Comparison of models to evaluate microbial sulphide generation and transport in the near field of a SF/HLW repository in Opalinus Clay

Abstract

In a deep geological repository for radioactive waste in the Opalinus Clay, disposal canisters may be corroded due to sulphide produced by sulphate reducing bacteria (SRB). This paper presents two computational models, a reactive transport model (RTM) and a simplified semi-analytical model (SM), to evaluate the potential of SRB to generate elevated sulphide concentrations, to assess sulphide fluxes to the canister and, in a simplified manner, the resulting canister corrosion.Calculations performed in the context of the repository's safety assessment based on a shared conceptual model reveal that the two computational models are complementary. The reactive transport model incorporates state-of-the-art understanding of the system's geochemistry, but is currently too computationally demanding to be applied in probabilistic safety assessment sensitivity analyses. The simplified model is fast and efficient, but some of its assumptions need to be verified, and some parameter values need to be calibrated using the more complete reactive transport model. Nonetheless, given the same set of assumptions, the two models predict comparable magnitudes of sulphide fluxes to the canister and comparable canister corrosion depths.