Comparative study of probabilistic fracture mechanics codes

Probabilistic fracture mechanics(PFM) analysis is an integral part of the plant specific PTS analysis required by PTS rule and regulatory guide. The purpose of the PFM analysis is to quantify the conditional vessel failure probability at the event of PTS transients. Though several PFM codes are available for this purpose, differences in analytical methods of the codes could have significant effect on calculated vessel failure probability. To understand the code dependency of the analysis, the details of the analytical methods of the code and the results were compared. From the comparative study, it was found that VISA-II code estimated greater failure probability, especially for circumferential cracks. The differences in treating thermal hydraulic boundary conditions as well as in treating the effects of cladding were thought to be in part responsible for conservatism in VISA-II