Progress of the long-term safety assessment of a reference disposal system for high level wastes in Korea

KAERI developed a reference repository system for the disposal of radioactive wastes resulting from the pyroprocessing of PWR spent nuclear fuels (A-KRS; Advanced Korean Reference Disposal System). To check the design feasibility of this system, we developed a total system performance assessment (TSPA) tool using Goldsim program (GoldSim, 2006) and assessed the exposure dose rates for the reference scenario and three alternative scenarios such as earthquake, well intrusion, and initial defect of waste packages by using this tool. And then, we compared the exposure dose rates for each scenario with a draft supplementary safety goal, 10 mSv/yr, which was suggested by the regulatory body in Korea. In the original TSPA tool, we use a single source term model by assigning the same reference radionuclide inventory data for each waste package and the same shortest distance from the waste package to the MWCF (Major Waster Conducting Features) for conservatism. We developed a multi-lattice source term model by assigning various radionuclide inventory data and various distance from the waste package to the MWCF for more realistic safety assessment. Then, we found that the exposure dose rates for the case of multi-lattice source term model was one order of magnitude lower than those for the case of single source term model. According to the draft safety guideline, the primary safety goal is expressed in risk, that is, the total annual risk for the representative person resulting from the radiation exposure should not exceed 1.0 × 10−6/yr. Therefore, we developed a methodology for complex scenarios to perform the risk-based safety assessment of a HLW repository, and applied it to a reference repository system. And we found that the suggested methodology can be used to perform the risk-based long-term safety assessment of a radioactive waste repository. We can make various risk profiles by making various kinds of complex scenarios with this methodology, and they can be used to support the development of safety cases for acquiring public acceptance.