Interaction of Pu, Np and Pa with anaerobic microorganisms at geologic repositories

摘要

While considering the geological disposal of radioactive wastes, the behavior of radionuclides such as plutonium was investigated in the presence of bacteria with bentonite which was used as a backfill to simulate conditions at geologic repositories. The interaction between radionuclides and bacteria was evaluated using the solid/liquid distribution coefficient (K_d) with bacteria and/or bentonite as the solid phase and radionuclides in the aqueous phase. The radionuclides were added with the liquid phase. Two types of anaerobic bacteria were used. The first type, non-sterilized active anaerobic bacteria, originally used for the treatment of pulp and paper wastewater, accumulated considerable amounts of plutonium at a neutral pH. This neutral pH condition was more suitable for the accumulation of plutonium when compared with acidic or alkaline conditions. When the anaerobic bacteria were sterilized, the K_d values for neutral pH decreased to nearly those for acidic and alkaline pH. The K_d values for neptunium and protactinium were compared with plutonium. Adsorption of neptunium was very little influenced by sterilization, whereas protactinium behaved like plutonium. The second type, Desulfovibrio desulfuricans, showed a markedly different behavior from the mixed anaerobic bacteria. This was due to differences in the bacteria themselves and to the chemical environment such as E_h.