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1 High-Level Radioactive Waste (HLW) Disposal WITPRESS WIT Press publishes leading books in Science and Technology. Visit our website for the current list of titles. WITeLibrary Home of the Transactions of the Wessex Institute, the WIT electronic-library provides the international scientific community with immediate and permanent access to individual papers presented at WIT conferences. Visit the WIT elibrary athttp://library.witpress.com

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3 High-level Radioactive Waste (HLW) Disposal A Global Challenge R. Pusch Luleå Technical University, Sweden R. Yong North Saanich, Canada M. Nakano The University of Tokyo, Japan

4 R. Pusch Luleå Technical University, Sweden R. Yong North Saanich, Canada M. Nakano The University of Tokyo, Japan Published by WIT Press Ashurst Lodge, Ashurst, Southampton, SO40 7AA, UK Tel: 44 (0) ; Fax: 44 (0) For USA, Canada and Mexico WIT Press 25 Bridge Street, Billerica, MA 01821, USA Tel: ; Fax: British Library Cataloguing-in-Publication Data A Catalogue record for this book is available from the British Library ISBN: Library of Congress Catalog Card Number: The texts of the papers in this volume were set individually by the authors or under their supervision. No responsibility is assumed by the Publisher, the Editors and Authors for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions or ideas contained in the material herein. The Publisher does not necessarily endorse the ideas held, or views expressed by the Editors or Authors of the material contained in its publications. WIT Press 2011 Printed in Great Britain by Short Run Press Ltd, Exeter. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the Publisher.

5 Preface The future of nuclear power for energy production depends more and more on how methods and materials can be found for safe disposal of highly radioactive waste HLW. In certain countries like Sweden such waste is represented by spent fuel while in others it is made up of rest products from reprocessed material. Most of the national organizations that are responsible for the disposal claim that their respective concepts follow the multibarrier principle by utilizing the isolating function of the host rock, the HLW containers ( canisters ), and dense clay embedding the containers. While the engineered barriers, the metal containers and the dense clay can be manufactured with high precision and all sorts of quality control, the heterogeneity of the host rock has made it difficult to ascribe any specific isolating ability to it and this has cast some doubt on its actual function, keeping in mind the impact of seismic events and of tectonic movements. The book deals with these matters and gives examples of common repository concepts, and describes their functions with special respect to the long-term performance. The advantages as well as weaknesses of the various engineered components are in focus and improvements suggested for increasing safety and reducing cost. The final part of the book deals with pragmatic matters like techniques for construction of repositories with respect to the structural constitution and stress conditions in the host rock and to installing the HLW containers and the protective clay in a safe and practical way. The need for planners of repositories to have insight and experience in engineering geology and to have deep understanding of how rock and expandable clay behave in practice is underlined. Too many unconstructable designs have been proposed in later years by people who are more interested in mathematical modeling than thinking practically and taking natural geological evidence as a basis for repository planning. The Editors, 2011

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7 Contents Chapter 1 Introduction Highly radioactive waste Radioactivity Heat production National and international work Principles for disposal of HLW, operational time, depths The multiple barrier principle Operational time Depth State-of art assessment of rock types for disposal of HLW Crystalline rock Argillaceous rock including clastic clay Salt rock Options for HLW disposal References Chapter 2 Geological basis What is the role of the host rock for the performance of an HLW repository? Rock types considered for HLW disposal Crystalline rock Argillaceous rock Salt rock Rock structure Definitions Categorization of structural elements Constitution and evolution of the shallow earth crust the far field Origin of small-scale discontinuities Evolution of large-scale rock structure Impact of earthquakes and glaciation on the large-scale rock structure and hydraulic performance Near-field rock... 34

8 2.5.1 Roles with respect to the function of engineered barriers Impact of repository construction on the performance of the near-field rock Impact of deposition holes on the performance of the surrounding rock Impact on the rock by boring and blasting tunnels and holes EDZ The constitution of different rock types hosting repositories Crystalline rock Salt and argillaceous rock, and clastic clay References Chapter 3 Engineered barriers How is release of radionuclides hindered? HLW Canisters Design and material Canister longevity Buffer The role of clays in a repository Smectite minerals Hydrated smectite minerals Maturation of the buffer The hydraulic conductivity of smectite clays The gas conductivity of smectite clays The ion diffusion capacity of smectite clays The stress/strain properties of smectite clays References Chapter 4 Performance of barriers Which are the most important functions of the barriers? What impact does the confining rock have on the engineered barriers? General Tectonic impact Structural implications for earthquakes and large rock strain Numerical modelling of large-scale strain Numerical modelling of small-scale strain Near-field stability issues Time-dependent strain... 97

9 4.2.8 Impact of glaciation on repository rock Canister performance General Performance of buffer clay Hydraulic conductivity Accuracy Expandability References Chapter 5 Long-term performance of the engineered barriers Canisters Buffer Conceptual model of the evolution of the buffer Maturation of the SKB buffer Theoretical modelling of buffer maturation Modelling of buffer evolution the Codes Accuracy of thermo-hydro-mechanical-chemical (THMC) prediction Anomalies caused by instrumentation Changes in buffer constitution and properties by hydrothermal processes Basic Natural analogues THMC laboratory tests Tentative conclusions Modelling of conversion of smectite to non-expanding minerals Conclusive remarks concerning mineralogical changes in buffer clay Rheological issues Impact of physical processes on the buffer performance References Chapter 6 Repository concepts for HLW Principles Crystalline rock General SKB s concept KBS-3V Closing the repository Borehole plugging SKB s concept KBS-3H

10 6.2.6 Other concepts Argillaceous rock General Examples of national concepts Salt rock General Description of disposal concepts Function of the repository Detailed design principles Performance Repositories in crystalline and argillaceous rock Repositories in salt rock Sealing of deep boreholes The SKB/POSIVA study Tight seals References Chapter 7 Alternative concepts General Canisters Identified risks The HIPOW canister Buffer Criteria set for safe function of the buffer Identified risks for SKB type concepts Historical overview Buffer candidates Longevity Impact of erosion on the buffer Stiffening, an issue of fundamental importance for the ultimate selection of a suitable candidate buffer Ranking of candidate buffers Buffer blocks Other buffer components, backfills Buffer geometry issues Alternative orientation of deposition holes Backfilling of tunnels and rooms with no waste Drainage conditions Materials and placement of earthen backfills References

11 Chapter 8 Risk assessment and challenges General Performance assessment of the repository Assessed scenarios Retrievability and monitoring Risk constraint of exposure Current repository design and risk issues Repositories in crystalline and argillaceous rock Repositories in salt rock Repositories in clastic clay Design requirements related to safety Containment of radionuclides Long-term radiological safety Safety in the operational phase Criticality Non-radiological environmental impact Flexibility Retrievability of the waste Technical feasibility References Chapter 9 Concluding remarks Lessons learned and potential areas for improvement General Construction phase Operation phase Transient phase Long term phase Final comment