DECOVALEX-THMC Project. Executive summary

The DECOVALEX-THMC project is an ongoing international co-operative project that was started in 2004 to support the development of mathematical models of coupled Thermal (T), Hydrological (H), Mechanical (M) and Chemical (C) processes in geological media for sitting potential nuclear fuel waste repositories. The general objective is to characterise and evaluate the coupled THMC processes in the near field and far field of a geological repository and to assess their impact on performance assessment: during the three phases of repository development: excavation phase, operation phase and post-closure phase; for three different rocks types: crystalline, argillaceous and tuff; with specific focus on the processes related to: the very near-field of tunnels and deposition holes, permanent property changes of near and far-field rock masses, and glaciation and permafrost phenomena. The project involves a large number of research teams supported by radioactive waste management agencies or governmental regulatory bodies in Canada, China, Finland, France, Germany, Japan, Sweden and USA, who conducted advanced studies and numerical modelling of coupled THMC processes under five tasks: Task A: Influence of near field coupled THM phenomena on performance assessment, initiated by CNSC, Canada. Task B: The Excavation Disturbed Zone (EDZ). MHC studies of the EDZ, initiated by SKB, Sweden. Task C: Excavation Damaged Zone (EDZ) in the argillaceous Tournemire site, France, initiated by IRSN, France. Task D: Permanent permeability/porosity challenges due to THC and THM processes, initiated by Department of Energy, USA. Task E: THM Processes Associated with long-term climate change: glaciations case study, initiated by OPG (now NWMO), Canada. Works defined in these five tasks are divided into different phases or steps so that detailed comparisons can be made among the research teams' results, progress can be monitored and achievements documented in project reports. This report presents a brief overall summary of the definition, approaches, achievements and outstanding issues of the five tasks studies in the project. The technical details are presented in the individual reports of the tasks