Proposal of performance-based fragility concept incorporating failure consequence and application to seismic fragility of piping systems

Abstract

After the Great East Japan earthquake, measures for beyond design basis events have become more important. For a component, mitigation of an influence of a failure on its safety performance is required in addition to prevention of the failure. These kinds of measures are reduced the risk of safety performance defined as multiplication of failure frequency and failure consequence regarding impact on safety performance. One of safety analyses regarding such measures is fragility analysis. However, the existing fragility is represented using failure probability, and does not take into account the failure consequence. In this paper, for the purpose of more rational fragility analysis, we propose a new concept of performance-based fragility incorporating failure consequence, which represents the risk of safety performance degradation. In addition, to present the effectiveness, the proposed fragility is quantified by applying to a piping system subjected to excessive earthquakes which is a key issue of beyond design basis event. A piping system subjected to excessive earthquake can fail by ratchet, fatigue, collapse, and break. These failure modes have different occurrence conditions and lead to different consequences about core cooling performance. After the analyses on occurrence probability and failure consequence on each failure modes, the proposed fragility is calculated as the multiplication of them.

Keywords

• fragility
• performance-based concept
• failure mode
• beyond design basis event
• core cooling performance
• flow rate
• piping system
• earthquake