Geochemical Behavior of Disposed Radioactive Waste

395 Pages·1984·6.19 MB·English

by  G. Scott Barney

ACS SYMPOSIUM SERIES 246
Geochemical Behavior of
Disposed Radioactive Waste
G. Scott Barney, EDITOR
Rockwell Hanford Operations
1
0
0
w
6.f James D. Navratil, EDITOR
4
2
0
4- Rockwell International Rocky Flats Plant
8
9
1
k-
b Wallace W. Schulz, EDITOR
1/
2
0
1 Rockwell Hanford Operations
0.
1
oi:
d
4 |
8
9
1
8, Based on a symposium
h
c
ar jointly sponsored by the Divisions of
M
e: Nuclear Chemistry and Technology,
at
D Industrial and Engineering Chemistry,
n
o
ati and Geochemistry at the 185th Meeting
c
bli of the American Chemical Society,
u
P
Seattle, Washington,
March 20-25, 1983
American Chemical Society, Washington, D.C. 1984
Library of Congress Cataloging in Publication Data
Geochemical behavior of disposed radioactive waste.
(ACS symposium series, ISSN 0097-6156; 246)
"Based on a symposium jointly sponsored by the
Divisions of Nuclear Chemistry and Technology,
Industrial and Engineering Chemistry, and
Geochemistry at the 185th Meeting of the American
Chemical Society, Seattle, Washington, March 20-25,
01 1983."
0
w Bibliography: p.
6.f Includes index.
4
2
0 1. Radioactive waste disposal in the ground—
84- Congresses. 2. Radioisotopes—Congresses.
19 3. Geochemistry, Analytic—Congresses.
k-
b I. Barney, G. Scott. II. Navratil, James D.,
21/ 1941- . III. Schulz, Wallace W. IV. American
10 Chemical Society. Division of Nuclear Chemistry and
0. Technology. V. American Chemical Society. Division of
1
oi: CInhdeumstirciaall Saoncdie Etyn. gDinieveirsiinogn Cofh Gemeoiscthreym. VisIt.r Ay.m erican
d
4 | VII. Series.
8
9 TD898.G35 1984 621.4838 83-3106
1
8, ISBN 0-8412-0827-1
h
c
ar
M
e:
at
D Copyright © 1984
n
o American Chemical Society
ati
c All Rights Reserved. The appearance of the code at the bottom of the first page of each
bli chapter in this volume indicates the copyright owner's consent that reprographic copies of the
u
P chapter may be made for personal or internal use or for the personal or internal use of specific

