Introduction

The DECOVALEX II project was an extension of the DECOVALEX I project (1992–1994), for a period of four years (1995-1999). The project was initiated by recognizing the need for a proper evaluation of the current capacities of numerical modeling of coupled thermo-hydro-mechanical (THM) processes in fractured geological media for less characterized, more complex and realistic in-situ experiments at larger scales—as compared to the small scaled, well characterized and relatively much simpler laboratory experiments investigated during the DECOVALEX I project.

The overall objective of the DECOVALEX II project was to increase the understanding of various coupled THM processes of importance for radionuclide release and transport from a repository to thebiosphere and how they can be described by mathematical models, with focus on large scale in-situ experiments. An additional objective was to evaluate how studies conducted in the DECOVALEX I and DECOVALEX II projects could be used for design and performance assessment of radioactive waste repositories.

Tasks

Motivated by the outstanding issue of the need to model field scale THM experiments and to enable better understanding of the constitutive behavior and modelling of rock fractures, from the DECOVALEX I project, four Tasks were defined for the DECOVALEX II project as follows.

Task 1:Numerical modeling of the effects of Nirex’s RCF Shaft excavation at Sellalfield, UK, in two steps. The 1st step was the numerical modeling of the coupled hydro-mechanical responses of the host rock mass to the RCF3 pumping test; and the second step was modeling the responses of host rock mass to the planned shaft excavation, including study of the excavation-induced disturbed zone (EDZ).

Task 2:Numerical study of PNC’s in-situ THM experiment at the Kamaishi Mine, Japan, which was an integrated investigation of a complete rock-buffer-heater system under in-situ conditions over a long period of heating-cooling time.

Task 3:Review of the state-of-the-art of the constitutive relations of rock joints.

Task 4:Production of a report on the current understanding of the coupled THM processes related to design and performance assessment of radioactive waste repositories.

Organization

The management style was the same as that for the DECOVALEX I project, with the Steering Committee deciding the Tasks to be studied and the project’s finances and schedule, SKI as the executive party managing the project finances, and the Division of Engineering Geology at KTH (Royal Institute of Technology, Stockholm, Sweden) serving as the project’s Secretariat. The funding organizations and research teams are listed in Table 1 and Table 2, respectively.

Table 1: Funding Organizations of the DECOVALEX II project (1995–1999)
Organisation, Country Acronym
Atomic Energy of Canada, Ltd., Canada (stopped in 1996) AECL
Ontario Hydro, Canada (started in 1996, replacing AECL) OH
Atomic Energy Control Board, Canada AECB
Agence Nationale Pour la Gestion des Dèches Radioactifs, France ANDRA
Environmental Agency, UK EA
Institut de Protection et de Sûreté Nucléaire, France IPSN
United Kingdom Nirex Ltd., UK Nirex
Japan Nuclear Cycle Development Institute (former PNC), Japan JNC
Swedish Nuclear Fuel and Waste Management Co., Sweden SKB
Swedish Nuclear Power Inspectorate, Sweden SKI
Empresa Nacional de Residoos Radioactivids, S. A., Spain ENRESA
Center for Radiation and Nuclear Safety, Finland STUK
Table 2: Research teams of the DECOVALEX II project (1995–1999)
Full name, Country Acronym FO
Centre d’Informatique Géologique (CIG), Ecole Nationale Supérieure des Mines de Paris, France PSM IPSN
School of Civil Engineering, Kyoto University, Japan
Faculty of Agriculture, Iwate University, Japan
HAZAMA Corporation, Japan
Geological Isolation Technology Section, Tokai Works JNC, Japan.
KIPH JNC
ITASCA Consultants s.a., France ITAf ANDRA
Technical Research Center of Finland, Communities and Infrastructure, VTT, Finland VTT STUK
Earth Science Division, Lawrence Berkeley Laboratory, USA LBNL SKI
ITASCA Rokmekanik AB, Sweden ITAs SKB
Division of Engineering Geology, Royal Institute of Technology, Sweden KTH SKI
CLAY Technology AB, Sweden CLAY SKB
Centre for Land Use and Water Resources Research, University of Newcastle, UK UNEW EA
Atomic Energy Control Board, Canada AECB AECB
Departmento Ingenieeria Hidràulica, Universidad Politécnica Valencia, Spain UPV ENRESA

Products

Six reports were generated during the time of DECOVALEX II project, published by SKI:

  • L. Jing, O. Stephansson, C.-F. Tsang, L. J. Knight, and F. Kautsky, DECOVALEX II project: Executive summary,SKI Report00:24,Swedish Nuclear Power Inspectorate, Stockholm, Sweden. ISSN1104-1374,ISRN SKI-R-99/24-SE.
  • L. Jing, O. Stephansson, C.-F. Tsang, L. J. Knight, and F. Kautsky, DECOVALEX II project: Technical Report –Task 1A and 1B. SKI Report 98:39,Swedish Nuclear Power Inspectorate, Stockholm, Sweden. ISSN1104-1374,ISRN SKI-R-98/39-SE.
  • L. Jing, O. Stephansson, L. J. Knight, F. Kautsky and C.-F. Tsang, DECOVALEX II project: Technical Report –Task 1C. SKI Report 99:22,Swedish Nuclear Power Inspectorate, Stockholm, Sweden. ISSN1104-1374,ISRN SKI-R-99/22-SE.
  • L. Jing, O. Stephansson, C.-F. Tsang, M. Chijimatsu and F. Kautsky, DECOVALEX II project: Technical Report –Task 2A and 2B. SKI Report 98:40,Swedish Nuclear Power Inspectorate, Stockholm, Sweden. ISSN1104-1374,ISRN SKI-R-98/40-SE.
  • L. Jing, O. Stephansson, L. Börgesson, M. Chijimatsu, F. Kautsky and C.-F. Tsang, DECOVALEX II project: Technical Report –Task 2C. SKI Report 99:23,Swedish Nuclear Power Inspectorate, Stockholm, Sweden. ISSN1104-1374,ISRN SKI-R-99/23-SE.
  • O. Stephansson, J. A. Hudson, C.-F. Tsang, L. Jing and, J. Andersson, DECOVALEX II project: Coupled THM issues related to repository design and performance – Task 4. SKI Report 99:7,Swedish Nuclear Power Inspectorate, Stockholm, Sweden. ISSN1104-1374,ISRN SKI-R-99/7-SE.

11 papers generated by the DECOVALEX II project were published in a special issue of the International Journal of Rock Mechanics and Mining Sciences, in 2001: Volume 38, Issue 1. Reference information about these papers generated by the research teams for the different Tasks in which they participated is listed at the end of the description of each Task in the following sections.