SKI Report 2005:19 Research DECOVALEX III PROJECT Mathematical Models of Coupled Thermal-Hydro-Mechanical Processes for Nuclear Waste Repositories Executive Summary Edited by: L. Jing C-F. Tsang J-C. Mayor O. Stephansson F. Kautzky February 2005 ISSN 1104-1374 ISRN SKI-R-05/19-SE SKi SKI Report 2005:19 Research DECOVALEX III PROJECT Mathematical Models of Coupled Thermal-Hydro-Mechanical Processes for Nuclear Waste Repositories Executive Summary Edited by: L. Jing1 C-F. Tsang2 J-C. Mayor3 O. Stephansson 1 F. Kautzky4 1 Royal Institute of Technology, Engineering Geology, Stockholm, Sweden 2 Lawrence Berkely National Laboratory, Earth Science Div., Berkeley, US 3 ENRESA, Madrid, Spain 4 Swedish Nuclear Inspectorate, Stockholm, Sweden February 2005 T This report concerns a study which has been conducted for the DECOVALEX III Project. The conclusions and viewpoints presented in the report are those of the author/authors and do not necessarily coincide with those of the SKI. Foreword DECOVALEX is an international consortium of governmental agencies associated with the disposal of high-level nuclear waste in a number of countries. The consortium’s mission is the DEvelopment of COupled models and their VALidation against Experiments. Hence theacronym/name DECOVALEX. Currently, agencies from Canada, Finland, France, Germany, Japan, Spain, Switzerland, Sweden, United Kingdom, and the United States are in DECOVALEX. Emplacement of nuclear waste in a repository in geologic media causes a number of physical processes to be intensified in the surrounding rock mass due to the decay heat from the waste. The four main processes of concern are thermal, hydrological, mechanical and chemical. Interactions or coupling between these heat-driven processes must be taken into account in modeling the performance of the repository for such modeling to be meaningful and reliable. The first DECOVALEX project, begun in 1992 and completed in 1996 was aimed at modeling benchmark problems and validation by laboratory experiments. DECOVALEX II, started in 1996, built on the experience gained in DECOVALEX I by modeling larger tests conducted in the field. DECOVALEX III, started in 1999 following the completion of DECOVALEX II, is organized around four tasks. The FEBEX (Full-scale Engineered Barriers EXperiment) in situ experiment being conducted at the Grimsel site in Switzerland is to be simulated and analyzed in Task 1. Task 2, centered around the Drift Scale Test (DST) at Yucca Mountain in Nevada, USA, has several sub-tasks (Task 2A, Task 2B, Task 2C and Task 2D) to investigate a number of the coupled processes in the DST. Task 3 studies three benchmark problems: a) the effects of thermal-hydrologic-mechanical (THM) coupling on the performance of the near-field of a nuclear waste repository (BMT1); b) the effect of upscaling THM processes on the results of performance assessment (BMT2); and c) the effect of glaciation on rock mass behavior (BMT3). Task 4 is on the direct application of THM coupled process modeling in the performance assessment of nuclear waste repositories in geologic media. This executive summary presents the motivation, structure, objectives, approaches, and the highlights of the main achievements and outstanding issues of the tasks studied in the DECOVALEX III project. The main sources of the materials came from summaries of the individual tasks prepared by the respective task force group leaders. They are: Task 1 (Chapter 2): E. Alonso and J. Alcoverro Task 2 (Chapter 3): R. Data and D. Barr Task 3-BMT1 (Chapter 4): T. S. Nguyen and L. Jing Task 3-BMT2 (Chapter 5): J. Andersson and J. L. Knight Task 3-BMT3 (Chapter 6): T. Chan and R. Christiansson Task 4 (Chapter 7): J. Andersson The editors of this summary, together with the Steering Committee of the DECOVALEX III project, feel very encouraged by the progresses which have been made during the project time and very positive about the usefulness of the achievements reached by the project to the larger international community of scientific research and management of radioactive wastes in different countries. A new phase of the DECOVALEX project, DECOVALEX-THMC, is under preparation and we sincerely hope that the continued efforts will advance the science and improve the numerical tools so that the disposal of radioactive waste could be managed on a more reliable scientific basis. L. Jing, F. Kautsky, J.-C. Mayor, O. Stephansson and C.