An Estimation of microorganisms impacts on geological disposal system for TRU waste.

Kato, Takashi; Honda, Akira; Nakanishi, Hiroshi; Inagaki, Manabu; Tsukamoto, Masaki*

(1) The denitrifying bacteria, the sulfate restoration bacteria, the methanation bacteria and the organic substrate (the cement admixture, the cellulose and the asphalt, TBP) decomposing bacteria were extracted as the important microbes which can be active on the basis of both previous studies on the microbes in deep underground and coexisting substrate. (2) The total amount of calcium hydrate in the repository exceeded the equivalent amount of that for reacting the total Co generated from microbial decomposition of organic substrate and phosphate generated from the microbial decomposition of TBP. Therefore, the impacts of lowering pH by the metabolic products was not considered to be significant. Furthermore, impacts of alteration of both bentonite and cementitious materials and metal corrosion due to the drop of pH are not considered to be significant. (3) The N gas evolution rate due to the denitrifying reaction by microorganisms dominated the total gas evolution rate, if time dependent reduction of corrosion rate was employed. However, the H gas evolution rate in the case is similar to those of N gas due to the denitrifying reaction mentioned above, if time dependent reduction of corrosion rate was neglected. (4) The information of the impacts of the complex formation between nuclides and metabolic products of microbes, colloid formation (including the colloidal behavior of microbes) and CH formation due to microbial activities is limited. The impacts are also considered to depend on the site character. Therefore the limited availability of information and site dependency prevent us from assessing the previous impacts at present. The further accumulation of knowledge is necessary for the assessments.