + .9 ± .8 ± .5 ± .1 ± .1 ± .1 ± .02 ± .25

*Cores #2, #5, and #8 were used twice f o r adsorption ex­ periments. The a c t i v i t y a p p l i e d during the f i r s t ad­ s o r p t i o n experiments was i n s i g n i f i c a n t when compared to the a c t i v i t y a p p l i e d i n the second experiment. The reported e r r o r s are f o r counting s t a t i s t i c s . +3 Table I I . Desorption Time, Seconds 10 20 60 360 1200 3600

Am

Desorption from Gray Hornblende S c h i s t : F i s s u r e Experiments ( s t a t i c ) Desorption Runs 5 7 7 6 5 7, 6 (core #8)

Percent of 3* (at e q u i l i b r i u m ) Desorbed Core #2 Core #8 8 13 31 8 13 14

+ 5

± ± ± ±

10 47 6 8 + 19

4 13 19 13 6 22

± ± ± ± ±

2 4 6 5 2 + 16

*3 i s the f r a c t i o n of a n u c l i d e i n s o l u t i o n a t e q u i l i b r i u m . The desorption values were determined assuming that 0.003 of the n u c l i d e would be i n s o l u t i o n a t e q u i l i b r i u m . The values that are presented are the a r i t h m e t i c mean and standard d e v i a t i o n s found f o r the number of experiments performed f o r each time i n t e r v a l .

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Nuclide

Migration

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch010

RiCKERT E T A L .

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

175

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch010

176

RADIOACTIVE W A S T E

IN GEOLOGIC

STORAGE

flow r a t e s of 1.13, 2.29, and 4.77 cm/hr r e s p e c t i v e l y . After stopping the flow of stock s o l u t i o n i n t o the f i s s u r e s , i t was r e moved from the r e s e r v o i r s above the f i s s u r e s and the s o l u t i o n i n each f i s s u r e was l e f t stagnant f o r a period of twenty-four hours. Based on the k i n e t i c data i n t a b l e 1, i t i s b e l i e v e d that the americium i n the stock s o l u t i o n becomes e q u i l i b r a t e d with the surface of the f i s s u r e s d u r i n g the twenty-four hour p e r i o d that the stock s o l u t i o n remained stagnant. At e q u i l i b r i u m 0.997 of the americium i s adsorbed; i t i s t h e r e f o r e expected that the americium d i s t r i b u t i o n on the f i s s u r e w a l l s , a f t e r the twenty-four hour period, represents the m i g r a t i o n of americium i n t o the f i s s u r e s during the 0.67 f i s s u r e volume e l u t i o n s . A f t e r the twenty-four hour period of contact, the s o l u t i o n i n the f i s s u r e s was r a p i d l y withdrawn. The s u r f a c e s of the f i s s u r e s were d r i e d under vacuum at 25°C and then dismantled. The d i s t r i butions of americium on the f i s s u r e surfaces were determined f i r s t q u a l i t a t i v e l y using autoradiographs of the f i s s u r e s u r f a c e s with POLAROID LAND black and white 3000 ASA type 47 f i l m . The autoradiographs are shown i n F i g u r e s 5, 7, and 9. The l i g h t e r areas on the autoradiographs represent areas of americium a d s o r p t i o n . The d i s t r i b u t i o n s o f americium on the f i s s u r e s u r f a c e s were then q u a n t i t a t i v e l y determined by scanning the face of each f i s sure with a Nal s c i n t i l l a t i o n c r y s t a l through a 0.3 cm s l i t i n lead s h i e l d i n g . The 59 keV gamma ray emitted by Am was moni t o r e d . Histograms of the americium d i s t r i b u t i o n s on the f i s s u r e surfaces were produced and a r e presented i n F i g u r e s 5, 7, and 9. The second s e t of f i s s u r e - e l u t i o n experiments was performed i n the same manner as described f o r the f i r s t set of f i s s u r e e l u t i o n experiments. The d i f f e r e n c e i n the second set o f e x p e r i ments was that a f t e r 0.67 f i s s u r e volumes of stock s o l u t i o n were drawn i n t o the f i s s u r e s a t t h e i r r e s p e c t i v e flow r a t e s , the stock s o l u t i o n i n the r e s e r v o i r s was replaced with r o c k - e q u i l i b r a t e d water. The s o l u t i o n metering pumps were not turned o f f during the exchange. Subsequently, a t o t a l of twenty f i s s u r e volumes of sol u t i o n was drawn through each f i s s u r e before the metering pumps were turned o f f . A f t e r the metering pumps were stopped, the rocke q u i l i b r a t e d water was removed from the r e s e r v o i r s and the s o l u t i o n i n the f i s s u r e s was r a p i d l y drawn o f f . The f i s s u r e s were d r i e d under vacuum at 25°C and were d i s mantled. The d i s t r i b u t i o n s of americium on the f i s s u r e s u r f a c e s i n the second set of experiments were determined as they were i n the f i r s t s e t , that i s : f i r s t q u a l i t a t i v e l y by autoradiography and then q u a n t i t a t i v e l y by gamma scanning the f i s s u r e faces through a 0.3 cm s l i t . Autoradiographs of the f i s s u r e surfaces from the second set of experiments are presented i n Figures 6, 8, and 10. Histograms r e p r e s e n t i n g the q u a n t i t a t i v e l y determined d i s t r i b u t i o n of americium on the f i s s u r e s u r f a c e s are a l s o presented i n F i g u r e s 6, 8, and 10. 2lfl

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

10.

Nuclide

RICKERT E T A L .

177

Migration

60η 50ζ 40»— 30ζ 20L U 10L U

Α.

ERC

Ο rvi

I '2 V 4 ' 5 ^ >

7 8 9Ίθ'ΐΐΊ2Ί3Ί4Ί5Ί6' Ι

,

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch010

Z0NES(0.3I75 cm)

ιοο

Ί

90L U 80Ζ Ο 70ΓνΙ Ζ 6050L U 40CC 30L U •_ 20-

ιο-

Ι 2Τ4 5 6 7 8 9 Ι0 || Ι2 Ι3 Ι4 Ι5 Ι6' Z0NES(0.3l75cm) ,

,

,

,

,

,

,

,

,

,

,

Ι

,

Figure 5. Distribution of americium on fissure surface, experimental and pre­ dicted, after 0.67 fissure volume elution. Flow rate of 1.13 cm/hr. (A), Americium distribution on surface of fissure; (B), model prediction of americium on sur­ face of fissure; (C) autoradiograph of fissure surface showing americium dis­ tribution. y

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

178

RADIOACTIVE W A S T E

Ο

IN GEOLOGIC

STORAGE

6050H 403020i OH

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch010

5 6 7 β^ΊοΊΓιζΊδΊ^ΐδΊθ ZONES (0.3175cm

1

β'θΊΟ'ΙΙ'^'β'^Ίδ'Ιο' ZONES (0.3175cm)

Figure 6. Distribution of americium on fissure surface, experimental and pre­ dicted, after 20 fissure volume elution. Flow rate of 1.13 cm/hr. (A), Americium distribution on surface of fissure; (B), model prediction of americium on sur­ face of fissure; (C), autoradio graph of fissure surface showing americium dis­ tribution.

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

10.

RiCKERT E T A L .

Nuclide

179

Migration

I '2

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch010

ZONES (0.3175 cm)

90η

Β.

LU 8 0 Ο 70-

(VI

605040ο 30ce UJ 2 0 10-

5 " V 7 8 9 Ï Ô i I ' 12 ' 13 ' 14 Ί 5 ' 16 ' T

T

T

r

ZONES (0.3175 cm)

Figure 7. Distribution of americium on fissure surface, experimental and pre­ dicted, after 0.67 fissure volume elution. Flow rate of 2.29 cm/hr. (A), Americium distribution on surface of fissure; (B), model prediction of americium on surface of fissure; (C), autoradio graph of fissure surface showing americium distribution.

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

RADIOACTIVE W A S T E

180

IN GEOLOGIC

STORAGE

A.

5040i 302010-

i^3V5V7V9 io iM2 m4 i5 i6' ZONES (0.3175 cm)

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch010

,

,

,

,

,

5 6 7 8 9 10 II 12 13 14 15 16 Z0NES(0.3l75cm)

Figure 8. Distribution of americium on fissure surface, experimental and predicted, after 20 fissure volume elution. Flow rate of 2.29 cm/hr. (A), Americium distribution on surface of fissure; (B), model prediction of americium on surface of fissure; (C), autoradio graph of fissure surface showing americium distribution.

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

10.

RiCKERT E T A L .

Nuclide

Migration

181

504030i 20ce 10ο

7 8 9 io ii i2 i3 i4 i5 i6 ZONES (0.3175 cm) Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch010

,

,

,

,

,

,

,

,

,

LU

Z0NES(0.3l75cm)

Figure 9. Distribution of americium on fissure surface, experimental and pre­ dicted, after 0.67 fissure volume elution. Flow rate of 4.77 cm/hr. (A), Americium distribution on surface of fissure; (B), model prediction of americium on surface of fissure; (C ), autoradio graph of fissure surface showing americium distribution.

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

182

RADIOACTIVE

WASTE

IN GEOLOGIC

STORAGE

60-, 50-4030201012' 13' 14' 1516'

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch010

ZONES (0.3175 cm

U J

ZONES (0.3175cm)

Figure 10. Distribution of americium on fissure surface, experimental and predicted, after 20 fissure volume elution. Flow rate of 4.77 cm/hr. (A), Americium distribution on surface of fissure; (B), model prediction of americium on surface of fissure; (C), autoradio graph of fissure surface showing americium distribution.

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

10.

RICKERT E T A L .

Nuclide

Migration

183

Model P r e d i c t i o n s . The r a t e f o r desorption of americium from the f i s s u r e surfaces i n t o s o l u t i o n was assumed to equal the r a t e f o r the adsorption of americium from s o l u t i o n by the f i s s u r e sur­ f a c e s . The s o r p t i o n r a t e and the e q u i l i b r i u m f r a c t i o n a t i o n of americium that were determined i n the s t a t i c experiments were used to determine input parameters to the ARDISC model. The ARDISC model p r e d i c t i o n s f o r the d i s t r i b u t i o n s of americium on the f i s ­ sure surfaces i n both sets of experiments are presented i n F i g u r e s 5 through 10 along with the autoradiographs and the experimental histograms r e p r e s e n t i n g the v a r i o u s d i s t r i b u t i o n s of americium on the f i s s u r e s u r f a c e s .

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch010

Strontium M i g r a t i o n Experiments i n Glauconite The work that was performed i n t h i s set of experiments was an extension of work performed by Inoue and Kaufman (7). In the previous work, the m i g r a t i o n of strontium i n g l a u c o n i t e was modeled using c o n d i t i o n s of l o c a l e q u i l i b r i u m f o r flows up to 6.3 kilometers per year (72 cm/hr). The d i f f e r e n c e s between the pre­ d i c t e d and experimental r e s u l t s i n the experiments performed by Inoue and Kaufman may be due to the existence of n o n - e q u i l i b r i u m behavior. Column I n f i l t r a t i o n Experiments. Six i n f i l t r a t i o n e x p e r i ­ ments, each at a d i f f e r e n t flow, were performed with one column of g l a u c o n i t e . The apparatus used i n the i n f i l t r a t i o n experiments c o n s i s t e d of a m i n e r a l column contained i n a s t a i n l e s s - s t e e l tube connected to a s a m p l e - i n j e c t i o n v a l v e and a solution-metering pump. G l a u c o n i t e [a hydrous s i l i c a t e , nominally (K,Na)(Al,Fe , Mg)2 (Al,Si)i*Oio ( 0 H ) 2 ] was prepared by s i f t i n g g l a u c o n i t e sand to o b t a i n a f r a c t i o n of uniform s i z e (70 mesh s i z e ) . The sand was washed repeatedly i n d i s t i l l e d water to remove dust ad­ h e r i n g to the p a r t i c l e s and was packed i n a s t a i n l e s s - s t e e l tube to form a column 15 cm long by 1.0 cm diameter w i t h 53 percent porosity. The column was conditioned by e l u t i n g i t with a s o l u t i o n of 0.01 M CaSOi* and 0.0001 M SrC03 . The s o l u t i o n used i n t h i s set of experiments was produced to simulate the s o l u t i o n used by Inoue and Kaufman. Strontium-85 with SrCl2 c a r r i e r was added to an a l i q u o t of the calcium-strontium s o l u t i o n to form a r a d i o a c t i v e s o l u t i o n with Μ . χ 10 M S r . At the s t a r t of an experiment, a small q u a n t i t y (20 y£) of the r a d i o a c t i v e s o l u t i o n was i n j e c t e d i n t o the s o l u t i o n stream above the g l a u c o n i t e column and the column was eluted w i t h s o l u t i o n u n t i l a l l the r a d i o a c t i v e strontium had moved through the column. The eluent was c o l l e c t e d i n f r a c t i o n s and each f r a c t i o n was analyzed to determine the m i g r a t i o n c h a r a c t e r i s t i c s of the strontium i n the column. The r a d i o a c t i v e strontium i n s o l u t i o n v s . the e l u a t e f r a c ­ t i o n s f o r each flow r a t e i s p l o t t e d i n Figure 11. The strontium 6

8 5

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

184

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch010

RADIOACTIVE W A S T E IN GEOLOGIC

Figure 11. Elution of strontium from the column of glauconite. Peak width increases with flow (top to bottom) indicating nonequilihrium behavior. Slowest flow rate is 0.1 mL/min or 14 cm/hr; fastest flow rate is 5 mL/min or 720 cm/hr.

150

200

250

VOLUME, mL

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

STORAGE

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch010

10.

RICKERT E T

AL.

Nuclide

Migration

185

peaks have a shape that i s dependent on the flow r a t e of the eluent. The sharpest peak i s produced with the slowest flow r a t e ; the widest peak i s produced with the f a s t e s t flow r a t e . The strontium peaks were delayed r e l a t i v e to the advancing water f r o n t (which would t r a v e r s e the column i n the f i r s t 6.5 mL of e l u e n t ) . Moreover, each of the strontium peaks seen i n F i g u r e 11, even the one produced with the slowest flow i s wider than p r e d i c t e d by the peak width (2 mL f u l l width at h a l f maximum) that was seen f o r peaks of t r i t i a t e d water that were e l u t e d through the column ( 8 ) . Therefore, the strontium has i n t e r a c t e d with the g l a u c o n i t e column and, as i n d i c a t e d by the d i f f e r e n t peak shapes, i n t e r a c t e d d i f ­ f e r e n t l y at each flow. The flows given i n Figure 11 were measured by c o l l e c t i n g eluate over s p e c i f i c periods of time. In each ex­ periment, a l l the r a d i o a c t i v e strontium was eluted i n the s i n g l e peak seen i n the f i g u r e . To r e l a t e the s i x curves obtained experimentally with the ARDISC model, the r a t e f o r adsorption, the r a t e f o r desorption and the e q u i l i b r i u m d i s t r i b u t i o n of the n u c l i d e between g l a u c o n i t e and s o l u t i o n had to be determined. The r e l a t i v e m i g r a t i o n r a t e of the peak c o n c e n t r a t i o n of strontium at a s o l u t i o n flow r a t e of 0.1 mL per minute was used to c a l c u l a t e the e q u i l i b r i u m f r a c t i o n a t i o n of strontium between g l a u c o n i t e and s o l u t i o n . I t was determined that at e q u i l i b r i u m 0.958 of the strontium would be adsorbed by the g l a u c o n i t e and 0.042 of the strontium would be i n s o l u t i o n (mobile phase). The r a t e f o r a d s o r p t i o n and the r a t e f o r desorption were determined by curve f i t t i n g with ARDISC. I t was assumed that the r a t e f o r d e s o r p t i o n equaled the r a t e f o r a d s o r p t i o n . The α and β parameters were h e l d constant at 0.958 and 0.042 r e s p e c t i v e l y . The F, G, and zone length input parameters to the ARDISC model were v a r i e d to f i t the strontium migration data at a flow r a t e of 2 mL per minute. Assuming f i r s t order r e a c t i o n k i n e t i c s , the s o r p t i o n r a t e that was determined f o r adsorption and d e s o r p t i o n was 0.187 sec"* . A r e a c t i o n r a t e of 0.187 sec" i m p l i e s a h a l f time of r e a c t i o n of 3.7 seconds. The curves p r e d i c t e d by the model f o r four of the s i x flow r a t e s are presented i n F i g u r e 12. D i s c u s s i o n and

Conclusions

Figures 5, 7, and 9 show the americium d i s t r i b u t i o n s on f i s ­ sure surfaces a f t e r the a d m i n i s t r a t i o n of 0.67 f i s s u r e volumes of stock s o l u t i o n a t flow r a t e s of 1.13, 2.29, and 4.77 cm/hr. The peak concentrations of americium were adsorbed at the top of the f i s s u r e s and l e a d i n g edges of americium were extended i n t o the f i s s u r e s . In general, a t f a s t e r flow r a t e s the r e l a t i v e q u a n t i ­ t i e s of americium sorbed at the top of each f i s s u r e decreased and the l e n g t h and r e l a t i v e amount of the l e a d i n g edge extending i n t o each f i s s u r e i n c r e a s e d .

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

RADIOACTIVE W A S T E IN GEOLOGIC

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch010

186

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

STORAGE

10.

RiCKERT E T A L .

Nuclide

Migration

187

The ARDISC model p r e d i c t i o n s f o r 0.67 f i s s u r e volume a d d i t i o n s of stock s o l u t i o n i n t o f i s s u r e s a t the three flow r a t e s a l s o show that the peak concentrations of americium w i l l be sorbed at the top of each f i s s u r e . The l e a d i n g edges of the n u c l i d e are p r e d i c t e d to extend i n t o the f i s s u r e s . The ARDISC model a l s o pred i c t s that at f a s t e r flow r a t e s , the r e l a t i v e amount of americium sorbed i n the peak concentration at the top of each f i s s u r e should decrease. A l s o , the length and r e l a t i v e amount of the l e a d i n g edge extending i n t o each f i s s u r e i s shown to i n c r e a s e . Figures 6, 8, and 10 show that the d i s t r i b u t i o n s of americium on the f i s s u r e surfaces a f t e r the a d d i t i o n of 0.67 f i s s u r e volumes of stock s o l u t i o n followed by the e l u t i o n of 20 f i s s u r e volumes of " s c h l s t - e q u i l i b r a t e d water through the f i s s u r e s at flow r a t e s of 1.13, 2.29, and 4.77 cm/hr. A comparison was made between the americium d i s t r i b u t i o n s found on the f i s s u r e surfaces a f t e r the a d d i t i o n of americium stock s o l u t i o n and that found a f t e r e l u t i o n of the americium by 20 f i s s u r e volumes of s c h i s t - e q u i l i b r a t e d water. I t was found that a f t e r the i n i t i a l loading of americium i n t o the f i s s u r e s i n the f i r s t 0.67 f i s s u r e volumes of s o l u t i o n , the peak concentrations of americium that were sorbed at the top of the f i s s u r e s decreased i n t h e i r r e l a t i v e c o n c e n t r a t i o n . The l e a d i n g edges of the detectable n u c l i d e concentration extending i n t o the f i s s u r e s had increased i n length and r e l a t i v e concentrat i o n with subsequent e l u t i o n by rock e q u i l i b r a t e d water through the f i s s u r e s . The ARDISC model p r e d i c t e d the same r e l a t i o n s h i p s . The ARDISC model q u a l i t a t i v e l y p r e d i c t e d the shape of the curves r e p r e s e n t i n g the d i s t r i b u t i o n of americium on the f i s s u r e s u r f a c e s . However, the model was not able to p r e d i c t a c c u r a t e l y the d i s t r i b u t i o n of americium on the f i s s u r e surfaces i n each experiment. A p l o t of the n a t u r a l logarithm of the f r a c t i o n of the n u c l i d e remaining i n s o l u t i o n v s . the absorption time does not produce a s t r a i g h t l i n e (Figure 13) f o r the f i r s t f i v e data p o i n t s obtained i n the s t a t i c f i s s u r e absorption experiments. A p l o t of the n a t u r a l logarithm of the f r a c t i o n remaining i n s o l u t i o n v s . time should produce a s t r a i g h t l i n e i f the r e a c t i o n were f i r s t order. The ARDISC model assumes that the s o r p t i o n r e a c t i o n s are f i r s t order. The discrepancy between the experimental and p r e d i c ted r e s u l t s may be due to higher order s o r p t i o n k i n e t i c s . In add i t i o n , d i f f e r e n c e s between the p r e d i c t e d and the experimental r e s u l t s may a l s o be due to a number of f a c t o r s such as non-homogeneous media, non uniform flow through the f i s s u r e s , small pH f l u c t u a t i o n s , p r e c i p i t a t i o n r e a c t i o n s , and c o l l o i d formation by some of the n u c l i d e . In the column i n f i l t r a t i o n experiments with strontium, the model p r e d i c t i o n s c l o s e l y resemble the experimental curves f o r the four flow r a t e s compared. The input parameters to the ARDISC model were derived from experimental data obtained i n i n f i l t r a t i o n experiments. The model p r e d i c t i o n s were based on the assumptions that the r a t e f o r adsorption and the r a t e f o r desorption were equal and that the s o r p t i o n r e a c t i o n s were both f i r s t order.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch010

l,

f f

f l

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch010

188

RADIOACTIVE W A S T E IN GEOLOGIC

-ι

-I 9I " 0

1

ι

ι

1 60

ι

ι

ι

I

1

120

ι

ι

I

1

180

ι

ι

I

ι

240

1

1

I

ι

300

1

1

1

1

1

1

STORAGE

p—r

1 1 1 1 1 « 1 360 420 480 540

Λ

600

seconds

Figure 13.

Plot of In fraction of americium in solution vs. time for the data ob­ tained in the static fissure absorption experiments

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch010

10.

RICKERT

E TA L .

Nuclide

Migration

189

The r e s u l t s o f the experiments presented i n t h i s paper demon­ s t r a t e that the m i g r a t i o n o f n u c l i d e s i n geologic media can be studied experimentally and t r e a t e d i n a t l e a s t a s e m i q u a n t i t a t i v e f a s h i o n u s i n g k i n e t i c and p a r t i t i o n i n g data. The ARDISC model i s a u s e f u l a i d i n a n a l y z i n g n u c l i d e m i g r a t i o n data obtained i n l a b ­ o r a t o r y experiments. But the ARDISC model i s l i m i t e d to f i r s t order s o r p t i o n k i n e t i c s . Phenomena such as n u c l i d e transport by p a r t i c l e s or n u c l i d e t r a n s p o r t i n c o l l o i d a l form w i l l i n t e r f e r e with a k i n e t i c approach to p r e d i c t i n g n u c l i d e m i g r a t i o n . The r e s u l t s i n d i c a t e that the measurement o f k i n e t i c parameters may be as important to under­ standing the migration of a n u c l i d e through a geologic media as the measurement of the e q u i l i b r i u m - s o r p t i o n value ( K ^ ) .

Literature Cited 1.

2.

3. 4.

5. 6.

7.

8.

Seitz, M. G . , Rickert, P. G . , Fried, S. M . , Friedman, Α. Μ., and Steindler, M. J., "Studies of Nuclear-Waste Migration in Geologic Media," Annual Report November 1976 - October 1977, ANL-78-8 (1978). Strickert, R., Friedman, A. M . , and Fried, S., "The Sorption of Technetium and Iodine Radioisotopes by Various Minerals," Nuclear Technology, in press (1978). Friedman, A. M . , E d . , "Actinides in the Environment," Am. Chem. Soc. Symposium Series No. 35, Washington, D . C . , 1976. Strickert, R. G . , Friedman, Α. Μ., and Fried, S. M . , "ARDISC: A Program to Calculate the Distribution of a Radioisotope in Pores of Partially Equilibrated Rock," Argonne National Lab­ oratory Report, in print (1978). Snyder, L . R., Principles of Adsorption Chromatography, Marcel Dekker, Inc., New York, pp. 12-16, (1968). Rickert, P. G . , Seitz, M. G . , Fried, S. M . , Friedman, A. M . , and Steindler, M. J., "Transport Properties of Nuclear Waste in Geologic Media," report to the Waste Isolation Safety Assessment Program, March, ANL program code 85249-00 (1978). Inoue, Y . , and Kaufman, W., "Prediction of Movement of Radio­ nuclides in Solution Through Porous Media," Health Physics, 9, pp. 705-715 (1963). Seitz, M. G . , Rickert, P. G . , Fried, S. M . , Friedman, A. M . , and Steindler, M. J., "Transport Properties of Nuclear Waste in Geologic Media," report to the Waste Isolation Safety Assessment Program, A p r i l , ANL program code 85249-00 (1978).

RECEIVED January 16, 1979.

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

11 Kinetic Effects in Migration A. M. FRIEDMAN and S. FRIED

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch011

Argonne National Laboratory, Argonne, IL 60439

The usual basis of predictions of migratory behavior of ions in geological strata is the treatment of this behavior as an equilibrium chromatographic elution (1,2). This then leads to the following expression for the migratory velocity (v) of a species:

where ν = velocity of the water front K = concentration ratio of absorbed and dissolved solute ε = porosity of the strata ρ = bulk density of the strata. This expression will predict the movement of a solute whose adsorption is in equilibrium with the surrounding strata. This equilibrium chromatographic motion will result in the migration of a band of activity whose concentration profile is gaussian and whose deviation will be a function of the hydrodynamic dis­ persion, T (due to statistical variations in path length) and absorptive dispersion T (due to statistical variations in the absorption and desorption process). While these dispersions are interactive and do not sum in a simple fashion they both depend on path length. The longitudinal hydrodynamic dispersion is given (3, 4, 5) by: w

d

h

a

Τ2h =1/3(λ + 0.173) d l w

(2)

where λ is related to the mean migration distance and grain size, d is the average distance of water flow and l is the pore size. The absorptive dispersion is given by: w

where A is the area of the column 0-8412-0498-5/79/47-100-191$05.00/0 © 1979 American Chemical Society

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

RADIOACTIVE

192

WASTE

IN GEOLOGIC

STORAGE

cF i s the d i s t a n c e absorbing s p e c i e s i s moved Ν i s the number_ o f t h e o r e t i c a l p l a t e s (% number of pores) If we take Ν = d/£, then:

Τ

2

a

2

= 8A (£)(d)

(4)

Therefore both types of d i s p e r s i o n w i l l be p r o p o r t i o n a t e to the square r o o t of the d i s t a n c e migrated. I f they add as a simple v e c t o r sum, (which may be a gross s i m p l i f i c a t i o n ) then:

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch011

Τ

2

= Τ

2

a

+ T h

2

= d(£)

[8A

2

+ 4 (λ + 0.173)] 3

(5)

T h i s type of behavior would produce d i s t r i b u t i o n s of a c t i v i t y shown i n Figure 1 where the v a r i o u s peaks are symmetric gaussians of i n c r e a s i n g width. However, i n many cases i n v o l v i n g g e o l o g i c a l m a t e r i a l s these normal behavior p a t t e r n s are not observed. Figures 2-A and 2-B are i l l u s t r a t i o n s of t h i s f o r Pu (6) and Cs (2) ions.. As can be seen i n the f i g u r e s the d i s t r i b u t i o n s are n e i t h e r symmetric (or gaussian) and tend to form a "plume i n the d i r e c t i o n of flow. This plume can, of course, lead to higher concentrations than normal a t d i s t a n c e s downstream from the main body of a c t i v i t y and thus are important to models of waste m i g r a t i o n . There are s e v e r a l types of mechanisms that could account f o r t h i s behavior. (A) There could be abnormal flow paths, such as f i s s u r e s which a l l o w a small amount of a c t i v i t y to migrate more q u i c k l y than the main body. (b) T h i s a c t i v i t y could be c a r r i e d on c o l l o i d a l , non-absorbing p a r t i c l e s . Or (C) the flow r a t e could be too f a s t f o r e q u i l i b r i u m to occur f o r the adsorption and d e s o r p t i o n processes. These p o s s i b i l i t i e s can be examined to determine which appears the most important. Figure 3 i l l u s t r a t e s the d i s t r i b u t i o n s found f o r P u and 11

2 3 7

2 4 1

Am when a mixed sample of these t r a c e r s was i n f i l t r a t e d i n t o a l a r g e (30 cm χ 30 cm) b l o c k of B a n d e l i e r t u f f ( 6 ) . The n u c l i d e a c t i v i t i e s were determined simultaneously by c o r i n g s e c t i o n s of the t u f f and represent the a c t i v i t y d i s t r i b u t i o n s i n the rock. I t i s obvious that although the a c t i v i t i e s are both normalized at 100% a t the surface the increased d i s p e r s i o n of the plutonium c o n c e n t r a t i o n d u r i n g e l u t i o n leads to an increase of almost an order of magnitude i n i t s a c t i v i t y r e l a t i v e to Am a t the 5-6 cm depth. I t i s h i g h l y u n l i k e l y that abnormal flow paths or movement of c o l l o i d a l c l a y p a r t i c l e s would d i s c r i m i n a t e between americium and plutonium; t h e r e f o r e t h i s experimental r e s u l t tends to discount these p o s s i b l e types of mechanisms. However, a pure Pu polymer could c a r r y the Pu more r a p i d l y downstream. A f u r t h e r u s e f u l p i e c e of information can be obtained from data such as i s i l l u s t r a t e d i n Figure 4 (_2) . In t h i s experiment a simulated groundwater s o l u t i o n t r a c e d with Pu and Am was shaken with a sample of b a s a l t and the c o n c e n t r a t i o n of ions i n

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

11.

