Microbial sulphide-producing activity in water saturated Wyoming MX-80, Asha and Calcigel bentonites at wet densities from 1500 to 2000kgm−3

Abstract Highly compacted bentonite is projected to function as a buffer against outward transport of radionuclides and inward transport of corrosive groundwater components for copper canisters with spent nuclear fuel in future Scandinavian geological repositories. The dominant long-term copper corrosive species will be sulphide from dissimilatory reduction of sulphate to hydrogen sulphide by sulphate-reducing bacteria (SRB). The effects from varying wet densities of MX-80, Asha and Calcigel bentonites, doped with SRB, on cultivability and sulphide-production of SRB were investigated. The studied commercial bentonites were all infested with cultivable SRB. While cultivability of SRB clearly decreased with increasing wet density of MX-80 and Calcigel, it remained relatively constant for most tested wet densities applied to Asha. The sulphide-production results for the three clays indicated intervals between 1740 and 1880 kg m − 3 in wet densities within which sulphide-producing activity dropped from high to very low or below detection. This work demonstrated that a high density of bentonite buffers in future spent nuclear fuel repositories will significantly reduce the risk for sulphide production in the buffer and concomitant corrosion of copper canisters.