Studies of the physico-chemical properties on the transuranian elements in connection with the migration phenomenon in the geosphereTask 3

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

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Characterization of radioactive waste forms: A series of final reports (1985-1989) No 30
Nuclear energy and safety

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• Publié par: EUROPEAN-COMMISSION-DIRECTORATE-GENERAL-FOR-THE-INFORMATION-SOCIETY-AND-MEDIA-DI
• Nombre de lectures: 4
• Langue: English
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ISSN 1018-5593
* *
Commission of the European Communities
Studies of the physico-chemical properties on
the transuranian elements in connection with
the migration phenomenon in the geosphere
Task 3
Characterization of radioactive waste forms
A series of final reports (1985-89)
No 30
EUR 13673 EN Commission of the European Communities
■■:■. .-''
1 ,.
Studies of the physico-chemical properties on
the transuranian elements in connection with
the migration phenomenon in the geosphere
Task 3
Characterization of radioactive waste forms
A series of final reports (1985-89)
No 30
P. Vitorge, J. Oliver, J. P. Mangin, A. Billon
CEA-Fontenay-aux-Roses
BPN06
F-92265 Fontenay-aux-Roses Cedex
Contract No FI1W/0035-F
Final report
This report was prepared for the European Atomic Energy Community's
cost-sharing research programme on radioactive waste management
and disposal (Task 3 - Section 3)
Directorate-General
Science, Research and Development
1991 EUR 13673 EN Published by the
COMMISSION OF THE EUROPEAN COMMUNITIES
Directorate-General
Telecommunications, Information Industries and Innovation
L-2920 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, 1991
ISBN 92-826-2907-4 Catalogue number: CD-NA-13673-EN-C
© ECSC-EEC-EAEC, Brussels · Luxembourg, 1991
Printed in France Abstract
Work under the "basic chemistry" contract from 1986 to January
1989 is reported. The properties of the transuranium elements (TRU)
mainly Pu Np Am have been investigated in terms of complexation by OH
and C03 ligands in aqueous solution. The aim of the research was to
identify the species which are formed in given physicochemical
conditions (ionic strength, concentrations ...) and to produce a set
of thermodynamical data relevant ot the system under investigation.
The reader must keep in mind that the approach has been essentially a
general one with no direct reference to well defined ground waters.
A careful attention has been paid to the determination of the
redox potential (formal) of the different couples of the TRU (M02-H- /
MO2+ and M4+ / M3+) in Perchlorate and carbonate media.
These different data (equilibrium constants of complexes and
redox potential values) are usefull in the drawing up of Pourbaix's
diagramms. Areas of stability of species in function of Eh pH pC02
are given for the different elements in a few cases.
The second part of this report deals with the study of the
transfer of tritiated water cesium and strontium through highly
compacted clay. It has been shown that the diffusion coefficient of
an element j, Dxj in the clay's pores is roughly independent of j.
In a third part a code for the computation of ion migration and
diffusion in areas close to radwaste storage facilities has been
developed. This type of application was found to require a mesh
pattern and boundary conditions different from the usual, which
justifies the writing of a new code.
Ill TABLE OF CONTENTS
Page
SUMMARY
XI
Part one : Transuranic Elements Basic Chemistry ]
1.1. Introduction 3
1.2. Thermodynamic data 4
1.2.1. Actinides complexing constants
1.2.1.1. Valency III
1.2.1.2.y IV 5
1.2.1.3.y V
12 14 Valency VI
12 2 Oxido-reduction potentials 9
12 2 1 HC104 1 M medium