FRIEDMAN AND

0.10 0.09

FRIED

Kinetic

1

ι Iι1'1

Effects

in

1

1

193

Migration

I ι1

1

1

1

1

—

0.08

—

0.07

—

0.06

-

0.05

—

0.04 Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch011

0.03 0.02 0.01

Ω

/

-

/ Λ ,

0

\/

/ , / 4 8

-

\

\ Χι , I

, \ « 1 ^ 12 16 20

ι

24

I 28

,

Γ*Ί^

32

36

d

Figure 1.

Predicted movement of elution peaks calculated by the use of Equation 5 for the dispersion and a linear absorption isotherm solution

Figure 2a. Concentrations of activity observed for Pu (originally in the IV oxidation state) when eluted into a (30 X 30-cm block of) Bandelier tuff and washed with various amounts of water: ( j, the distribution calculated for a gaussian shape; (- · -), the residual ac­ tivity; (O), 150 mL rainfall; (χ), 500 mL rainfall; 7000 mL rainfall. 238

0.01

0.001

DEPTH,cm

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch011

194

RADIOACTIVE W A S T E IN GEOLOGIC

STORAGE

Figure 2b. Activity curve for concentrations of Cs* absorbed on a column of Selma chalk. Two series of samples of chalk were analyzed after the experiment and their radioactivities are indicated by the histograms. The smooth curve is the distribution inferred from these results. Column 24-3, selma chalk, Cs-134. ( ), First series of samples; ( ), second series of samples. 134

Figure 3. Relative activities of Pu and Am* found in Bandelier tuff after simultaneous elution. Values are normalized to 100 at the surface. (O), Pu; (χ Am; 1.0 L rainfall. 237

+4

2 4 1

3

237

2 4 1

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch011

F R I E D M A N A N D FRIED

0

Kinetic

200

Effects in

400

Migration

600

800

1000

ADSORPTION TIME , hr Figure 4.

Relative absorption rates of Am* and Pu* on basalt. Experiment No. 19, Columbia River basalt; (•), Pu (O), Am. 2 4 1

3

237

237

4

;

241

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

196

RADIOACTIVE W A S T E

IN GEOLOGIC

STORAGE

Table I

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch011

S t a t i c Absorption Experiments with Plutonium and Americium Added Simultaneously to Each S o l u t i o n at Ambient Temperat u r e . The experiments were each run f o r 900 h or more. Characteristic Reaction Time, h Rock Type

Expt.

Pu

Partition Coefficient,

Am

Pu

Am

a

VL60

30

a

5

150

230

a

180

5

39

25

450

^20

130

28

50

400

41

Limestone, Salem Formation

13-A

40

10

>150

Granite, LI-6152

16

25

160

Columbia River B a s a l t

19

60

T u f f , Nevada Test S i t e

22

Low-Temperature Metamorphic Magenta

a

320 370

a

2.6

a

47

In these experiments, a c o n s i d e r a b l e amount (>50%) of the r a d i o n u c l i d e a s s o c i a t e d with the s o l u t i o n was r e t a i n e d on the w a l l s of the polyethylene tube. The a c t i v i t y i n the s o l u t i o n was determined by s u b t r a c t i n g the a c t i v i t y on the w a l l s from the a c t i v i t y of the tube plus s o l u t i o n . The c o r r e c t i o n s are l a r g e and may have l e d to e r r o r s i n the c a l c u l a t e d p a r t i t i o n coefficients.

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

FRIEDMAN

A N D FRIED

Kinetic

Effects

in

Migration

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch011

VERTICAL DISTRIBUTION OF Py AS A FUNCTION OF RATE OF DEPOSITION ON ROCK

DEPTH,cm

Figure 5. Vertical distribution of Pu* as a function of rate of deposition on Bandelier tuff. Total deposit: approximately 2 Χ 10 d/m; ( ), Site A, Pu ap­ plied at rate of 2 mL/min; ( ), Site B, Pu applied at rate of 0.02 mL/min. 237

4

6

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

197

RADIOACTIVE W A S T E IN GEOLOGIC

STORAGE

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch011

RADIAL DISTRIBUTION OF Pu AS A FUNCTION OF RATE OF DEPOSITION ON ROCK

DISTANCE FROM SITE OF DEPOSITION, cm

Figure 6. Radial distribution of Pu+ as a function of the rate of deposition on Bandelier tuff. Total deposit: approximately 2 Χ 10 d/m; ( ), Site A, Pu ap­ plied at rate of 1 mL/min; ( j, Site B, Pu applied at rate of 0.01 mL/min. 237

4

6

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch011

11.

F R I E D M A N A N D FRIED

Kinetic

Effects

in

Migration

199

the aqueous phase was determined a t v a r i o u s i n t e r v a l s o f time. As can be seen the time dependence o f a b s o r p t i o n i s d i f f e r e n t f o r the two elements. T h i s i s g e n e r a l l y true, and i n Table I are f i v e n a few o f the values found i n r e f e r e n c e ( 2 ) . As can be seen i n Table I the time f o r e q u i l i b r a t i o n o f Pu i n t u f f i s much longer than that f o r Am. Furthermore, the time needed f o r e q u i l i b r a t i o n i s much longer than the t r a n s i t time of the s o l u t i o n through the pores o f the rock ( l e s s than 1 h o u r ) . F o r example, i f the average pore s i z e i s 1 mm and i f the flow r a t e i s as low as 10 meters per year, then the average r e s i d e n c e time f o r s o l u t i o n s i n the pores w i l l be 0.88 hours, and e q u i l i brium would not be a t t a i n e d . F u r t h e r evidence that t h i s k i n e t i c e f f e c t i s important can be seen i n F i g u r e s 5 and 6 ( 6 ) . These f i g u r e s demonstrate the r e s u l t s of f u r t h e r experiments on the i n f i l t r a t i o n o f Pu i n t o B a n d e l i e r t u f f . I t i s seen i n these f i g u r e s that both the r a d i a l and l o n g i t u d i n a l d i s p e r s i o n o f the Pu d i s t r i b u t i o n s a r e increased with i n c r e a s i n g flow r a t e . T h i s s e t o f o b s e r v a t i o n s , then, leads to the c o n c l u s i o n that the k i n e t i c s of a d s o r p t i o n and d e s o r p t i o n may s e v e r e l y e f f e c t the d i s p e r s i o n of n u c l i d e s i n geomedia. The f o l l o w i n g paper i n t h i s symposium w i l l d e s c r i b e i n d e t a i l f u r t h e r e x p e r i ments aimed a t q u a n t i f y i n g these e f f e c t s . References (1)

(2)

(3)

(4) (5) (6)

"Actinides in the Environment," p. 16, A. M. Friedman, E d . , Amer. Chem. Soc. Sympos. Series #35, ACS, Washington, D . C . , 1976. "Studies of Nuclear-Waste Migration in Geologic Media," p. 34, M. G. Seitz, P. G. Rickert, S. M. Fried, A. M. Friedman, and M. J. Steindler, Argonne National Laboratory Report ANL-78-8, 1978. J . Bear i n "Flow Through Porous Media," R. J. M. DeWiest, E d . , Chap. 4, p. 140, Acad. Press, N . Y . , 1969 (see r e f . 4,5 for corrections to Bear's formula). "Migration of Plutonium in Rock: Incorrect Dispersion Formula," H. Krugmann, Science, 200, 88 (1978). "Comment," A. M. Friedman and S. Fried, Science, 200, 88 (1978). "Migration of Plutonium and Americium i n the L i t h o s p h e r e , " S. Fried, A. M. Friedman, J. J. Hines, R. W. Atcher, L . A. Quarterman, and A. Volesky, Argonne National Laboratory Report ANL-76-127, 1976.

RECEIVED January 16, 1979.

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

12 Sorption Behavior of Trivalent Actinides and Rare Earths on Clay Minerals

1

G. W. BEALL, B. H. KETELLE, R. G. HAIRE, and G. D. O'KELLEY

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch012

Oak Ridge National Laboratory, Oak Ridge, TN 37830

Much interest in the past few years has been generated in connection with problems of radioactive waste isolation in a growing nuclear economy. Many studies have been initiated to find the most suitable sites for waste repositories, and the environmental impact i f breaches occur in such repositories. These studies must ultimately result in safe methods of storage for nuclear waste for the present and for times that are measured on a geologic scale. Salt mines have been suggested as possible sites for such repositories owing to their geologic stability and limited presence of water. The experiments which we wish to report in this paper were fashioned with this type of repository in mind. Clay minerals are potentially useful in several applications of exchange of radionuclides. They have been shown to be quite useful in removal of specific nuclides from waste streams (1). In connection with the Swedish waste isolation program they are being considered for secondary containment (2). A special case of secondary containment occurs i f waste material should escape from their casks and from the surrounding salt beds. They can be expected to be held by geologic formations surrounding such beds. Therefore, studies of rates of exchange and equilibrium constants are important. Experimental Distribution coefficients were measured employing batch methods. The solution (ml) to clay (mg) ratios were approximately as follows: 1:5 attapulgite; 1:60 montmorillonite; and 1:25 kaolinite. The solutions were brines (NaCl) buffered with pH 5 acetate solution. The original stock solution contained 3 M NaCl and 1 M Na acetate buffer. The lower [Na] solutions were made by Research sponsored by the Office of Basic Energy Sciences, Division of Nuclear Sciences, U.S. Department of Energy, under contract (W-7405-eng-26) with the Union Carbide Corp. 1

0-8412-0498-5/79/47-100-201$05.00/0 © 1978 American Chemical Society

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

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appropriate dilution of this stock solution. The clays employed were obtained from Source Clay Minerals Repository (3:). Attapulgite and kaolin were used as received. A 2% dispersion montmorillonite was prepared and centrifuged to remove approximately 80% of the sand. The remaining suspended clay was converted to the sod­ ium form by passing i t through a Dowex-50 cation exchange column (Na form) at 60°C. The tracers employed in the exchange studies were Am, ^ C m , C f , 5 3 - ^ E s , *UoLaj i 5 7 i69 i34 R b , *+K and S r . The actinides and most of the other isotopes were made at the High Flux Research Reactor at Oak Ridge National Laboratory. The Yb, C s , R b , and S r isotopes were ob­ tained from New England Nuclear. 2l+1

2

2 i + 9

2

2

S

86

2

1 6 9

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch012

m

j

Y

b

i

C

S

j

8 5

13l+

86

8 5

Results The three clays used in this study have different morpholo­ gies. The montmorillonite and kaolinite are typical sheet or plate-like clays, whereas the attapulgite exhibits a needle-like morphology (4j. The distribution coefficients (D) in units liters/kg have been measured as a function of concentration of sodium varying from .25 M to 4 M. They were studied as a function of [Na] be­ cause from the ion exchange equilibrium (5) the equation relating D to [Na] is given by: d log D = -M/N d log[Na] where: Ν = charge of cation on the exchanger M = charge of cation exchanging with cation of charge N. The distribution coefficients (D) in units liters/kg for the rare earths and actinides studied are listed in Tables 1, 2, and 3. Graphical representation of the data for typical rare earths and actinides, contained in Tables 1, 2, and 3, can be seen in Fig­ ures 1 and 2, where log D's vs. log [Na] are plotted. Under a given set of conditions there is very l i t t l e difference between the rare earths and actinides in any of the clays. All the clays exhibit slopes of -1.1 to -1.7, which is in better agreement with a monoacetate complex that would be expected to y i e l d slopes of -2 than the bare Am ion. There are no good activity coefficients available for NaCl, Na acetate and AmCl mixtures; therefore, no attempt was made to correct the experimental numbers. The D val­ ues for kaolinite and montmorillonite are in reasonable agreement when normalized by their respective capacities of 3.0 and 78 m.e./ 100 gm, indicating that the mechanism of exchange for the two clays are quite similar. In contrast, the D values for attapul­ gite are completely out of proportion with its respective 13 m.e./ 100 gm capacity. Another striking difference can be seen in the kinetics of exchange between the clays. Kaolinite and montmorillonite have very rapid exchange reactions that take less than fifteen minutes to come to equilibrium. Attapulgite in contrast takes as long as nine days to come to equilibrium (Figure 3). The D values for Am in a 0.5 M [Na] solution are given as a function of time in Figure 4. It can be seen that there is a very rapid i n i t i a l re+3

3

21+1

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

12.

BEALL ET AL.

Sorption

Behavior

on Chy

Minerah

203

Table 1

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch012

Distribution Coefficients U / k g ) for M(III)/Na(I) Exchange on Kaolinite at pH 5 Molarity [Na] Am Cm Cf Sm Es(pH 4) La 4 2 1 0.5 0.25

0.22 0.45 1.07 1.9 4.3

0.3 0.5 0.7 1.5 3.2

0.16 0.5 1.1 2.2 5.3

0.5 2.0 1.4 2.4 4.9

0.2 0.33 0.44 0.85 3.0

Yb

0.15

0.07 0.11 0.32 0.63 1.83

-

0.44

-

3.95

Table 2 Distribution Coefficients U / k g ) for M(III)/Na(I) Exchange on Montmorillonite at pH 5 Molarity [Na] Am Cm Yb Cf Es(pH 4) La Sm 4 2 1 0.5 0.25

2.2 2.9 6.4 11.5 33.9

2.4 3.6 6.6 14 37

1.6 3.8 7.7 18.0 43.5

3.1 3.5 9.1 25.0 54.0

1.7 2.2 4.0 12.2 38.5

1.7 2.5 5.4 13.7 39.2

1.5 3.1 5.5 18.2 48.7

Table 3 Distribution Coefficients U / k g ) for M(III)/Na(I) Exchange on Attapulgite at pH 5 Molarity [Na] Am Cm Sm Yb Cf La 4 2 1 0.5 0.25

163 550 1,700 6,600 20,400

251 600 1,600 4,000 13,800

310 778 2,300 9,500 24,600

98 201 306 680 1670

99 194 437 1000 1490

103 177 248 490 830

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

RADIOACTIVE W A S T E IN GEOLOGIC

204

Π 10,000

I—I—I—F

Ο Sm • Yb

/ /

/ 1000

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch012

STORAGE

ATTAPULGITE

A

100

MONTMORILLONITE

/ /

, 8

10

/O

ν 6

•

0.1 '

iZl 4

2

KAOLIN

I 1

I L 0.5

0.25

[Να] Figure 1.

Flot of Sm and Yb exchange on kaolin, montmorillonite, and attapul­ gite: log D vs. log [Na].

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

12.

BEALL E T AL.

Sorption

Behavior

on Clay

Minerah

τ

O Am • Cf

/Ο

V

10,000 h —

/ο

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch012

/ο

1000

/ ATTAPULGITE /Ο

• / / /

ο'

100

/ο MONTMORILLONITE · '

/ο

10

V ,

/ D

/

/

KAOLIN

/ 0.1

Figure 2.

J 4

L 2

J

L

1 0.5 0.25 [Να]

Plot of Am and Cf exchange on kaolin, montmorillonite, and attapul­ gite: log D vs. log [Na].

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

205

RADIOACTIVE W A S T E IN GEOLOGIC

STORAGE

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch012

206

Figure 3.

Log D vs. log [Na] for Am on attapulgite as a function of time of equilibrium

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

12.

BEALL ET AL.

Sorption

Behavior

on Clay

207

Minerals

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch012

100,000

10,000 h—

1000

100

60

80

100

120

140

160 180

TIME (hr) Figure 4.

Kinetics of exchange of Am on attapulgite

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch012

208

RADIOACTIVE W A S T E IN GEOLOGIC

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action requiring less than a day for equilibrium, with a second very slow reaction requiring days to come to equilibrium. The D values for Am, Cs, Rb, Κ and Sr on attapulgite are plotted in Figure 5. The D values increase from Κ to Rb and f i n ­ ally Cs. The Cs behavior has been previously reported (7,8). The rates of exchange also follow this order. The Κ and Rb are quite rapid reactions while Cs has a two component reaction, one rapid requiring approximately thirty minutes with a second requir­ ing almost a day. A l l of the preceding data indicate some highly unusual and specific reactions of attapulgite for the rare earths, actinides, and Cs. These highly specific reactions cannot be ex­ plained satisfactorily by analogy to the comparable reactions of kaolin and montmorillonite. The most striking difference between these three clays has already been mentioned previously. The morphological differences deserve more scrutiny as to their structural origins. Structural representation of kaolin, montmorillonite, and attapulgite are given in Figures 6, 7 and 8, respectively. It can be seen that kaolin and montmorillonite do derive their morphologies largely from their structures. These two clays are basically layered stru­ ctures consisting of aluminum oxygen octahedra, and silicon oxygen tetrahedra, differing only in the order of stacking of the com­ ponents. Attapulgite likewise is built up of these basic units, but the major difference occurs in the arrangement of these units. The f i r s t two clays were extended layers of alternating planes of Al and S i . Attapulgite has this same layered structure on a micro­ scopic level. These microscopic units are then linked across a single oxygen shared between two Si tetrahedra. This linking bond exhibits prominent cleavage which results in the needle-like morph­ ology of attapulgite. This linking of the microscopic layered structures also result in a very open channeled structure which contains about 8 z e o l i t i c waters per unit c e l l . These channels could possibly be sources of the high specificity for the rare earths and actinides. It can be speculated that the size of the channels must also be the reason for the differences in both the kinetics and D values seen for Cs, Rb, and K. The two rates of reaction seen for Am and Cs could be explained by these channels also, since the needles would contain two types of channels. The f i r s t would be channels that are quite open resulting from the pro­ minent cleavage exhibited across the weak bond shown in Fig. 8. The second type of channel would be internal having only ends ex­ posed to exchange. The rapid reaction could result from interac­ tion with these highly exposed channels, with the second slower reaction limited by diffusion into the inner channels. The D values on the three clays studied indicate very l i t t l e difference between the rare earths and actinides. The D values also indicate that there is a small increase in D when going from low atomic number to higher atomic number in agreement with re­ sults of (9). The most unexpected results are that geometric or structural considerations can cause high specificity for some

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

BEALL ET AL.

Sorption

Behavior

on Clay

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch012

12.

209

Minerah

Sr ON ν Κ ATTA

0

,I

Figure 5.

I

I

4

2

I

I

I

I

1 0.5 0.25 [No]

Comparison of the exchange of Am, Cs, Rb, K, and Sr on attapulgite

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

210

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch012

RADIOACTIVE W A S T E IN GEOLOGIC

Figure 6.

Structural representation of kaolin

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

STORAGE

BEALL ET AL.

Sorption

Behavior

on Clay

Minerals

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch012

12.

Figure 7.

Structural representation of montmorillonite

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

211

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch012

RADIOACTIVE W A S T E

IN GEOLOGIC

YJk&r^&o—o-o—Λ-Α-Ρ

οο

οο /S^t

Figure 8.

V-*»V

V-*-V

ν-Κ/

Ν#«*>ν

VÎSV

Structural representation of attapulgite

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

STORAGE

12.

BEALL ET AL.

Sorption

Behavior

on Chy

213

Minerals

ions. This high specificity for the actinides in particular has important implications for waste isolation,since * the long term these elements present the greatest hazards in nuclear waste. This behavior of attapulgite toward the actinides could also have possible applications in purification of waste streams or in cleanup of radioactive s p i l l s . Ί

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch012

Literature

η

Cited

1. Tamura, Τ and Jacobs, O. G . , Health Phys. 5, 149-154 (1961). 2. "Handling of Spent Nuclear Fuel and Final Storage of Vitri­ fied High Level Waste," Technical Reports by the Swedish Nuclear Fuel Safety Project (KBS),1978. 3. Source Clay Mineral Repository, University of Missouri, Rolla, Mo. 4. Grim, Ralph E., "Clay Mineralogy," 2nd E d . , McGraw-Hill, Ν. Y . , New York (1968). 5. Nelson, F., Murase, T., and Kraus, K . , J. Chromatog. 13, 503-535 (1963). 6. Choppin, Gregory R., and Schneider, Joan K . , J. Inorg. Nucl. Chem., 32, 3283-3288 (1970). 7. Chandra, Umesh, Master's Thesis, University of Bombay (1969). 8. Merriam, C.Neale, and Thomas, Henry C., J. Chem. Phys., 24, 993-995 (1956). 9. Adgaard, P . , Bull. Groupe franc. Argiles, 26, pp 193-199. RECEIVED January 16, 1979.

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

13 Studies of Actinide Sorption on Selected Geologic Materials R. J. SILVA, L. V. BENSON, and J. A. APPS

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch013

Earth Sciences Division, Lawrence Berkeley Laboratory, Berkeley, CA 94720

The long term objective of this program is to establish a basis f o r the prediction of radionuclide sorption in geologic environments of the type anticipated for terminal radioactive waste storage. In order to begin to identify parameters which should be incorporated in a predictive sorption model, a study of the interaction of U, Np, Pu, Am, and Cm with basalt, shale and granite was i n i t i a t e d . The following discussion covers the experimental results to date. The mineral makeup of the rocks and the composition of the solutions were determined so that as the dependence of nuclide adsorption on these parameters becomes better known, the results of these experiments may be understood in greater d e t a i l . The sorption/desorption processes were studied by a batchtype technique. Aqueous solutions were prepared by mixing rock powders with distilled-deionized water. For the sorption experiments, portions of these aqueous solutions were loaded with tracer quantities of a single radioactive nuclide and contacted with wafers of a given rock type. For the desorption experiments, wafers from the sorption experiments were contacted with the remaining portions of the aqueous solutions. The progress of the contact experiments was monitored by gamma-ray counting of solutions. Actinide tracer concentrations on the wafers and in the solutions were measured at the end of the contact period by alpha and gamma-ray counting. These data were used to calculate sorption coefficients. Autoradiography of the wafers i s being performed to gather information on sorption s p e c i f i c i t y . Selection of Rock Samples and Tracers Radionuclides. Isotope selection was based primarily on three experimental requirements: (1) both alpha and gamma emitters present for counting purposes; (2) alpha emitter present for autoradiography; (3) approximately equal 0-8412-0498-5/79/47-100-215$06.50/0 © 1979 American Chemical Society

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

RADIOACTIVE W A S T E IN GEOLOGIC

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STORAGE

molar concentration of the elements at the start of sorption experiments. Table I shows the isotopic compositions of the tracer solutions and the photons used for gamma counting of samples. In the case of U, Np, and Am, the single isotopes 233u 237|\jp j 243/\ | f both alpha and gamma counting. In the case of Pu, the isotope 237p j f gamma counting, while P u was used for alpha counting and for adjusting the molar concentration. The 243ç used for both alpha and gamma counting and 248ç to adjust the molar concentration. Small amounts of other isotopes made during the production processes were also present in most of the samples. s

s

a n (

m

w

e

r

e

u s e c

o r

u

w

a

s

u s e (

o r

2 4 2

m

w

a

s

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch013

m

Rock Samples. Three rock types were selected as substrates: basalt from the Umtanum unit in the Pasco Basin in Washington state, quartz monzonite from the Climax Stock of the Nevada Test Site, and shale (metashale) from the Eleana Formation of the Nevada Test Site. Since both the basalt and the quartz monzonite exhibited different kinds and amounts of alteration within the same rock type, two samples from each rock type were used in the experiments. However, there was i n s u f f i c i e n t material to study the interaction of the more altered of these rock types with all five actinides, therefore, only the interaction with Pu was studied. Sample Characterization Physical and chemical analyses of the samples wera made in order to i n t e r p r e t the r e s u l t s of the sorption experiments and to provide basic data for the calculation of mass transfer which occurred in the rock dissolution experiment. Cores, 3.2 cm in diameter, were taken from each of the rock samples and sectioned in tap water for subsequent analyses (Figure 1 ) . P é t r o g r a p h i e Studies. Polished t h i n sections were examined by optical methods to determine original mineralogy and alteration phases. The sections were taken and oriented in such a manner to allow comparison of the microscopic mineralogy with the results of the autoradiography experiments The shale was too fine-grained to be characterized in d e t a i l . Both basalt samples (DC3-3600 and DH5-2831) are composed primarily of glass (40-50 percent) and plagioclase feldspar (35-40 percent). They contain in addition minor amounts of clinopyroxene (3-5 percent) orthopyroxene (1 percent), and opaques ( 1 - 2 percent). The r e l a t i v e l y unaltered basalt (DC3-3600) possesses several intersecting fractures f i l l e d with clay. There are dark gray alteration zones adjacent to certain fractures where a smectitic clay has replaced In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Curium

Americium

243 Cm

Cm

Cm

Cm

Am

Am

Pu

Pu

Pu

244

246

248

241

243

237

238

240

Pu

242

Plutonium

T

232

237, Np

t

233

Uranium

Neptunium

Isotope

95.76 3.87 0.0014

1.86 5.45 0.51

0.38

0.15

92.17

99.84

0.02

2.54

0.003 ~ 0.0002

11.32

97.42

0.091

99.91

100

0.0002

99.99+

% by weight

Tracers

4.58

84.08

100

0.43

99.57

% by a l p h a activity

I s o t o p i c Abundances o f A c t i n i d e

Element

Table I.

Pu Κ X - r a y s

75 k e v γ-rays

Np Κ X - r a y s

86 and 29 k e v y - r a y s

Th L X - r a y s

Photon used f o r γ counting

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RADIOACTIVE W A S T E IN GEOLOGIC

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glass and feldspars. Both plagioclase and clinopyroxene have been replaced by secondary minerals (clay, chlorite) along crystal faces and cleavage planes. In the vesicular b a s a l t , (DH5-2831) approximately 40-50 percent of the vesicles remain unfilled; the rest are usually f i l l e d with cristobalite. The quartz monzonite samples (U15E-7 and U15E-7a) were originally composed of 70-80 percent feldspar, 10-15 percent biotite, 3-8 percent quartz, and 2-8 percent opaques. Both samples have been hydrothermally altered; U15E-7a being the more altered. The original feldspars in both samples have been sericitized and/or altered to clinozoisite. Secondary cal cite also occurs in both samples. Pyrite is an abundant secondary mineral and minor amounts of both epidote and chlorite replace biotite and f i l l fractures. Scanning electron microscopy (SEM). SEM studies of the shale and the quartz monzonite samples were not feasible since the morphology of secondary minerals could not be e x p l i c i t l y identified by this technique. Energy dispersive analysis by x-rays (EDAX) of the clay in fractures of the DC3-3600 basalt sample indicated the presence of Fe, Mg, Ca, K, A l , and Si which suggets that the clay is an Fe- and Mg-rich smectite (nontronite). SEM and EDAX studies of DH5-2831, the amygdalic basalt, indicated the presence of a pure s i l i c a phase coated by small clay (smectite) particles. Other vesicles "floored" with pure s i l i c a were covered with a relatively thick coating of the smectite. In addition, one vesicle was f i l l e d with gypsum fibers intermixed with an irregularly-shaped aluminosilicate containing Na, K, and Ca. X-ray diffraction studies. The highly-altered quartz monzonite (U15E-7a) was examined with x-ray diffraction techniques. Four regions, distinguishable in hand specimens by their color, (metallic, pink, dark-gray, and yellow-gray) were sampled and analyzed. The results (Table II) support the pétrographie observations and indicate that the original calcic feldspars have been altered to potassium-bearing phases (potassium feldspar or sericite) or to other secondary calcium-bearing minerals (calcite and c l i n o z o i s i t e ) . Bulk chemical analysis of the solids. The three rock types were chemically analyzed by neutron activation (NAA) and x-ray fluorescence (XRF). The r e s u l t i n g data (not included in this report) were used for depth-of-leaching calculations given below. With the measurement of volatile components in the basalt and shale, the t o t a l measured abundances in a l l three samples was close to 100 percent. Characterization of physical properties. A variety of physical properties were measured including density, specific In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979. Calcite Muscovite/Sericite K-keldspar

PINK SAMPLE

Muscovite/Sericite K-feldspar Quartz

Calcite

Muscovite/Sericite

Quartz

YELLOW-GREY

Pyrite

Calcite

Muscovite/Sericite

Clinozoisite

K-feldspar

Quartz

Pyrite

Pyrite

Altered

DARK-GREY SAMPLE

X-ray D i f f r a c t i o n Data f o r H i g h l y Q u a r t z M o n z o n i t e (U15E-7a)

METALLIC SAMPLE

TABLE I I .