clients. This consent is given on the condition, however, that the copier pay the stated per
copy fee through the Copyright Clearance Center, Inc., 21 Congress Street, Salem, MA 01970,
for copying beyond that permitted by Sections 107 or 108 of the U.S. Copyright Law. This
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 a new collective work, for resale, or for information storage and retrieval systems.
The copying fee for each chapter is indicated in the code at the bottom of the first page of the
chapter.
The citation of trade names and/or names of manufacturers in 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.
Registered names, trademarks, etc., used in this publication, even without specific indication
thereof, are not to be considered unprotected by law.
PRINTED IN THE UNITED STATES OF AMERICA
American Chemical
Society Library
1155 16th St., N.W.
Washington, D.C. 20036
ACS Symposium Series
M. Joan Comstock, Series Editor
Advisory Board
1 Robert Baker Geoffrey D. Parfitt
0
0
w U.S. Geological Survey Carnegie-Mellon University
6.f
4
02 Martin L. Gorbaty Theodore Provder
84- Exxon Research and Engineering Co. Glidden Coatings and Resins
9
1
k-
b Herbert D. Kaesz James C. Randall
1/
2 University of California—Los Angeles Phillips Petroleum Company
0
1
0.
doi: 1 ORfuficdeo olpf hN aJv. aMl Raersceaursch CMhasasralcehsu sNet.t sS Iantstteitruftiee lodf Technology
4 |
8
19 Marvin Margoshes Dennis Schuetzle
8, Technicon Instruments Corporation Ford Motor Company
h
arc Research Laboratory
M Donald E. Moreland
ate: USDA, Agricultural Research Service Davis L. Temple, Jr.
D Mead Johnson
n
o W. H. Norton
cati J. T. Baker Chemical Company Charles S. Tuesday
bli General Motors Research Laboratory
u
P Robert Ory
USDA, Southern Regional C. Grant Willson
Research Center IBM Research Department
FOREWORD
1
0
0
w
6.f The ACS SYMPOSIUM SERIES was founded in 1974 to provide
4 a medium for publishing symposia quickly in book form. The
2
0
4- format of the Series parallels that of the continuing ADVANCES
8
19 IN CHEMISTRY SERIES except that in order to save time the
k-
b papers are not typeset but are reproduced as they are sub
1/
02 mitted by the authors in camera-ready form. Papers are re
1
0. viewed under the supervision of the Editors with the assistance
1
oi: of the Series Advisory Board and are selected to maintain the
d
4 | integrity of the symposia; however, verbatim reproductions of
8
9 previously published papers are not accepted. Both reviews
1
8, and reports of research are acceptable since symposia may
h
arc embrace both types of presentation.
M
e:
at
D
n
o
ati
c
bli
u
P
PREFACE
FOR A COMPLEX TECHNOLOGY to reach a productive maturity, the dispar
ate scientific disciplines underlying that technology must be gathered into a
coherent whole. It is difficult to imagine a technology for which this is better
exemplified than the geological disposal of radioactive wastes. The underly
ing scientific areas include surface chemistry (sorption-desorption, dissolu
tion, ion exchange, corrosion), solution chemistry (hydrolysis, complexation,
01 oxidation-reduction, precipitation), colloid chemistry, ceramics, metallurgy,
0
pr hydrology, rock mechanics, and geology. These and other fields of study
6.
4 must be synthesized into a useful, practical whole through modelling and
2
0
4- rational thought. Finally, the rationalized body of information and conclu
8
19 sions drawn must be substantiated by tests performed in the actual waste
k-
b disposal environment.
1/
02 This volume makes an important contribution to the information
1
0. needed for disposal of wastes in geological media, demonstrating the
1
oi: advanced state of knowledge in many of the above fields of research. It
d
4 | represents a major part of what must be known before high-level radioactive
8
9 waste disposal may become a reality.
1
8, Governmental agencies in the United States and other countries have
h
arc sponsored a large amount of research on the behavior of radioactive wastes
M
e: in various environmental settings. The overall objective of this research has
at been to protect the health and safety of the public by assessing the potential
D
n hazard of radionuclides in disposed wastes over periods of time when these
o
cati radionuclides are significantly active. Making such an assessment requires an
ubli understanding of radionuclide distribution and inventory in or near the
P
disposal site, and of the transport processes (chemical, physical, and biotic)
that control the movement of radionuclides. The geochemistry of radionu
clides in disposal environments is clearly one of the most important aspects
of safety assessment because radionuclide release from the disposal site is
controlled by complex chemical processes. The goal of this volume is to
provide the reader with a single source of the most recent and significant
findings of research on the geochemical behavior of disposed radioactive
wastes.
Radioactive wastes of concern include wastes that result from operation
of the nuclear fuel cycle (mining, fuel fabrication, reactor operation, spent
fuel reprocessing, and waste storage), from nuclear weapons testing, and
from medical and research activities. In recent years, the emphasis has been
on predicting the behavior of disposed high-level wastes in deep geologic
vii
repositories. The many chapters on high-level waste reflect this emphasis.
However, the chemical behavior of the individual radionuclides described
will apply to many types of waste in geologic environments.
The chapters of this volume are organized into sections that cover the
chemical aspects that are important to understanding the behavior of dis
posed radioactive wastes. These aspects include radionuclide sorption and
desorption, solubility of radionuclide compounds, chemical species of
radionuclides in natural waters, hydrothermal geochemical reactions, mea
surements of radionuclide migration, solid state chemistry of wastes, and
waste-form leaching behavior. The information in each of these sections is
necessary to predict the transport of radionuclides from wastes via natural
waters and thus to predict the safety of the disposed waste.
Radionuclide transport in natural waters is strongly dependent on
1
0
0 sorption, desorption, dissolution, and precipitation processes. The firstt wo
pr
6. sections discuss laboratory investigations of these processes. Descriptions of
4
02 sorption and desorption behavior of important radionuclides under a wide
4-
8 range of environmental conditions are presented in the firsts ection. Among
9
1
k- the sorbents studied are basalt interbed solids, granites, clays, sediments,
b
1/ hydrous oxides, and pure minerals. Effects of redox conditions, groundwater
2
10 composition and pH on sorption reactions are described.
0.
oi: 1 Solubility constraints define the maximum concentrations of radionu
d clides at the point of release from the waste. In the second section,
84 | radionuclide solubilities in natural waters are reported as measured values
9
8, 1 and estimated values from thermodynamic data. In addition, information is
h given concerning the chemical species of radionuclides that could be present
c
Mar in natural waters.
e: If the heat generated from the waste by radioactive decay is great
at
D enough (as in the case of high-level waste disposed of in deep geologic
n
atio repositories), hydrothermal reactions will occur between the groundwater,
blic host rocks, and waste. The resulting alteration of these solids and ground
Pu waters will affect the behavior of radionuclides in these systems. In the third