1.2.2.2. Standard state
1.3. Predominance diagrams 10
1.3.1. Carbonate-hydroxide competition
1.3.1.1. Am(III)1
1.3.1.2. U(IV) Π
1.3.1.3. Np (V)
1.3.1.4. U(VI)2
1.3.2. Oxido-reduction4
1.3.2.1. Neptunium
1.3.2.2. Other actinides 1
2. Conclusion of part one9
Appendix 21
Bibliography5 Part two : Studies on transfer of radioelements in clay
materials 27
INTRODUCTION9
1. REVIEW OF THE MAJOR ANALYTICAL RELATIONSHIPS USED FOR
CHARACTERIZING MATERIAL TRANSFER IN TWO-PHASE, POROUS
MEDIA 2
1.1. MEASUREMENT OF THE EFFECTIVE DIFFUSION COEFFICIENT Dej
IN THE STEADY STATE
1.2. MEASUREMENT OF Dej UNDER TRANSIENT CONDITIONS) 31
2. COMPARATIVE STUDY OF TRITIATED WATER CAESIUM AND
STRONTIUM TRANSFERS IN Fo-Ca3 CLAY (0app =2.14 g/cm3).. 3
2.1. Tritiated water transfer 31
2.1.1. Description of equipment
2.1.2 Measurement of effective diffusion coefficient DeHto 3
2.1.2.1. Value of DeHT02
2.1.2.2. Determination of tiHt0/L·2
2.2. CAESIUM TRANSFER 33
2.2.1. Equipment and procedures
2.2.2. Results4
2.2.2.1. Demonstration of the existence of steady-state
conditions
2.2.2.2. Measurement of effective diffusion coefficient DeCs. 3
2.2.2.3. Interaction of Caesium with exchangeable ions in
clay 38
2.2.2.3.1. Mass of exchanged Caesium 39
2.2.2.3.2. Kinetics of exchange between Caesium and clay ions. 4
2.3. STRONTIUM TRANSFER 42
3. COMPARISON OF OUR RESULTS WITH PUBLISHED DATA 4
3.1. SUMMARY OF OUR CONCLUSIONS
VI 3.2. PUBLISHED DATA
45
3.2.1. Principle of measurements 45
3.2.2. Results and modelization.
45
DISCUSSION 3.3
46
46 4. CHARACTERIZATION OF MATERIAL TRANSFERS IN COMPACTED CLAY.
4.1. MATERIAL TRANSFER (in semi-infinite geometrical con­
figuration) in highly compacted clay: leaching 47
49' 4.1.1. Investigtion of extreme values ofg rate
49 4.1.1.1. The maximum rate case
4.1.1.2. Case of a rate approaching zero 50
4.2. PRACTICAL APPLICATIONS
54
4.2.1. Investigation of Caesium transfer by leaching
experiments 54
4.2.1.1. Effect of Caesium concentration 54
4.2.1.2. Effect of sand addition
58
4.2.2. Investigation of the transfer of major clay ions 58
CONCLUSION
63
APPENDIX 1: SUMMARY OF BASIC CONCEPTS RELATING TO MATERIAL
TRANSFER BY MOLECULAR DIFFUSION °5
1. FICK'S LAWS
6
2. COEFFICIENT Dv diffusion coefficent in infinite volume 6
3. Coefficient D, n coefficient in a pore 65
4.t D, effective diffusion coefficient through a
porous solid.. 66
Coefficient D*x: apparent diffusion coefficient. 67
VII 6. INVESTIGATION OF MATERIAL TRANSFERT BY DIFFUSION THROUGH
A THIN PLATE; MEASUREMENT OF COEFFICIENT De and Dex 68
APPENDIX 2: DESCRIPTION OF EQUIPMENT 69
APPENDIX 3: CORRECTION REQUIRED FOR CHANGING FROM LEACHING
IN SEMI-INFINITE MEDIUM TO ACTUAL SPECIMEN
CONDITIONS 70
71
Part three : Modeling of the source-term
1. Introduction 73
2. Writting the equation for a simple ion transport 74
72.1. Discretization principles
2.2. Calculation of Darcy velocity5
2.3.n of the convection-diffusion equation7
2.4.n of divergence in upper half-mesh9
2.5. Interface of two media 82
2.6. Discretization of the lower half-mesh 8
2.7. Implicit discretization scheme
2.8. Solution of time step
84
3. Boundary conditions
3.1. Initial and boundary conditions 84
3.2. Dirichlet's conditions5
3.3. Newmann's conditions6
3.4. Cauchy's condition7
3.5. Solubility limits8
3.6. The case of iron filings 90
3.7. Summary
3.8. Verification
4. Radioactivity. Filiation2
4.1. General equations
4.2. Discretization of the time-dependant term 9
4.3. The case of boundary conditions3
4.4. The steady-state in the presence of radioactivity
4.5. Filiation 94
4.6. Practical process
4.7. Concentration and activity6
4.8. Available version of the program 97
4.9. Verifications
5. Conservative form of discretized equations8
5.1. Requirement for a conservative form
5.2. Computation of the velocity field
5.3. New mass balance gg
VIII