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220

RADIOACTIVE W A S T E IN GEOLOGIC

STORAGE

surface area, permeability, and pore characteristics (Table III). Pore volume was determined by the mercury injection method on a Micromeritics Model 900/910 Porosimeter and also by measuring the volume of gas which flowed into the sample under ambient conditions. Specific surface area was determined both on a Model 2100 Orr Analyzer and on a QUANTAS0RB Surface Area Analyzer by the standard multipoint BET technique using krypton and nitrogen adsorption. Permeability was measured by introducing a gas pressure pulse and monitoring pressure decay (transient method). Certain of the physical data (Table III) appear to be less than satisfactory. In general, agreement between the two types of porosity measurements is not good and the values for DC3-3600, UE15-7 and UE15-7a appear excessively large. The densities of the quartz monzonite appear unusually low, i . e . , values in the range 2.6 to 2.7 were expected

(I). Purification

and C h a r a c t e r i z a t i o n of A c t i n i d e Tracers

Before the tracer solutions were used, i t was necessary to insure elemental purity and freedom from other contaminants. In addition, one oxidation state was selected for each element as the starting point for the experiments. The 6+ oxidation state for U, 5+ for Np, 4 + for Pu, and 3+ for both Am and Cm were used. These selections were accomplished through the use of cation-exchange chromatography. A given radionuclide was f i r s t sorbed on the top of a cation-exchange resin column from a dilute hydrochloric acid solution and, after washing, selectively eluted with a hydrochloric acid solution appropriate for the given oxidation state. The column characterist i c s and chemical form of each radionuclide are shown in Table IV. After column elution, a l l tracers were made up to nearly equal molar concentration in 2M HC1. The Dissolution Experiment It was necessary to prepare an aqueous e l e c t r o l y t e s o l u t i o n f o r the sorption study. To simulate sorption processes which occur in natural systems, the electrolyte solution should f u l f i l l two c r i t e r i a : (1) The composition of the s o l u t i o n should c l o s e l y approximate the natural aqueous phase so that the e f f e c t s of ion pairing and complexation are accounted for. (2) The solution should be in equilibrium with the s o l i d ' s surface with respect to a l l chemical processes excepting sorption/desorption. If the solid dissolves, the surface energy distribution and the composition of the aqueous phase w i l l constantly change. If precipitation occurs, the surface of the solid may become coated with preIn Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

(1) (2) (3) (4)

Fracture Analysis Analysis Analysis

TT

LBL

(4)

7x10

4.57

3x10

16.4

8.36

7

7

6.44

8.54

7.7

UP; (Ah Pu; (Π), A m ; (Ο), Cm.

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

13.

SILVA E T A L .

Actiniae

231

Sorption

100 90 : 80

;

7 0

> 60

!

5 0

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch013

î 40 j 30 ; 20 !0 10

15

T i m e

20

25

30

( d a y s )

Figure 9. Percentage of initial concentrations of tracers left in solution as a function of time for the sorption experiments with the basalt samples. (Φ), U; M)> UP; (Αλ Pu; (Π), Am; (Ο), Cm.

I0O 90| 80 70 60 50 40 30 20 10 0,

10

15

T i m e

20

25

30

( d a y s )

Figure 10. Percentage of initial concentrations of tracers left in solution as a function of time for the sorption experiments with the shale samples. (Φ), U; βλ Np; (A), Pu; (Π), Am; (Ο), Cm.

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

RADIOACTIVE WASTE IN GEOLOGIC STORAGE

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch013

232

100 90 \ 80 ï 70 ! 60 : 50 '. 40 j 30 ; 20 10 0

10

15

T i m e

20

25

30

( d a y s )

Figure 11. Percentage of initial concentrations of tracers left in solution as function of time for the sorption experiments with the quartz monzonite samples. (·}> U; « λ Np; (Ah Pu; (Π), Am; (Ο), Cm.

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

SILVA E T A L .

13.

TABLE V I I .

I = Basalt,

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch013

Sample

I II III I II III I I II III III

—

-

Actiniae

Adsorption Coefficients,

1.51

0.316

0. 343

Np

1.09

0.416

0. 394

Np

0.797

1.53

1. .29

Np

1.53

0.199

0.,204

Pu

4.33

Pu - A

7.00

48.9

423

Pu

3.50

188

Pu

7.37

261

2973

I _ Cm

4.35

Cm

2.78

Cm

3.29

0.459 48.7 0.471 60.1 139

137 729

6.02

III

0.287

0.761

Am

-

2.80 6.65

7.78

7.73

II

2. 01

2.33

11.0

K(gamma)

1.87

υ

3.02

III

K(filter)

υ

Am

II

K(alpha)

0. 797

Pu - A

^/m/gm d/m/ml

I I = S h a l e , I I I = Quartz monzonite, A = A l t e r e d

Am

I

Κ =

r

r^Down υ

Sorption

145 225 143

113 14300

1033

394

962

1290

12700

1323

746

4900

525

724

219

6460

171

1270 97.8

44.2 164

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

234

RADIOACTIVE

TABLE VIII. Desorption Coefficients,

WASTE

IN

GEOLOGIC

Κ=

1= Basalt, 11 = Shale, 111= Quartz monzonite, A= Altered

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch013

Sample

I - U

Up Down

K(alpha)

K(filter)

3.65

2.57

3.50

II

- U

3.83

1.04

1.10

III

- U

2.52

2.26

1.82

I - Np

1.35

1.45

1.19

II

- Np

1.20

0.675

0.570

III

- Np

1.10

3.86

2.90

I - Pu

5.20

I - Pu - A

2.18

345

67.3

777

II

- Pu

1.32

201

122

III

- Pu

2.98

108

103

III

- Pu - A

11.07

779

4.33

274

I - Am

5331

II

- Am

1.01

480

798

III

- Am

4.71

186

1664

I - Cm

5.57

850

12672

II

- Cm

1.75

187

1118

III

- Cm

4.08

561

2676

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

STORAGE

13.

SILVA E T A L .

TABLE V I . DC3-3600 Na

52

235

Sorption

Comparison o f Prepared Waters W i t h Waters From N a t u r a l Systems (mg/1) (1) 37

U15E-7 20

(2)

(3)

93

6.0

Κ

8.0

7.0

26

Mg

4.4

8.0

19

18

38

117

Ca

11

Fe Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch013

Actiniae

1.2

Al Si0

CI

0.2

2

63 6.4

3

190 1.5

2.3

-

.12

pH HC0

19

55 7.8 150 10

3.0

.01 42 6.6 290 1.5

1.6 1.7 10

0.2

.01

0.2 33 7.6 214 32

UE-17E (4)

6.8 57 1.1

12

77 9.0

18

1.1

1.5

13

16

19

32

29

96 .02

1.4

.02 25

(5)

.01 33 6.8 380 0.8

1.0

0

0

16

15

4.9

7.8

126

133

12

25

22 208 2 2.4 SO, 20 2 3 337 4 (1) A v e r a g e c o m p o s i t i o n o f g r o u n d w a t e r s f r o m C o l u m b i a R i v e r b a s a l t s (525 s a m p l e s ) . (2) Seepage w a t e r s f r o m c l i m a x s t o c k ( q u a r t z m o n z o n i t e ) . (3) A v e r a g e c o m p o s i t i o n o f p e r e n n i a l s p r i n g s i n q u a r t z m o n z o n i t e s and g r a n o d i o r i t e s o f t h e S i e r r a Nevadas (56 s a m p l e s ) . (4) G r o u n d w a t e r f r o m t h e B r u n s w i c k S h a l e o f New J e r s e y . (5) G r o u n d w a t e r f r o m t h e C h i c o p e e S h a l e o f M a s s a c h u s e t t s .

ificantly. A blank s o l u t i o n not containing wafers was prepared in a similar manner for each of the five actinides by mixing 50 ml of each of the three water types. The containers were sealed, removed from the inert atmosphere box, and gently agitated with an Eberbach variable-speed shaker for six weeks. The concentrations of tracers in solutions were deter­ mined p e r i o d i c a l l y . The polyethylene containers were constructed in such a way that, when inverted, 50 ml of solution passed from the wafer compartment into a second compartment. The second compartment of the container was inserted through a hole in a lead shield which housed a 3.5 cm diameter by 1.2 cm deep high-purity Ge gamma-ray detector. The other compartment containing the solution and wafers was shielded from the detector by the lead housing. At the end of the six weeks, the containers were returned to the inert atmosphere box and the wafers removed. One wafer was immediately placed in a new container with 50 ml of aqueous solution for the desorption study. The other wafer was rinsed l i g h t l y , allowed to dry and counted.

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

236

RADIOACTIVE W A S T E IN GEOLOGIC

STORAGE

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch013

Aliquots of the solutions (50 ml) were placed in polyethylene bottles f o r gamma-ray counting and 0.5 ml samples were evaporated on platinum plates for alpha count­ ing In addition, 10 ml of each of the solutions were passed through 0.05 ym Nucleopore f i l t e r s . Aliquots (0.5 ml) of the last 2 ml passing the through f i l t e r s were evaporated on platinum plates f o r alpha counting. Both alpha and gamma count rates on the v/afers v/ere measured. Results and Discussion. Changes in concentrations of the actinides in solution in the blank containers are shown in Figure 9. A large fraction of the Pu, Am and Cm was removed from solution while only a small amount of the U and none of the Np was l o s t from s o l u t i o n . Since the starting concentration of Pu exceeds the solubility for the hydroxide (or hydrated oxide), the Pu probably precipitated as colloidal-size particles (2); the behavior of Am and Cm cannot be explained by a similar mechanism. However, there is recent experimental evidence that indicates the solubility products for Am and Cm carbonates may be of the order 10""41 (3). i f t h i s is the case, there was s u f f i c i e n t carbonate ion concentration in the solutions to cause precipitation of these compounds. Figures 10, 11 and 12 show the results of the contact experiments f o r the b a s a l t , shale and quartz monzonite samples. The rate of adsorption was rapid during the f i r s t two weeks and changed slowly thereafter. In these experiments Pu, Am and Cm exhibited behavior similar to the results obtained in the blank experiments. Uranium showed moderate adsorption ( ^ 5 0 percent) on the basalt but only slight adsorption (10-20 percent) on the shale and quartz monzonite wafers. Neptunium showed strong adsorption (70-80 percent) on the shale and slight adsorption ( ^ 1 0 percent) on the basalt and quartz monzonite. The calculated adsorption coefficients (K) are pre­ sented in Table VII. Κ (alpha) refers to r e s u l t s from alpha counting the wafers and solutions, while Κ (gamma) refers to results from gamma counting. Κ ( f i l t e r ) refers to r e s u l t s from the alpha counting of wafers and f i l t e r e d solutions. Measurement precision of the Κ values is _+ 5-10 percent for Κ (alpha) and Κ ( f i l t e r ) . Precision of the Κ (gamma) measurements are _+ 5-10 percent for Am and Cm; + 20 percent for Pu; and +30-35 percent for Np and U. These values represent only errors associated with the counting. Except for Np, alpha counting showed that wafer surfaces facing upward consistently had higher counting rates than surfaces facing downward. The up/down r a t i o s are also presented in Table VII. This behavior suggests that a process such as settling may be involved.

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch013

13.

s i L V A ET AL.

Actiniae

Sorption

Comparisons of Κ (alpha) and Κ (gamma) show good agreement f o r each given rock type and element except for the shale samples. With the exception of Pu, Κ (gamma) values for the shale samples were considerably larger than Κ (alpha) values. Since alpha counting detects only material on the surface while gamma counting detects both surface and bulk-adsorbed material, adsorption on the basalt and quartz monzonite samples represents a surface process while the shale samples exhibit a diffusional effect in addition to surface sorption. Differential migration of the actinides into the samples was not expected since the measured perme­ a b i l i t i e s and p o r o s i t i e s f o r the three rock types were nearly equivalent. However, as was noted above, the perme­ a b i l i t y and porosity data may be substantially in error. F i n a l l y , a comparison of Κ (alpha) and Κ ( f i l t e r ) for each rock type and element show that, while the values for U and Np agree quite well, the values d i f f e r substan­ t i a l l y for Pu, Am and Cm. Apparently, there were s t i l l considerable amounts of f i l t e r a b l e or adsorbable species l e f t in solution after the six weeks contact time. The observed differences between the elements could presumably be attributed to differences in sorption prop­ erties of the chemical species present. Unfortunately, with the possible exception of Np, the lack of a complete set of thermodynamic data precludes a quantitative predict­ ion of the concentrations of the various possible species in s o l u t i o n or of the conditions f o r the formation of solid phases. However, our data suggest that precipitation or colloid formation were the major reactions of Pu, Am and Cm in our solutions and, perhaps, a minor reaction of U. The data obtained from the f i l t e r e d solutions can be used to estimate an upper limit to the concentrations of soluble U, Pu, Am and Cm under the conditions of our experiments. These concentrations were approximately 4xl0" M for U, 2xl0" M for Pu, and 2 x l 0 " M for Am and Cm. 8

10

N

Estimates of the concentrations of possible chemical species in solution for the four actinides were made using measured or estimated s o l u b i l i t y , complexation and hydrolysis constants (4-8), and the measured OH", CO32", SO42-, and CI" concentra­ tions given in Table VI. The results showed that hydroxide and carbonate are the ligands that need to be considered; c h l o r i d e and s u l f a t e concentrations are s u f f i c i e n t l y low that their effects may be neglected. The hydroxide and carbonate concentrations in our solutions were about 4x10" and 1X10"6M, respectively. Solubility product constants of 1 0 " · and 1 0 " · 4 have been reported (8) for uranyl carbonte and hydroxide, respectively. The hydroxide was calculated to be the stable solid phase under the conditions of our experiments. For 1 1

7 3

2 2

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

238

RADIOACTIVE W A S T E IN GEOLOGIC STORAGE

the uranium concentrations used in our experiments, the dominant hydrolysis product was most l i k e l y U02(0H)2; Κ [U0 + 20H- = U0 (0H) ] = 10 I · (8), saturated solution concentra­ tion = 10"'M. The dominant carbonate complex was estimated as U0 C0§; Κ [ U 0 + CO3 - = U0 C0§] = 1 0 · (8), saturation concentration = 5χ10"^Μ· Since the starting concentration of U was 5xlO" M, precipitation was not expected to occur. Therefore, the reasons for the behavior of U in our experi­ ments is not understood. The hydroxide was expected to be the stable solid phase for P u under the conditions of our experiments. Reported and estimated s o l u b i l i t y product constants range from 10" ( 7 J to 10~ ( 6 ) . The major hydrolysis product for P u was estimated to be Pu(0H)4; Κ [ P u + 40H" = Pu(0H)4] = ΙΟ^β.δ (5j^ saturation concentration range = 10"'M to 10"16M. Using t h i s hydrolysis constant, an apparent solubility product quotient of 1 0 ~ 5 6 was calculated from our data. Unfortunately, reliable information does not exist for estimating the effects of carbonate complexing on the system. In addition, i t has been suggested that Pu0 is the major soluble species in equilibrium with the hydroxide precipitate under conditions similar to our experiments (9). Since neither of these e f f e c t s were included, the c a l ­ culated solubility quotient could be in error, i . e . , too large. In general, the chemical behavior of Am and Cm in s o l u t i o n are quite s i m i l a r and s i m i l a r to that of the trivalent lanthanides. The americium hydroxide and carbonate solubility product constants were estimated as 1 0 " · ( 6 ) and 10-33 (]_g) r e s p e c t i v e l y , from published values on lanthanide compounds. The values for Cm would be expected to be nearly the same. The carbonate was calculated to be the stable solid phase. Because of the lack of experimental data on the hydrolysis and carbonate complexation constants, i t is not possible to calculate the concentrations of the major species in our s o l u t i o n s . However, Am(0H) has been estimated (1J) as the dominant hydrolysis product; Κ 2+

2

5

2

9 8

2

2 +

2

2

1 0

2

3

2

8

4 +

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch013

52

62

4 +

4+

+

2

2 3

3

s

2+

[Am + OH" = Am(0H) ] = 1 0 · (4). A saturation concentra­ tion of 10- M was calculated for this species in equilibrium with the solid carbonate. Since the starting concentration of Am was 5 x l 0 " M , p r e c i p i t a t i o n was not a n t i c i p a t e d . However, as mentioned previously, the assumed carbonate s o l u b i l i t y may be high by eight orders of magnitude. From our data, solubility product quotients for the possible compounds, Am fC03)3 and Am0HC03 were estimated as 10-^1 j ι ο - 2 5 respectively. The values for Cm should be similar. 3+

2+

8

0 8

7

8

2

a n c

5

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

13.

s i L V A ET AL.

Actiniae

Sorption

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch013

Rock/Tracer Desorption Experiments Procedures. One of the rock wafers from each of the containers used in the adsorption experiments was placed in a new polyethylene bottle containing 50 ml of the appropri­ ate aqueous solution. The containers v/ere removed from the inert atmosphere box and gently agitated for six weeks. Tracer concentrations in the solution were measured period­ i c a l l y as described previously. At the end of six weeks, the experiments were terminated, the wafers removed from the containers, and the tracer concentrations of the components of the system determined in the same manner as in the adsorption experiments. Results and Discussion. The data obtained from the gamma-ray spectra taken during the course of the desorption experiments were not useful for monitoring the rates of desorption. For the samples containing U and Np, only a small amount of activity appeared in solution and therefore the counting errors precluded a meaningful analysis. Though the counting errors f o r samples containing Pu, Am and Cm were small, large fluctuations in the measured values again made detailed analysis f r u i t l e s s . However, there were some general trends that should be mentioned: most of the material that appeared in solution did so in 2 to 3 days; in general, the basalt and quartz monzonite wafers desorbed 3 to 5 times more tracer than the shale wafers; and the Pu, Am, and Cm values fluctuated a factor of 2 to 3 about the mean. The distribution coefficients calculated from the alpha counting data are given in Table VIII. The gamma counting of the solutions is s t i l l in progress. The symbols are the same as used previously. For Κ (alpha), the counting pre­ cision is + 10 percent for the U, Am and Cm samples and + 20-30 percent for the Np and Pu samples. For Κ ( f i l t e r ) , the counting precision i s + 10 percent f o r U, + 10-20 percent for Np, Am and Cm and +30-40 percent for the Pu samples. The up/down effect was also apparent in the data of the desorption experiment (Table VIII). However, only desorption data for shale d i f f e r significantly from the sorption data, i . e . , the up/down ratios are closer to unity in the desorpt­ ion experiments. A comparison of Κ (alpha) and Κ ( f i l t e r ) show substantial differerences for Am, Cm, and Pu (basalt) samples. Autoradiography of Rock Wafers Procedure. At the completion of the sorption and desorption experiments, the rock wafers were placed in

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

RADIOACTIVE WASTE IN GEOLOGIC STORAGE

240

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch013

contact with Kodak AR.10 nuclear emulsion films to obtain alpha p a r t i c l e induced autoradiographs. Due to the low concentrations of tracers on many of the wafers, rather lengthy exposure times (up to three months) are needed to obtain autoradiographs that can be readily studied under low magnification (X5). The autoradiographs will be com­ pared with the microstructure and mineral phases of the wafer surfaces and correlations made between sorption and these parameters. Individual mineral phases exhibiting selective uptake will be used as sorptive substrates in future experiments. Literature Cited 1. 2.

3.

4.

5.

6. 7. 8.

9.

10.

11.

Izett, G. Α . , U. S. Geol. Surv. TEM-836-C 1960. Lloyd, M. H. and Haire, R. G . , "Studies on the Chemical and Colloidal Nature of Pu (IV) Polymer" the XXIV th International Union of Pure and Applied Chemistry Congress", Hamburg, Germany, September, 1973. Private Communication from Gary Beall (Oak Ridge National Laboratory) at the WISAP Contractors Information meeting, Seattle, Oct. 1-5, 1978. Rai, D. and Serne, R. J., "Solid Phases and Solution Species of Different Elements in Geologic Environments", Pacific Northwest Laboratory Report - 2651, March 1978. Apps, J. Α . , Lucas, J., Mathur, A. K., and Tsao, L., "Theoretical and Experimental Evaluation of Waste Transport in Selected Rocks: 1977 Annual Report of LBL Contract No. 45901AK". Lawrence Berkeley Laboratory Report - 7022, p. 8, September 1977. Baes, C. F. and Mesmer, R. E. "The Hydrolysis of Cations", p. 169, Wiley-Interscience Publications, Ν. Y . , 1976. Cleveland, J. M. "The Chemistry of Plutonium", p. 81, Gordon and Breach Science Publications, Ν. Y . , 1970. S i l l e n , L . G. and Martell, A. E., "Stability Constants of Metal Ion Complexes", Spec. Publ. No. 17, The Chemical Society, London, 1964. Rai. D . , Serne, R. J. and Swanson, J. L., "Solution Species of 239Pu in Oxidizing Environments: II. Plutonyl (V)", Pacific Northwest Laboratory Report - 7027, June, 1978. Smith, R. M. and Martell, A. E., "Critical Stability Con­ stants", vol. 4: Inorganic Complexes, p. 37, Plenum Press, Ν. Y . , 1976. Allard, B. and Beall, G. W., "Predictions of Actinide Species in the Groundwater", Workshop on the Environmental Chemistry of the Actinide Elements, Warrington, Virginia, October 9, 1978.

RECEIVED January 16, 1979. In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

14

Biogeochemistry of Actinides: A Nuclear Fuel Cycle Perspective

E. A. BONDIETTI, J. R. TRABALKA, C. T. GARTEN, and G. G. KILLOUGH 1

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch014

Oak Ridge National Laboratory, Oak Ridge, TN 37830

Nuclear fuel cycles based on U, Th and Pu produce long-lived α - e m i t t i n g isotopes of the actinide elements. Man-made actinide element releases to the biosphere occur primarily through weapons testing, nuclear fuel reprocessing, fuel fabrication, and nuclear waste disposal a c t i v i t i e s . While the global inventory of dis­ persed Pu and Am, for example, is largely of military origin, the advent of nuclear fuel reprocessing and waste disposal activities associated with nuclear power will inevitably lead to localized contaminated landscapes. Because of their physiological property of concentrating p r i ­ marily in bone and the low penetrating power of the α particle, internal deposition from ingestion and inhalation intakes are the most important exposure modes to man. Most of the actinides show low water solubilities and consequently drinking water typically will not dominate over diet with respect to ingestion. The purpose of this paper is to compare the biogeochemical behavior of the actinides which are important constituents of nuclear fuel cycles. To the extent possible, the environmental behavior of the essentially man-made elements Pu, Am, Cm and Np will be compared to Th and U, which are ubiquitous in the environ­ ment. By comparing the man-made actinides to naturally occurring actinides, a generic perspective of the potential hazard of the synthetic actinides to people is obtainable. Natural U and Th Intakes by People Through inhalation and ingestion, people assimilate small quantities of natural U and Th. The U and Th which is assimilated from the lung and gastrointestinal tract (G.I. tract) tends to deposit the skeleton (1,2,3).

1

Research sponsored by the Division of Ecological Research, U.S. Department of Energy under Contract W-7405-eng-26 with Union Carbide Corporation. ESD Publication No. 1284.

0-8412-0498-5/79/47-100-241$06.50/0 © 1979 American Chemical Society

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

242

RADIOACTIVE W A S T E

IN

GEOLOGIC

STORAGE

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch014

The literature suggests that the concentrations in bone which result from environmental exposure are about 1 to 30 ng U/g bone ash and about 10 ng Th/g bone ash (2,3,4). Thus U may become more concentrated in bone than thorium. However, Th is more abundant in the lithosphère than U; this is exemplified by average abundances in soil of 6 yg Th/g and 2 yg U/g (4,5,6). Modeling Intakes. To determine the significance of diet and inhalation as sources of internally deposited U and Th, dietary and inhalation estimates for the general population were used in an Oak Ridge National Laboratory (ORNL) model, INREM II (7). A schematic of the intake and deposition pathways considered by the model are depicted in Fig. 1. Uranium in the typical diet is about 1.3 yg/day (2,8). Thorium, while more abundant in soil than U, is not as available to plants and consequently a dietary contribution of 0.8 yg/day has been estimated (2). The inhalation of U approximates 7 ng/day in New York (2). Assuming a soil Th/U ratio of 3, the Th inhalation is about 21 ng/day. For inhalation, two activity median aerodynamic diameters (AMAD) of aerosol particulates were considered. In addition, two ICRP (9) solubility classes of U and Th aerosols were considered. The resulting predictions of Th and U bone concentrations after 70 years of exposure to environmental U and Th were then compared to literature values (Table 1). For natural Th, the inhalation of 21 ng/day and ingestion (via the diet) of 0.8 yg/day results in bone ash concentrations of about 13 ng/g for the class W solubility case and about 6 to 9 ng/g for the class Y case. Ingestion contributes 50% or less of this bonedeposited Th. Because an absorption coefficient of 0.1% from the G.I. tract was used, the contribution from ingestion is probably overestimated. Nevertheless, the estimated bone concentrations agree with literature means (2). For natural U, the situation is different. The amount in bone after 70 years is about 1 ng U/g bone ash. Ingestion dominates inhalation as the contributing intake mode. The inhalation value (7 ng/day) is based on a New York study (10), and would need to be raised substantially in the model to make a significant contribution of U to bone. However, the Th inhalation value, which was derived from the U value, would need to be adjusted (upward) accordingly, significantly altering the subsequent estimate of bone Th. However, measured Th-232 concentrations in surface air under arid conditions (11) do not suggest that the U-Th inhalation value is low. The daily U intake via ingestion (1.3 yg) appears to be a reasonable estimate since i t is based on numerous studies in several countries (8). The G.I. tract assimilation coefficient for natural U may be higher than the 1% assumed here. Two studies over a 3 year period on a number of Japanese hamlets (12,13) suggested that the amount of U excreted daily in the urine of the sampled population ranged from between 1 to 3% of the amount in the diet. Since both urine and feces are potential routes for excretion of assimilated U, the urinary data are minimum values for daily U assimilation assuming

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

14.

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Biogeochemistry

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243

Actinides

INTAKE MODES

INHALATION

INGESTION

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch014

RESPIRATORY TRACT MECHANICAL REMOVAL G.I. TRACT

I

ABSORPTION

ABSORPTION

BLOOD (CUMULATIVE UPTAKE)

OTHER ORGANS

Τ Τ Figure 1.

τ •=•

BIOLOGICAL REMOVAL

Schematic representation of radioactivity movement as modeled hy the INREM II code

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

4

2

3

2

4

3

U0 ] 7

7 1.3

1.3

0.8

0.8

0.9(0.8)

1.0(0.8)**

9(3)

13(3)**

0.3

0.9(0.8)

1.0(0.8)

6(3)

13(3)

1.0

Assumed AMAD (urn)

Bone ash, (ng/g)*

l i t e r a t u r e mean is 12 ng Th/g bone ash; 1 to 30 ng U/g bone ash. **Contribution from diet, assuming 0.1% (Th) and 1% (U) absorption, is shown in parenthesis. tICRP s o l u b i l i t i e s for inhaled aerosols incorporated into model; soil-bound element may not be similar.

4

W · [UF ; UC1 ]

D · [U0 (N0 ) ;

Uranium

21

2

Y · [Th0 ; Th(0H) ]

4

(yg/day)

(ng/day)

21

3

Ingestion

Inhalation

Intake Mode

[Th(N0 ) ]

W·

Thorium

Assumed Solubility Class^

Table I. Estimated Th-232 and U-238 Contents of Human Bone Ash After 70 Years of Exposure to Naturally-Dispersed Th-232 and U-238 via inhalation and diet

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Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch014

that bone and other organs are at equilibrium with respect to U_ intakes. A Site-Specific Application. Wei ford et a l (14) have e s t i mated the skeletal U content at 3.2 yg based on analyses of 63 vertebrae samples from New York residents. This U concentration is equal to about 1.1 ng/g bone ash, assuming 28% ash in the skeleton (10 kilograms) of reference man (15). The agreement between the model results and the New York bone data is significant because the inhalation and ingestion parameters are from New York studies. Considering the apparent uniformity of dietary U contribution (8), reported U values of 20 to 30 ng/bone ash (2,8) appear high, suggesting that drinking water contributes significantly to U in some diets (14). Since a 1% G.I. tract assimilation coefficient (as used here) results in a good approximation of the New York bone values, the use of a 32% value (8) is questionable. Modeling Conclusions. This exercise indicates that Th and U span the interface between the case where inhalation appears to dominate in the contribution of actinides in bone, and the case where ingestion is the more important pathway. The reasons for these differences l i e in two important transfers: The s o i l / s e d i ment to organism transfer (as i t affects dietary concentrations) and the assimilation from the vertebrate GI tract. While terrestrial-derived foodstuffs dominate our diet, other components of the diet ( i . e . , aquatic-derived foods) may also make a contribution to intakes. Exceptions to the inhalation case may therefore occur in special populations where certain aquatic foods are consumed in greater amounts, i . e . , shellfish (16). In attempting to understand the biogeochemical behavior of the transuranium elements, i t may be convenient to compare their behavior to U and Th. Although we have meager, but important, data on U and Th accumulations from lifetime exposure, our a b i l i t y to assess transport pathways of transuranium elements to people will be enhanced i f a body of comparative literature is established. Plant Uptake of the Actinides To the extent that diet contributes to internal body burdens, a comparison of the relative plant uptake of actinides from soil is of interest. Several studies have compared the uptake of various transuranium elements by plants (17,18,19). However, studies which include U and Th are not as available. Figure 2 presents recent results for field-grown vegetation of soil originally contaminated in 1944 with soluble forms of U, Th and Pu (and daughter Am) (20.21). The crops examined include soybeans, snapbeans, Japanese M i l l e t , squash, tomatoes, carrots, and radishes. All plant samples were washed in a manner approximating food preparation (although the leaves and stems of these crops are not usually eaten). Data set 1 comes from a study of U, Th and Pu comparisons, while

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

RADIOACTIVE W A S T E IN GEOLOGIC

STORAGE

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch014

246

Figure 2. Actinide field concentration ratios ([phnt]/[soil]) for phnts grown on a floodphin soil contaminated with soluble U, Th, and Vu(Am) in 1944 (21). Up to six species were analyzed; Ν refers to total harvest composite samples examined from three growing seasons.

