Camille Rolland, 1st Prize for the Best poster Award

In Switzerland, radioactive waste will be disposed of several hundred meters below ground in a stable geological layer. A major challenge is the risk of pressure build-up due to hydrogen gas production resulting from the anoxic corrosion of steel waste-containing canisters. Gas-porous sand-bentonite will be used as a backfill material to enable the transport of gas out of the disposal caverns. Sand-bentonite also offers an appropriate pore space for an active hydrogenotrophic microbial community to thrive. We need to answer three questions: (1) Can hydrogenotrophic microorganisms adapt to backfill material where water availability is limited? (2) How fast do they consume hydrogen? (3) Is this effective for total pressure reduction? We designed hydrogen-tight reactors to mimic the expected repository conditions. By monitoring the total pressure and gas composition for 3 months, we quantified hydrogen consumption and the resulting total pressure decrease. Gas-phase analysis indicates the activity of methanogens and sulfate-reducing bacteria. This study provides an accurate rate of hydrogen consumption in a porous repository backfill, which can be used to model the evolution of pressure in the repository.