-F. Tsang Stockholm January 2005 Summary This report is an executive summary of the works performed for the international co­ operative research project DECOVALEX III (1999-2002). The report is divided into seven chapters. Chapter 1 provides a brief introduction to the project’s goals, organizations, task definitions, implementation steps, overall achievements and lessons learned. The rest of the chapters are devoted to executive summaries of individual tasks covering mainly the case definitions, objectives, participating organizations and research teams, the tools and approaches applied, main achievements and the lessons learned with outstanding issues for future studies. Content Page 1 Introduction 1 2 Executive summary-Task 1 5 2.1. Case definition and objectives 5 2.2. Participating organizations and research teams 8 2.3. Summary of results 8 2.4. Summary of scientific achievements of the task 11 2.5. Lessons learned and outstanding issues 12 3 Executive summary-Task 2 14 3.1. Introduction 14 3.2. Problem definition and work organization 15 3.3. Modelling approaches 15 3.4. Scientific achievements 16 3.5. Lessons learned and outstanding issues 17 4 Executive summary-BMT1, Task3 18 4.1. General definition of the problem 18 4.2. Implementation steps 18 4.3. Work organization and the physical processes concerned 20 4.4. Summary on scientific achievements 21 4.5. Lessons learned and outstanding issues 23 5 Executive summary-BMT2, Task 3 26 5.1. Background and objectives 26 5.2. Task organization 26 5.3. Problem definition 27 5.4. Modelling approaches 28 5.5. Scientific achievements 29 5.6. Lessons learned and outstanding issues 32 6 Executive summary - BMT3, Task 3 35 6.1. Background and objectives 35 6.2. Work organization 35 6.3. Problem definition 36 6.4 Modelling approaches 38 6.5 Summary of results 39 6.6 Scientific achievements 41 6.7 Lessons learned and outstanding issues 42 7 Executive summary - Task 4 44 7.1 Background 44 7.2 Objectives and scope 44 7.3 Works performed 44 7.4 Major findings through the questionnaire-answer forum 44 7.5 Presentation cases at the Task 4 themes of the 46 DECOVALEX III workshops 7.6 Issues discussed at DECOVALEX III workshops 46 7.7 Findings and implication of the different DECOVALEX III tasks 46 7.8 Lessons learned and outstanding issues 52 7.9 Conclusions 55 References 56 1. Introduction The DECOVALEX III project is the third stage of an ongoing international co-operative project to support the development of mathematical models of coupled Thermal (T), Hydrological (H) and Mechanical (M) processes in fractured geological media for potential nuclear fuel waste repositories. During the first stage (May 1992 to March 1995), called DECOVALEX I, the main objective was to develop computer codes for coupled T-H-M processes and their verification against small-scale laboratory or field experiments. In the second stage, called DECOVALEX II, the main objective was to further develop and verify the computer codes developed in DECOVALEX I against two large-scale field tests with multiple prediction-calibration cycles, the pump test at the Sellafiled, UK, with a hypothetical shaft excavation and the in-situ THM experiment at the Kamaishi Mine, Japan. The DECOVALEX III project is the third phase of the DECOVALEX project series and was run through the period of 1999-2003. The DECOVALEX III project is initiated with two main objectives. The first is the further verification of computer codes by simulating two additional large scale in-situ experiments: the FEBEX T-H-M experiment performed in Grimsel, Switzerland, designated as Task 1, and the drift scale heater test at Yucca Mountain, Nevada, USA, designated as Task 2. The second objective is to determine the relevance of THM processes on the safety of a repository. To achieve the second objective of DECOVALEX III project, three benchmark tests (BMT) are proposed to examine the relevance of THM processes to performance and safety assessments: 1) BMT1: the impact of THM processes in the near-field of a hypothetical repository in fractured hard rocks; 2) BMT2: homogenisation and upscaling of hydro-mechanical properties of fractured rocks and their impact on far- field performance and safety assessments; and 3) BMT3: Impact of glaciation process on far-field performance and safety assessments. These three BMTs are designated as Task 3. An additional Task 4 was also organized to present the states of the current understandings on the impacts and treatments of the THM issues on PA and SA of nuclear waste repositories, from the views of the Funding organizations of the project, through compilation of answers to a questionnaire prepared for this purpose. On September 25, 2000 the European Commission (EC) signed a contract of FIKW- CT2000-00066 "BENCHPAR" project with a group of European members of the DECOVALEX III project. The BENCHPAR project stands for 'Benchmark Tests and Guidance on Coupled Processes for Performance Assessment of Nuclear Waste Repositories' and is aimed at improving the understanding to the impact of the thermo ­ hydro-mechanical (THM) coupled processes on the radioactive waste repository performance and safety assessment. The project has eight principal contractors, all members of the DECOVALEX III project, and four assistant contractors from universities and research organisations.The project is designed to advance the state-of- the-art via five Work Packages (WP). In WP 1 is establishing a technical auditing methodology for overseeing the modeling work.