Research on swelling clays and bitumen as sealing materials for radioactive waste repositories

Research on swelling clays and bitumen as sealing materials for radioactive waste repositories

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Commission of the European Communities
nuclear science
and technology
Research on swelling clays and bitumen
as sealing materials for radioactive
waste repositories
Report
EUR 13522 EN Commission of the European Communities
nuclear science
and technology
Research on swelling clays and bitumen
as sealing materials for radioactive
waste repositories
J. A. Allison, J. Wilson, J. M. Mawditt, J. C. Hurt
Bullen & Partners
Consulting Engineers
185 London Road
Croydon CR9 1PT
United Kingdom
Final report
1
PÀRL n;n:? »ih.
Contract No FI1W/0162
N.C.
Work carried out under cost-sharing contract
with the European Atomic Energy Community,
within the framework of its third R&D programme on
Management and storage of radioactive waste
Directorate-General
PARL EURCP Biblioth. Science, Research and Development
N.C. EUR 13522 E* 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 92-826-2647-4 Catalogue number: CD-NA-13522-EN-C
© ECSC-EEC-EAEC, Brussels • Luxembourg, 1991
Printed in Germany SUMMARY
This report describes a programme of research to investigate the performance of composite
seals incorporating adjacent blocks of swelling clay and bitumen. It is shown that the
interaction of the materials can promote a self-sealing mechanism which prevents water
penetration, even when defects are present in the bitumen layer.
A review of the swelling properties of highly compacted bentonite and magnesium oxide is
presented, and the characteristic sealing properties of bituminous materials are described. On
the basis of this review, it is concluded that bentonite is the preferred candidate material for
use in composite clay/bitumen seals for intermediate-level radioactive waste repositories.
However, it is thought that magnesium oxide may have other sealing applications for high-
level waste repositories.
A programme of laboratory experiments is described in which relevant swelling and intrusion
properties of highly compacted bentonite blocks and the annealing characteristics of oxidised
and hard-grade industrial bitumens are examined. The results of composite sealing
experiments involving different water penetration routes are reported, and factors governing
the mechanism of self-sealing are described.
The validation of the sealing concept at a laboratory scale indicates that composite
bentonite/bitumen seals could form highly effective barriers for the containment of radioactive
wastes. Accordingly, recommendations are made concerning the development of the research,
including the implementation of full-scale demonstration experiments to simulate conditions
in an underground repository.
Ill ACKNOWLEDGEMENTS
Assistance provided by the following organisations is gratefully acknowledged :
City University (Geotechnical Research Centre)
Provision of laboratory testing facilities
Birmingham University (Civil Engineering Department)
Provision of facilities for casting and trimming of bitumen samples
Imperial College, London University (Department of Mineral Resources Engineering)
Bitumen permeability tests
British Petroleum Ltd (Sunbury Research Centre)
Advice on bitumen properties
VolclayLtd (Wallasey, UK)
Supply of Wyoming bentonite (MX-80) samples
La porte Industries Ltd (Redhill, UK)
Supply of 'Surrey Powder' and 'Fulgel' bentonite samples
Steetley Refractories Ltd (Worksop, UK)
Supply of magnesium oxide samples
Colas Building Products Ltd (Chester, UK)
Supply of bitumen samples
IV CONTENTS
SUMMARY III
ACKNOWLEDGEMENTS IV
1 INTRODUCTION 1
General
Background to the Research
Sealing Concept 4
PART 1 - MATERIALS 9
2 BENTONITE CLAYS 11
Origin of Bentonites
Mineralogy2
Relevant Properties3
Material Used in Experiments8
3 MAGNESIUM OXIDE 2
Origin and Commercial Production1
Relevant Properties2
Potential Sealing Applications4
4 BITUMEN5
Origin and Composition 2
Relevant Properties7
Sealing Applications 31
Material Used in ExperimentsPART 2 - LABORATORY EXPERIMENTS 33
PROGRAMME AND EQUIPMENT 35
General 3
Bentonite Tests6
Bitumen Tests8
Composite Sealing Tests 42
Temperature and Scale Effects3
BENTONITE TESTS5
Preliminary Testing
Swelling Pressure Tests7
Intrusion Tests 50
BITUMEN TESTS3
Uniaxial Compression Tests
Annealing Tests4
Permeability Tests6
COMPOSITE SEALING TESTS 59
General 5
Base Irrigation Tests
Slotn Tests 61
VI PART 3 - CONCLUSIONS AND RECOMMENDATIONS 65
CONCLUSIONS 67
Candidate Materials
Bentonite Swelling and Intrusion Properties 68
Bitumen Annealing Properties 70
Performance of Composite Seals1
Implications for Design of Repository Seals2
Summary3
10 RECOMMENDATIONS5
Bitumen Properties 7
Intrusion and Annealing Tests
Demonstration Projects
REFERENCES7
FIGURES 8
TABLES 131
VII LIST OF FIGURES
FIG 1 Generalised concept for a deep underground radioactive waste repository
FIG 2 Postulated mechanisms of radionuclide release and migration
FIG 3 Illustration of potential application of the sealing concept
FIG 4 Types of imperfection in a bitumen block barrier
FIG 5 Smectite clay mineral structure
FIG 6 Ions held at inter-layer positions in smectite structures
FIG 7 Bulk density of Na-bentonite as a function of compaction pressure and moisture
content (after Wheelwright et al)
FIG 8 Relationship between permeability, k, and equilibrium bulk density, y , for
Na-bentonite showing effects of temperature and hydraulic gradient (after
Pusch, 1980)
FIG 9 Relationship between permeability and bulk density at equilibrium for Ca-
bentonite based fill mixtures (adapted from Geneste et al, 1988)
FIG 10 Representation of swelling test apparatus used by Pusch et al
FIG 11 Basic silicate units
FIG 12 Hydration of MgO as a function of grain-size and temperature (after Simpson,
1983)
FIG 13 Block form 'refractory-grade' magnesium oxide and magnesium oxide grain
FIG 14 Aliphatic and aromatic hydrocarbon series
FIG 15 Gel-type and sol-type bitumen structures
FIG 16 Conceptual rheological models for bitumen
FIG 17 Basic components of test apparatus
FIG 18 Apparatus for bentonite intrusion tests
VIII