Impacts of thermo-hydro-mechanical experiments on the microbial activity in compacted bentonite at the Kamaishi Mine, Northeast Japan

The coupled thermo-hydro-mechanical (T-H-M) experiments named “engineered barrier experiments” were carried out to examine the in situ performance of buffer material. At the end of the heating and cooling phases, bentonite samples were taken for microbial analysis to determine if the naturally present microbial population in the buffer material survived the conditions (i.e. compaction, heat and desiccation) in a simulated vault environment. Heterotrophic aerobic bacteria were enumerated by the pour plate method using R2A media. The results confirmed the existence of heterotrophs, which disappeared in bentonite samples with low water content (< 12%). These results suggest that microbial activity is severely limited near waste container in the vault for some time after disposal, due to desiccation as a result of the heat output of the waste container. Such knowledge will be useful in assessing the potential effects of microbial activity on deep geological disposal of high level radioactive waste.