Experimental and Numerical Studies on Colloid-Enhanced Radionuclide Transport; The Effect of Kinetic Radionuclide Sorption onto Colloidal Particles

Kurosawa, Susumi; Ibaraki, Motomu*; Yui, Mikazu; Ueta, Shinzo*; Yoshikawa, Hideki

We conducted a series of laboratory experiments to investigate the effects of radionuclide sorption onto colloids and the surfaces of rock fractures. We focused on overall effects related to the kinetic behavior of those sorption processes. A mixed solution of cesium and clay colloids was injected into an artificially-created single fracture in a granite column. Numerical simulations were conducted to analyze the experiment results using a numerical code COLFRAC which can simulate colloid-facilitated solute transport in discretely-fractured porous media. A series of experimental and numerical analyses show that migration of cesium is facilitated by mobile colloidal particles which can sorb cesium and migrate in the fracture. The analyses also demonstrate that cesium migration is significantly enhanced if desorption of cesium from the colloids is a slow kinetic process and illustrate the importance of evaluating the parameters which describe such kinetic processes. Furthermore, radionuclide transport is likely to be retarded if mobile colloidal particles which sorb radionuclides are vigorously filtered on the fracture surfaces.