HLW Long-term Management System Development. Development of confidence improvement technologies for disposal safety

The final goal of this study is to enhance the reliability of safety assessment of a HLW repository through the development of safety case based on KURT environment. We secured the bases for the risk-based safety assessment by making element analysis and developing the integrated analysis method for complex scenarios, making multiple source term analysis, and upgrading the existing safety assessment program. We built the foundation for enhancing the reliability of safety assessment of a HLW repository through safety case analysis of each stage of waste disposal, establishment of safety assessment framework, and making a safety case report. The impact analysis of temperature and metal ions on the radionuclide migration, the impact of corrosion products and gas in the boundary of waste package and buffer materials on the radionuclide migration, and the effects of microbes on the sorption behavior of uranium onto bentonite and granite were analyzed through experimental studies. We developed the TRLFS to develop methodologies for quantifying uranium contents in groundwater. By using TRLFS, we identified the chemical species of uranium in groundwater and analyzed the oxidation-reduction reaction of uranium in KURT groundwater. We also developed radionuclide transport model considering geochemical reaction and long-term geochemical reaction model of uranium in KURT groundwater. They can be used to support the development of safety case for the HLW repository. The results of this study are expected to contribute the reliability enhancement of safety assessment of a HLW repository through being used in the development of safety case.