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch014

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Biogeochemistry

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Actinides

set 2 is derived from Pu and Am comparisons. Different analytical methods (isotope dilution mass spectrometry for Th and U; a-spectrometry for Pu and Am) are the reason for the separate groups of data. Each set represents analyses on the same plant materials. The number of samples analyzed (N) is found below each range bar. As illustrated by Figure 2, the relative order of plant uptake (based on concentration ratios, C.R.*) is U > Am > Pu % Th, although substantial overlap occurs. The ranges associated with each element C.R. primarily reflect plant species variation. The figure therefore represents a composite view of a l l plants analyzed, much as a value for diet would reflect i t s diverse constituents. Not included in this example are Cm and Np. Curium is very similar to Am with respect to plant uptake (17,22). Neptunium represents a peculiar case since i t can be argued that both Np(IV) and Np(V) are important oxidation states in the environment (20). Several investigators (17,19) have demonstrated that in alkaline s o i l s , Np (probably Np(V)) shows a higher plant availability than either Pu or Am. On the other hand, our studies (unpublished) indicate that reduction to Np(IV) can occur in acid to neutral s o i l s , resulting in plant uptake values characteristic of Pu. The high uptakes noted for alkaline soils ( i . e . , Np(V)) is probably due to the low charge characteristic of the NpOt cation, possibly coupled with the formation of a carbonate complex analogous to U(VI). The low specific activity of Np-237 and low nuclear production rates, however, minimizes i t s potential as a radiological hazard. Based on an earlier hypothesis (20), we can expand the actinide ranking with respect to plant uptake to the following: Np(V) > U(VI) > Am(III) £ Cm(III) > Pu(IV) * Th(IV) = Np(IV). This ranking reflects the dominant chemical states we expect in the environment. Comparative Terrestrial Transport of Actinides to Mammals Actinides in soil reach people and other animals via inhalation of resuspended soil particles and ingestion of contaminated food. Absorption from the lung depends heavily on physical properties of the inhaled particles and the chemical form of actinides sorbed to particulates. As a rule, assimilation of actinides via inhalation is greater than assimilation from food via the intestines. For example, the absorption of Pu(IV) citrate and Pu(IV) nitrate from the rat lung was 60% and 12% of the administered dose, respectively, while the corresponding absorption via ingestion was 0.03% and 0.003% (23). Regardless of the pathway, animal experiments show that 75 to 100% of the internal Pu body burden is usually deposited in l i v e r and skeleton (23). For long term assessments of health hazard to the general public from actinides in the terrestrial environment, we will i n i t i a l l y emphasize ingestion as the route of C.R. = [ p l a n t (dry w e i g h t ) ] / [ s o i l

(dry weight)]

American C h e L i b r a r y

m

i

c

a

l Society

In Radioactive1155 Waste 16th in Geologic Storage; St., N .W. Fried, S.; ACS Symposium Series;Washington, American Chemical D.C.Society: 20036Washington, DC, 1979.

RADIOACTIVE W A S T E IN GEOLOGIC

248

STORAGE

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch014

exposure to people because f i e l d studies show a decreasing suscep­ t i b i l i t y of plutonium-contaminated soil particles to resuspend with time, resulting in air concentrations over contaminated soil declining by half every one to two years (24). The extent to which ingestion will dominate inhalation depends on many factors, many of which have not been investigated. Since our previous example of U and Th transport to people gives some perspective on the relative importance of ingestion, attention to this path­ way is j u s t i f i e d . Assimilation from the Gastrointestinal Tract. There are several sources of variation in the assimilation of actinides from the mammalian intestine. Among the most important are chemi­ cal form and age of the animal. The comparative metabolism of different actinides administered to rats as nitrates has been studied by Sullivan and Crosby (25,26). The consistency of experi­ mental technique in their administration of actinides to adult and newborn rats permits comparisons between the assimilation of different actinides. The fractional assimilation, expressed as the amount in liver and carcass together, 7 days post-dose, was approximately 10" for isotopes of U, Pu, Am and Cm in adult rats. In young rats, the assimilation was about two orders of magni­ tude greater. On a comparative basis, Pu, Am and Cm tend to be assimi­ lated from the G.I. tract into the internal body in the follow­ ing order: Pu < Am < Cm (Figure 3). When Pu-nitrate is inhaled in aerosol form by dogs (27), daughter Am-241 tends to be trans­ ported more from lung and lymph nodes to l i v e r than does plutonium (Fig. 3). Another example of potential Am enrichment is that when the rumen contents of fistulated cattle grazing on the Nevada Nuclear Test Site were leached with simulated gastric f l u i d s , Am-241 was more soluble than Pu-239 (28). The administration of actinides in n i t r i c acid solutions to animals lacks biological realism from the standpoint of foodchains. Uranium has been studied best in this regard. The calcu­ lated assimilation of U from food by domestic animals ranges from 0.6% in cattle (2) to 2% in swine (2). In people, estimated values for the assimulation of U from food vary from approximately 2% to 12% and 32% (2j. These estimates are greater than the mea­ sured assimilation of nitrate forms and i l l u s t r a t e the errors which can be incurred by extrapolating data from rat experiments to man. In laboratory experiments, the chemical form which prob­ ably simulates the intake of actinides from natural foods best is citrate. This is because c i t r i c acid is a fundamental compound in plant metabolism. Baxter and Sullivan (29) have shown that when Pu is intragastrically administered to rats in citrate form, the assimulation is approximately 2 χ 10" , about 2 orders of magnitude greater than assimilation of the nitrate form (1 χ 10 ) . A more significant study (30), indi­ cated that about 1% of plant (tumbleweed) incorporated Pu fed 14

3

5

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch014

BONDIETTI E T A L .

10 ~ " -

Bio geochemistry

INGESTION: ASSIMILATION BY RATS (SULLIVAN AND CROSBY 1975)

of

Actinides

249

INHALATION: ASSIMILATION BY DOGS (BAIR 1970)

Cm-244

LIVER

Am-241 NO FRAC1ΊΟΝΑΤΙΟΝ LYMPH NODES

Ζ

LUNG

Figure 3. Enrichment of trivalent actinides over Pu(IV) across biological mem­ branes. The assimifotion of Am-241 and Cm-244 from the rat GI tract is greater than for plutonium. When plutonium nitrate is inhaled by dogs, daughter Am-241 is preferentially transported to the liver, resulting in depletion in lung and lymph nodes.

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

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STORAGE

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch014

to rats was found in internal tissues 2 4 hours after feeding. How­ ever, Am and Cm uptake was lower than for Pu, possibly due to i n ­ soluble oxalates in the plant. Field Studies. We have attempted to compare the relative a v a i l a b i l i t y of actinides to small mammals living in contami­ nated environments near ORNL. Shrews, rats and mice have been collected from a 3 0 year old contaminated floodplain forest eco­ system (21_). Cotton rats (Sigmodon hispidus) have been collected from the banks of a former liquid radioactive waste pond which con­ tains Pu, Am and Cu in sediments and shoreline vegetation. Analy­ ses were performed by isotope dilution mass spectrometry (U, Th and Pu) or by alpha spectrometry (Pu, Am and Cm). In shrews and mice, U tends to be more available than Pu or Th (Fig. 4 ) . These comparisons are based on concentration ratios: the concentration of actinides in the internal body (bone, muscle and internal organs) of shrews, mice and rats ratioed to their respective concentrations in soil or sediment. Due to differences in analytical technique, species d i f ­ ferences, and different collecting sites, direct comparisons between the availability of Th, U and Am, Cm are not valid. However, Am and Cm tend to be more available than Pu to the rats examined (Fig. 4 ) although the differences are not significant when sample variability is considered. Evidence for Am enrich­ ment in the f i e l d may in fact be totally obscured by biological v a r i a b i l i t y . Field studies at the Nevada Test Site with cattle exemplify this problem. When 5 tissue types from up to 2 0 animals which had grazed on contaminated soil were examined for Pu and Am, Pu/Am ratios varied by almost 2 orders of magnitude ( 3 ] J . The outstanding limitation of observations such as these which are based on f i e l d studies is the lack of control of animal exposure. Although laboratory experiments can be c r i t i ­ cized for a lack of biological realism, they are more carefully controlled than observations based on animals collected under f i e l d conditions where accumulation is via inhalation as well as ingestion. By ratioing the concentrations in the body to soil concentrations, this analysis bypasses the question of whether inhalation or ingestion is the more important route of exposure. Comparative Actinide Behavior in Aquatic Food Chains The major repository of transuranic elements entering aquatic systems is the bed sediment ( 1 - 4 ) . A significant portion is thought to arrive at the bed sediment surface as a result of association with, and subsequent settling of, suspended particu­ late matter. Concentrations of plutonium and americium in sedi­ ments relative to those in water reportedly range from 1 χ 10 * to 3 χ 1 0 ( 3 2 , 3 3 , 3 4 ) . L i t t l e information is currently available for other actinides of interest relative to nuclear fuel cycle wastes (Th, U, Cm and Np). 1

5

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch014

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Figure 4. Comparative accumuhtion of actinides by small mammals from contaminated soil or sediment relative to the accumulation of plutonium-239. Accumulation factor (AF) = concentration of nuclide in the internal small mammal body ~- concentration of nuclide in dry soil. Twelve shrews and seven rats and mice from a floodplain forest were composited to yield four and three separate analyses, respectively. Twelve cotton rats inhabiting the banks of a liquid waste pond (3513) also were analyzed.

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

RADIOACTIVE W A S T E IN GEOLOGIC

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch014

252

STORAGE

Until relatively recently, data on aquatic food chain behavior of the actinides was relatively scarce. Recent reviews have pointed to the fact that most of the available information was limited to the marine environment (35,36). This is s t i l l the case for data on distribution of actinides in tissues of aquatic organ­ isms, particularly vertebrates. The available data suggest that patterns are similar to those reported for terrestrial animals; highest concentrations were found in the gastrointestinal tract (G.I. tract) and mineralized tissues (bone and liver in vertebrates and shells and exoskeletons in invertebrates). Recent data from studies in fresh-water environments suggest that g i l l s may con­ tain an additional important component of the body burden for plu­ tonium (37,38). Laboratory studies on the channel catfish using a Pu-237 tracer indicate that the G.I. tract skeleton, l i v e r , and kidney should contain most of the body burden resulting from envi­ ronmental exposure (39,40). Edible muscle has been found to con­ tain the lowest actinide tissue concentrations (33,35,37,38,40,41) in aquatic organisms studied to date. Surface Phenomena. Non-metabolic associations appear to play a major role in food chain behavior of the actinides (32-35,42). Noshkin (35) pointed out that marine organisms associated with the sediment-water interface contain 100 times higher plutonium burdens than marine free-swimming vertebrates. This has also been shown to be true for plutonium and americium in the v i c i n i t y of Windscale (33). Thus some association with the sedimentary actinide pool, whether by surface sorption to plant cell walls, exoskeletons, G. I. Tract linings, or perhaps by direct uptake from sediments (and associated i n t e r s t i t i a l water) consumed during feeding, is indicated in many instances. Laboratory gavage studies using Pu-237 fulvate (an organic chelating agent found in sedi­ ments) indicated that channel catfish could deposit a small (1 χ 10~ ), but not insignificant, fraction of ingested plutonium into edible tissues (39). Plutonium-239 concentrations in chironomids (important fresh-water fish food organisms) held in simple laboratory environments (microcosms) were approximately 1 χ 10" that of the sediments on which they fed (G.I. tract removed to eliminate external contamination) (43). When G.I. tract contents were included, the fraction present rose to 7% of the sediment con­ centration. Concentrations in emergent portions of aquatic plants have been shown to be an order of magnitude less than submerged plants in the same system (Pu-237 in complex laboratory microcosms, 42:, and Pu-239 and Am-241 in f i e l d studies at Hanford's U-Pond (37). Thus the sedimentary pool cannot be ignored as the potential direct source of actinide elements for a major fraction of the aquatic biota which reaches the human diet. Transuranic elements (and other actinides) have a very high a f f i n i t y for particulate matter (and surfaces in general) in aquatic ecosystems. It is d i f f i c u l t to use the traditional con­ centration ratio referenced to water (often assumed to be the source without support) as a measure of the tendency of biota to accumulate 3

3

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch014

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Bio geochemistry

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253

these elements in tissues. As will be seen, concentration ratios based on water decline up the trophic ladder. This behavior, coupled with the known limited tendencies of the actinides to penetrate biological membranes, suggests that discrimination against actinide uptake occurs at each food chain transfer - leading to dilution of actinide concentrations the further along a food chain the element is transferred. We believe that i t may be more useful to relate the observed concentrations of actinides in aquatic biota to that in the primary biotic source in the system: sediment (both suspended and bottom). The underlying hypothesis is that due to the high sediment concentration ratios relative to water, observed element accumulation in tissues of higher trophic levels will be dominated by G. I. tract discrimination rather than by direct uptake from water. External contamination on surface and G. I. tract loadings with sedimentary particulates are not considered to be true uptake and should be considered separately. This may be considered analogous to contamination of the pelt and G. I. tract by soil activity in terrest r i a l mammals. Comparative Actinide Behavior. The data from existing freshwater actinide radioecology studies have been digested and condensed for presentation in Tables II (radium and uranium) and III (transuranics). Information on thorium in fresh-water environments is extremely fragmented; hence its omission. Concentration ratios were calculated and averaged for relatively broad ecological groups in order to f a c i l i t a t e generalized comparisons between data from different water bodies and between different elements. There are rather apparent gaps in existing data sets (ours included) which make some comparisons d i f f i c u l t . Concentration ratios have been calculated relative to both sediment and water wherever existing data permitted. Environmental studies on the behavior of actinide elements in fresh-waters have been conducted at a variety of sites throughout the world. These range from large, deep natural lakes, such as Lake Michigan and Lakes Issyk-kul and Sevan in the Soviet Union, to relatively small, shallow ponds (Pond 3513, former final radioactive waste settling basin at Oak Ridge National Laboratory (ORNL) and U-Pond, on the Hanford Reservation) and impoundments (White Oak Lake at ORNL and those at the Jaduguda uranium mining and m i l l ing complex, Bihar, India). Higher actinide concentrations are observed in the aquatic environments at nuclear fuel cycle f a c i l i t i e s , while the levels in the natural lakes are extremely low by comparison, derived primarily from weapons-testing fallout and natural sources. Lake Issyk-kul has been intensively studied because its watershed lies in an area whose soils have a naturally high uranium content. Some generalizations are applicable to virtually a l l data sets presented. As noted e a r l i e r , concentration ratios decline with increasing trophic level: herbivores < l i t t o r a l f l o r a ; piscivores < planktivores < zooplankton < phytoplankton. Perhaps

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979. -1.9 r i c e

(1.0)

(-0.3)

(-0.4)

- 1 . 8 (0.9)

- 3 . 3 (-0.6)

-1.4 (1.3)

-1.2 (1.5)

-1.1 (1.6)

-0.1 (2.6)

- 0 . 8 (1.9)

(0.8)

(0.4)

(2.7)

(2.0)

U.S.S.R. (41 ,47,48) Lake Moscow Issyk-Kul Ponds

•Expressed as the log-,Q [organism (dry wt.)]/[sediment, water] to f a c i l i t a t e comparisons; values based on water shown in parentheses.

-piscivores

bone

-planktivores

-2.9 (0.8)

muscle

(1.8)

-2.1 (1.6)

Vertebrates-herbivores

bone

(1.6)

L i t t o r a l Fauna

(0.7)

(1.6)

- 0 . 3 (3.4)

L i t t o r a l Flora

-3.1 r i c e

(1.4)

Zooplankton

Ra

Lake Michigan (34)

(2.2)

2 2 6

Jaduguda Mine Area

India (43,44,45)

Radium and Uranium Concentration Ratios in Fresh-Water Organisms Referenced to Both Sediment and Water*

Phytoplankton

Organism

Table II.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch014

Lake Sevan

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

-3.4(2.9)

-2.1(4.2)

-2.4(3.9)

Zooplankton

L i t t o r a l Flora

L i t t o r a l Fauna

a k

a

t

1

o

n

a

l

L

a

b

o

r

a

0

r

*

-3.4(2.1)

-2.0(3.5)

-2.0(3.5)

-1.8(3.7)

t

-3.0(1.5)

-1.5(2.9)

-1.4(3.0)

239 "*Pu

White Oak Lake

-4.9(0.6)

-4.1(1.4)

-2.3(3.2)

-1.8(3.7)

-3.0(2.5)

-1.5(4.0)

Michigan (34,39)

-3.1

-1.5

-0.9

-0.8

-0.7

-0.3

KS" (37,50)

•Expressed as the log-jQ [organism (dry wt.)]/[sediment, water] to f a c i l i t a t e comparisons; values based on water in parentheses.

Pu. 2itl

226

An indication of what one might eventually expect to obtain for a generalized pattern of relative bio-availability for the actinides of interest in nuclear fuel cycles is shown in Table IV. This represents a recent data set in which concentration ratios have been obtained for a l l five actinides in tissues of a vertebrate (used as human food) from a single aquatic ecosystem (Pond 3513 at ORNL); comparisons are thus f a c i l i t a t e d . The values for bone (Table IV) suggest a pattern of bio-availability as follows: U > Am, Cm > Th, Pu. Taken in its entirety, the data set in Table III indicates essentially the same pattern. Exposure Pathways to People: Summarizing Importance From the preceding sections, the greater tendency for U to transfer to both people and small mammals when compared to Pu, Th, Am and Cm is evident. Availability comparisons for vertebrates in In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

2.5xl0~

l.OxlO"

muscle (male)

muscle (female)

4

5

4

238

7.8 4.9

7.4 30.0

1.9

64.0

5.0

Am/Pu

3.3

241

40.0

8.1

U/Pu 244

6.0

3.7

1.2

3.8

3.0

Cm/Pu

232

3.0

5.7

2.7

0.42

0.32

Th/Pu

Concentration in tissue (ash wt.) -f Concentration in sediment (ash wt.). Plutonium determined by both mass spectrometry and solvent extraction-alpha spectrometry techniques; Th and U by mass spectrometry, and Am and Cm by solvent extraction-alpha spectrometry.

4

7.0xl0"

bone (female)

2.6xl0~

adult- bone (male)

3

1.9xl0"

pu

239,240 *

immature-carcass without G.I. tract

Specimen

Table IV. Comparisons of the Actinide/Pu Concentration Ratios in the Bullfrog (Rana catesbeiana) from Former Waste Settling Basin at Oak Ridge National Laboratory

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch014

BONDIETTI

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch014

14.

E T A L .

Bio geochemistry

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259

Actinides

a q u a t i c f o o d c h a i n s , a l t h o u g h more l i m i t e d , s u g g e s t no s u b s t a n t i a l a l t e r a t i o n i n t h i s p a t t e r n . F o r n a t u r a l Th and U, i n g e s t i o n i s t h e dominant environmental r o u t e t o p e o p l e , a l t h o u g h n o t n e c e s s a r i l y the important c o n t r i b u t o r of i n t e r n a l l y - d e p o s i t e d elements. A s i m i l a r s t a t e m e n t c a n be made f o r f a l l o u t Pu s i n c e a t m o s p h e r i c t e s t i n g has a l m o s t c e a s e d ( 1 6 ) . B o t h Pu and Th w i l l p r o b a b l y e n t e r t h e s k e l e t o n and o t h e r i n t e r n a l t i s s u e s predominantly from i n h a l a t i o n . This statement i s b a s e d on t h e f a c t t h a t i n t h e f i e l d , Pu and Th d e m o n s t r a t e s i m i l a r t r a n s f e r s f r o m s o i l t o s m a l l mammals and l a b o r a t o r y s t u d i e s demons t r a t e s i m i l a r metabolic c h a r a c t e r i s t i c s (1,3,23). S o i l chemical b e h a v i o r i s a l s o s i m i l a r ( 2 0 ) . As d e m o n s t r a t e d i n T a b l e I, n a t u r a l Th i n human bone o r i g i n a t e s l a r g e l y f r o m i n h a l a t i o n , even a s s u m i n g t h a t a d s o r p t i o n f r o m t h e d i e t i s 0 . 1 % . A n o t h e r s t r o n g agrument f o r t h e importance o f i n h a l a t i o n i s found i n t i s s u e d i s t r i b u t i o n s o f T h - 2 3 2 and T h - 2 3 0 i n humans. T a b l e V summarizes work by Wrenn, e t a l . ( 5 3 ) w h i c h shows t h a t l u n g s o f n o n - o c c u p a t i o n a l l y e x p o s e d i n d i v i d u a l s c o n t a i n s b u r d e n s o f Th i s o t o p e s c o m p a r a b l e t o t h e skeleton. Thorium-228 d i s t r i b u t i o n s a r e d i f f e r e n t from Th-230, 232 d i s t r i b u t i o n s and r e f l e c t a s s i m i l a t i o n o f p a r e n t Ra-228 f r o m the d i e t . As t h e r e l a t i v e t r a n s f e r c o e f f i c i e n t s f r o m s o i l t o p l a n t s and f r o m d i e t t o t h e b l o o d i n c r e a s e , i n g e s t i o n t a k e s on more i m p o r tance. T h i s c e r t a i n l y a p p e a r s t o be t h e c a s e f o r U. I t may be t h a t i n g e s t i o n w i l l be more i m p o r t a n t f o r Am and Cm t h a n f o r Pu o r t h o r i u m . Neptunium r e m a i n s i n enigma b e c a u s e o f t h e p a u c i t y of data. T a b l e V. D i s t r i b u t i o n s o f T h - 2 3 2 , T h - 2 3 0 , and Th-228 i n s e l e c t e d n o n - o c c u p a t i o n a l l y e x p o s e d human o r g a n s *

Distribution

Organ

(%)**

Th-232

Th-230

20

21

1.8

6

6

0.7

Spleen, l i v e r , kidney

13

17

2.6

Skeleton

62

56

94.9

Lung Lymph nodes

Th-228

* A f t e r Wrenn, e t a l . ( 5 3 ) . Median v a l u e s

f o r 5 i n d i v i d u a l s n o r m a l i z e d t o s t a n d a r d man m a s s e s .

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

RADIOACTIVE W A S T E IN GEOLOGIC

260

STORAGE

Assessing Hazards of EnvironmentallyDispersed Actinides to People The U.S. Environmental Protection Agency has proposed that "The annual alpha radiation dose rate to members of the c r i t i c a l segment of the exposed population as the result of exposure to transuranium elements in the general environment should not exceed either 1 millirad per year to the plumonary lung, or 3 millirad per year to the bone" (54). The USEPA also derived a soil contamination level of 0.2 yCi/m Tl cm depth, soil particles less than 2 mm) as a reasonable "screening" level for which the resultant dose rates to the c r i t i c a l segment of the exposed population could be reasonably predicted to be less than the guidance recommendations. Current estimations of dose rates to c r i t i c a l organs from environmentally-dispersed transuranics rely on environmental transport and metabolic models (9,15,54). The rather short time period that these elements have been in the biosphere (from the a c t i v i t i e s of people) makes validation of environmental transport models extremely d i f f i c u l t . To approximate the maximum possible lifetime accumulation in the skeletons of people exposed to actinides in the general environment, one approach would be to use a bone/soil accumulation factor. A principal advantage of this method is that i t is independent of the exposure pathway. However, i t assumes that aquatic components of the diet are insignificant, and thus would not apply to circumstances where only sediments are contaminated. Bone is a c r i t i c a l tissue because the deposition of a c t i nides in bone is i n i t i a l l y high after entry into the bloodstream, and retention times are long. For example, in rats more than 70% of the body burden is found in the skeleton 16 days after oral administration of Pu-citrate or Pu-nitrate (23:). The Cm content of rat bone, 256 days after intramuscular injection, was 20 times greater than the amount in any other internal tissue excluding the injection site (54). Approximately 81% of the 86.3 yg of natural U estimated to be in man is in the skeleton (56). Of the actinides we have considered here, only U comes to equilibrium in bone in man's lifetime (3). The amount of Pu, Th, Am, Cm and Np in human bone continually accumulates. Because of this, the bone/soil ratio is time dependent. However, i t is interesting to note that existing data sets on Th-232 (57,58) in human bone do not show a strong age-dependent trend. This probably reflects the diversity of inhalation exposures people are subject to.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch014

2

Bone-Soil Ratios. In man, the typical concentration of natural U in bone has been considered to be about 20 ng/g bone ash (8) although a comprehensive data set (10) suggests a substantially lower value (1 ng). Thorium is present at concentrations near 10 ng/g bone ash. The concentration of U and Th in terrestrial soils is approximately 2 and 6 yg/g respectively (2,4,5). The calculated adult human bone ash/soil ratio for U is therefore greater than that for Th (Table VI). This comparison is consistent with observed differences in the accumulation of U In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

14.

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Biogeochemistry

of

Actinides

261

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch014

and Th in small mammals (Fig. 4) and frogs (Table IV). For purposes of comparison, the bone/soil ratio has been calcu­ lated for Th, U, and Pu in small mammals collected from the pre­ viously mentioned contaminated floodplain forest near ORNL. A bone/soil ratio for Am was also calculated from published data (59). These ratios are listed in Table VI. The v a r i a b i l i t y around the average ratios in small mammals is great with coefficients of variation near unity. Nevertheless, the relative ranking of aver­ age values indicates the following order of a v a i l a b i l i t y : Pu ^ Th < Am < U for small mammals. Table VI. The accumulation of actinides by small mammals and man from soil expressed as the concentration ratio of element in internal small mammals bodies (skeleton and internal organs) or the concentration in human bone ash to a measured soil concentration. Thorium, U, Pu data from ORNL floodplain studies; Am data from (59). Human data calculated from information in (2).

Group Small mammals

People

Average

CV

7

0.0003

0.66

7

0.004

0.92

Pu

7

0.0003

0.83

Am

2

0.001

0.80

Th

1

0.002

U

1

0.01

Nuclide

N

Th U

a

b

— —

Number of values averaged.

a

CV =s standard deviation τ average From the calculated bone/soil ratios in man for the naturallyoccurring actinides as well as the laboratory and f i e l d studies on small mammals, the availability of Pu, Am, and Cm relative to U and Th can be deduced. F i r s t , the f i e l d studies indicate a similar degree of uptake by mammals for Pu and Th (Fig. 4, Table VI) which are both characterized by the tetravalent state in the terrestrial environment (20). Second, the trivalent actinides, Am and Cm, tend to exhibit similar (Fig. 3) or slightly greater (Fig. 4) uptake by mammals than Pu. Last, U exhibits consistently greater uptake in mammals than Th or Pu (Fig. 4, Table VI). On the basis of a v a i l ­ able data, the following rank order of bone ash/soil ratios for

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

RADIOACTIVE W A S T E IN GEOLOGIC

262

STORAGE

people might be used for evaluating lifetime accumulation: Th, Pu < Am, Cm < U 0.002

0.005

0.01

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch014

This ranking suggests that about 2.5 times as much Am and Cm may accumulate in bone than Pu or Th assuming identical chemical and physical forms in the s o i l . Uranium may show about a 5-fold greater relative accumulation. Estimating Dose to Bone from Chronic Exposure. Using these accumulation factors, the maximum amount of Pu, U, and Am in bone after 70 years exposure to soil contaminated at the proposed EPA screening level might be estimated. Since Pu-238 and U-232 con­ tribute the most α - a c t i v i t y in breeder fuels (U-233 and Pu-239), they were chosen for dose comparisons. For a soil with a bulk density of 1.3 g/cm , 0.2 yCi/m (1 cm depth) corresponds to about 15 pCi/g soil (top 1 cm). Using the 0.002 accumulation factor for Pu and the reference man value of 54% ash in bone (as differen­ tiated from skeleton), the lifetime accumulation of Pu is calcu­ lated to be 0.016 pCi/g in situ bone. Assuming uniform distribu­ tion in bone and converting the activity concentration to dose (3) results in a dose rate for Pu-238 of about 1.7 mrad/year. This estimate, which is based on an independent methodology, suggests that the proposed EPA soil screening level is not unreasonable i f the projected dose rate to bone is not to exceed 3 mrad/year. The same exercise applied to an identical U-232 activity concentration in soil would result in 0.08 pCi/g bone or 8.2 jnrad/year contribution from U-232 alone. This value may be high considering the uncertainties of what the typical natural U con­ tent of bone i s . However, the α-emitting daughters of U-232 (Th-228, Ra-224, Rn-220, and Po-216) would raise this dose rate by about a factor of 4 (60). If the estimate of the trivalent actinide bone ash/soil accumulation factor is v a l i d , then 15 pCi Am-241/gram of soil would contribute 0.04 pCi/g bone and a 4 mrad/year dose rate at age 70. Because Am-241 may accumulate in the skeleton to a greater degree than Pu, i t would be a greater contributor of transuranic activity to bone even though its activity level in soils contaminated with Pu-239, 240, etc., may be lower. The physical form of the Pu will be very important in this instance. For example, lung inhalation data has shown l i t t l e Am-241 enrichment from inhaled Pu0 but substantial enrichment from Pu-nitrates. 3

2

2

Summary. Through an examination of the comparative behavior of the actinide elements in terrestrial and aquatic food chains, the anticipated accumulation behavior of the transuranium elements by people was described. The available data suggests that Pu, Am and Cm will not accumulate to a greater degree than U in the skele­ tons of individuals exposed to environmentally dispersed a c t i v i t y . The nature of the contamination event, the chemical and physical associations in soils and sediments, the proximity to the In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

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Biogeochemistry

of

Actinides

263

contamination site - a l l will influence observed behavior. Because of the establishment of regulatory guidelines for limiting chronic exposure to transuranium elements, research on environmental behavior must address the question of accumulation by people. In the absence of lifetime accumulation data and the paucity of contaminated sites, approaches such as those documented in this paper may aid in understanding and evaluating the hazards of releasing actinide elements to the biosphere. Literature Cited

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch014

1. 2. 3.

