Performance assessment of confinements for medium-level and ?-contaminated waste

Performance assessment of confinements for medium-level and ?-contaminated waste

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Pacoma project: Rock salt option
Nuclear energy and safety

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Commission of the European Communities
^lear science
technology
Performance assessment of confinements
for medium-level and a-contaminated waste
Pacoma project
Rock salt option Commission of the European Communities
nuclear scienr
and technology
Performance assessment of confinements
for medium-level and a-contaminated waste
Pacoma project
Rock salt option
R. P. Hirsekorn, A. Nies, H. Rausch, R. Storck
GSF - Forschungszentrum fur Umwelt und Gesundheit, IfT, GmbH
Theodor Heuss Straße 4
D-W-3300 Braunschweig
Contract NFI1W/0044-D
Final report
This study has been performed under cost sharing contract FI1W/0044-D as part of the European
Atomic Energy Community's programme on 'Management and storage of radioactive waste',
Task 5: Safety of geological disposal.
Directorate-General
Science, Research and Development PARL EUROP BLIiolh.
NC EUR 13634 EH 1991 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 92-826-2967-8 Catalogue number: CD-NA-13634-EN-C
© ECSC-EEC-EAEC, Brussels • Luxembourg, 1991
Printed in Belgium Abstract
In the frame of the European R&D programme on "Management and Stor­
age of Radioactive Waste, Task.5" the project "Performance Assessment of
Confinement of Medium-level and a-contaminated Waste, PACOMA" was car­
ried out. The overall objective of this project is the assessment of the
consequences associated with deep disposal of radioactive waste in three
types of geological formations. The objective of the present contribu­
tion to the PACOMA project is to develop and demonstrate procedures for
radiological safety of repositories in salt domes. An analogue study is
performed by the Netherlands Energy research Foundation ECN, where al­
ternative disposal concepts in different salt formations were investi­
gated. In the present report it is discussed, how far appropriate choise
of the repository design parameters can improve the whole system. The
research covers deterministic calculations for three scenarios, the nor­
mal evolution scenario with subrosion of the salt dome, the combined
brine intrusion scenario with brine intrusion from brine pockets and via
an anhydrite vein, and the humann scenario of solution mining
of a storage cavern. For the combined brine intrusion scenario alterna­
tive waste inventories, different disposal concepts, variants of the
layout of dams and sealings are investigated, and results obtained from
variations of parameter values are discussed. Additionally, for this
scenario comprehensive probabilistic calculations have been carried out
with the help of a Monte Carlo simulation. Results are discussed in form
of an uncertainty analysis of the maximum dose and global sensitivity
studies of system parameters. The assessment main result is, that the
reference case, where the reference repository design and the reference
disposal concept are applied, deterministic calculations with best esti­
mate values as well as probabilistic calculations do not manifest unac­
ceptable risk. Investigation of alternative concepts and design variants
indicate a high potential for system optimization.
Ill Contents Page
1 Introduction 1
2 Waste description and radionuclide inventory 5
2.1e categories from reprocessing 6
2.2 Reactor operating waste 10
2.3 The PACOMA reference inventory of medium-level and a
waste 12
2.4 Inventory variants9
3 Disposal concepts 25
4 Site selection and repository design 27
4.1 The reference repository
4.1.1e central field 30
4.1.2 The chamber wing
4.1.3e borehole wing3
4.2 Repository design variants6
4.2.1 Alternative layout of dams and sealings 3
4.2.2 Modifications of the design for alternative disposal
concepts 37
5 Release Scenarios9
5.1 Normal evolution scenario
5.2 Alteredn scenarios 40
5.2.1 The combined brine intrusion scenario
5.2.2 Human intrusion scenarios5
6 Input data and modelling procedures 53
6.1 Leaching model for waste forms6
6.1.1 Waste container failure 57
6.1.2 Degradation of the waste matrix8
6.2 Segment models for the repository 60
6.2.1 Disposal chamber model
6.2.2 MLW borehole model 63
V -Page
6.3 Modelling of physical and chemical effects 66
6.3.1 Production and transport of corrosion gas9
6.3.2 Density gradient induced exchange processes 70
6.3.3 Migration of the cement induced density gradient5
6.4 Temperature distribution along the borehole wing 77
6.5 Calculation of the collective doses 81
7 Results of the deterministic calculations5
7.1s for the reference case
7.1.1 Normal evolution scenario 90
7.1.1.1 Temporaln of the repository2 Results for the subrosion scenario2
7.1.2 Combined brine intrusiono6
7.1.2.1 Calculation with best estimate values of parameters 9
7.1.2.2 Variation of parameter values 11
7.1.2.2.1n of the time of brine intrusion via an anhy­
drite vein 117
7.1.2.2.2 Variation of the volumes of brine inclusions 132 3n of the permeability of dams 144
7.1.2.2.4 Variation of the initial convergence rate 155 5 Results obtained with modified solubility limits 16
7.1.2.2.6sd withd Kd-values of the geo-
sphere 173
7.1.3 The human intrusion scenario of a solution mined ca­
vern7
7.1.3.1 Modelling assumptions of the solution mined cavern 17
7.1.3.2 Results of a deterministic calculation 182 3 Comparison of results with those of the combined brine
intrusion scenario 188
7.2 Results for design variants of the repository 190
7.2.1 Design variant with sealings instead of dams on the
chamber wing 191
7.2.1.1 Best estimate value of the brine intrusion time 19
7.2.1.2 Altered value of the brine intrusion time 196
VI -Page
7.2.2 Design variant with one dam per flank drift of the
chamber wing 202
7.2.2.1 Best estimate value of the brine intrusion time 20
7.2.2.2 Altered value of the brine intrusion time 203
7.3 Results for alternative disposal concepts for the re­
ference waste9
7.3.1 Disposal of iodine filters in boreholes
7.3.2l of LLW-oc in boreholes 217
7.4 Results obtained with alternative inventories 228
7.4.1 Inventories with reprocessed M0X fuel elements
7.4.2 Supplementary disposal of HLW in boreholes 233
7.4.2.1 Results for the variant with the HLW field behind the
MLW field 23
7.4.2.2 Results for the variant with the HLW field between MLW
borehole wing and the central field 234
7.4.3 Disposal of non heat-producing waste, only6
7.5 Comparison of the results obtained for the German re­
pository and for the Dutch mined repository in salt
domes8
8 Probabilistic calculations 257
8.1 Introduction
8.2 Survey of the results of the Monte Carlo simulation 261
8.3 Uncertainty analysis of the maximum doses 269
8.4 Time-dependent uncertainty analysis 273
8.5 Global sensitivity analysis 280
9 Summary and conclusions5
References 29
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