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

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. (C) 2016 Elsevier B.V. All rights reserved.