Microbial processes relevant for the long-term performance of high-level radioactive waste repositories in clays

Abstract

Abstract The primary purpose of the present work was to qualitatively evaluate the relevance of microbial activity for the long-term performance of a deep geological repository for high-level radioactive waste and spent nuclear fuel utilizing clay and to identify which safety-relevant processes and properties can be potentially influenced by this activity. Deterioration of clay properties accompanying destabilization and destruction of clay mineral structure as a result of microbial actions can be considered as the primary microbial impact on clay. The present analysis identified eight clay properties essential for maintaining safety functions of containment and retardation of the disposal system – swelling pressure, specific surface area, cation exchange capacity, anion sorption capacity, porosity, permeability, fluid pressure and plasticity – which can potentially be influenced by microbial processes in clay-based materials and claystone within a repository. Radioactive waste canisters and over-packs made from cast metal or steel represent a further component of the engineered barrier system which can be strongly affected by microbial activity in the clay buffer or in the adjacent host rock. This work should provide a basis for a follow-up quantitative estimation of the maximum possible effects of microbial processes on the barrier system of a deep geological repository in clay.