An estimation of microorganisms impacts on geological disposal system for TRU waste

Some of TRU waste will be disposal in underground of several hundred meters depth. The environment condition of such deep underground is considered to be anaerobic. It is also thought that the high alkaline environment of exceeding pH 12.5 is considered to be maintained for long period of time in the repository for TRU waste because of the use of cementitious material. It was believed that the microorganisms cannot be active in such of anaerobic high alkaline environment mentioned above. However, the recent researches have suggested the possibility of the activities of microorganisms in the previous environment. The microorganisms are not always considered to be active in the geological disposal facilities for TRU waste. The microorganisms become active in both the place and period in which the preferable environmental conditions for the microorganisms are formed. Therefore, the microorganisms which are possible to be active in the repository for TRU waste were extracted. In addition, the impacts of microbial activities on geological disposal system for TRU waste were estimated with considering the metabolism system of the extracted microorganisms. The analysis results suggested followings. Negative impacts of microbial activities on the safety of geological disposal system for TRU waste through the processes of pH evolution, redox reaction, alteration of both cementitious material and bentonite buffer, metal corrosion, clogging of pore space by biofilm were estimated to be negligible. On the other hand, the impacts of complex formation between the metabolic products and radioactive nuclides, the colloid formation (including the colloidal behavior of microbes) and gas production (including the evolution of radioactive gas) were identified as the subjects of future works because of the lack of information. (author)