section, the effects of these hydrothermal reactions are described.
Field measurements of radionuclide migration can be used to help
substantiate laboratory measurements of sorption, solubility, and identifica
tion of important chemical species. The fourth section describes three field
investigations that provide information on the effects of organics, colloids
and environmental conditions (Eh, pH, and temperature) on radionuclide
transport. The chemical species of radionuclides that are mobile under
specific fieldc onditions are identified.
Solid state chemistry of potentially important waste forms is covered in
the fifth section. Solid state reactions can determine the oxidation state and
physical and chemical stability of radionuclides in various host waste forms.
This information can be used to evaluate the utility of crystalline materials as
potential hosts for radioactive wastes.
viii
Groundwater leaching of radionuclides from waste forms is the first step
in radionuclide transport from a disposal site. The release rate of radionu
clides from the waste form is dependent on the waste form's leaching
behavior. The sixth section describes the factors that affect the leaching
behavior of several potential waste forms and radionuclides.
Finally, Mike McCormack, former Washington state Congressman,
discusses the Federal legislation affecting nuclear waste disposal in the
United States and the impact of several new laws passed by the Congress—
the Nuclear Waste Policy Act of 1982 and the Low-Level Radioactive Waste
Policy Act of 1980.
This volume covers ongoing research and, thus, leaves many questions
unanswered and many problems unsolved. The geochemistry of disposed
radioactive wastes involves many complex issues that will require years of
1
00 additional research to resolve. High-priority problems include: integration of
6.pr geochemical data with computer models of chemical interaction and trans
4
2 port, definition of environmental conditions that affect the behavior of
0
84- radionuclides at specific disposal sites, evaluation of complex formation of
9
k-1 dissolved radionuclides with inorganic and organic complexants, and deter
b
1/ mination of radionuclide solubilities in natural waters.
2
10 The editors would like to express their deep appreciation and admira
0.
1 tion to Teresa Bess of Rockwell Hanford Operations whose editorial assist
doi: ance greatly speeded the publication of this volume.
4 |
8
9
8, 1 G. SCOTT BARNEY
h Rockwell Hanford Operations
c
Mar Richland, Washington
e:
at
D JAMES D. NAVRATIL
n
atio Rockwell International Rocky Flats Plant
blic Golden, Colorado
u
P

WALLACE W. SCHULZ
Rockwell Hanford Operations
Richland, Washington
RAYMOND G. WYMER
Oak Ridge National Laboratory
Oak Ridge, Tennessee
December 1983
ix
1
Radionuclide Sorption and Desorption Reactions
with Interbed Materials from the Columbia River
Basalt Formation
G. S. BARNEY
Rockwell International, Energy Systems Group, Richland, WA 99352
The sorption and desorption behavior of radionuclides in
01 groundwater-interbed systems of the Columbia River
0
h basalt formation was investigated. Radionuclides
c
6. chosen for study were those of concern in assessing the
4
02 safety of a high-level radioactive waste repository in
84- basalt (isotopes of technetium, neptunium, plutonium,
9
1 uranium, americium, cesium, strontium, and radium).
k-
b Sandstone and tuff materials from selected interbed
1/
2 layers between basalt flows were used in these
0
0.1 experiments. Effects of groundwater composition and
doi: 1 dreedsoorxp tipoont eonnti athl e (gEehol)o goicn sorlaiddsio wnuercleid setu dsioerdp.t iSoond iaunmd,
4 | potassium, and calcium in the groundwater decrease
8
9 sorption of cesium, strontium, and radium by ion
1
8, exchange reactions. Groundwater Eh strongly affects
ch sorption of technetium, neptunium, plutonium, and
Mar uranium since chemical species of these elements
e: containing the lower oxidation states are more
Dat extensively sorbed by chemisorption than those
on containing higher oxidation states. Effects of
ati radionuclide complexation by groundwater anions on
c
bli sorption were not observed except for neptunium
u
P carbonate (or bicarbonate) complexes and plutonium

