Authors previously reported that magnetic data obtained by using Eddy current method and AC magnetization method showed correlation with the increase of susceptibility of the irradiation assisted stress corrosion cracking (IASCC) on neutron irradiated austenitic stainless alloy specimens. To discuss the mechanism of the correlation, microstructure observation was conducted on the irradiated specimen, and magnetic permalloy phase (FeNi₃) formation along grain boundary was revealed in this work. From this result, the radiation induced magnetic phase formation along grain boundary seems to be a factor of the magnetic property change of the irradiated materials, and related to the correlation between magnetic data and IASCC susceptibility. In addition, sensor probe development was conducted in this work to obtain higher sensitivity and resolution. It was applied for magnetic measurement on type304 stainless steel irradiated up to different doses. In this case, magnetic ferrite phase was existed in the type304 stainless steel sample before irradiation therefore it was concerned that magnetic measurement on the irradiated ones would be disturbed by the magnetic signal from the pre-existing ferrite phase. In the magnetic measurements, increase of the magnetic data was clearly seen on the irradiated specimens. Thus, it was thought that the developed magnetic measurement technics can be applied for the irradiated austenite stainless steels which contain certain quantity of ferrite phase before irradiation.

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We re-evaluated the tsunami at Onagawa Nuclear Power Plant based on the latest scientific knowledge obtained from the 3.11 earthquake with both deterministic and probabilistic methods. As a result, we recognized that the maximum tsunami run-up height could be 23.1m above sea level with an annual excess probability of approx. 10-4. To keep the site ground away from tsunami effect and to secure enough safety margins for the defense in depth in case of emergency, we decided to raise the tsunami-wall up to 29m above the sea level and to deploy varied mobile equipment. The main structure of the 29m-high tsunami-wall is a steel pipe-type vertical wall (L=680m), and a cement improved soil embankment (L=120m).

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