Bentonite sterilization methods in relation to geological disposal of radioactive waste: comparative efficiency of dry heat and gamma radiation.

This article evaluates the effectiveness of two sterilization methods—dry heat and gamma irradiation—on microorganisms in bentonite clay, which is used as a buffer material around metal canisters in deep geological repositories (DGR) for long-lived radioactive waste. The study found that dry heat sterilization at 121°C for 4 hours, even after nine cycles, failed to eliminate heat-resistant spore-forming bacteria in dry bentonite powder but was effective after four cycles in bentonite suspensions. In contrast, gamma irradiation at doses of 30 kGy or higher effectively sterilized bentonite powder, eliminating microbial survivability without significant alteration of bentonite properties at tested doses. These findings underscore gamma irradiation as a preferable method for preparing sterile bentonite controls in experiments assessing microbial impacts on nuclear waste repositories, while also noting the need for further research on potential physicochemical changes induced by irradiation.