Geochemical studies with abyssal Red clays

Pertinent geochemical phenomena required to assess the feasibility of emplacing high-level radioactive waste in subseabed formations are being identified and experimentally investigated. The geologic formation selected for study is the abyssal red clay. Investigations of phenomena occurring in the sediment beyond the hydrothermal environment associated with the waste have focused on sorption equilibria, solution chemistry of the actinides, and radionuclide diffusion experiments. Most data from the diffusion experiments are consistent with the experimentally observed sorption equilibria. Studies of processes occurring in the hydrothermal environment near the canister have addressed heat-induced sediment-seawater interactions and their effects on canister, waste form, and radionuclide source term. Significant changes in oxidation potential and pH have been found in the hydrothermal environment and are related to variations in temperature and mineralogy. Studies of processes occurring near the sediment-seawater interface have emphasized the establishment of a data base for evaluating the geochemical, biological, and fluid-mechanical mechanisms determining radionuclide fluxes across that interface.