4. 5. 6. 7. 8.

9. 10. 11. 12. 13. 14.

15. 16. 17. 18.

19.

Durbin, P. W., Health Phys., (1960), 2, 225-238. Bondietti, Ε. Α . , Garten, C. T., Jr., Francis, C. W. and Eyman, L. D. J . Environ. Qual. (1979), in press. Wrenn, M. E., International Symposium on Areas of High Natural Radioactivity, T. L. Cullen and E. Penna Franca, (Eds.), pp. 131-158, Academia Brasileira de Ciencias, 1975. Beninson, D. J., Bouville, Α . , O'Brien, B. J., and J. O. Snihs, Ibid, pp. 75-106. Klement, A. W., Jr., Radioactive Fallout, Soils, Plants, Foods, Man, Ε. B. Fowler (Ed.), pp. 113-156, Elsevier, New York, 1965. Bowen, H. J. M . , Trace Elements in Biochemistry, pp. 39-40, Academic Press, New York, 1966. Killough, G. G . , Dunning, D. F., Jr., Plesant, J . C., ORNL/ NUREG/TM/84, National Technical Information Service, 1978. Hursh, J . B. and Spoor, W. L., Uranium, Plutonium, Transplutonia Elements, H. C. Hodge, J. N. Stannard, and J. B. Hursh (Eds.), pp. 197-239, Springer-Verlag, New York, 1973. International Commission on Radiological Protection, ICRP Publication 19, Pergamon Press, Oxford, May 1972. Welford, G. A. and R. Baird, Health Phys., (1967) 13, 13211324. Thomas, C. W., Young, J. Α . , BNWL-1751 (pt. 2), pp. 42-45, National Technical Information Service, 1973. Yamamoto, T., Yunoki, E., Yamakawa, M., Shimizu, M. and Nukada, K., J . Radiat. Res., (1974), 15, 156-162. Masuda, Κ., Japanese J. Hyg., (1971), 26. Welford, G. Α . , Baird, R., Fisenne, I. M . , i n P r o c., 12th Mid­ -year Topical Symposium, Health Phys. Soc., Saratoga, New York, 1976. International Commission on Radiological Protection, ICRP Publi­ cation 6, Pergamon Press, Oxford, 1964. Bennett, Burton, G . , IAEA-SM-199/40, pp. 367-383, IAEA, Vienna, 1976. Price, Keith, R., BNWL-1688, Battelle Northwest Laboratory, Richland, Wash., Oct. 1972. Adams, W. H., Buchholz, J . R., Christenson, C. W., Johnson, G. L., and Fowler, E. B . , LA-5661, Los Alamos Scientific Laboratory, Los Alamos, New Mexico, 1975. Schreckhise, P. G . , Cline, J. F., Abstract P/184, Twenty-Third Annual Health Physics Society Meeting, 1978.

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

264 20.

21.

22.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch014

23. 24. 25. 26. 27. 28.

29. 30. 31.

32.

33.

34. 35. 36. 37. 38. 39. 40. 41. 42.

RADIOACTIVE WASTE IN GEOLOGIC STORAGE Bondietti, E. A. and Sweeton, F. H. Transuranics in Natural Environments, (NVO-178), M. G. White and P. B. Dunaway (Eds.), pp. 499-476, National Technical Information Service, 1977. Dahlman, R. C. and McLeod, K. W., Transuranics in Natural Environments," (NVO-178), M. G. White and P. B. Dunaway (Eds.), pp. 303-320, National Technical Information Service, 1977. Weimer, W. C., Laul, J . C., Kutt, J. C., Bondietti, E. A., in Proceedings, Third International Conference on Nuclear Methods in Environmental and Energy Research, 1978, in press. Durbin, P. W., Health Phys., (1975), 29, 495-510. Volchok, H. L., Schonberg, M . , Toonkel, L., Health Phys., (1977), 33, 484-485. Sullivan, M. F. and A. L. Crosby, BNWL-1950 (Pt. 2), pp. 105-108, 1975. Sullivan, M. F. and A. L. Crosby, BNWL-2000 (pt. 1), pp. 91-94, National Technical Information Service, 1976. Bair, W. J., BNWL-1221, pp. 7.7-7.10, National Technical Information Service, 1970. Barth, J., Transuranics in Natural Environments (NVO-178), M. G. White and P. B. Dunaway, (Eds.), pp. 419-434, National Technical Information Service, 1977. Baxter, D. W., and Sullivan, M. F., Health Phys., (1972), 22, 785-786. Ballou, J. E., Price, K. R., Gies, R. Α . , Proctor, P. G. Health Phys., (1978), 34, 445-450. Smith, D. D . , Bernhart, D. E., Transuranics in Desert Ecosystems, (NVO-181), M. G. White, P. B. Dunaway, Wireman, (Eds.), National Technical Information Service, 1978. Eyman, L. D . , and Trabalka, J. R., Transuranics in Natural Environment, (NVO-178), pp. 477-488, Nevada Applied Ecology Group, Las Vegas, Nevada (1977). Hetherington, J . Α . , Jefferies, D. F., Mitchell, Ν. T. Pentreath, R. J., and Woodhead, D. S., IAEA-SM-199/11, pp. 139153, IAEA, Vienna, 1976. Wahlgren, Μ. Α . , Alberts, J . J., Nelson, D. Μ., and Orlandini, Κ. Α . , IAEA-SM-199/144, pp. 9-23, IAEA, Vienna, 1976. Noshkin, V. E., Health Phys., (1972), 22, 537-549. Hanson, W. C., Health Phys., (1975), 28, 529-537. Emery, R. M . , Klopfer, D. C., and Weimer, W. C., BNWL-1867, Battelle Northwest Laboratory, Richland, Wash., 1974. Alberts, J . J., Bartett, G. E., and Wayman, C. W., ANL-78-88, Part III, pp. 40-42, 1976. Eyman, L. D. and Trabalka, J. R., Health Phys., 32 (1977), 475-478. Trabalka, J. R., Eyman, L. D . , Bergman, H. L., and Frank, M. L., Health Phys., (1978), in press. Kovalsky, V. V., Voronitskaya, I. Ye., and Lekarev, V. S., USAEC Conf. P r o c , CONF-660405, pp. 329-332, 1966. Trabalka, J. R. and Eyman, L. D . , Health Phys., (1976), 31, 390-393. In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

14.

44.

45. 46.

47.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch014

48. 49.

50. 51. 52.

53.

54. 55. 56. 57. 58. 59.

60.

BONDIETTI ET AL.

Bio geochemistry of Actinides

265

Viswanathan, R. Bhatt, Y. M. Sreekumaran, C., Doshi, G. R . , Cogate, S. S., Bhagwat, Α. Μ., and Unni, C. Κ., Indiana Acad. Sci., (1966), 64B, 301-313. Iyengar, M. A. R. and Markose, P. M . , USAEC Conf. Proc., CONF-701227, pp. 143-153, 1970. Markose, M. P . , Eappen, K. P . , Venkataraman, S., and Kamath, P. R., Proceedings, Third International Symposium on the Natural Radiation Environment, Houston, Texas, April 23-28, 1978, in press. Kovalsky, V. V. and Voronitskaya, I. Y e . , Geochem. Internat. (1965), 2, 544-552 (Engl. Translation of Geochimiya). Kovalsky, V. V. and Voronitskaya, I. Ye., Ukr. Biokhim, Z h . , (1966), (4), 419-424. Edgington, D. N . , Alberts, J . J., Wahlgren, Μ. Α . , Karttunen, J . O., and Reeves, C. Α . , IAEA-SM-199/47, 493-516, IAEA, Vienna, 1976. Emery, R. M . , Klopfer, D. C., and McShane, M. C., Health Phys., (1978), 34, 255-269. Auerbach, S. I., et al., ORNL-5257, pp. 66-67, Oak Ridge National Laboratory, Oak Ridge, Tennessee, 1977. Healy, J . W., Eyman, L. D . , and Trabalka, J. R., Transuranic Uptake by Aquatic Organisms, (Appendix I) in an Examination of Possible Limits for the Shallow Earth Burial of Trans­ uranic Wastes, Los Alamos Scientific Laboratory, Los Alamos, New Mexico, in press. Wrenn, M. E., Singh, N. P . , Ibrahim, S. A. Cohen, N . , Saccomanno, G . , in Proc. Third International Symposium on the Natural Radiation Environment, Houston, Texas, April 23-28, 1978, in press. United States Environmental Protection Agency, EPA 520/4-77-016, USEPA, Washington, D. C., 1977. Scott, K. G . , Axelrod, D. J., Hamilton, J. G . , J. B i o l . Chem., (1949), 177, 3025-335. Hamilton, Ε. I . , Health Phys. (1972), 22, 149-153. Lucas, H. F., Edington, D. N . , Markum, F., Health Phys., (1970). 19, 739-742. Clifton, R. J., M. Farrow, Hamilton, Ε. I., Ann. Occup. Hyg. (1971), 14 303-308. Bradley, W. G . , Moor, K. S. Naegle, S. R., Transuranics in Natural Environments, (NVO-178), M. G. White and P. B. Dunaway (Eds.), pp. 385-406, National Technical Information Service, 1977. Till, J., ORNL/TM-5049, National Technical Information Service, 1976.

RECEIVED January 16, 1979.

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

15

1

Radionuclide Sorption Studies on Abyssal Red Clays KENNETH L . ERICKSON 2

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch015

Sandia Laboratories , Albuquerque, N M 87185

In order to provide data required by the U.S. Seabed Disposal Program to assess the f e a s i b i l i t y of emplacing radioactive wastes in sub-seafloor geologic formations, the radionuclide sorption properties of a widely distributed abyssal red clay are being ex­ perimentally investigated. These properties are extremely impor­ tant and should be investigated in detail since the adequacy of the sediment to serve as a barrier to the migration of nuclides away from the waste form should largely be determined by the sorption behavior of those nuclides. In this regard, sorption of the actinide elements is generally considered to be of principal concern. However, before pursuing an extensive experimental pro­ gram involving the actinides, a preliminary investigation was conducted to examine the sorption of several nuclides having r e l a ­ t i v e l y much less complicated solution chemistries. The generali­ zations being developed to describe the sorption of the prelimi­ narily investigated nuclides w i l l then be used in planning an efficient program for investigating the sorption and complex chemistry of the actinide elements. In most mathematical analyses used to establish bounds for radionuclide migration rates through the abyssal red clays, the sorption properties of the sediment are generally represented mathematically by the sorption equilibrium distribution coeffi­ cients for each of the species involved. These coefficients are usually denoted by Kp. and are defined by υ± where C.

= C./C ι ι 7

=

the equilibrium solid-phase concentration of species i , mg-atom/gm

1

This work supported by the United States Department of Energy (DOE), under Contract AT (29-1)-789. A U.S. DOE facility. 2

0-8412-0498-5/79/47-100-267$06.00/0 © 1979 American Chemical Society

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

RADIOACTIVE W A S T E IN

268 C.

=

the e q u i l i b r i u m solution-phase o f species i , mg-atom/ml

GEOLOGIC STORAGE

concentration

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch015

For a given m a t e r i a l , the d i s t r i b u t i o n c o e f f i c i e n t s are f u n c t i o n s o f temperature, pressure, the concentration of species i , and the concentrations o f a l l other competing s p e c i e s . In the sediments being studied, i t i s b e l i e v e d that n u c l i d e m i g r a t i o n away from the waste form w i l l p r i m a r i l y be due t o molecu l a r d i f f u s i o n . The simpler mathematical analyses o f d i f f u s i o n which y i e l d a n a l y t i c a l s o l u t i o n s show t h a t , t o a f i r s t approximation, the m i g r a t i o n r a t e o f species i should g e n e r a l l y be i n v e r s e l y p r o p o r t i o n a l to the magnitude o f ( l ) . Hence, the adequacy of the sediment to serve as a b a r r i e r t o n u c l i d e migrat i o n depends, i n an i n v e r s e l y p r o p o r t i o n a l manner, on the values o f the various d i s t r i b u t i o n c o e f f i c i e n t s , which, depending on species and c o n d i t i o n s , could be expected to vary from near zero to 10^ ml/gm or greater. Therefore, the p r e l i m i n a r y i n v e s t i g a t i o n d e s c r i b e d h e r e i n examined s e v e r a l aspects o f the behavior o f the e q u i l i b r i u m d i s t r i b u t i o n c o e f f i c i e n t s f o r the s o r p t i o n of rubidium, cesium, strontium, barium, s i l v e r , cadmium, cerium, promethium, europium, and gadolinium from aqueous sodium c h l o r i d e s o l u t i o n s . These s o l u t i o n s i n i t i a l l y contained one and only one o f the n u c l i d e s o f i n t e r e s t . For the n u c l i d e s s e l e c t e d , values o f Kp. were then ^i determined as f u n c t i o n s o f the concentration o f species i i n the e q u i l i b r i u m s o l u t i o n and t o a l i m i t e d extent as f u n c t i o n s o f s o l u t i o n pH. The data used t o c a l c u l a t e the values f o r K-p. were obtained from batch e q u i l i b r a t i o n experiments. The experimental procedures used are discussed l a t e r and were considered t o be such that the values obtained f o r the v a r i o u s d i s t r i b u t i o n c o e f f i c i e n t s provided a reasonable r e p r e s e n t a t i o n o f the s o r p t i o n p r o p e r t i e s o f the sediment a t l o c a t i o n s s u f f i c i e n t l y d i s t a n t from the waste form so t h a t the c l a y remains p h y s i c a l l y and chemically e s s e n t i a l l y unaltered. Red

Clay

Samples o f the red c l a y having uniform p h y s i c a l and chemical c h a r a c t e r i s t i c s were provided by G. R. Heath o f the U n i v e r s i t y o f Rhode I s l a n d . The samples were obtained from core L l M - G P C - 2 , c o l l e c t e d on October 11, 1976, at 30° 20.Ç/N, 157° 50.85'w, water depth 5821 meters, and are r e p r e s e n t a t i v e o f the s m e c t i t e - r i c h region o f the red c l a y s which occurs i n the sediment at depths below about ten meters. In t h i s r e g i o n , the sediment appears t o contain about f i v e t o s i x percent by weight leachable i r o n and manganese i n the form of hydrous oxides. The remaining m a t e r i a l appears to be dominated by i r o n - r i c h smectite and l e s s e r , v a r y i n g amounts o f p h i l l i p s i t e (2). The r e s u l t s o f a semi-quantitative ( p r e c i s i o n i n data i s w i t h i n a f a c t o r o f 2) elemental a n a l y s i s

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performed on the r e d c l a y (by emission spectroscopy) are given i n Table I . Table I . Semi-quantitative A n a l y s i s o f Red C l a y (Done by Emission Spectroscopy) Concentration (mg-atom/i

Element

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(ppm) Rb Sr Ba Na Κ Ca Mg Fe Mn Al Si Li Ni Cu Ti Cr V Zr Be

80 810 63Ο 810 I3OOO 10000 25000

0.0009 0.0092 0.00U6 0.035 0.33 0.25 1.0 1.1

63ΟΟΟ 13000 81000 160000 16 1300 l600 3300 130 250 200 50

0.2*4-

3.0 5.7 0.023 0.022 0.025 Ο.Ο69 0.0025 0.00^9 0.0022 Ο.ΟΟ56

The nature o f the solid-phase concentrations o f rubidium, strontium, and barium given i n Table I are o f some concern since those concentrations must be a p p r o p r i a t e l y accounted f o r when d i s ­ t r i b u t i o n c o e f f i c i e n t s and solution-phase concentrations a r e c a l ­ c u l a t e d from experimental data. Since the average concentrations (given i n Table I I ) o f rubidium, strontium and barium i n seawater are r e l a t i v e l y s u b s t a n t i a l , the concentrations given i n Table I could c e r t a i n l y be the solid-phase concentrations o f rubidium, strontium and barium which are i n s o r p t i o n equîLibrium with the concentrations o f the r e s p e c t i v e elements i n the o r i g i n a l i n t e r s t i t i a l seawater. Table I I .

Average Concentrations o f Rubidium, Strontium and Barium i n Seawater (3)

Element

Average Concentration i n Seawater (mg-a torn/ml)

Rb Sr Ba

2 Λ χ 10"? 1.5 x 10"£ 3.6 χ 10"

The concentrations o f rubidium,

(

strontium and barium given i n

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Table I c o u l d a l s o represent the presence o f s a l t s o f those elements. However, f o r the reasons given below, i t was concluded t h a t the solid-phase concentrations o f rubidium, strontium and barium were probably the r e s u l t o f s o r p t i o n r a t h e r than the p r e s ­ ence o f s a l t s The p r i n c i p a l rubidium s a l t s which would probably have been present i n the sediment ( c h l o r i d e , s u l f a t e , bicarbonate, e t c . ) are a l l s o l u b l e i n water. As d i s c u s s e d l a t e r , the r e d c l a y was thoroughly d i a l y z e d p r i o r t o use ( i n c l u d i n g p r i o r t o a n a l y s i s by emission spectroscopy). Any rubidium s a l t s i n i t i a l l y present i n the c l a y samples would, t h e r e f o r e , have been removed by the d i a i y z i n g s o l u t i o n . Hence, i t was assumed t h a t the rubidium concen­ t r a t i o n given i n Table I represented sorbed rubidium which had been i n e q u i l i b r i u m w i t h the rubidium i n the o r i g i n a l i n t e r s t i t i a l seawater. Then when c a l c u l a t i n g d i s t r i b u t i o n c o e f f i c i e n t s from experimental data, the c o n c e n t r a t i o n g i v e n i n Table I was used as the i n i t i a l clay-phase rubidium c o n c e n t r a t i o n , r a t h e r than zero as used w i t h most o f the other species s t u d i e d . Many o f t h e p r i n c i p a l compounds o f strontium and barium which c o u l d have been present i n the sediment a r e a l s o s o l u b l e i n water, but t h e carbonates and s u l f a t e s are r e l a t i v e l y i n s o l u b l e . In s o l u t i o n s o f low i o n i c s t r e n g t h the s o l u b i l i t y product con­ s t a n t s f o r strontium carbonate and s u l f a t e are 1.1 χ 1 0 " ^ and 3.2 χ 10"7 r e s p e c t i v e l y , and f o r barium carbonate and s u l f a t e are 5.1 χ 10"9 and 1.1 χ 1 0 " , r e s p e c t i v e l y (h). Again, any s o l u b l e s a l t s should have been removed by the d i a l y z i n g s o l u t i o n . Furthermore, when the d i a l y z i n g s o l u t i o n from t h e f i r s t d i a l y s i s was concentrated by a f a c t o r o f about one hundred, no p r e c i p i t a t e was observed. A f t e r the f i r s t d i a l y s i s , the carbonate concentra­ t i o n i n the d i a l y z i n g s o l u t i o n should have been s u f f i c i e n t l y s m a l l (due t o the n e a r - n e u t r a l c o n d i t i o n s e x i s t i n g i n the solution) so t h a t the corresponding s a t u r a t i o n concentrations o f strontium and barium should have been l a r g e enough t o y i e l d n o t i c e a b l e pre­ c i p i t a t e s when the s o l u t i o n was concentrated. However, the s u l f a t e c o n c e n t r a t i o n ( r e s u l t i n g from the s u l f a t e i n seawater) was probably s u f f i c i e n t l y l a r g e so t h a t o n l y the corresponding s a t u r a t i o n c o n c e n t r a t i o n o f strontium would have been great enough t o y i e l d a n o t i c e a b l e p r e c i p i t a t e . Therefore, the b u l k d i a l y z i n g s o l u t i o n was probably under s a t u r a t e d w i t h respect t o strontium carbonate and s u l f a t e and with respect t o barium c a r ­ bonate. Since each d i a l y s i s was conducted f o r a t l e a s t twentyf o u r hours, and the d i a l y s i s bags were o n l y about two centimeters i n diameter, the concentrations o f nonsorbing species i n the i n t e r s t i t i a l and b u l k d i a l y z i n g s o l u t i o n s should not have been g r e a t l y d i f f e r e n t . Hence, the i n t e r s t i t i a l s o l u t i o n was a l s o probably under s a t u r a t e d , and any strontium i n i t i a l l y present as a carbonate o r s u l f a t e and any barium present as a carbonate should have been removed by the d i a l y z i n g s o l u t i o n o r sorbed by the c l a y (due t o the f a v o r a b l e e q u i l i b r i a f o r strontium and barium s o r p t i o n , which are d i s c u s s e d l a t e r ) . The d i a l y z i n g 5

1 0

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s o l u t i o n from the next t o l a s t d i a l y s i s was concentrated by a f a c t o r o f about twenty and d i d not y i e l d a n o t i c e a b l e p r e c i p i t a t e . The s u l f a t e c o n c e n t r a t i o n (as a r e s u l t o f the s u l f a t e i n seawater) i n t h a t s o l u t i o n should have been s u f f i c i e n t l y s m a l l so that the corresponding s a t u r a t i o n c o n c e n t r a t i o n o f barium would have y i e l d e d a n o t i c e a b l e p r e c i p i t a t e . The b u l k d i a l y z i n g s o l u t i o n and the i n t e r s t i t i a l s o l u t i o n were, t h e r e f o r e , probably undersaturated with respect t o barium s u l f a t e . Then a f t e r the l a s t d i a l y s i s , the maximum i n t e r s t i t i a l solution-phase c o n c e n t r a t i o n o f barium s u l f a t e was probably much l e s s than 10"5 mg-atom/ml. Since the r a t i o of the volume o f i n t e r s t i t i a l s o l u t i o n t o mass o f c l a y was on the order o f 5 ml/gm, the maximum c o n c e n t r a t i o n o f barium s u l f a t e which should have been p o s s i b l e i n the d r i e d s o l i d would have been on the order o f o n l y 10"^ mg-atom/gm, which i s c o n s i d e r a b l y l e s s than the barium c o n c e n t r a t i o n g i v e n i n Table I . I t was, t h e r e f o r e , assumed t h a t the strontium and barium concentrations g i v e n i n Table I represent sorbed strontium and barium which had been i n e q u i l i b r i u m w i t h the strontium and barium, r e s p e c t i v e l y , i n the i n s i t u i n t e r s t i t i a l seawater o r which had been sorbed during d i a l y s i s . Again when c a l c u l a t i n g d i s t r i b u t i o n c o e f f i c i e n t s from experimental data, t h e concentrations g i v e n i n Table I were used as the i n i t i a l clay-phase strontium and barium c o n c e n t r a t i o n s , r a t h e r than u s i n g a value o f zero. Experimental I t was f e l t t h a t the presence o f r e s i d u a l s a l t s i n the c l a y would complicate the a n a l y s i s o f experimental data. Therefore, i n order t o remove such s a l t s p r i o r t o u s i n g the c l a y , the samples of sediment were d i a l y z e d (using d e i o n i z e d water) u n t i l a twentyf o l d c o n c e n t r a t i o n o f the d i a l y z i n g s o l u t i o n d i d not y i e l d a p r e c i p i t a t e upon a d d i t i o n o f s i l v e r n i t r a t e . (Also, no p r e c i p i t a t e was observed upon c o n c e n t r a t i o n o f the s o l u t i o n . ) The s o l i d s were then d i a l y z e d once more, vacuum d r i e d , and s t o r e d i n s e a l e d containers i n a d e s i c c a t o r u n t i l needed. (The preceding procedure may have r e s u l t e d i n some a l t e r a t i o n o f the s o r p t i o n propert i e s o f the r e d c l a y , p a r t i c u l a r l y with regard t o the hydrous oxides. I t i s intended t o assess the extent o f such a l t e r a t i o n , i f any, during the course o f f u t u r e work.) As discussed l a t e r , i t was suspected and l a t e r experimentally determined that c a t i o n exchange i s a major mechanism r e s p o n s i b l e f o r r a d i o n u c l i d e s o r p t i o n . Therefore, the cation-exchange capaci t y o f the c l a y (defined here as the t o t a l m i H i e q u i v a l e n t s o f exchangeable c a t i o n s per gram o f c l a y ) was evaluated u s i n g both cesium and barium exchange. (For a given s p e c i e s , the c a t i o n exchange c a p a c i t y o f the c l a y should be reasonably constant, independent o f solution-phase concentrations o f t h a t s p e c i e s , as long as the p h y s i c a l and chemical c h a r a c t e r i s t i c s o f the s o l i d remain u n a l t e r e d , p a r t i c u l a r l y the charge d i s t r i b u t i o n which determines the nature o f the e l e c t r i c a l double l a y e r s i n the

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r e g i o n s of the s o l i d - l i q u i d i n t e r f a c e s . ) The cation-exchange c a p a c i t y f o r cesium was determined from the i s o t o p i c r e d i s t r i b u t i o n o f Cs^37 between 0.01 M CsCl s o l u t i o n s and cesium-saturated c l a y . The ceslum-saturated c l a y was prepared by c o n t a c t i n g 0.25 t o 0.55 grams o f c l a y w i t h 50 t o 100 ml o f 1.0 M C s C l s o l u t i o n ( s t a b l e C s ) . A f t e r a l l o w i n g s u f f i c i e n t time f o r e q u i l i b r a t i o n (k8 t o 96 h o u r s ) , the o r i g i n a l 1.0 M s o l u t i o n was reduced t o 0.01 M by repeated c e n t r i f u g i n g of the suspension f o l ­ lowed by decanting o f the supernatant and then d i l u t i n g o f the remaining s o l u t i o n . An a p p r o p r i a t e amount o f C s 3 7 then added to the suspension, and 3-0-ml samples were p e r i o d i c a l l y removed and analyzed f o r Cs-^-37 (^y gamma counting) u n t i l i s o t o p i c r e d i s ­ t r i b u t i o n o f the cesium i s o t o p e s was a p p a r e n t l y complete. Then, f o r reasonably complete i s o t o p i c r e d i s t r i b u t i o n , the d i s t r i b u t i o n c o e f f i c i e n t c a l c u l a t e d f o r Cs- 37 ( f m the change i n the s o l u t i o n phase c o n c e n t r a t i o n o f Cs-^-37) should have been e s s e n t i a l l y the same as the d i s t r i b u t i o n c o e f f i c i e n t f o r both s t a b l e and r a d i o ­ a c t i v e cesium. A l s o s i n c e the solution-phase c o n c e n t r a t i o n o f Cs^37 was much l e s s than the c o n c e n t r a t i o n o f s t a b l e Cs and since the c l a y was s a t u r a t e d w i t h cesium, the cation-exchange c a p a c i t y f o r t h a t element should be equal to i t s solid-phase c o n c e n t r a t i o n (which should have remained e s s e n t i a l l y constant upon d i l u t i o n o f the C s C l s o l u t i o n ) and was c a l c u l a t e d from 1

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch015

w

a

s

L

r 0

Cs Exchange C a p a c i t y = Kp^

^.37

x

°·°1

mequiv/ml

The c a t i o n exchange c a p a c i t y f o r barium was determined i n an analogous manner. The data used t o c a l c u l a t e the values o f Kj)^ f o r each n u c l i d e s t u d i e d were obtained from batch e q u i l i b r a t i o n experiments i n which 0.68 Ν NaCl s o l u t i o n s (or o c c a s i o n a l l y other s o l u t i o n s ) having v a r i o u s concentrations o f the n u c l i d e o f i n t e r e s t were contacted w i t h the red c l a y a t k°C ( o c c a s i o n a l l y a t 11°C) and ambient p r e s s u r e . The 0.68 Ν NaCl s o l u t i o n s were used i n s t e a d of a r t i f i c i a l seawater i n order t o p r o v i d e somewhat simpler systems f o r study. A temperature o f k°C was g e n e r a l l y used s i n c e t h i s i s approximately the ambient temperature i n the sediment. Since s o r p t i o n phenomena are g e n e r a l l y l i t t l e a f f e c t e d by p r e s ­ sure, i t f u r t h e r was assumed t h a t any e f f e c t s due t o d i f f e r e n c e s between the pressure on the s e a f l o o r and the ambient l a b o r a t o r y pressure would g e n e r a l l y be s m a l l . (The v a l i d i t y o f t h i s assump­ t i o n should be v e r i f i e d , and i t i s intended t o do so during f u t u r e experimentation.) The g e n e r a l procedure f o r the batch e q u i l i b r a t i o n experiments was as f o l l o w s . About 0.25 t o 0.55 grams of c l a y and 1*5 t o 70 ml of 0.68 Ν NaCl s o l u t i o n were added t o a 125-ml polyethylene bottle. Next 2.5 ml o f a 0.68 Ν NaCl s o l u t i o n , b u f f e r e d with predetermined amounts o f sodium bicarbonate and/or b o r i c a c i d , were added. (In order t o o b t a i n data at low values o f the s o l u t i o n pH, a d d i t i o n

