Impact of the hydrogenotrophic microbiome on iron and sulfur speciation in backfill material of a radioactive waste repositories

Hydrogen (H2) gas production leading to corrosion of steel canisters containing nuclear waste is one of the greatest concerns regarding the safety of future deep geological repositories. As a safety parameter, microbial H2 consumption is proposed to be an effective H2 sink in repository sand/bentonite backfill. H2 metabolism can be coupled, for instance, to sulfate reduction, producing hydrogen sulfide. Hydrogen sulfide is highly corrosive; therefore, the question becomes whether microbial activity resulting in sulfide production could negatively impact canister safety. Sulfide readily reacts with ferrous iron to produce iron-sulfide minerals. Understanding iron (Fe) and sulfur (S) cycling in backfill material is critical to predicting the mobility of dissolved hydrogen sulfide. We propose to use X-ray absorption to study S and Fe speciation in a backfill material, after incubation with native microorganisms and hydrogen.