Radiation Effects on Sorption and Mobilization of Radionuclides during Transport through Geosphere

Abstract

Site restoration activities at DOE facilities and the permanent disposal of nuclear waste generated at DOE facilities involve working with and within various types and levels of radiation fields. Radionuclide decay and the associated radiation fields lead to physical and chemical changes that can degrade or enhance material properties. The principal sources of radiation at the DOE sites are the actinides and fission-products contained in high-level wastes currently in storage. Alpha-decay of the actinide elements and beta-decay of the fission products lead to atomic scale changes in the material (radiation damage and transmutation). During site restoration, materials will be exposed to radiation fields that exceed 104 rad/hr. The radiation exposure due to the release and sorption of long-lived actinides (e.g., 237Np) and fission products (e.g., 137Cs and 90Sr) may cause changes in important properties (e.g., cation exchange capacity) in geological materials (e.g., clays and zeolites) along transport pathways. Among these materials, clays and zeolites, which are expected to sorb and immobilize radionuclides, are known to be extremely susceptible to radiation-induced structure changes (e.g., bubble formation and solid state amorphization) through both collisional displacement and ionization processes. These changes will inevitably affect (either negatively or positively) the further sorption and themore » migration of radionuclides at waste sites (e.g., vadose zone at Hanford). Current models used for the longterm prediction of radionuclide transport have proven to be inadequate and unrealistic; however, these previous models did not take radiation effects into consideration.« less