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o f the b u f f e r was omitted and 0.25 ml o f 1.0 Ν HCL was added t o the b o t t l e . ) The pH b u f f e r i n g or adjustment was followed by a d d i ­ t i o n o f 2.5 ml of a 0.68 Ν NaCl s o l u t i o n c o n t a i n i n g predetermined amounts o f s t a b l e and/or r a d i o a c t i v e isotopes o f the n u c l i d e s o f interest. (The r a d i o a c t i v e isotopes used were C s l 3 7 , s r 5 , 133, E u ^ S , G d l 5 3 , Pm ^, C e ^ , and A g . ) The polyethylene b o t t l e s were then p l a c e d i n a shaker bath maintained at k ± 1 or 11 ± 1 °C. Samples were then p e r i o d i c a l l y removed f o r a n a l y s i s by atomic ab­ s o r p t i o n (only s t a b l e isotopes present) or by gamma or beta count­ ing. Samples were removed u n t i l the analyses i n d i c a t e d t h a t the solution-phase concentration o f the n u c l i d e was no longer changing with time. The sampling procedure c o n s i s t e d o f a l l o w i n g the c l a y to s e t t l e from suspension and then removing a l i q u i d sample (of known volume) which was f i l t e r e d through a 0.2 Mm Gelman f i l t e r . At the conclusion o f s e v e r a l o f the e q u i l i b r a t i o n experiments, samples of the s o l i d were removed and analyzed f o r the n u c l i d e o f i n t e r e s t . For each such experiment, the n u c l i d e concentration a s s o c i a t e d with the s o l i d g e n e r a l l y accounted f o r the change i n n u c l i d e concentration observed i n the s o l u t i o n . The r e l a t i v e d i f ­ ference between the t o t a l amount of n u c l i d e determined as l o s t from s o l u t i o n and the t o t a l amount determined as gained by the s o l i d was u s u a l l y l e s s than ± 10$. A l s o , f o r most n u c l i d e s and most sets of experimental c o n d i t i o n s , "blank" experiments were conducted i n order t o determine i f n u c l i d e s were l o s t from s o l u ­ t i o n due t o phenomena other than s o r p t i o n by the c l a y . The "blank" experiments were done s i m i l a r l y t o the s o r p t i o n e x p e r i ­ ments (to include sample removal and a n a l y s i s ) except that the c l a y was omitted. y

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch015

1

1

Ba

1 1 0 1 1 1

For reasons given l a t e r , i t was b e l i e v e d that the hydrous i r o n and manganese oxides i n the sediment were of major importance i n determining the s o r p t i o n p r o p e r t i e s of the c l a y . As an i n i t i a l attempt t o assess the s i g n i f i c a n c e of those hydrous oxides, e q u i l i b r a t i o n experiments were performed i n which, t o the extent p o s s i b l e the hydrous i r o n and manganese oxides were removed from the c l a y . The method used f o r removing the hydrous oxides was that recom­ mended by Mehra and Jackson (5), and involved a reduction-complexat i o n - e x t r a c t i o n process (using a d i t h i o n i t e - c i t r a t e - b i c a r b o n a t e s o l u t i o n ) followed by washing and c e n t r i f u g i n g of the s o l i d . The procedure removed about t e n percent by weight of the s o l i d s , the remaining p o r t i o n of which was green c o l o r e d . H e r e a f t e r , the samples prepared using the above method are g e n e r a l l y r e f e r r e d t o as " d e f e r r a t e d . " Results and

Discussion

General. The abyssal red clays were, i n p a r t , o r i g i n a l l y s e l e c t e d f o r study because previous i n v e s t i g a t i o n s of t h e i r s o r p t i o n p r o p e r t i e s had been encouraging (6,7)> and because g e n e r a l l y the types of minerals o c c u r r i n g "in~the sediment e x h i b i t v e r y favorable ion-exchange and adsorption p r o p e r t i e s . In

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

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p a r t i c u l a r , the ion-exchange e q u i l i b r i a a s s o c i a t e d with smectite minerals (which c o n s t i t u t e a major p o r t i o n of the sediment) have been found t o show strong preferences f o r cesium, strontium, barium, y t t r i u m , and cerium ( 8 - 1 3 ) . These e q u i l i b r i a , at l e a s t i n the case of cesium, appear t o depend l i t t l e on pH i n the range of 3 t o 10 ( 7 j l l ) A l s o , the smectites g e n e r a l l y have r e l a t i v e l y large ion-exchange c a p a c i t i e s , on the order of 0.8 t o 1.5 milliequivalent per gram ( l ^ ) . Furthermore, hydrous i r o n and manganese oxides (which c o n s t i t u t e a reasonably s i g n i f i c a n t p o r t i o n of the sediment) have been found t o s t r o n g l y adsorb strontium, barium and various t r a n s i t i o n m e t a l s ( 1 5 , l 6 , 1 7 ) . I t has a l s o been proposed t h a t these hydrous o x i d e " c o n t r o l the concentrations of c o b a l t , n i c k e l , copper and z i n c i n s o i l s and f r e s h water sediments (l8). The adsorption e q u i l i b r i a a s s o c i a t e d with the hydrous i r o n and manganese oxides have been found very dependent on s o l u t i o n P (15 >16,17)> and i o n exchange has been suggested as one o f the dominating s o r p t i o n phenomena. The s o r p t i o n c a p a c i t i e s of the hydrous oxides are a l s o dependent on pH and appear t o be considera b l y l e s s than the c a p a c i t i e s of the smectite minerals ( 1 7 , 1 9 ) . Therefore, based on a v a i l a b l e l i t e r a t u r e , the f o l l o w i n g sorpt i o n r e s u l t s were expected: ( l ) as a r e s u l t of the smectite minerals, the s o r p t i o n c a p a c i t y o f the red c l a y would be p r i m a r i l y due t o i o n exchange a s s o c i a t e d w i t h the smectites and would be on the order of 0.8 to 1.5 m i l l i e q u i v a l e n t s per gram; (2) a l s o as a r e s u l t o f the smectite minerals, the d i s t r i b u t i o n c o e f f i c i e n t s f o r n u c l i d e s such as cesium, strontium, barium, and cerium would be between 10 and 100 ml/gm f o r solution-phase concentrations on the order of 10"3 mg-atom/ml; (3) as a r e s u l t o f the hydrous oxides, the d i s t r i b u t i o n c o e f f i c i e n t s f o r n u c l i d e s such as s t r o n tium, barium, and some t r a n s i t i o n m e t a l s would be on the order of 1 0 ml/gm or g r e a t e r f o r solution-phase concentrations on the order o f 10~7 mg-atom/ml and l e s s ; (k) a l s o as a r e s u l t o f the hydrous oxides, the solution-phase pH would s t r o n g l y i n f l u e n c e the d i s t r i b u t i o n c o e f f i c i e n t s f o r most n u c l i d e s except the a l k a l i metàls; (5) as a r e s u l t of both smectites and hydrous oxides being present, the s o r p t i o n e q u i l i b r i u m data would probably r e f l e c t the i n f l u e n c e of m u l t i p l e s o r p t i o n mechanisms. As discussed below, the experimental r e s u l t s were indeed s i m i l a r to those which were expected. S o r p t i o n Capacity. The average s o r p t i o n c a p a c i t y o f the c l a y determined from i s o t o p i c r e d i s t r i b u t i o n o f Cs-^-37 between aqueous 0.01 M C s C l s o l u t i o n s and cesium-saturated c l a y was 0.91 mequiv./ gm. The average s o r p t i o n c a p a c i t y s i m i l a r l y determined by isotopic r e d i s t r i b u t i o n of Ba-*-33 0.7^ mequiv./gm. The maximum r e l a t i v e e r r o r i n these c a p a c i t i e s was estimated a t ± 10$. I f those s o r p t i o n c a p a c i t i e s were due to i o n exchange, i t would be expected that p r e p a r a t i o n o f the cesium- and bariumsaturated c l a y s would have caused v a r i o u s counter ions such as those o f sodium, potassium, magnesium, and calcium t o be desorbed from the c l a y and t o appear i n .the 1.0 M s o l u t i o n s . The t o t a l H

4

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a

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In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

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amount of desorbed species ( i n m i l l i e q u i v a l e n t s ) per gram o f s o l i d should be approximately equal t o the measured i o n exchange capac­ ities. Furthermore, s i n c e the c l a y had been e x t e n s i v e l y d i a l y z e d before use, the amounts o f any s a l t s of sodium, potassium, magne­ sium, and calcium which might have been present should have been n e g l i g i b l e ( f o r reasons s i m i l a r to those given when d i s c u s s i n g s a l t s o f rubidium, strontium, and barium), and i t i s reasonable t o expect t h a t the concentrations given f o r those elements i n Table I represent concentrations o f exchangeable counterions or ( e s p e c i a l l y i n the case of magnesium) c o n s t i t u e n t s of the c l a y m i n e r a l l a t ­ tices. The amount o f each desorbed species ( i n mg-atoms) per gram o f c l a y should then be approximately equal t o the corresponding concentrations given i n Table I. Such behavior was, i n f a c t , observed experimentally as discussed below. When p r e p a r i n g the cesium- and barium-saturated c l a y s , the 1.0 M s o l u t i o n s used were decanted ( a f t e r c e n t r i f u g i n g ) and ana­ l y z e d s e m i q u a n t i t a t i v e l y by emission spectroscopy. From those analyses, i t appears t h a t the f o l l o w i n g species were desorbed: sodium, potassium, calcium, magnesium, and strontium. It further appeared that desorption o f potassium was almost unique t o cesium s o r p t i o n ; whereas, desorption o f the other species appeared to be common t o both cesium and barium s o r p t i o n . Small amounts o f other elements such as n i c k e l and copper were a l s o detected by the analyses. However, to what extent the observed concentrations may represent desorption and t o what extent they may represent the d i s s o l u t i o n of s p a r i n g l y s o l u b l e substances ( p a r t i c u l a r l y hydroxide species) i s as y e t - u n c e r t a i n . The apparent concentrations o f the desorbed species per gram of c l a y are given i n Table I I I . Table I I I .

Apparent Concentrations Desorbed Species

Element

of

Concentration (mequiv./gm) (mg-atom/gm)

Κ (Cs s o r p t i o n ) Κ (Ba s o r p t i o n ) Na Ca Mg Sr

0.21 0.01 0.06

T o t a l (Cs s o r p t i o n ) T o t a l (Ba s o r p t i o n )

0.8^ o.6h

o.kk

0.11 0.02

0.21 0.01 o.o6 0.22 o.o6 0.01

For both cesium and barium s o r p t i o n , there i s reasonable agreement between the t o t a l concentrations o f desorbed species and the i o n exchange c a p a c i t i e s determined by i s o t o p i c r e d i s t r i b u t i o n . The small d i f f e r e n c e s which e x i s t could e a s i l y be due t o the p r e c i s i o n i n the elemental analyses. (Also, the experimental technique would not have detected desorption o f hydrogen i o n s . ) The s o l i d phase concentrations of sodium, potassium, magnesium, calcium,

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strontium from Tables I and I I I a r e compared i n Table IV. Table IV.

Element

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch015

Κ (Cs s o r p t i o n ) Na Ca Mg Sr

Comparison o f I n i t i a l Solid-Phase Concentrations and Solid-Phase Con­ c e n t r a t i o n s o f Desorbed Species Solid-Phase Concentration (mg-atom/gm) I n i t i a l (Table I ) Desorbed (Table I I I )

0.33 0.0k 0.25 1.0 0.01

0.21 0.06 0.22 0.06 0.01

In the case o f potassium (cesium s o r p t i o n ) , calcium, and strontium, the agreement i s f a i r l y good and i n the case o f sodium, somewhat poorer but w e l l w i t h i n the p r e c i s i o n o f the a n a l y s e s . In the case of magnesium, the agreement i s v e r y poor. However, the magnesium c o n c e n t r a t i o n given i n Table I c o u l d , t o a l a r g e extent, be due t o i n c o r p o r a t i o n o f magnesium i n t o the l a t t i c e s t r u c t u r e o f the c l a y minerals ( 2 0 ) . Therefore, a t solution-phase concentrations (on the order o f 1 0 m g - a t o m / m l o r g r e a t e r ) a t which the solid-phase c o n c e n t r a t i o n o f the n u c l i d e o f i n t e r e s t would be a s i g n i f i c a n t f r a c t i o n o f the s o r p t i o n c a p a c i t y o f the c l a y , i t appears reason­ a b l e t o conclude t h a t s o r p t i o n does r e s u l t from i o n exchange. The extension o f t h i s c o n c l u s i o n t o lower solution-phase concentrations at which the solid-phase c o n c e n t r a t i o n o f the n u c l i d e o f i n t e r e s t would be a n e g l i g i b l e f r a c t i o n o f the ion-exchange c a p a c i t y o f the c l a y may o r may not be j u s t i f i e d . The ion-exchange c a p a c i t i e s d i s c u s s e d above (and the i d e n t i f i ­ c a t i o n o f the p r i n c i p a l desorbing s p e c i e s ) appear c o n s i s t e n t w i t h c a p a c i t i e s o f about O.k t o 0.8 mequiv./gm ( p r i n c i p a l desorbing species b e i n g sodium, potassium, calcium and magnesium) r e p o r t e d for a related p a c i f i c red clay (7). The s o r p t i o n c a p a c i t i e s given above a l s o appear reasonably c o n s i s t e n t w i t h c a p a c i t i e s o f about 0.8 t o 1.5 mequiv./gm, which have been reported f o r r e l a t e d c l a y minerals found w i t h i n the c o n t i n e n t a l U n i t e d States (8,9>10,12,lU). Distribution Coefficients. The d i s t r i b u t i o n c o e f f i c i e n t s determined f o r rubidium ( a t 11°C) and f o r cesium (at 11°C f o r - l o g C i l e s s than 5 and a t k°C f o r - l o g g r e a t e r than 5) are summa­ r i z e d i n F i g u r e 1. Over the range o f solution-phase concentrations i n which both rubidium and cesium were s t u d i e d , the rubidium coef­ f i c i e n t s appear t o behave very s i m i l a r l y t o those f o r cesium. F o r solution-phase concentrations on the order o f 10"3 mg-atom/ml, the c o e f f i c i e n t s a r e on the order o f 100 ml/gm, as was expected. Furthermore, the d i s t r i b u t i o n c o e f f i c i e n t s obtained f o r cesium g e n e r a l l y appear c o n s i s t e n t with the corresponding c o e f f i c i e n t s obtained f o r s i m i l a r oceanic sediments and r e l a t e d c l a y minerals found w i t h i n the c o n t i n e n t a l U n i t e d S t a t e s ( 6 , 7 , 8 , 9 , 1 0 , 1 2 , 1 3 ) . In the pH range o f 6 . 3 t o 8 . 0 , the cesium c o e f f i c i e n t s appear t o

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch015

ERiCKSON

Radionuclide

I

1

Sorption

I

1

1

Studies

1

I I I

I

1

1

8 *

7*V

4

5

1

6

Ο

ι

i

7

ι

18

9

-LOG Cj (mg-atom/ml) Figure 1. Distribution coefficients for Cs and Rb in 0.68N NaCl solutions: ( Π λ Cs (pH 6.5, deferrated); (Φ), Cs (pH 2.7); (0),Cs (pH 6.3-8.0); (V), Rb (pH 7.07.6).

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch015

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i n c r e a s e r a t h e r g r a d u a l l y as the solution-phase c o n c e n t r a t i o n de­ creases from about 3 χ 1 0 " ^ " t o 3 χ 1 0 " ^ mg-atom/ml. The c o e f f i ­ c i e n t s then undergo a f a i r l y sharp i n c r e a s e as the c o n c e n t r a t i o n decreases from 3 x 1 0 ~ 6 t o about 3 x 1 0 " ° mg-atom/ml and then appear to be approaching constant values as the solution-phase concentration decreases f u r t h e r . A l s o , lowering the s o l u t i o n pH to 2.7 and t r e a t i n g the c l a y t o remove hydrous i r o n and manganese oxides do not appear t o g r e a t l y a f f e c t the cesium d i s t r i b u t i o n coefficients. (Furthermore, the c o e f f i c i e n t s f o r cesium at - l o g of about k.l were obtained from desorption data and appear c o n s i s t e n t w i t h the other c o e f f i c i e n t s obtained from s o r p t i o n data.) The sharp increase observed i n the d i s t r i b u t i o n c o e f f i c i e n t s f o r cesium between concentrations o f about 3 x 1 0 " " and 3 x 1 0 " " mg-atom/ml suggests t h a t s o r p t i o n o f cesium may r e s u l t from at l e a s t two d i f f e r e n t mechanisms. I f so, apparently one mechanism dominates at lower solution-phase n u c l i d e concentrations (on the order of 3 x 1 0 " ^ mg-atom/ml or l e s s ) because o f a r e l a t i v e l y much more f a v o r a b l e e q u i l i b r i u m constant f o r the corresponding s o r p t i o n phenomena. However, t h i s mechanism has a r e l a t i v e l y small sorp­ t i o n c a p a c i t y which e s s e n t i a l l y becomes exhausted at higher solution-phase c o n c e n t r a t i o n s . The other mechanism i n v o l v e s a r e l a t i v e l y l e s s favorable e q u i l i b r i u m constant, but has a r e l a t i v e ­ l y much g r e a t e r s o r p t i o n c a p a c i t y and, t h e r e f o r e , dominates a t higher solution-phase c o n c e n t r a t i o n s . The mechanism dominating at higher concentrations i s probably an i o n exchange phenomena having a s o r p t i o n c a p a c i t y e s s e n t i a l l y equal t o that which was determined by i s o t o p i c r e d i s t r i b u t i o n o f Cs^37 The mechanism dominating at lower concentrations may or may not be an ion-exchange phenomena. Furthermore, the f a c t that s o l u t i o n pH and removal o f hydrous oxides do not appear t o a p p r e c i a b l y a f f e c t the cesium d i s t r i b u t i o n c o e f f i c i e n t s suggests t h a t both mechanisms are a s s o c i a t e d w i t h the s i l i c a t e phases ( r a t h e r than at l e a s t one mechanism being a s s o c i ­ ated w i t h the hydrous i r o n and manganese oxides.) The d i s t r i b u t i o n c o e f f i c i e n t s determined f o r strontium (at k°C) and f o r barium (at 1 1 ° C f o r 3 . 0 < - l o g C < h.5 and at k°C f o r a l l other values of - l o g C i ) are summarized i n Figure 2. Due to the r e l a t i v e l y h i g h concentration o f strontium i n seawater (and hence the r e l a t i v e l y high concentration i n i t i a l l y i n the c l a y phase) o n l y l i m i t e d data f o r strontium were obtained. The d i s t r i ­ b u t i o n c o e f f i c i e n t s which were obtained appear t o behave s i m i l a r l y to the r e s p e c t i v e c o e f f i c i e n t s f o r barium but are somewhat smaller i n magnitude. For solution-phase concentrations on the order of 1 0 ~ 3 mg-atom/ml, the barium c o e f f i c i e n t s appear t o be between 1 0 and 1 0 0 ml/gm, and f o r solution-phase concentrations on the order o f 1 0 " 7 , the barium c o e f f i c i e n t s appear to be on the order o f K r , as was expected. Furthermore, the c o e f f i c i e n t s f o r both strontium and barium are g e n e r a l l y c o n s i s t e n t w i t h the corresponding data obtained f o r s i m i l a r oceanic sediments and r e l a t e d c l a y minerals found w i t h i n the c o n t i n e n t a l United States ( 6 , 7 , 8 , 1 3 ) . The e

±

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d i s t r i b u t i o n c o e f f i c i e n t s f o r barium i n c r e a s e s t e a d i l y as the solution-phase concentration decreases from about 10"^ t o about 10~7 mg-atom/ml. At solution-phase concentrations of about 10 mg-atom/ml, there appears t o be l i t t l e d i f f e r e n c e between the barium d i s t r i b u t i o n c o e f f i c i e n t s at pH 2.6 and those a t pH 7.0 and g r e a t e r . However, at concentrations l e s s than 10"^ the d i s t r i b u t i o n c o e f f i c i e n t s at pH 2.6 are s i g n i f i c a n t l y reduced r e l a t i v e t o the c o e f f i c i e n t s at pH 7.0 and g r e a t e r . (No a p p r e c i a b l e d i s s o l u t i o n of the hydrous oxides was observed at pH 2.6.) Also, the chemical removal (to the extent p o s s i b l e ) o f the hydrous i r o n and manganese oxides appears to have d r a s t i c a l l y reduced the (deferrated) d i s t r i b u t i o n c o e f f i c i e n t s (at values o f o f about 10~7 mg-atom/ml) r e l a t i v e to the c o e f f i c i e n t s f o r untreated c l a y . Furthermore, i t appears that the e f f e c t o f low pH and hydrous oxide removal are s i m i l a r , s i n c e the data f o r both s i t u a t i o n s appear t o n e a r l y l i e along the same h o r i z o n t a l l i n e . (However, such c l o s e agreement may be f o r t u i t o u s . ) These r e s u l t s seem reasonable. The i s o e l e c t r i c p o i n t s determined f o r hydrous i r o n and manganese oxides are g e n e r a l l y on the order o f pH h or g r e a t e r , although lower pH values have been r e p o r t e d (17,21). Therefore, a t a s o l u t i o n pH of 2.6, the hydrous i r o n and manganese oxides would probably have l o s t t h e i r cation-exchange c a p a c i t y , and the net r e s u l t o f a low s o l u t i o n pH would be s i m i l a r t o c h e m i c a l l y removing the hydrous oxides. ( A l s o , the c o e f f i c i e n t s f o r barium at - l o g C i o f about k.l were obtained from desorption data and appear c o n s i s t e n t with the other c o e f f i c i e n t s c a l c u l a t e d from s o r p t i o n data.) The strong dependence (at lower solution-phase n u c l i d e conc e n t r a t i o n s ) of the d i s t r i b u t i o n c o e f f i c i e n t s on s o l u t i o n pH and on the removal o f the hydrous i r o n and manganese oxides suggests the existence of at l e a s t two separate s o r p t i o n mechanisms. Again, apparently one mechanism dominates at lower solution-phase n u c l i d e concentrations (probably on the order o f 10" 3 mg-atom/ml or l e s s ) because o f a r e l a t i v e l y much more f a v o r a b l e e q u i l i b r i u m constant f o r the corresponding s o r p t i o n phenomena. However, t h i s mechanism has a r e l a t i v e l y small s o r p t i o n c a p a c i t y which e s s e n t i a l l y becomes exhausted at h i g h e r solution-phase c o n c e n t r a t i o n s . The other mechanism i n v o l v e s a r e l a t i v e l y l e s s favorable e q u i l i b r i u m constant but has a r e l a t i v e l y much greater s o r p t i o n c a p a c i t y and, t h e r e f o r e , dominates at higher solution-phase c o n c e n t r a t i o n s . The mechanism dominating at higher concentrations i s probably an ion-exchange phenomena which i s a s s o c i a t e d with the s i l i c a t e phases and which has a s o r p t i o n c a p a c i t y e s s e n t i a l l y equal t o t h a t which was d e t e r mined by i s o t o p i c r e d i s t r i b u t i o n o f B a ^ S . The mechanism dominating at lower concentrations i s probably an ion-exchange or other s o r p t i o n phenomena which i s a s s o c i a t e d with the hydrous i r o n and manganese oxides. F i n a l l y , as d i s c u s s e d below, the clay-phase concentrations given f o r strontium and barium i n Table I appear t o provide a v e r y l i m i t e d " f i e l d v e r i f i c a t i o n " of the strontium and barium

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch015

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RADIOACTIVE

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d i s t r i b u t i o n c o e f f i c i e n t s obtained experimentally. I t was men­ t i o n e d p r e v i o u s l y t h a t when the values o f C-? and Κγ, shown i n ^i F i g u r e 2 were c a l c u l a t e d , the i n i t i a l clay-phase concentrations given i n Table I were used. For convenience below the concentra­ t i o n s and c o e f f i c i e n t s so c a l c u l a t e d have been r e f e r r e d t o as " c o r r e c t e d . " For each s e t o f c o r r e c t e d values o f and K p given i n F i g u r e 2 , a corresponding set o f "uncorrected" values o f and K-p, were a l s o c a l c u l a t e d u s i n g the same experimental data but ^i assuming an i n i t i a l clay-phase concentration o f zero. Some t y p i ­ c a l uncorrected values o f C_- and K-p, and the corresponding values i

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch015

from Figure 2 are shown i n Table V. Table V.

Uncorrected Versus Corrected Values o f C^ and Kp^. Uncorrected Data -log C log K

Corrected Data (Figure 2) -log C log K

Sr

T728 5Λ0

1.85 2.11

"T97 1+.36

1.85 2.11

Ba

U.15 8.06 9.01

2.39 1+.09

^.15 6.12 6.57

k.09

Element

±

±

D-

k.23

D i

ι

2Λ9 ^.23

The data f o r barium corresponding t o the value o f - l o g C^ (uncor­ r e c t e d ) o f U.15 was obtained from changes i n solution-phase concentrations determined by atomic a b s o r p t i o n . The uncorrected value o f C i i s , t h e r e f o r e , the best a v a i l a b l e value f o r C^ and was used i n F i g u r e 2 . However, the uncorrected value o f K j ^ does not account f o r any barium i n i t i a l l y present i n the clay-phase and should represent the minimum value which the d i s t r i b u t i o n c o e f f i c i e n t would have. A l l other data given i n Table V were ob­ t a i n e d from changes i n solution-phase concentrations o f r a d i o ­ a c t i v e t r a c e r s (determined by gamma c o u n t i n g ) . Assuming reason­ a b l y complete i s o t o p i c r e d i s t r i b u t i o n , the experimental data should have given the d i s t r i b u t i o n c o e f f i c i e n t s f o r a l l strontium or barium present, both that i n i t i a l l y i n the clay-phase and t h a t which was subsequently sorbed from s o l u t i o n . The uncorrected values o f K j ^ obtained from the experimental data should, t h e r e ­ f o r e , be the best a v a i l a b l e values f o r Κ and were used i n F i g u r e ^i 2. But, the values o f C i c a l c u l a t e d o n l y from changes i n s o l u t i o n phase concentrations would be l e s s than o r equal t o the a c t u a l values o f C i when strontium o r barium was i n i t i a l l y present i n the c l a y . The uncorrected values o f C. should, t h e r e f o r e , represent minimum values f o r the a c t u a l solution-phase c o n c e n t r a t i o n s . π

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch015

15.

ERiCKSON

Radionuclide

1

c 0

1

1

Sorption

1

1

I

Studies

1

1

1

J

1

1

1 1

4 Ε

° ft, οοJB

—

—

_

3

8

2

1

η

υ9 I

%

Φ

6

-

i 1

1 ι 1 1

2

—

-

I

3

ι

I

4

ι

I ι I . 1 5

6

7

106 Cj (mg-atom/ml) Figure 2. Distribution coefficients for Sr and Ba in 0.68N NaCl solutions: ( Π λ Ba (pH 8.3, deferrated); (%), Ba (pH 2.6); (O), Ba (pH 7.0-8.1); ( V ) , Sr (pH 7.17.3).

