高レベル放射性廃棄物地層処分における処分容器材料の腐食寿命評価の現状と課題

抄録

Overpack is a metallic container, which is one of the components of the engineered barrier system. It is expected to prevent the high level radioactive waste from contact with groundwater for 1000 years and this function will be lost by corrosion. Carbon steel, copper and titanium are chosen as the candidate materials in Japan. This paper presents the current status and future studies for long-term lifetime prediction of overpack materials. It was shown that the corrosion type of carbon steel in contact with bentonite would be general corrosion. The corrosion depth of carbon steel for 1000 years was estimated to be about 32mm by considering the contribution of oxygen and water reduction. For titanium, critical conditions of the initiation of crevice corrosion have been evaluated by repassivation method and localized corrosion can be avoided by selecting appropriate alloys that are compatible with environmental conditions of the actual repository site. The corrosion and hydrogen absorption of titanium under reducing condition have been studied and shortterm corrosion test data have just been obtained. The corrosion depth of copper was estimated on the basis of current understanding taking into account of corrosion due to oxygen and sulfide.