(GRS 291) Microbial Processes Relevant for Long-Term Performance of Radioactive Waste Repositories in Clays

A number of investigations on occurrence and viability of microbes in compacted clays have been aimed at studying possible microbial effects on long-term performance of a deep geological repository (DGR) for high-level radioactive waste (HLW) and spent nuclear fuel (SF). Compacted clays are considered in current DGR designs either as a buffer material (compacted bentonite) or as a host rock (claystone). Accordingly, those investigations have been carried out in countries pursuing concepts of final HLW/SF disposal utilizing not only a claystone formation as a host rock for a DGR (Switzerland, France, Belgium1), but also a granitic formation (Sweden, Finland, Canada), for which the DGR performance largely relies on confinement properties of copper canisters amended by favourable chemical and mechanical properties of enveloping clay buffer /OND 01/, /NTB 02/, /AND 05/, /NWM 05/, /SKB 06/, /POS 07/. Therefore, a survey of investigations of microbes in compacted clays in the current analysis provides a compi-lation of issues relevant for the long-term performance of a DGR in granitic and clay-stone formations.