The overpack which is a disposal package for high-level radioactive waste has been required containment of radionuclides to prevent contact between groundwater and vitrified waste for a specified period. The method for ensuring long-term integrity of the over pack was considered on the condition that it corrodes as predicted. The structural integrity is ensured by strength design and flaw evaluation taking the effect of material deterioration into consideration. The material deterioration event that affects structural integrity is thought embrittlement due to exposure to radiation and absorption of hydrogen. The structural integrity of the overpack is ensured by confirmation that flaw size detected using non-destructive inspection is less than allowable flaw size calculated by fracture mechanics. The research and development issues are prediction method of embrittlement, and reduction of flaw size measurement error using ultrasonic testing in the future.
