Diffusion and Leaching of Selected Radionuclides (Iodine-129, Technetium-99, and Uranium) Through Category 3 Waste Encasement Concrete and Soil Fill Material

An assessment of the long-term performance of Category 3 waste-enclosing cement grouts requires data about the leachability and diffusion of radionuclide species, specifically iodine-129, technetium-99, and uranium, when these waste forms come into contact with groundwater. To achieve this, leachability data were collected through the conduction of dynamic and static leach tests on radionuclide-containing cement specimens. Additionally, the diffusivity of the radionuclides in both soil and concrete media was determined by executing soil-soil and concrete-soil half-cell experiments. The findings revealed that the effective diffusion coefficients for iodine-125 under dynamic leaching conditions ranged from 4 x 10-11 to 1 x 10-10 cm2/s, which are substantially higher—about an order of magnitude—than the values measured under static leaching conditions, which ranged from 3 x 10-12 to 7 x 10-11 cm2/s. For technetium-99, the effective diffusion coefficients under dynamic conditions were found to be between 2 x 10-9 and 8 x 10-9 cm2/s.