Application of probabilistic fracture mechanics to seismic fragility analysis of piping systems

配管系の地震フラジリティ評価における確率論的破壊力学解析の活用

東 喜三郎*; 山口 義仁 ; 勝山 仁哉  ; Li, Y. 

Azuma, Kisaburo*; Yamaguchi, Yoshihito; Katsuyama, Jinya; Li, Y.

本研究では、確率論的破壊力学解析コードPASCAL-SPを用いて、SCCや疲労等の経年事象を考慮して、長期に供用される炭素鋼及びオーステナイトステンレス鋼配管のフラジリティ評価手法を示し、代表的な解析条件及び代表的事例を検討した。

Lessons learned from the TEPCO Fukushima Daiichi accident indicate the importance of risk assessment for extreme external events. Seismic probabilistic risk assessments (SPRAs) are the standard methods to quantify the seismic risk of operating nuclear power plants. One of the major factors that affect the results of SPRAs is the quality of the seismic fragility analysis. Seismic fragilities represent the failure probabilities of components under earthquakes and the associated uncertainties. However, seismic fragility data of aging pipes are not readily available due to the complex behavior under seismic loading. For example, stress corrosion cracking (SCC) is one of the main material degradation phenomena of aging pipes. There is a possibility that extreme seismic loading on aging pipes may cause the propagation of cracks originally initiated by SCC. It is unclear how these crack propagations can affect the seismic fragility of the piping system. In this study, failure probabilities of carbon steel pipes and austenitic stainless steel pipes were evaluated using a probabilistic fracture mechanics code, PASCAL-SP. SCC and fatigue crack growth were considered as age-related degradations of the pipes. Comparing the failure probabilities for brand new pipes and those for aging pipes, we discussed the effects of crack growth on seismic fragilities.