Experimental determination of distribution behavior of radionuclides in the presence of colloidal substance

Kuno, Yoshio; Morooka, Koichi*; Sasamoto, Hiroshi   ; Yui, Mikazu

In the performance assessment of the geological disposal of radioactive wastes, the retardation of radionuclide migration is generally evaluated by using sorption distribution coefficient (Kd). The Kd values would, however, be influenced by the presence of colloidal substance in aqueous phase because these colloids may have the potential abilities to sorb the radionuclides. In this study, Cs-137, bentonite colloids and quartz sands were used for the batch-type sorption tests in order to investigate the influence of colloids on the sorption behavior of radionuclides. The Kds of Cs-137 onto quartz sands (Kd) and bentonite colloids (Kd) were determined from the distributed amounts in solid phase, colloidal phase and aqueous phase, which were distinguished by the pore size of filters used for the separation of experimental solutions. Distribution behavior of radionuclides in the coexistence of quartz sands and bentonite colloids was able to be evaluated from the Kd and Kd those were obtained from other sorption tests carried out in the separate presence of sands and colloids. To select a suitable filtration method for the separation of the colloidal solutions enables to estimate the influence of colloids on the sorption behavior of radionuclides to solid phase.