Long-term performance of materials used for high-level waste packaging. Annual report, year four, April 1985-March 1986. Volume 4

As part of the information needed by the Nuclear Regulatory Commission to assess the Department of Energy's application to construct geologic repositories for high-level radioactive waste, Battelle's Columbus Division is investigating the long-term performance of materials used for high-level waste packages. Waste form studies have been directed toward investigating spent fuel leaching/dissolution behavior. The experimental validation of a glass dissolution/reprecipitation model has been concluded. Experiments are generating data on UO2 and spent-fuel leach rates in simulated anoxic groundwaters, and initial data indicate that only brine leachants contain any measurable levels of uranium. The influence of groundwater species on the susceptibility of cast steel to pitting corrosion and stress-corrosion cracking is being studied by electrochemical techniques. Potential cracking agents are being investigated by slow strain rate experiments. The pitting-corrosion model was further developed, taking into account cation dissolution at the pit base and chemically active pit walls. Groundwater-radiolysis modeling has continued, with the description being extended to include additional species. Spent-fuel specimens are being used in integral tests with flowing simulated groundwater to study the role of cladding in radionuclide release and to identify possible combined-effects processes. This report documents investigations performed during the period April 1985 through March 1986