Effects of Colloids and Microorganisms on Radionuclide Migration in Fractured Rock

Kurosawa, Susumi; Yui, Mikazu; Yoshikawa, Hideki

On the geological disposal of high-level radioactive waste (HLW), it is known that the actinide ion which is released from the HLW generates true-colloids with hydrolysis reaction, and forms pseudo- colloids by sorption reaction onto the colloids in the groundwater. Recently, it is reported that the radionuclide migration in groundwater is enhanced by transport behavior of colloids compared with the migration behavior of the solute. For example, the in-situ experiment on the colloids and radionuclide retardation (CRR experiment) in the Grimsel test site in Switzerland had been performed by the collaboration among NAGRA (Switzerland), ENRESA (Spain), ANDRA (France), FZK-INE (Germany), USDoE/SNL (U.S.A) and JNC (Japan), the possibility of the radionuclide migration enhancement by the influence of the colloids was indicated. We will present the modeling results by numerical code COLFRAC which describes colloid-facilitated solute transport in fractured media. Moreover, in order to evaluate the impact of microorganisms on the performance assessment for geological disposal of HLW, we simulated effects of microorganism as a colloid on radionuclide migration by using the COLFRAC code.