Integrity Evaluation of Boundary Function of Main Components in Nuclear Plants During Severe Accidents

Abstract

After the accident at the Fukushima Daiichi nuclear power plant, very strict safety measures were implemented for nuclear power plants in Japan. It thus becomes a crucial issue if the safety of a plant is maintained or not at beyond design basis events, that is, whether it is possible or not to keep radioactive materials inside the facility during severe accidents. In other words, it is crucial to determine whether the integrity of the boundary of the components that contain radioactive materials can be maintained under beyond design basis loading, such as during mega-earthquake and excessive temperature and/or pressure increase. In this study, head plates and bellows were examined as components that compose the parts of the boundary of vessels that contain the primary coolant of a prototype fast breeder reactor. The behaviors of buckling, post-buckling deformation, and penetration failure, that is, loss of boundary function of these components with increasing pressure were investigated. The series of this research program started in FY2013 and the research proceeded step by step. The new result in this paper is the application of the proposed criteria to head plates and bellows, and a conservative estimation of penetration failure of these components is obtained. We would like to summarize previous results before the final results to clarify the coherence and the relation of each result in the whole research.