Geochemical studies supporting the US subseabed disposal program

The important chemical phenomena associated with emplacing high-level radioactive waste in subseabed geologic formations are being identified and experimentally investigated. Studies of processes occuring in the hydrothermal environment near the canister have focused on sediment-seawater interactions at elevated temperatures and pressures and the resulting potential effects on canister, wasteform, and radionuclide source term. Significant changes in oxidation potential and pH have been related to variations in temperature and mineralogy. Investigation of phenomena occurring in the sediment outside of the hydrothermal environment have focused on actinide solution chemistry, sorption phenomena, and radionuclide diffusion rates. Data for several radionuclides and sediment types are being used to compare predicted and experimental results from diffusion experiments. Studies of processes occurring near the sediment-seawater interface have emphasized establishing a data base for evaluating the geochemical, physical, biological, and fluid-mechanical mechanisms determining radionuclide fluxes across the interface