Academic Articles | |||||
Regular Paper | Vol.8 No.2 (2016) p.32 - p.42 | ||||
Development of Resilience Evaluation Method for |
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Masayuki KAMAYA1 , and Takao NAKAMURA2 | |||||
1Institute of Nuclear Safety System, Inc., 64 Sata, Mihama-cho, Fukui 919-1205, Japan 2Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan |
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Abstract | |||||
Resilience index is proposed to be applied to evaluate the capability to recover safety performance of systems under severe accident of nuclear power plant. 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. NPP components consist of dynamic and static components, and this model focused on static components. Crack initiation due to fatigue damage was assumed and its depth was determined by 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. The fracture strength of the cracked component was calculated according to the fitness-for-service code, which took into account scatter in the flow stress. The developed 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, and that it was about 8.7 ´ 10-4 when the applied stress was equivalent to the maximum allowable stress for the component design. 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. | |||||
Keywords | |||||
failure probability, low-cycle fatigue, seismic load, crack growth, aftershock, residual heat removal system | |||||
Full Paper: PDF
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