Hydrogen (H₂) generation from the corrosion of steel in low- and intermediate-level radioactive waste containers poses a significant safety concern for geological repositories. The resulting gas pressure buildup can compromise the integrity of the host rock, which serves as the ultimate barrier to radio-nuclide migration. The Swiss repository, located in the Opalinus Clay formation, is designed to incorporate an engineered gas transport system that directs the gas generated in disposal rooms towards backfilled operational tunnels. By increasing the available gas volume, this system mechanically reduces pressure. In addition, microbial H₂ consumption has been demonstrated in Opalinus Clay formation water when sufficient pore space is available, such as in the excavation damaged zone, and in sand–bentonite mixtures (bentonite MX80, 80/20 w), which is a candidate backfill material for operational tunnels. Sand–bentonite exhibits favorable properties, including high water retention and gas permeability; however, the high cost of MX80 bentonite will likely limit its use to critical components, such as the seals of disposal rooms and high-level waste near-field backfill. Crushed Opalinus Clay has therefore been proposed as a more cost-effective alternative backfill material for less sensitive areas such as operational tunnels. In this study, we (a) investigate whether hydrogenotrophic microbial communities can establish in crushed Opalinus Clay backfill, (b) characterize their associated metabolic activities, and (c) assess whether microbial processes can contribute to reducing gas pressure.
Rolland et al. (Thu,) studied this question.