Effect of colloids on radionuclide migration for performance assessment of HLW disposal in Japan

Abstract

Colloidal effect is one of the major factors to enhance the migration of radionuclides in groundwater. The experimental and theoretical studies of colloid mobility and colloid-facilitated radionuclide transport for the performance assessment of high-level radioactive waste (HLW) geological disposal is presented in this paper. The major aims of the study are (1) to study the filtration effect on colloids by the engineered barrier system, (2) to study bentonite colloid generation by erosion of the engineered barrier system, and (3) to calculate radionuclide migration with groundwater colloids through fractured rock systems. Alternative coagulants based on prehydrolyzed forms of aluminium or iron can be more effective than the traditional materials in many cases, but their mode of action is not completely understood, especially with regard to the role of charge neutralization and hydroxide precipitation. Basic principles of colloid stability and metal ion hydrolysis are briefly reviewed, and the action of hydrolyzing metal coagulants is then discussed, with some examples from recent experimental studies. Although it is possible to interpret results reasonably well in terms of established ideas, there are still some uncertainties that need to be resolved