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

RADIOACTIVE W A S T E IN

282

GEOLOGIC STORAGE

The average concentrations o f strontium and barium i n sea­ water are 1.5 χ 10~^ mg-atom/ml (-log Cj_ = 3.82) and 3.6 χ 10"? mg-atom/ml (-log = 6.kk) r e s p e c t i v e l y . For strontium ( r e f e r ­ r i n g to Table V) the minimum value o f l o g corresponding t o a 9

solution-phase c o n c e n t r a t i o n o f 1.5 x 1 0 w o u l d be about 1.7^ (obtained by l i n e a r e x t r a p o l a t i o n o f the uncorrected d a t a ) , and the maximum value o f l o g Kp^ would be about I . 8 5 . Therefore, the

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch015

clay-phase strontium c o n c e n t r a t i o n which would be i n e q u i l i b r i u m with the average concentration o f strontium i n seawater would be about 10~2 mg-atom/ml, which i s v e r y n e a r l y the clay-phase con­ c e n t r a t i o n given i n Table I. For barium, the minimum value o f l o g Kp^ corresponding t o a solution-phase c o n c e n t r a t i o n o f 3·6 χ 10"' would be about 3·^· (obtained by l i n e a r i n t e r p o l a t i o n between uncoi»r e c t e d d a t a ) , and the maximum value o f l o g Kp^ would be about k.l. Therefore, the clay-phase barium c o n c e n t r a t i o n which would be i n e q u i l i b r i u m w i t h the average c o n c e n t r a t i o n o f barium i n seawater would be between about 0.001 and 0.004 mg-atom/ml, which i s i n reasonable agreement with the clay-phase c o n c e n t r a t i o n given i n Table I. Assuming t h a t the average concentrations given f o r strontium and barium i n seawater are not g r e a t l y d i f f e r e n t from the concentrations o f those elements i n the i n s i t u i n t e r s t i t i a l seawater, then the concentrations given i n Table I appear to be i n reasonable agreement w i t h the concentrations o f strontium and barium which the experimentally determined d i s t r i b u t i o n c o e f f i ­ c i e n t s i n d i c a t e would be i n s o r p t i o n e q u i l i b r i u m with the i n s i t u i n t e r s t i t i a l seawater. Therefore, t o a l i m i t e d extent, the data given f o r strontium and barium i n Table I appear t o provide a " f i e l d v e r i f i c a t i o n " o f the strontium and barium d i s t r i b u t i o n co­ e f f i c i e n t s which were obtained i n the l a b o r a t o r y . The d i s t r i b u t i o n c o e f f i c i e n t s determined f o r cadmium (at 11°C) are given i n F i g u r e 3· The c o e f f i c i e n t s appear somewhat l e s s than the corresponding data f o r strontium and barium. Such r e s u l t s could be due to e i t h e r a n i o n i c complex formation (22) and/ or a l e s s f a v o r a b l e s o r p t i o n e q u i l i b r i u m . The d i s t r i b u t i o n c o e f f i c i e n t s evaluated f o r s i l v e r (at ^°C) are a l s o given i n F i g u r e 3· The s i l v e r c o e f f i c i e n t s determined i n 0.68 Ν NaCl s o l u t i o n s are somewhat l e s s than the corresponding c o e f f i c i e n t s f o r cesium and rubidium, and a l s o f o r strontium and barium. Such r e s u l t s are probably due t o e i t h e r a n i o n i c complex formation (22) and/or a l e s s f a v o r a b l e s o r p t i o n e q u i l i b r i u m . (Furthermore, the experiments done using s i l v e r i n sodium c h l o r ­ ide s o l u t i o n s r e q u i r e d e q u i l i b r a t i o n times on t h e order of 90 days, as opposed t o two t o f o u r days f o r most other experiments, and i t appears that processes, which may or may not be important, are involved which are not understood.) I n order t o o b t a i n a b e t t e r understanding of the behavior of s i l v e r , d i s t r i b u t i o n c o e f f i c i e n t s were evaluated using d e i o n i z e d water and 0.68 Ν NaNO^, s o l u t i o n s . The c o e f f i c i e n t s obtained from

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch015

ERiCKSON

Radionuclide

ι

c 0

1

ι

Sorption

I

I

ι

283

Studies

ι

I

1

1

1

1 I

1

1

-

•

*

4

—

ε \

X ο ο

— — —



„ J

V_

(1)

(n

a+ i s the concentration of A in solution, moles/liter. (A ) i s the c o n c e n t r a t i o n on the s o l i d , i n moles/ k g dry s o l i d , (n^) ^ and (n^) are the counts of r a d i o a c t i v e t r a c e r on the s o l i d and i n the s o l u t i o n , r e s p e c t i v e l y , at e q u i l i b r i u m (or the amounts of A, i f analy­ s i s i s done by other methods). ^ A^i "** * ^ I t l a l t o t a l counts i n the aqueous phase, w i s the weight of dry s o l i d i n monoionic form i n kg, V i s the volume of s o l u t i o n , i n l i t e r s . A Nal w e l l - t y p e s c i n t i l l a t i o n was used to count the γ emission of the t r a c e r s i n the s o l u t i o n before and a f t e r e q u i l i b r a t i o n . Most of the c l a y samples were p r e - e q u i l i b r a t e d with the aqueous media to be used i n the adsorption measurements to insure a t t a i n ­ ing the s p e c i f i e d pH, u s u a l l y 5, maintained with acetate b u f f e r . M o n t m o r i l l o n i t e , e s p e c i a l l y the sodium form, swells i n lowi o n i c - s t r e n g t h s o l u t i o n s ; consequently, c e n t r i f u g a t i o n i n moder­ a t e l y high f i e l d s i s needed to separate the c l a y p a r t i c l e s and the s o l u t i o n s . Clay suspensions were c e n t r i f u g e d w i t h a Du Pont S o r v a l l RC-5 r e f r i g e r a t e d super-speed c e n t r i f u g e at 15,000 rpm (28,000 g) f o r 15 minutes, and the supernatant was then withdrawn f o r a n a l y s i s . No c o r r e c t i o n was made f o r p o s s i b l e ion e x c l u s i o n where

(A

a+

( M

I W Λ

clay A

)

a+

y

n

s

t

i e

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

300

RADIOACTIVE

WASTE

IN GEOLOGIC

STORAGE

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch017

i n the water i n the c l a y pack at the bottom of the c e n t r i f u g e tube; i t was assumed t o have the same c o n c e n t r a t i o n as that of the supernatant. For s o l u t i o n - c l a y r a t i o s used here, there would probably be no s i g n i f i c a n t e r r o r i f there were some i o n e x c l u ­ s i o n i n the c l a y pack. Polypropylene tubes were used f o r e q u i l i ­ b r a t i o n and c e n t r i f u g a t i o n . Under the c o n d i t i o n s of these exper­ iments, the a d s o r p t i o n of r a d i o a c t i v e t r a c e r s on the tubes was found not to have a s i g n i f i c a n t e f f e c t on r e s u l t s . Cation Exchange Capacity. Various techniques have been used to measure the c a t i o n exchange capacity of the c l a y samples. Unless otherwise noted, i n computation of e q u i l i b r i u m q u o t i e n t s , we s h a l l use a value of 0.78 equivalents/kg c l a y , determined by a column method (14) on the calcium form of Wyoming montmoril­ l o n i t e at pH 5. a +

Equations. The e q u i l i b r i u m between A and (in a solu­ t i o n with a common monovalent anion, X~) i n aqueous (no sub­ s c r i p t ) and s o l i d ( s u b s c r i p t " c l a y " ) phases, a

b

bA

a +

+

aB t

- b c l a y -«-

At

+ aB

b +

(2)

clay

can be expressed by

(A )!L„ m;a , b

a + va+

!

*

« W

O" ' e l . ,

where the a c t i v i t y c o e f f i c i e n t quotient i s d e f i n e d and can be evaluated by / \κ

/ \

/

xMa+l)/

( O Heu, M

r

x

a(b+l)

clay a(b+l) Γ , Γ = Γ c l a y aq clay /

\b(a+l)

(4)

The symbol, γ , denotes the mean i o n i c a c t i v i t y c o e f f i c i e n t . Customarily, i n the s o l u t i o n phase, the symbol γ i s used i n con­ j u n c t i o n with c o n c e n t r a t i o n s i n m o l a l i t y u n i t s , or moles per kg +

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch017

17.

SHiAO ET AL.

Ion-Exchange

301

Equilibria

of s o l v e n t . We have expressed solution-phase concentrations i n Equation 3 i n m o l a l i t y , m, f o r consistency; D i s the d i s t r i b u t i o n c o e f f i c i e n t corresponding to t h i s convention. For present pur­ poses, there i s l i t t l e d i f f e r e n c e between m o l a l i t y and m o l a r i t y s c a l e s up to one molar NaCl; d i f f e r e n c e s i n the range of 10% are i n c u r r e d near saturated NaCl. The s e p a r a t i o n of T^g i n t o r a t i o s f o r the s o l u t i o n and s o l i d phases i s u s e f u l when s o l u t i o n phase a c t i v i t y c o e f f i c i e n t s are a v a i l a b l e (see, e.g., 15) because i t allows e v a l u a t i o n of v a r i a t i o n s from i d e a l i t y of the c l a y phase over a range of experimental c o n d i t i o n s . When measurements f o r the aqueous mixed e l e c t r o l y t e systems i n question are not a v a i l ­ able, adequate estimates can f r e q u e n t l y be made by Debye-Huckel equations or by v a r i o u s methods from measurements on two-component systems (see, e.g., 16). C e r t a i n s p e c i a l cases are of i n t e r e s t here. When one i o n i s present at concentrations low enough f o r l o a d i n g of the s o l i d phase to be only a small f r a c t i o n of i o n exchange c a p a c i t y , C, expressed i n equivalents/kg of s o l i d , Equation 3 may be w r i t t e n

a — a

£ /r _ " Κ — AB AB - A A R

n

A

b

~ — ,

( c / h )

( (

/ 1 3

b+v

/ b )

a

a

(5)

If i s constant over the range of c o n d i t i o n s , and i f the e x c l u s i o n of coion X" from the c l a y phase i s e s s e n t i a l l y complete, Equation 5 can be d i f f e r e n t i a t e d to give d log

D

d log

(B )

A

-a/b

(6)

b +

+

i . e . , a p l o t of l o g vs l o g (B^ ) w i l l be l i n e a r , with slope - ( a / b ) , or, e.g., -2 i f A is Ca and B i s Na . The r e s t r i c t i o n of coion e x c l u s i o n , although i m p l i c i t l y i n ­ cluded i n " i d e a l " behavior here, i s a somewhat d i f f e r e n t a p p r o x i ­ mation than constancy of or r ^ . Equations which take i n ­ vasion of coions i n t o the c l a y phase i n t o account can r e a d i l y be developed, f o r example by a s s i g n i n g the same r e f e r e n c e s t a t e to both phases and expressing concentration of ions i n the c l a y phase i n terms of moles/kg water, equivalent to Κ = 1 (17). The behavior of l o g ^ v s l o g (B^ ) given by Equation 6 i s approached as i o n i c strength i s decreased, and coion concentration i n the c l a y presumably becomes n e g l i g i b l e i n comparison with c a p a c i t y . We have not measured coion i n v a s i o n i n t h i s work and t h e r e f o r e w i l l d i s c u s s r e s u l t s i n terms of the equations given. I t i s perhaps worthwhile to d i s t i n g u i s h between the j u s t discussed coion e x c l u s i o n i n the l a y e r s of m o n t m o r i l l o n i t e , where presumably most of the ion-exchange c a p a c i t y i s l o c a t e d , from the e a r l i e r reference to p o s s i b l e e f f e c t s of e x c l u s i o n i n the water a +

2 +

c

b +

+

a v

+

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

RADIOACTIVE W A S T E IN GEOLOGIC STORAGE

302

of the c l a y pack on i n t e r p r e t a t i o n of experimental r e s u l t s . The l a t t e r , which we have assumed t o be n e g l i g i b l e , would a r i s e from the i n f l u e n c e on i n t e r s t i t i a l s o l u t i o n between p a r t i c l e s of charges on the surface of the p a r t i c l e s , the charge d e n s i t y of which, averaged over pack-water volume, would be f a r l e s s than the fixecj-charge d e n s i t y i n the l a y e r s , i f the l a y e r s are only 10 - 20 A apart. Results reported here do not c l a r i f y the degree of coion e x c l u s i o n i n e i t h e r environment.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch017

Results We s h a l l f i r s t d i s c u s s e f f e c t s of loading of the c l a y on d i s ­ t r i b u t i o n c o e f f i c i e n t s . With these r e s u l t s , we hope to i d e n t i f y c o n d i t i o n s under which d i s t r i b u t i o n c o e f f i c i e n t s are independent of l o a d i n g ( " l i n e a r isotherm" r e g i o n s ) . Measurements made i n these regions can then be used to evaluate e f f e c t s o f other v a r i ­ a b l e s , p r i m a r i l y of i o n i c strength. I t i s expected, of course, from Equation 3 that Ό w i l l decrease s u b s t a n t i a l l y at high l o a d ­ i n g ; what we are concerned with here are s i g n i f i c a n t e f f e c t s at lower l o a d i n g than p r e d i c t e d f o r constant r c i a v . Because d i s t r i b u t i o n c o e f f i c i e n t s are o f t e n dependent on pH, b u f f e r s were used. The pH o f 5 was s e l e c t e d . f o r most of the ex­ periments because montmorillonite i s s t a b l e at t h i s a c i d i t y , i n ­ t e r f e r e n c e of observations from h y d r o l y s i s and from p r e c i p i t a t i o n of a l k a l i n e earth carbonates i s precluded, and adsorption on p o s s i b l e hydrous oxide i m p u r i t i e s i s minimized. An acetate b u f f e r was u s u a l l y used t o maintain pH because acetate does not have a strong tendency to complex many i o n s . Loading Sodium Form of Montmorillonite (Wyoming). C s ( I ) : F i g u r e 1 summarizes the d i s t r i b u t i o n c o e f f i c i e n t s of C s from 0.5 M NaCl, pH 5, s o l u t i o n s , as a f u n c t i o n of l o a d i n g of C s from t r a c e l e v e l to w e l l over 10% o f c a p a c i t y . There i s an appreciable d i f f e r e n c e between t r a c e and the lowest macro concentration, and a s i g n i f i ­ cant, though not p r e c i p i t o u s , d e c l i n e up to about 10% l o a d i n g . Wahlberg and Fishman (_3) reported l o a d i n g curves f o r C s on two samples of montmorillonite a t s e v e r a l concentrations of NaCl up to 0.2 M. They a l s o found a gentle decrease of DQ with i n c r e a s i n g loading. A l k a l i n e earths: The e f f e c t o f S r ( I I ) l o a d i n g on D$ f o r s e v e r a l d i f f e r e n t concentrations of Na+ i s shown i n Figure 2. Up to 0.01 moles S r ( I I ) / k g c l a y , e f f e c t s are very s m a l l , and values at t r a c e r l e v e l s agree with those at macro concentrations. Wahl­ berg, et a l . (7) report l o a d i n g curves f o r a sample of montmoril­ l o n i t e a t N a concentrations up to 0.2 M. T h e i r values o f D$ . appeared constant with l o a d i n g up t o about the same S r ( I I ) loading as i n Figure 2, and t h e i r values of D i n the l i n e a r isotherm r e ­ gion were about 50% higher than those i n Figure 2 a t overlapping +

+

+

S

R

+

T

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

17.

SHIAO

Ion-Exchange

E T A L .

Equilibria

1000^1 ι ι ι m u — ι ιι1—I

t o o

ζ ο

I

303

| | | | | | | — I

I

l|ll|||

I I l|llfl|

I

I

M

b r

Ul

ο ο

m

10 -5

TRACE

3

i o ~

10" L0A0IN6, mole Cs(I)/kg 4

10" 10"

Figure 1. Ε feet of loading on distribution coefficients of Cs(I) on the sodium form of Wyoming montmorillonite (0.5M NaCl + 0.01M NaOAc, pH 5, equili­ bration for 74 hr)

1 1 1

...i t I Γ

Sr /Na 2 +

:

V

1

1 1

M

EXCHANGE ON MONTMORILLONITE

+

1

I

:

!1 Il 1 1 1 ι 1 1

1 ! J

1

1 1 1

R>

1

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch017

10

1

1 1 1 1 1 1

I I

η°

Ο ,

,

;

"

1

-«*·

-i*

M*

1

1 i ti 1 1 i 1 1 11 1

TRACE

IM

:

0.0001

1

1 1

0.001

1

0.01

1 1 11 11 11 11 0.1

LOADING, moles/kilogram 1 1 1 1 1

Figure 2. Effect of loading on distribution coefficients of Sr(H) on the sodium form of Wyoming montmorillonite. NaCl and pH 5 acetate buffer: (O), 0.1 M N a ; (Φ), 0.2M Na+; (+), 0.6M Na+; (χ), LIU Na\

A

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

+

RADIOACTIVE W A S T E IN GEOLOGIC STORAGE

304

i o n i c s t r e n g t h . The agreement i s considered good, i n view of d i f ­ ferences i n c l a y samples and p u r i f i c a t i o n s ( i n r e f . _7, c l a y s were exposed to hot 1 M HC1-1 M NaCl s o l u t i o n s ) . F i g u r e 3 summarizes e f f e c t s of l o a d i n g on Ό f o r C a ( I I ) , S r ( I I ) , and B a ( I I ) , f o r the sodium form of montmorillonite. The S r ( I I ) r e s u l t s are from a d i f f e r e n t set of measurements than those i n F i g u r e 2, but are i n good agreement with them. E f f e c t s of l o a d ­ i n g are small up to the s e v e r a l percent of ion-exchange c a p a c i t y covered. Values of d i s t r i b u t i o n c o e f f i c i e n t s f o r these three ions f a l l i n a narrow range. E u ( I I I ) : The l o a d i n g e f f e c t on the d i s t r i b u t i o n c o e f f i c i e n t of E u ( I I I ) on the Na form of montmorillonite f o r both a c e t a t e b u f f e r e d and unbuffered s o l u t i o n s i s shown i n F i g u r e 4. The Ds are f a i r l y constant i n the low l o a d i n g range. We s h a l l comment l a t e r on the d i f f e r e n c e s i n presence and absence of b u f f e r .

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch017

%

Calcium Form of M o n t m o r i l l o n i t e (Wyoming). A l k a l i metal i o n s : We present these r e s u l t s i n terms of p l o t s of K/Tclay * a f u n c t i o n of l o a d i n g (Figures 5 and 6 ) . The solution-phase a c t i ­ v i t y c o e f f i c i e n t r a t i o f o r sodium was obtained from a compilation of l i t e r a t u r e data on the N a C l - C a C l 2 - H 2 0 systems (15), and the same values were used f o r cesium. E q u i l i b r i u m quotients f o r the d i f f e r e n t Ca(II) concentrations agree w e l l . In comparison w i t h the r e s u l t s on the sodium form of m o n t m o r i l l o n i t e , the most s t r i k ­ ing d i f f e r e n c e i s the low f r a c t i o n a l l o a d i n g (about 0.1% of i o n exchange c a p a c i t y ) at which v a r i a t i o n s i n D, r e f l e c t e d as changes i n K/T ± y, become apparent, f o r both sodium and cesium. Wahlberg and Fishman (3) a l s o r e p o r t strong decreases i n DQ s t a r t i n g at low l o a d i n g from s o l u t i o n s up to 0.1 M C a C l 2 . The values of t h e i r D's at t r a c e loadings imply much higher values of e q u i l i b r i u m quotients than those at lowest l o a d i n g i n F i g u r e 6, two orders of magnitude f o r one c l a y sample they used and a f a c t o r of about 600 f o r the other. T h e i r K/T values imply that at the same Ca(II) c o n c e n t r a t i o n , t h e i r DQ would be a f a c t o r of 10 to 25 lower than ours. Van B l a d e l , et a l . , (9), report e q u i l i b r i u m quotients f o r Na(I)/Ca(II) exchange from aqueous N a C l - C a C l 2 s o l u t i o n s of t o t a l n o r m a l i t y up to 0.025. I t i s not c l e a r from t h e i r g r a p h i c a l pre­ s e n t a t i o n whether t h e i r measurements i n the low-sodium-fraction r e g i o n i n c l u d e p o i n t s i n the range of r a p i d l y i n c r e a s i n g % (de­ c r e a s i n g K/T i y), although at l e a s t at t h e i r highest Ca(II) con­ c e n t r a t i o n , t h e i r values of the e q u i l i b r i u m quotient appear to l e v e l o f f , at values corresponding to those i n F i g u r e 6 at l o a d ­ ings of N a of about 1 to 10% of ion-exchange c a p a c i t y . In t h i s regard, we wish to comment on some p r e l i m i n a r y r e s u l t s reviewed at a recent meeting (18). At that time, we had not com­ p l e t e d the l o a d i n g s t u d i e s of D and of K/T. The values f o r the calcium form i n Figures 15 and 16 of Ref. are i n the l o a d i n g r e g i o n i n which they are r a p i d l y changing. This accounts f o r d i f ­ ferences with the r e s u l t s i n Figure 6 of t h i s paper, and probably a n c

c

a

s

a

S9

S

a

c

a

+

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

17.

SHiAO ET AL.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch017

100 b cr

~

Ion-Exchange

I

I

l

305

Equilibria

jMllj

1

I I

llllll

1

I I

I

lltt

10

ο υ ζ ο t3 CD

ο

0.1 10"

ι ι Ιιιιιΐ

I ι ι Ιιιιιΐ

10 -2 10" LOADING,mole /kg

1 ιι Im 10"

Figure 3. Effect of loading on distribution coefficients of Ca(ll), Sr(II), and Ba(H) on the sodium form of Wyoming montmorillonite (0.5M NaCl O.J M NaOAc, pH 5, equilibration for more than 90 hr): (·), Ca(II); (Αλ Ba(II); β λ Sr(II).

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch017

306

RADIOACTIVE

ι Γ Α Ι 111 mil TRACE

1 0

~

I ι ilinil 5

I ι ilinil

WASTE

IN

I i ilinil

GEOLOGIC

I I 11iml I I

*0~ 10~ 10~ LOADING, mole Eu (IH)/kg 4

3

STORAGE

2

10"

1

Figure 4. Effect of loading on distribution coefficients of Eu(HI) on the sodium form of Wyoming montmorillonite (pH 5, equilibration for 44 hr): f | ) , O.J M NaCl; (Φ), O.J M NaCl + 0.0JM NaOAc.

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch017

17.

SHiAO ET AL.

Ion-Exchange

307

Equilibria

Ξ 1 ll|lilll 1 m u m

l|llll|

11

1

1 M |HN|

M|l

1

/

7

J

/ ~ l 10"

Mill

ll ^ΗΊΤΙΙΙΙ -5

10

I lllllll 1

iliiiil

1

10" mole

ΙΟ" LOADING, 4

—£

11

1 11 Hull

i l l

10-1

10" Cs (I)/kg

Figure 5. Effect of loading on equilibrium quotients lm Vaq/(Ca *) i yD c ] of Wyoming montmorillonite predominately in the calcium form (pH 5, equilibra­ tion for 77 hr): (φ), 0.5M CaCl + 0.01M Ca(OAc) ; « λ 0.05M CaCl + 0.01M Ca(OAc) . 2

Ca

2

2

2

c a

8

2

2

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

10

u

RADIOACTIVE W A S T E IN

308

GEOLOGIC STORAGE

as w e l l f o r the d i s c r e p a n c i e s noted i n Ref. 18^ from those i n Ref. 9. S r ( I I ) : The e f f e c t of S r ( I I ) l o a d i n g on ϋ$ on the Ca(II) form of montmorillonite i s shown i n Figure 7. Up to 10" moles S r ( I I ) / k g c l a y , values of Ός are e s s e n t i a l l y constant, and do not vary g r e a t l y up to 10~ moles S r ( I I ) / k g c l a y . As we have j u s t d i s ­ cussed, e f f e c t s were apparent at a f a c t o r of ten lower l o a d i n g f o r Cs+ and Na . Wahlberg, et a l . , (7) report very s i m i l a r l o a d i n g e f f e c t s on a calcium montmorillonite. The value of P g they report f o r t h e i r c l a y at t r a c e S r ( I I ) , from 0.01 M C a ( I I ) , i s about 40% higher than the value i n F i g u r e 7. τ

3

τ

2

+

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch017

r

D at Low Ion

Loading as a Function of Concentration of E q u i l i b r a t i n g

Sodium Form of M o n t m o r i l l o n i t e : A l k a l i metal i o n s : Distribution c o e f f i c i e n t s of C s as a f u n c t i o n of sodium concentration are summarized i n Figure 8 f o r c l a y s from four d i f f e r e n t sources. As we discussed i n connection with F i g u r e 1, there i s a m i l d de­ pendence on cesium loading f o r t h i s exchange i n the range of loading of these experiments, 0.02 to 5% of ion-exchange c a p a c i t y . The slopes of l o g DQ VS l o g (Na ) from 0.5 to 4 molar sodium are however c l o s e to the i d e a l value, -1 (Equation 6), f o r i n d i v i d u a l c l a y samples. As l o a d i n g i s higher at low (Na ) and DQ therefore r e l a t i v e l y lower, the f a c t that the slopes appear s l i g h t l y l e s s than u n i t y i s i n the r i g h t d i r e c t i o n f o r a l o a d i n g e f f e c t . These c l a y s had been subjected to a l l steps i n the Jackson p u r i f i c a t i o n procedure except removal of f r e e i r o n oxide. With one sample, measurements were c a r r i e d out at pH 5 (0.1 M sodium acetate p l u s a c e t i c a c i d b u f f e r ) as w e l l as 8 (0.1 M NaHC03 b u f f e r ) , and there appeared to be l i t t l e e f f e c t on D. Values of D at a f i x e d sodium concentration v a r i e d by about a f a c t o r of three between the montm o r i l l o n i t e s of highest DQ ( c l a y #31) and of the lowest (Wyoming and #27). E x t r a p o l a t i o n of the r e s u l t s i n Figure 8 to 0.2 molar Na , the highest concentration of measurements i n Ref. 3^, gives a range of DQ of about 60 to 180. Wahlberg and Fishman r e s u l t s f o r t r a c e Cs at t h i s sodium concentration were about 250 f o r one c l a y and 550 f o r the other. Some of the d i f f e r e n c e may a r i s e from the higher loading i n our experiments, but i n any case t h i s much v a r i ­ a t i o n between c l a y samples i s probably not s u r p r i s i n g . T h e i r slopes of l o g D vs l o g sodium concentration at t r a c e C s were some­ what l e s s (absolute value) than minus one. Tamura and Jacobs (19) report adsorption on a montmorillonite sample from 6 M NaN03, from which we compute DQ - 5, i n the range of extrapolated values from Figure 8. Lewis and Thomas (4) report K/T of about 40 f o r low cesium loading and 0.04 M s a l t concentra­ t i o n , and Gast (10) about 35 f o r 0.001 M. These values are i n the range implied by r e s u l t s i n Figure 8 (K/T 15 to 50). +

+

S

+

S

S

+

S

+

S

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

17.

SHiAO ET AL.

10

2Γ

309

2

ο

·

HT

•Λ

k/Γ IC/rclay • • 0.01 M Ca(0Ac) tz.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch017

Equilibria

Ξ ι ιιμιιιι ι ιιμιιιι | ιΐ|ΐιιΐ| | ιιμιιιι | ι

1

oc ο t-, 0.1

Ion-Exchange

0.05 M CaCIg + O.OI Μ Co (0Ac)

2

b=

0.01 10"

10i - 6

10" 10" LOADING, mole

10"

10"

Να (I)/kg

10"

Figure 6. Effect of loading on equilibrium quotients [mcaV q/(Ca *) i yO ] of Wyoming montmorillonite predominately in the calcium form (pH 5, equilibra­ tion for 14 hr) 2

a

LOADING, mole

2

c

a

Na

Sr(II)/kg

Figure 7. Effect of loading on distribution coefficients of Sr(II) on the calcium form of Wyoming montmorillonite (0.01M Ca(OAc) , pH 5, equilibration for 65 hr) 2

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

RADIOACTIVE W A S T E IN GEOLOGIC

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ch017

310

_

0.3

Ο Να

BICARBONATE

8

Δ Co

BICARBONATE

8

Ο NO. 27

BICARBONATE

8

0 NO. 34

BICARBONATE

8

0.5

1.0

2.0

STORAGE

4.0

Ν α (I) (moles/1)

Distribution of Cs (I) Between Aqueous NaCi Solutions and Montmorillonite from Several S o u r c e s Γ~10~ M C s ( I ) ] 3

Figure 8. Adsorption of Cs(I) on the sodium form of montmorillonites from sev­ eral sources (Loading: 2 X 10~ — 4 X 10 mol Cs(I)/kg, equilibration for 24 hr.). 4

2

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

17.

SHiAO ET AL.

