The Fate of Se(VI) in Microbially-Active Systems Relevant to Disposal of High-Level Radioactive Waste

Selenium-79, a fission product in higher-activity radioactive wastes destined for deep geological disposal facilities (GDF), can be highly mobile in the environment in its oxic forms, Se(IV) and Se(VI). Three-month batch microcosm experiments containing Wyoming MX80 bentonite (a candidate GDF backfill material), with or without steel coupons (representative canister materials) and with lactate as an electron donor demonstrated biogeochemically mediated Se(VI)(aq) removal. The reduction of Se(VI)(aq) to poorly soluble Se(0)/(-II) by indigenous bentonite microbial communities under GDF representative conditions presents a positive prospect for the biobarrier system enhancing long term Se mobility in a GDF.