The international Mont Terri rock laboratory; research in an argillaceous gormation for deep geological disposal

Repositories for radioactive waste have to provide long-term safety and security for radioactive materials. Generic and site specific rock laboratories play an important role in the characterisation of such repositories. The experimental results gained in these underground facilities are used, together with information from natural analogues, deep drilling programmes and modelling, to assess the evolution and performance of a geological disposal-repository.
Over the past ten years, the twelve Mont Terri Partner organisations ANDRA, BGR, CRIEPI, ENRESA, GRS, HSK, IRSN, JAEA, NAGRA, OBAYASHI, SCK-CEN and SWISSTOPO have jointly carried out and financed a research programme in the generic Mont Terri Rock Laboratory, an underground research facility adjacent to the security gallery of the Mont Terri motorway tunnel, in the vicinity of St-Ursanne, Canton Jura, Switzerland. The aim of the project is the geological, hydrogeological, geochemical and geotechnical characterisation of a clay formation, specifically of the Opalinus Clay. The experiments can be assigned to the following three categories: 1) process and mechanism understanding in undisturbed Opalinus Clay, 2) experiments related to repository-induced perturbations and 3) experiments related to repository performance during the operational and post-closure phases. The experimental results provide input for assessing different phases of repository evolution and the performance assessment.
Key experiments are: self-sealing of open discontinuities in the host rock and in the excavation damaged zone (EDZ), characterisation of rock-pore water interactions (undisturbed and disturbed argillaceous formations), optimisation of sealing materials for different geological disposal concepts, understanding of the THM processes in the near-field (bentonite backfill and host rock), understanding of gas flow processes and identification of corresponding flow paths and, finally, diffusion and retention processes of various radionuclides in the bentonite and argillaceous host rock. The performance and results of some of these key experiments will be presented in more detail.