sufate complexes.
Sorption and desorption isotherms were obtained
for sorption of radionuclides under oxidizing and
reducing conditions. The Freundlich equation
accurately describes most of these isotherms. Most
radionuclides are apparently irreversibly sorbed on each
of the geologic solids since the slopes of sorption and
desorption isotherms for a given radionuclide are
different. This hysteresis effect is very large and will
cause a significant delay in radionuclide transport. It,
therefore, should be included in modeling radionuclide
transport to accurately assess the isolation capabilities
of a repository in basalt.
0097-6156/84/0246-0003S06.00/0
© 1984 American Chemical Society
4 GEOCHEMICAL BEHAVIOR OF RADIOACTIVE WASTE
The groundwater transport of radionuclides through water
bearing interbed layers in the Columbia River basalt formation
will be controlled by reactions of the radionuclides with
groundwater and interbed solids. These interactions must be
understood to predict possible migration of radionuclides from a
proposed radioactive waste repository in basalt. Precipitation and
sorption on interbed solids are the principle reactions that retard
radionuclide movement in the interbeds. The objective of the work
described herein was to determine the sorption and desorption
behavior of radionuclides important to safety assessment of a high-
level radioactive waste repository in Columbia River basalt. The
effects of groundwater composition, redox potential, radionuclide
concentration, and temperature on these reactions were
determined.
Geochemical models of sorption and desorption must be
1
00 developed from this work and incorporated into transport models
h
c that predict radionuclide migration. A frequently used, simple
6.
4 sorption (or desorption) model is the empirical distribution coeffi
2
0
4- cient, Kd. This quantity is simply the equilibrium concentration of
98 sorbed radionuclide divided by the equilibrium concentration of
1
k- radionuclide in solution. Values of Kd can be used to calculate a
b
1/ retardation factor, R, which is used in solute transport equations
2
0 to predict radionuclide migration in groundwater. The
1
0. calculations assume instantaneous sorption, a linear sorption
1
oi: isotherm, and single-valued adsorption-desorption isotherms.
4 | d These assumptions have been shown to be erroneous for solute
8 sorption in several groundwater-soil systems (1-2). A more
9
8, 1 accurate description of radionuclide sorption is an isothermal
h equation such as the Freundlich equation:
c
ar
M
e: S = KCN (1)
at
D
n where
o
ati
ublic S = mthoel eesq/gu ilibrium concentration of sorbed radionuclide in
P
C = the equilibrium concentration of radionuclide in solution
in moles/L
K and N = empirical constants.
This equation has been successfully applied to many sorption and
desorption reactions of dissolved metals and organic compounds.
In the case of irreversible sorption (hysteresis), sorption and
desorption isotherms are not identical. However, both sorption
and desorption Freundlich isotherm equations can be substituted
into the transport equation(2):
pS dC _ Da2c ac (2)
<t> t dt dx dx
1. BARNEY Sorption and Desorption 5
where
D = dispersion coefficient
v = average pore water velocity
p = bulk density
0 = saturated water content
x = distance in the direction of flow
t = time.
This equation can be used to describe one-dimensional transport of
radionuclides through porous media (e.g. radionuclide elution
curves from laboratory columns packed with interbed solids)
assuming instantaneous sorption and desorption. Van Genuchten
and coworkers have demonstrated the importance of using both
sorption and desorption isotherms in this equation when
1
00 hysteresis is significant. Isotherm data for sorption and desorption
h
c reactions of radionuclides with interbed materials are presented in
6.
4 this paper which can be used to predict radionuclide transport.
2
0
4-
8
9
1
k- Experimental
b
1/
2
10 Materials, The groundwater compositions of waters in the major
10. water bearing zones of the Columbia River basalts at the Hanford
oi: Site have been determined (3). There are two distinct
d
4 | groundwaters present in the basalts: a sodium-bicarbonate
8 buffered groundwater (pH 8 at 25°C) characteristic of the Saddle
9
8, 1 Mountains and Upper Wanapum basalts and a sodium-silicic acid
h buffered groundwater (pH 10 at 25°C) characteristic of the Lower
c
ar Wanapum and Grande Ronde Basalts. Synthetic groundwater
M
e: compositions have been established that simulate these two
at groundwater types. The compositions of the synthetic
D
n groundwaters used in the sorption experiments are given in
o
ati Table I. The GR-1A groundwater simulates the groundwater
blic composition of the Mabton Interbed in the Saddle Mountain
u Basalts. The GR-2 and GR-2A groundwaters simulate the
P
dominant groundwaters in the Lower Wanapum and Grande
Basalts. Synthetic groundwaters are used rather than actual
groundwaters in order to ensure the availability of a stable,
compositionally consistent groundwater for the sorption
experiments.
Three interbed materials from the Columbia River Basalt
Group have been investigated in the radionuclide sorption
experiments. Interbeds are porous sedimentary layers located
between many of the basalt flows in the Columbia River Basalt
Group and comprise a potential preferential pathway for
groundwater and, therefore, radionuclide transport.
Two interbed samples, a sandstone and a tuff, were taken
from as outcrop of the Rattlesnake Ridge Interbed above the