Probabilistic fracture mechanics analysis of nuclear piping considering variation of seismic loading

摘要

In conventional probabilistic fracture mechanics (PFM) analyses, seismic loading is considered as a large deterministic value, although there exists the variation of the seismic load as well as response of building and components. On the other hand, such stochastic behaviours have already been taken into account in the field of seismic probabilistic safety assessment. This paper proposes a new PFM model for nuclear piping that takes into account the variation of seismic loading. The distribution in ground acceleration is modelled with the seismic hazard curve. The distribution in piping response during a seismic event is modelled with a log-normal distribution. Since the seismic load has large variation, when not adopting an upper limit to the distribution in seismic stress, the break probability calculated from the present PFM analysis becomes equal to the probability that the seismic stress exceeds the collapse stress of a sound pipe. This implies that the existence of a crack has no effect in these PFM analyses, and this result does not satisfy the purpose of PPM analysis to evaluate the failure probability per crack. Therefore, the seismic stress was limited to the collapse stress of a sound pipe in the present PPM analysis to evaluate the conditional break probability per crack.