Safety assessment of geological disposal for HLW in Japan

The paper explains geological environment in Japan, design of disposal, general methodology for safety assessment, classification and treatment of scenarios, nuclide transport pathway considered in the reference case, nuclide migration processes in the EBS, components and geometry of the EBS, the one-dimensional parallel-plate model and key parameters relevant to these processes, one-dimensional multi-pathway model, model chain used in the H12 safety assessment and associated databases, reference case dose evolution, the maximum dose for various transport distances (40,000 waste packages). The maximum dose of 40,000 waste package is 0.005 μ Sv/y after 800,000 year. The natural barrier performance increased with the base rock a few ten meters distance from the waste disposal. Results of total system performance analysis showed the maximum dose is lower than the protection level (100 to 300 μSv) proposed by many countries. (S.Y.)