Characteristics of metal waste forms containing technetium and uranium

Multi-phase alloy waste forms are being developed to immobilize radioactive waste streams generated during the reprocessing of used nuclear fuels. The waste forms are formulated to ensure that all waste elements become sequestered within a small number of durable metallic phases. The flexibility of those phases to accommodate a range of waste stream compositions will benefit assessments of long-term waste form performance and tracking production consistency. Several prototype alloys suitable for a wide range of waste stream compositions are being evaluated to support development of a waste form degradation model that can be used to calculate radionuclide source terms for a range of waste form compositions and disposal environments. Tests and analyses to support formulation of waste forms and development of the degradation model include detailed characterizations of the constituent phases using SEM/EDS and TEM, electrochemical tests to quantify the oxidation behavior and kinetics of the individual and coupled phases under a wide range of environmental conditions, and corrosion tests to measure the gross release kinetics of radionuclides under aggressive test conditions. Initial experimental results for two prototype waste forms are discussed.