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概要

The resilience index has been proposed to evaluate the capability for recovering safety performance of systems subjected severe accident for nuclear power plants. In this study, a failure probability assessment model was developed for the resilience evaluation of static components in nuclear power plants. This model took into consideration the effect of material degradation caused by low-cycle fatigue. Crack initiation due to fatigue damage was assumed and its depth was determined from the magnitude of fatigue damage. Then, crack growth was predicted for seismic loads consisting of a main quake and aftershocks. Finally, the failure probability was calculated for the seismic load of various magnitudes. The model was successfully applied to a pipe of the residual heat removal system of a pressurized water reactor power plant. It was shown that the failure probability was hardly affected by the degree of fatigue damage. Although the crack depth had little influence on the fracture strength of the cracked pipe, an increase in the number of aftershocks could increase the probability of leakage.

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