Ion-Exchange

311

Equilibria

D i s t r i b u t i o n c o e f f i c i e n t s f o r potassium on one c l a y are sum­ marized i n Figure 9. The i d e a l slope of -1 f o r l o g D^vs l o g sodium concentration was c l o s e l y approximated. Values of Ό were about 1/3 those f o r cesium on the same c l a y . A value o f K/T [(K+) lay(Na+)/(K+) (Na+) c l a y ! °f about 3.75 can be estimated from Figure 9. T h i s agrees s a t i s f a c t o r i l y with values o f about 2.5 r e ­ ported both by Gast (10) f o r 0.001 M Na+ and by Shainberg and Kemper (20) f o r 0.05 M Na+. A l k a l i n e earth i o n s : The d i s t r i b u t i o n c o e f f i c i e n t s of C a ( I I ) , S r ( I I ) , and Ba(II) on the Na form of Wyoming montmorillonite are shown i n Figures 10a, b, and c. Values o f #ca> ^Sr> * % a s i m i l a r f o r equal sodium concentration. The slope of l o g D vs log sodium concentration i s c l o s e t o -2, the slope f o r i d e a l divalent-monovalent i o n exchange. Measurements were c a r r i e d out i n the presence of sodium acetate b u f f e r o f 0.1 M and 0.01 Af, and the r e s u l t s were not s i g n i f i c a n t l y d i f f e r e n t at the same sodium concentration. T h i s i n d i c a t e s that there i s no i n t e r f e r e n c e from formation of complexes between the a l k a l i n e earths and acetate ions. One sample of Wyoming montmorillonite was p u r i f i e d only by passage through a Dowex 50 ion-exchange column i n the sodium form. The # c i s sample agreed w i t h i n s c a t t e r with the same c l a y which had been subjected to the complete Jackson procedure. From the r e s u l t s i n Figures 10a, b, c, the computed values o f K/T [ ^ ) c l a y ( ) / ( X N a * " ^ ] were approximately 3. A value of 1.4 i s reported f o r Ca(II) i n 0.025 M NaCl (9) and of about 1 f o r Ba(II) i n 0.04 M NaCl (4). Tamura (5) reported l i n e a r de­ pendence o f l o g D vs l o g sodium concentration from 0.01-0.6 molar sodium with a slope o f -2; h i s values of Z)g were about h a l f of those of Figure 10b a t the same sodium concentrations. From r e ­ s u l t s reported by S p i t s y n and Gromov (1), we c a l c u l a t e a D$ of about 70 a t 0.1 M NaCl, t h e i r highest concentration, i n comparison with about 100 i n Figure 10b. E u ( I I I ) : Figure 11 summarizes the adsorption of Eu(III) on the Na form of Wyoming montmorillonite a t pH 5, c o n t r o l l e d with 0.01 M acetate b u f f e r , and adjusted to the same a c i d i t y without b u f f e r by HC1. The values o f Z? i n the presence of acetate are about a t h i r d of those without, a d i f f e r e n c e s i m i l a r to that seen i n the l o a d i n g curve, Figure 4. Formation of Eu(III) acetate com­ plexes, presumably the source of the d i f f e r e n c e s , has been r e ­ ported elsewhere (21). For the unbuffered system, the p l o t of l o g D

e a c n

r a

e

a

s

193/ 252

a

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

83/

22 167 22 311 224/

RADIOACTIVE W A S T E IN GEOLOGIC STORAGE

338 P r e p a r e d waters w i t h waters f r o m n a t u r a l systems, c o m p a r i s o n of .... 235i Pressure sintering 138 P r e s s u r i z e d w a t e r samples f r o m R N M - 2 S , analyses of 164* Principle, multi-barrier 47 Project Salt V a u l t 2 Proliferation-resistant f u e l cycles 2 P r o m e t h i u m , d i s t r i b u t i o n coefficients for 285/, 286/

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ix001

Q Quartz monzonite 216 samples 218,232/, 236 water 228 x-ray d i f f r a c t i o n data for 219i x-ray d i f f r a c t i o n studies of 218

R R A 2 2 6 C o n c e n t r a t i o n profile at 0.83 m i — L L W R a d i a t i o n , fragmentation of clays f r o m R a d i a t i o n f r o m sorbed t r a n s p l u t o n i u m elements o n clays, consequences of Radioactive h i g h - l e v e l waste glass studies, l e a c h i n g of isotopes w i t h groundwater, l e a c h i n g of isotopes i n stored h i g h - l e v e l wastes waste(s) f r o m c o m m e r c i a l nuclear f u e l cycle c o m p o s i t i o n of s i m u l a t e d high-level D e p a r t m e n t of E n e r g y p r o g r a m for l o n g - t e r m isolation of forms, d e t e r m i n i n g l e a c h rates of s i m u l a t e d glass c o m p o s i t i o n i n granitic bedrock, d i s p o s a l of .. h y d r o l o g i e considerations related to management of h y d r o l o g i e uncertainty i n geologic isolation of isolation i n geologic m e d i u m locations of b u r i a l grounds of l o w - l e v e l objective of geologic isolation of permanent isolation of i n rock salt, emplacement of on southeastern N e w M e x i c o , W I P P — b e d d e d salt repository for defense z i n c borosilicate glass, p r e p a r a t i o n a n d l e a c h testing of

27/ 293 291 75 115 116t

1 118f 1 115 78f 47 37 40 40 39/ 37 5 13 13 75

R a d i o a c t i v i t y movement as m o d e l e d b y the I N R E M II code 243/ R a d i o a c t i v i t y f r o m s o l i d waste f o r m to environment, release rate of .... 115 R a d i o c h e m i c a l analyses of samples removed from R N M - 1 155 R a d i o e c o l o g y studies, fresh-water actinide 253 Radioisotopes, l e a c h rate of 33 Radioisotopes w i t h the minerals, absorption coefficients of various 9 Radionuclide(s) 215 a c t i v i t y i n effluent f r o m titanate solidification, c o m p a r i s o n of .... 14It to the biosphere, m e c h a n i s m for release of 8 c h e m i c a l interactions o n m i g r a t i o n of 68 "getter" 34 i n the g r o u n d , c h e m i c a l retention of 52 a n d g r o u n d material, p h y s i c o c h e m i c a l conditions b e t w e e n .. 55 b y groundwater, leach rates of 51 i n g r o u n d w a t e r f r o m sites of underg r o u n d nuclear explosions, u n d e r g r o u n d m i g r a t i o n of 93 h y d r o l o g i e e v a l u a t i o n associated w i t h the transport of 37 leached f r o m c h i m n e y r u b b l e 94 leached f r o m melt glass 94 l e a c h i n g rates for Sb Ill m i g r a t i o n , a field study of 149 m i g r a t i o n p r o g r a m at the N e v a d a Test Site 93 nature of solid-phase concentrations of 269 observed i n leachate samples 101* observed i n melt glass samples 101* r e m a i n i n g i n h i g h - l e v e l waste after b a t c h e q u i l i b r a t i o n , activities of 135t sorption b e h a v i o r of l o n g - l i v e d 55 sorption i n geologic environments, p r e d i c t i o n of 215 sorption studies o n abyssal r e d clays 267 species i n g r o u n d w a t e r 66 species i n n o n o x i d i z i n g granitic groundwater 69f tracer o x i d a t i o n state selection of .... 229t tracer p u r i f i c a t i o n of 229t transport, barriers to 9 used i n laboratory measurements of d i s t r i b u t i o n coefficients 59* R a d i u m vs. transuranics, u r a n i u m and 256,257 R a r e earths ( R E ) 123 on clay minerals, sorption b e h a v i o r of 201

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

INDEX

339

R a r e earth ( s ) ( continued ) d i s t r i b u t i o n coefficients for 202 l e a c h rates 123 trivalent Eu 121 Rate of g r o u n d w a t e r i n f l o w 8 Rats, cotton 250 R E ( see R a r e earths ) 123 R e a c t i o n rates of rock samples 222 Reactor, A r g o n n e C P - 5 Research 123 R e d clay 268 r a d i o n u c l i d e sorption studies o n abyssal 267 semi-quantitative analysis of 269* sorption capacity 274 R e d o x p o t e n t i a l of groundwaters 53 R e d o x reactions a n d valence states .... 65 Re-entry hole, C a m b r i c ( R N M - 1 ) 151 Release cumulative fraction 86 diffusion-controlled 86 experiment outline, waste f o r m 89/ using F i c k s L a w , fractional 86 fractions after 639 days, element .... 84* mechanisms, slopes of i n i t i a l a n d long-term 87* rate of p l u t o n i u m 86 rate of r a d i o a c t i v i t y f r o m s o l i d waste f o r m to e n v i r o n m e n t 115 Repository (ies) b u o y a n c y effects of heated 32 deep geologic 167 for defense radioactive waste i n southeastern N e w M e x i c o , W I P P — b e d d e d salt 13 gas generation i n 34 geochemistry of 52 geologic design 5 for h i g h - l e v e l waste 43 integrity, l o n g - t e r m 22 location 45 n u c l e a r waste 297 risk assessment i n s i t i n g geologic ... 9 i n salt, N R C l i c e n s i n g of H L W 31 system, canister-salt— 31 u n d e r t h e r m a l l o a d , stability of salt 31 Resins, i o n exchange 119,138 Retention in backfill material 70 factor ( E ) 68 i n granite 71* K B S report 70 for n u c l i d e s 160 i n hostrock 70 R e t r i e v a b l e surface storage 3 R e t r i e v a b l e Surface Storage F a c i l i t y (RSSF) 3 R e v i e w s c o n c e r n i n g the D O E waste isolation p r o g r a m 5

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ix001

1 5 2

d

R i s k assessment i n d e s i g n i n g a n d siting geologic repositories 9 RNM-1 152/ a c t i v i t y levels of ^ S r i n w a t e r f r o m re-entry of 164* a c t i v i t y levels of C s i n w a t e r f r o m re-entry of 164* analyses of water samples p u m p e d from 158* c a m b r i c re-entry hole 151 construction details of 156/ r a d i o c h e m i c a l analyses of samples removed from 155 s a m p l i n g points at 153/ source, ratios for 154* γ-spectral analyses of samples removed from 155 w a t e r samples, a c t i v i t y levels i n .... 162* RNM-2S 152/ analyses of pressurized w a t e r samples f r o m 164* c a m b r i c satellite w e l l 151,160 future p u m p i n g at 165 Rock(s) dissolution experiment for sorption study of 220,222 d i s t r i b u t i o n coefficient of 55 - e q u i p i b r a t e d water 171,173 groundwaters f r o m igneous 53 ion-exchange properties of the host 9 mechanics, properties of the h o s t . . . . 8 nuclide migration i n fractured 167 n u c l i d e m i g r a t i o n i n porous 167 salt, emplacement of radioactive waste i n 13 sample(s) b r e a k d o w n , release of cations from 222 b u l k c h e m i c a l analysis of 218 characterization 216 p h y s i c a l properties of 218, 220 d e p t h - o f - l e a c h i n g calculations for 229* pétrographie studies of 216 p h y s i c a l p r o p e r t y d a t a of 221* reaction rates of 222 selection of 215 sorption differences a m o n g 237 specific surface area of 220 - t r a c e r contact experiments 228 —tracer desorption experiments 239 types, dissolution f r o m aqueous s i l i c a release d u r i n g 227/ c a l c i u m release d u r i n g 225/ m a g n e s i u m release d u r i n g 226/ potassium release d u r i n g 224/ s o d i u m release d u r i n g 223/ wafers, a u t o r a d i o g r a p h y of 239 1 3 7

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

340

RADIOACTIVE W A S T E IN GEOLOGIC STORAGE

Rock(s) (continued) —waste interactions and brine migration 32 water velocity in fractured 68 RSSF (Retrievable Surface Storage Facility) 3 Rubidium distribution coefficients for 276,277/, 278 salts in clay 270 in seawater, average concentration of 269i Ru, leaching rate of 109/ Rutile 139 Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ix001

106

S Safety Assessment Program at PNL, Task #2 of the Waste 87 Safety Assessment Program, Waste Isolation (WISAP) 76 Salt bedded 2 repository for defense radioactive waste in southeastern New Mexico, WIPP— 13 emplacement of radioactive waste in rock 13 high-level waste canister motions in 31 mines 201 NRC licensing of H L W repositories in 31 repositories under thermal load, stability of 31 -repository system, canister31 Vault, Project 2 Samarium exchange on kaolin, montmorillonite, and attapulgite, plot of 204/ Sandia Laboratories 13 Sb nuclides Ill Sb radionuclides, leaching rates for .... I l l Sb, leaching rates of 110/ Sb, leaching rate of 110/ Scenario I 23,24/ Scenario II 25 Sr 90, Cs concentration 30/ TRU concentrations 29/ Scenarios, geologic storage 129 Schist-equilibrated water 173 Seawater barium concentration in 269f, 282 rubidium concentration in 269t strontium concentration in 269i, 282 Secondary containment 201 Sediment, bed 250 124

125

SEM photographs of Glass # 1, Glass #2, and Glass #3 99/ studies of quartz monzonite samples 218 studies of shale samples 218 Semi-quantitative analysis of red clay 269i Shale (metashale) 216 Shale samples results of the contact experiments for 236 SEM studies of 218 tracers and sorption experiments with 231/ Shale water 228 Shrews 250 Silica release during dissolution from rock types, aqueous 227/ Silver, distribution coefficients for 283/ Simulated high-level radioactive waste, composition 118i Simulated radioactive waste forms, determining leach rates of 115 Single-pass leaching for melt glass experiment 95, 98 Single-pass leaching of nuclear melt glass by groundwater 93 Sintered granules, leaching of 123 Sintering, cold pressing/ 138 Sintering, pressure 138 Site effect of waste emplacement on hydrologie properties of 42 selection, geologic features in 22 -specific application of uranium .... 245 WIPP 18f,21i Size analysis, melt glass 103£ Small mammals from soil, accumulation of actinides by 26l£ Sodium and calcium on clay minerals, exchange of 298 Sodium form of montmorillonite 302, 308 adsorption of Ba(II) on 315/ Ca(II) on 313/ Cs(I) on 310/ Eu(III) on 316/ K(I) on 312/ Sr(II) on 314/ niobate 132 release during dissolution from rock types 223/ titanate 144 batch equilibrations of 134 column, elemental distribution offissionwaste nuclides on .. 136/

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341

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INDEX

S o d i u m titanate (continued) material, characterization of 131 preparation 131 Soil a c c u m u l a t i o n of actinides b y s m a l l mammals a n d m a n from 261* actinides i n 247 - b o n e ratios of actinides 260 c o m p a r a t i v e a c c u m u l a t i o n of a c t i ­ nides b y m a m m a l s f r o m contaminated 251/ - s e d i m e n t t o o r g a n i s m transfer 245 T h - U ratio 242 Solid-phase concentrations of desorbed species 276i Solid-phase concentrations of radionuclides, nature of 269 S o l i d waste f o r m t o environment, release rate of r a d i o a c t i v i t y f r o m 115 S o l i d waste forms, neutron i r r a d i a t i o n of 121 Solidification, c o m p a r i s o n of r a d i o ­ n u c l i d e a c t i v i t y i n effluent f r o m titanate 141* Solidification, h i g h - l e v e l waste 132,144 Solution-phase concentrations 301 a n d d i s t r i b u t i o n coefficients, correlation b e t w e e n 279 Solutions d e t e r m i n a t i o n of concentrations of tracers i n 235 gamma-ray c o u n t i n g of 215 ion-exchange e q u i l i b r i a b e t w e e n montmorillonite a n d 297 S o r b e d t r a n s p l u t o n i u m elements o n clays, consequences of r a d i a t i o n from 291 Sorption of a m e r i c i u m 66,167 of a m e r i c i u m I I I 172/ of a n i o n i c t e c h n e t i u m 59 b e h a v i o r of long-lived radionuclides 55 rare earths o n c l a y minerals 201 trivalent actinides o n c l a y minerals 201 capacity, r e d c l a y 274 of c e s i u m ( C s ) 59,66 coefficient, surface area ( K ) 171 - d e s o r p t i o n processes 215 differences a m o n g rock samples 237 e q u i l i b r i u m d i s t r i b u t i o n coefficients (K ) 267 experiments w i t h basalt samples 231/ b l a n k containers 230/ q u a r t z m o n z o n i t e samples 232/ shale samples 231/ s

I ) 5

S o r p t i o n (continued) i n geologic environments, p r e d i c ­ t i o n of r a d i o n u c l i d e 215 o n geologic materials, a c t i n i d e 215 isotope 34 kinetics 65,167 measurements 55 mechanisms 65 of p l u t o n i u m 34,167 of p l u t o n i u m I V 172/ of s t r o n t i u m 66 studies o n abyssal r e d clays, radionuclide 267 study of rocks, dissolution experi­ ment f o r 220,222 Sorptive b e h a v i o r of n a t u r a l clays t o w a r d m e t a l ions 291 Source C l a y M i n e r a l s R e p o s i t o r y 202 Source m a t e r i a l 38 Soxhlet apparatus, l e a c h i n g w i t h 119 S p e c i a l nuclear m a t e r i a l 38 Species ( F ) , rate of a d s o r p t i o n of 168 Specific surface area of rock samples .. 220 γ-Spectral analyses of samples removed from R N M - 1 155 Spent f u e l , d i s p o s a l of 2 Spent u r a n i u m f u e l ( S U F ) 47 i n the g r o u n d , K B S storage of 49/, 5 0 i Static absorption experiments w i t h p l u ­ tonium and americium 196f ( batch ) leaching procedure 94 fissure adsorption experiments, adsorption curves o b t a i n e d f o r 175/ fissure adsorption experiments, apparatus u s e d i n 172/ Storage of H L W i n the g r o u n d , K B S 48/, 5 0 i retrievable surface 3 scenarios, geologic 129 of S U F i n the g r o u n d , K B S 49/, 50* S t r u c t u r a l b r e a k d o w n of geologic materials 222 Strontium f r o m c o l u m n of glauconite, e l u t i o n of 184/, 186/ c o l u m n infiltration experiments of .. 183 compounds 270 concentration, clay-phase 282 concentration i n seawater 282 d i s t r i b u t i o n coefficients f o r 278, 281/ " f i e l d v e r i f i c a t i o n " of 282 m i g r a t i o n experiments i n glauconite 183 m i g r a t i o n rate of peak concentra­ t i o n of 185 i n seawater, concentration of 269i sorption of 66 ( Sr) 121 5 8

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RADIOACTIVE W A S T E IN GEOLOGIC STORAGE

S r i n w a t e r f r o m re-entry of R N M - 1 , a c t i v i t y levels of 164f Sr(II) 304,308 l o a d i n g , effect of 302 on distribution coefficients 303/, 305/, 309/ o n the c a l c i u m f o r m of mont­ m o r i l l o n i t e , a d s o r p t i o n of 319/ o n the s o d i u m f o r m of mont­ m o r i l l o n i t e , adsorption of 314/ STx-1 C a - m o n t m o r i l l o n i t e 298 S U F ( see Spent u r a n i u m f u e l ) Supercalcine 130 Surface area measurement of 119 m e l t glass 103t sorption coefficient ( K ) 171 phenomena and food chain b e h a v i o r of actinides 252 storage, retrievable 3 -to-mass ratios for elements o n granite, d i s t r i b u t i o n coefficients as functions of 67/ S w e d e n , nuclear p o w e r p r o g r a m i n .... 47 SWy-a Na-montmorillonite 298

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ix001

9 0

s

Τ T (absorptive dispersion) 191 T (hydrodynamic dispersion) 191 T a s k # 2 l e a c h i n g p r o g r a m , W I S A P .. 89/ T e c h n e t i u m , mass related d i s t r i b u t i o n coefficients for 66f T e c h n e t i u m , sorption of a n i o n i c 59 T e c h n i c a l issues a n d the D O E technical program 4 T e m p e r a t u r e effects o n d i s t r i b u t i o n coefficients 65 T e m p e r a t u r e a n d waste f o r m 138 T e r r e s t r i a l transport of actinides to mammals, comparative 247 Test f a c i l i t y , H a n f o r d reservation near-surface 7 Tetravalent cerium ( C e ) 121 Tetravalent elements 68 T h e r m a l gradient, b r i n e m i g r a t i o n i n 32 T h e r m a l l o a d , stability of salt repositories u n d e r 31 Thorium i n bone injection 242 i n fresh-water environments 253 i n h u m a n organs, distributions of .... 259f ingestion 241 inhalation 241, 242 intakes 241, 242 isotopes 23 - u r a n i u m ratio, soil 242 a

h

1 4 1

T h - 2 3 2 contents of h u m a n bone ash .... 244f T i m e — u p p e r - m i d d l e glass section, l e a c h rate as a f u n c t i o n of 80/, 81/ Titanate a n d the h y d r o g e n i o n 132 reactions 131 solid-solution 139 solidification, c o m p a r i s o n of r a d i o ­ n u c l i d e a c t i v i t y i n effluent f r o m 141i waste, consolidated 139 waste f o r m , transmission electron p h o t o m i c r o g r a p h of a c e r a m i c 140/ waste l e a c h i n g 142 T i t a n i u m d i o x i d e ceramic f o r m 130 T i t a n i u m d i o x i d e matrix, a t o m i c a l l y dispersed waste oxides i n a ceramic 130 T o p glass section, c u m u l a t i v e f r a c t i o n l e a c h e d as a f u n c t i o n of t i m e 85/ Tracer(s) actinide characterization of 220 isotopic abundances of 2111 purification of 220 contact experiments, r o c k 228 desorption experiments, r o c k 239 o x i d a t i o n state selection of radionuclides 229i p u r i f i c a t i o n of. radionuclides 229£ selection of 215 i n solutions, d e t e r m i n a t i o n of concentrations of 235 w i t h basalt samples 231/ w i t h b l a n k containers 230/ w i t h quartz m o n z o n i t e samples 232/ w i t h shale samples 231/ Transmission electron p h o t o m i c r o ­ g r a p h of a c e r a m i c titanate waste f o r m 140/ T r a n s p l u t o n i u m elements o n clays, consequences of r a d i a t i o n f r o m sorbed 291 T r a n s p o r t of r a d i o n u c l i d e s , h y d r o l o g i c evaluation associated w i t h .. 37 T r a n s p o r t of transuranic isotopes 23 Transuranic(s) elements 252 isotope concentrations 24/ isotopes, transport of 23 vs. u r a n i u m a n d r a d i u m 256, 257 T r a n s u r a n i u m c o n t a m i n a t e d wastes (TRU) 4,38 concentrations, Scenario 2 29/ waste contact-handled 17/ disposal 15 d e c o m p o s i t i o n of organics i n 34 defense 15

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

343

INDEX

T r e n c h covers Tritium concentration as a f u n c t i o n of v o l u m e of water p u m p e d T r i valent actinides o n c l a y minerals, sorption b e h a v i o r of over P u ( I V ) across b i o l o g i c a l membranes, enrichment of T r i v a l e n t elements T r i v a l e n t rare earths ( E u ) T R U (see T r a n s u r a n i u m c o n t a m i n a t e d wastes ) 1 5 2

44 149 163/ 121 201 249/ 68 121

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ix001

U U n d e r g r o u n d m i g r a t i o n of r a d i o nuclides i n g r o u n d w a t e r 93 U n d e r g r o u n d nuclear explosions 93 U n i t e d States G e o l o g i c a l Survey (USGS) 13 U n s a t u r a t e d zone, c h e m i c a l b e h a v i o r of waste i n 44 U p p e r - m i d d l e glass section, l e a c h rate as a f u n c t i o n of t i m e 80/, 81/ Uranium 76,149 i n bone injection 242 f u e l , spent ( S U F ) 47 ingestion 241 inhalation 241, 242 intake a n d diet 242 intakes b y people, n a t u r a l 241 isotopes 23 mass related d i s t r i b u t i o n coefficients f o r 66* a n d r a d i u m vs. transuranics 256, 257 site-specific a p p l i c a t i o n of 245 U-236 concentration profile at 0.83 m i — L L W 28/ U-238 contents of h u m a n bone a s h .... 244* U S G S ( U n i t e d States G e o l o g i c a l Survey ) 13 U . S . Seabed D i s p o s a l P r o g r a m 267

V a l e n c e states, redox reactions a n d .... V i t r i f i e d wastes

65 129

W Waste(s) a n d biosphere, barriers b e t w e e n .... categories of c o n s o l i d a t e d titanate depository, g r o u n d w a t e r - r o c k system a r o u n d a defense (1985) disposal p r o b l e m

6/ 38 139 57/ 18* 40

W a s t e ( s ) (continued) emplacement o n t h e h y d r o l o g i e properties of the site, effect of .. 42 enter the biosphere, p a t h w a y s b y which 37 form(s) 7,51 ceramic 138 d e t e r m i n i n g l e a c h rates of s i m u l a t e d radioactive 115 to environment, release rate of radioactivity f r o m solid 115 P W - 4 i n d i s t i l l e d water, l e a c h rates of 124* release experiment o u t l i n e 89/ temperature a n d 138 transmission electron p h o t o m i c r o g r a p h of a c e r a m i c titanate 140/ glass 129 l e a c h a b i l i t y of 142 neutron i r r a d i a t i o n of s o l i d 121 u s i n g N A A technique, l e a c h rate measurements o n 122 —geologic e n v i r o n m e n t i n t e r a c t i o n studies, l e a c h i n g of 75 glass 142 canister, sectioning of h i g h - l e v e l 77/ isotopic l e a c h rates f r o m 79 making 76 nuclear 76 studies, l e a c h i n g of radioactive high-level 75 high-level ( H L W ) 13,40,47 after b a t c h e q u i l i b r a t i o n , activities of r a d i o n u c l i d e s remaining i n 135* canister motions i n salt 31 cesium i n 144 compositions of A G N S B a r n w e l l 133* glass canister, sectioning of 77/ immobilization program 75 radioactive isotopes i n stored 116* repository f o r 43 solidification 132,144 interactions 7 isolation 291 E R D A Office of 3 Pilot Plant ( W I P P ) 4,13,143 artist's concept of 14/ concept, u n d e r g r o u n d l a y o u t proposed for 16/ c o n c e p t u a l design 15 Experimental Program 25 site evaluation for 18* geologic cross section 20/ l o c a t i o n m a p for p r o p o s e d .. 19/ selection factors c o n s i d e r e d .. 21*

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Publication Date: April 6, 1979 | doi: 10.1021/bk-1979-0100.ix001

344

RADIOACTIVE W A S T E IN GEOLOGIC STORAGE

W a s t e ( s ) (continued) isolation (continued) p r o g r a m , elements of D O E ' s p r o g r a m , reviews c o n c e r n i n g the D O E Safety Assessment P r o g r a m (WISAP) at P N L , T a s k # 2 of T a s k # 2 l e a c h i n g p r o g r a m .... studies leaching titanate low-level b u r i e d w i t h i n the conterminous U n i t e d States, yearly total v o l u m e of c o m m e r c i a l l o c a t i o n of b u r i a l grounds of Management Program, organization of D O E ' s m i g r a t i o n , n a t u r a l barrier t o nuclear c e r a m i c forms f o r w i t h geologic material, inter­ actions of glasses repositories nuclides o n a s o d i u m titanate c o l u m n , elemental d i s t r i b u t i o n of fission oxides i n a c e r a m i c t i t a n i u m d i o x ­ i d e matrix a t o m i c a l l y dispersed oxides, m e t a l o r graphite encapsu­ lated radioactive f r o m c o m m e r c i a l nuclear f u e l cycle c o m p o s i t i o n of s i m u l a t e d high-level D e p a r t m e n t of E n e r g y p r o g r a m f o r l o n g - t e r m isolation of .... glass c o m p o s i t i o n i n granitic bedrock, d i s p o s a l of .. h y d r o l o g i e uncertainty i n geologic isolation of objective of geologic isolation of permanent isolation of i n rock salt, emplacement of i n southeastern N e w M e x i c o , W I P P — b e d d e d salt reposi­ tory f o r defense - r o c k interactions a n d b r i n e migration solutions, cation exchange a n d aqueous solutions, methods for c o n t a c t i n g ion-exchange materials w i t h .... storage i n granite bedrock

6t 5 76 87 88/ 42 33 142 38

41/ 39/ 3 8 129 167 76 297 137

136/ 130 130

1 118* 1 78* 47 40 37 5 13

W a s t e ( s ) (continued) transuranium contaminated ( T R U ) 4 contact-handled 15,17/ d e c o m p o s i t i o n of organics i n 34 defense 15 i n the unsaturated zone, c h e m i c a l b e h a v i o r of 44 vitrified 129 Water composition o n distribution coefficients, effect of 62 inflow, rate of g r o u n d 8 f r o m n a t u r a l systems, c o m p a r i s o n of p r e p a r e d waters w i t h 235* p u m p e d , t r i t i u m concentration as a f u n c t i o n of v o l u m e of 163/ quartz monzonite 228 f r o m re-entry of R N M - 1 , a c t i v i t y levels of S r a n d C s i n 164* rock-equilibrated 171,173 samples activity levels i n 159* RNM-1 162* f r o m C a m b r i c , Zone I I , analyses of 157/ E *s f r o m 161* p u m p e d f r o m R N M - 1 , analyses of 158* f r o m R N M - 2 S , analyses of pressurized 164* shale 228 schist-equilibrated 173 transport, m i g r a t i o n characteristics of a m e r i c i u m b y 173 velocity i n f r a c t u r e d rock 68 W e l l - 5 B water, N T S , c o m p o s i t i o n of .. 103* W e l l R N M - 1 , C a m b r i c re-entry 151 W I P P (see W a s t e Isolation P i l o t Plant) W I S A P (see W a s t e Isolation Safety Assessment P r o g r a m ) 9 0

d

X X - r a y diffraction analysis of gray h o r n b l e n d e schist.. 170 analysis of N T S m e l t glass samples 101* d a t a for q u a r t z m o n z o n i t e 219* studies of q u a r t z monzonite 218 X - r a y fluorescence ( X R F ) 218

13 32 131 132 47

1 3 7

Ζ Zeolite Z i n c borosilicate f r i t Z i n c borosilicate glass l e a c h testing of radioactive Z i r c a l o y C o n v e r s i o n Process Z r , l e a c h i n g rate of 9 5

In Radioactive Waste in Geologic Storage; Fried, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

137 142 142 75 144 109/