On disposal of radioactive wastes

Safety assessment is necessary to estimate the risk imposed to the public by the radioactive waste repository. A model of radionuclide migration in the rock-groundwater system is one of the most important subsystem models for the assessment of underground disposal of high-level radioactive wastes. A number of study has been conducted in soil science, agricultural science and environmental science, concerning the behavior of trace elements in the porous media, especially in soil. In the present study, the methodology of these sciences are applied to elucidate the behavior of radionuclides in the rock-groundwater systems. Diffusion of radionuclides in the micropore of rock matrices was examined and was shown to be representable either by a Fickian diffusion model or under certain constraints by a simple first-order kinetic model. The performance of a geological layer as a natural barrier to retard migration of the radionuclides leached from the underground repository was assessed by applying the simple kinetic model. The mechanisms of radionuclide sorption in rocks were also examined. (author)