Impact of environmental factors on the migration of Pu, Am, Np and Tc in geological systems

European Commission Directorate-General For The Information Society And Media Directorate-General For Research And Innovation

Description

Nuclear energy and safety
Environment policy and protection of the environment

Informations

• Publié par: EUROPEAN-COMMISSION-DIRECTORATE-GENERAL-FOR-THE-INFORMATION-SOCIETY-AND-MEDIA-DI
• Nombre de lectures: 29
• Langue: English
• Poids de l'ouvrage: 2 Mo

Extrait

Commission of the European Communities
r science
and technology
Impact of environmental factors
on the migration of
Pu, Am, Np and Tc in geological systems
»J 1.
1
Report
EUR 10920 EN Commission of the European Communities
iiip ^cienes
filili j||ygj"~»j| . llllllf
BIII WLM HLHL8 mÆm ' H^agß ?B JE
Impact of environmental factors
on the migration of
Pu, Am, Np and Tc in geological systems
M. Prins, R.M.J. Pennders, M.J. Frissel
National Institute of Public Health and Environmental Hygiene (RIVM)
Laboratory for Radiation Research
PO Box 1, 3720 BA Bilthoven,
The Netherlands
Contract No WAS-366-83-7
Final report
Work performed in the framework of the R&D programme
'Management and storage of radioactive waste'
(shared cost action) of the
European Atomic Energy Community
I PARI. ÍURCP. B^idhl
Directorate-General
N.C..
Science, Research and Development
CL,/EUR 10920 EN 1986 Published by the
COMMISSION OF THE EUROPEAN COMMUNITIES
Directorate-General
Telecommunications, Information Industries and Innovation
Bâtiment Jean Monnet
LUXEMBOURG
LEGAL NOTICE
Neither the Commission of the European Communities nor any person acting on
behalf of then is responsible for the use which might be made of the
following information
Cataloguing data can be found at the end of this publication
Luxembourg: Office for Official Publications of the European Communities, 1987
ISBN 92-825-7007-X Catalogue number: CD-NA-10920-EN-C
© ECSC-EEC-EAEC, Brussels • Luxembourg, 1987
Printed in Belgium SUMMARY
RIVM has a model under construction to describe the migration of
radionuclides through the geosphere. Its hydrologicai part is known as
METROPOL. The aim of this study was to provide geochemical data to be
included in this model.
Three questions had to be answered:
- How large delays in migration can be expected because of adsorption of
radionuclides on geological material?
- Is it possible to determine such delays by batch experiments instead of
by column experiments?
- What might be the role of microorganisms in isolated geological systems?
Special attention was given to the conditions which prevail round salt
formations, i.e. a region in which the salt concentration ranges from
saturation to very diluted systems.
To answer the first two questions a large series of distribution
coefficients was determined by batch and column experiments. The
radionuclides were: Americium-241, Plutonium-238 and 239,240, Neptunium-237
and Technetium-99. Geological materials were glauconite containing sand and
materials from near Gorleben (FRG). The main variables of which the impact
was studied were: pH, redox potential (Eh), salt concentration and contact
time. Also the influence of textural composition, CEC, organic matter
content and ionic composition of the associated ground waters on the
sorption of the radionuclides was studied.
The results are expressed as Kß values. The KQ is a measure for the
retardation of migration which can be expected due to adsorption of
radionuclides on geological materials.
The first conclusion which could be drawn was that the differences between
KQ factors determined by column and batch experiments was comparatively
small. A second conclusion was that Americium and Plutonium behaved in a
very similar way upon changes in the environmental conditions, although the
Kp values for Plutonium generally were higher than for Americium. The
adsorption of these actinides primarily was influenced by the pH, cation
exchange capacity and redox potential of the system. Technetium and
Neptunium behaved in different ways, although there is some similarity,
because the adsorption of both nuclides is higher in the presence of
organic matter. In aerobic systems Technetium will not be adsorped at all
as long no reduction occurs. The Kp ranges are :
Pu 126 - 14 250 cn^.g"1
Am 185 - 6 530 ciAg"1
Np 1.2 - 661
Tc 0-16 607 ciAg"1
To answer the third question a microcosm experiment was set up. A microcosm
is a closed vessel in which by means of particular additions the pH, redox
potential and microbial activity can be varied over a rather wide range.
