The purpose of this study is to investigate environmental effects on low cycle fatigue crack growth of SUS316. Low cycle fatigue test and periodical observation on inner surface of a hollow specimen was conducted by developing new type of replica observation. The crack growth in PWR environment was measured and the investigation of environmental effects on crack initiation and propagation was conducted. Crack initiation rate of fatigue test in PWR environment is faster than in air condition. Crack propagation is accelerated apparently by the increase of coalescence of cracks. Consideration of crack initiation in earlier period of fatigue test, acceleration of crack growth rates in PWR environment and coalescence of cracks by short initiation time and high density of cracks are necessary to quantify environmental effects in addition to the acceleration of crack growth rates in PWR environment.

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We have developed a new index, called the resilience index, that evaluates the dynamic stability of the system safety of a nuclear power plant during a severe accident by considering the ability to recover system safety functions that have become lost in the situation. In this paper, a detailed evaluation procedure for the resilience index is described. The system safety of a PWR plant during a severe accident is then assessed according to the resilience index in order to discuss the applicability of the index. We find that the resilience index successfully represents management capability and, therefore, the resilience capability of a nuclear power plant.

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