A Study of the Radionuclide Diffusion in Clay Materials Taking into Account the Coupled Physicochemical Processes

The diffusion of manmade radionuclides in pore solutions of compacted clay materials is accompanied not only by the sorption retention on the surface of clay minerals, which is typical for many radionuclides, but also by other physicochemical processes occurring simultaneously. These processes, termed coupled, are associated mainly with the precipitation–dissolution of radionuclide compounds in pore solutions, as well as with the sorption–desorption of radionuclide particles on the surface of solid phases as a result of their diffusion transfer in the pore medium together with chemically contrasting components of leachates of technogenic materials used in the radioactive waste disposal. Without taking into account the coupled processes, it is impossible to correctly interpret the experimental results, as well as to reliably predict the migration of manmade radionuclides and justify the safety of radioactive waste disposal facilities.