Thus, this system simulates environmental changes which e.g. occur in
depositories which during the operation phase are aerobic due to the inward
diffusion of atmospheric oxygen, but thereafter become anaerobic due to
microbial activity of the present microorganisms. After some time the
microorganisms starve due to depletion of nutrients, the system remains
then, however, anaerobic. The changes of the solubilities appeared to be
dramatic, e.g. Pu and Am were rather insoluble at normal aerobic conditions
but the solubility increased with a factor of more than 100 for aerobic
conditions. For Np just the opposite behaviour was observed, for average
aerobic conditions Np was rather mobile, for anaerobic conditions it was
not. The solubility of Tc followed again another pattern. These dramatic
changes can be explained with help of thermodynamically derived Eh,pH
diagrams.
Kp ranges obtained are :
Pu 30 - 24 600 ciAg'1
Am 21-10 000 ciAg*1
Np 10-2 010 ciAg"1
Tc 0 - 99 cm^g'1
From the data of the batch, column and microcosm studies it can be
concluded that the migration of Pu, Am, Np and Tc will be strongly delayed
due to adsorption of these nuclides on geological material. In anaerobic
systems at low pH values Pu and Am will migrate faster than Np. For
aerobic conditions, but also for anaerobic conditions at high pH, Np will
migrate faster than Pu and Am. Tc may migrate in aerobic systems; it will
becqme less mobile if reduction occurs. As far as modelling concerns:
without a rather detailed knowledge of the local redox potential and pH a
fair estimate of the migration is not possible.
IV CONTENTS page
SUMMARY III
GENERAL INTRODUCTION
1.1. Introduction
1.2. The scope of the project
1.3. Description of the aims and general outline of the project
MATERIALS
2.1. Glauconite sand 5
2.1.1. Solid phase 5
2.1.2. Liquide 7
2.2. Gorleben sand 8
2.2.1. Solid phase 8
2.2.2. Liquide 9
3. METHODS 12
3.1. Introduction 12
3.2. Column experiments 14
3.2.1. Setup 14
3.2.2. Labelling 15
3.2.3. Reducing atmosphere 17
3.2.4. Porosity 17
3.2.5. Treatment of the columns 18
3.3. Batch experiments 19
3.3.1. Glauconite sand - aerobic conditions 19
3.3.2.e sand - anaerobics 22
3.3.3. Gorleben sand -cs 23
4. RESULTS 25
4.1. Column experiments 25
4.1.1. Americium columns 25
31 4.1.2. Plutoniums
37 4.1.3. Neptunium columns
42 4.1.4. Technetiums
4.2. Batch experiments 52
52 4.2.1. Glauconite sand - aerobic conditions
52 4.2.1.1 Distribution coefficients for 99Tc
for 241Am 54 2ns
for 239,240Pu 56 4.2.1.3ns
57 4 Distribution coefficients for 237Np
58 4.2.2. Glauconite sand - anaerob ic conditions
99 58 4.2.2.1ns for Tc
61 2 Distribution coefficients for 241Am
for 239,240pu 62 4.2.2.3ns
64 4ns for 237Np
4.2.3. Gorleben sand - anaerobic series 65
for 99Tc 66 4.2.3.1 Distribution coefficients
67 2ns for 241Am
68 4.2.3.3ns for 238Pu and 239,240pu
72 4 Distribution coefficients for 237Np
V -page
5. THE ROLE OF MICROORGANISM IN ISOLATED SYSTEMS 75
5.1. Introduction 75
5.1.1.Microbialeffects75
5.1.2.Objectives75
5.2. Materialsandmethods76
5.2.1.Designofexperiment76
•. 5.2.2.Materials76
•■ 5.2.3.Radionuclides, analysis77
5.3. Experiments77
•5.3.1. Experiment 177
' 5.3.2. Experiment 279
> 5.3.3. t 3 80
5.A. Results81
5.4.1.Experiment181
5.4.2.t293
5.4.3.Experiment393
5.5. K values96
- 5.6. Discussionoftheresults obtained with isolated system97
5.7. Conclusionsofchapter 598
CONCLUSIONS 99
IAmericium100
IIPlutonium100
IIINeptunium101
IVTechnetium102
ACKNOWLEDGMENT104
REFERENCES 105
APPENDIXI-IV108
- VI -Chapter 1 GENERAL INTRODUCTION
1.1. Introduction
This research has been performed by RIVM under contract with the Commission
of the European Communities. It is a part of the socalled MIRAGE-project
(Migration of Radionuclides in the Geosphere) in which several European
Countries participate.
The research is a part of Section 2 of the Mirage project, which deals with
the Integral Simulation Experiments and a part of section 6, which deals
with micro-organisms. The research project is financed by the CEC and the
Dutch Government (Ministry of Economic Affairs).
This report describes the complete results of an 18 months during study
(1-7-1984 till 31-12-1985) on the mobility of Plutonium, Americium,
Neptunium and Technetium in geological systems, in relation to the eventual
disposal of radioactive waste in such.
The investigation has been carried out by Drs.M.Prins, Dr.M.J.Frissel,
R.M.J.Pennders, M.J.Schouten, B.T.J.Abbenhuis and J.H.de Winkel.
1.2. The scope of the project
A considerable part of radioactive waste has to be isolated from the
biosphere for a r