Comparison of PRO-LOCA 2009 and WinPRAISE 2007 for estimating rupture probability of dissimilar metal weld susceptible to PWSCC

This paper presents a preliminary study using probabilistic fracture mechanics codes (PRO-LOCA 2009 and WinPRAISE 2007) to estimate the rupture probability of Dissimilar Metal Weld (DMW) in CANDU® small diameter feeder piping subject to potential Primary Water Stress Corrosion Cracking (PWSCC). In spite of the significant differences in the deterministic fracture mechanics models and algorithms used for speeding up Monte Carlo calculations, both PFM codes consistently conclude the following observations: The rupture probability of a single DMW under normal operating conditions is extremely small. Timely response to leakage can substantially reduce the rupture probability. In-service inspection (every three years) has insignificant effect on the rupture probability. Residual stress (231 MPa vs 400 MPa) has insignificant effect on the rupture probability. The leak probability is several orders of magnitude larger than the rupture probability. The mode of failure of DMW is leak-before-break. (author)