Abstract
In this paper, several studies are described to compare the current SRP 3.6.3 deterministic leak-before-break (LBB) approach to a corresponding probabilistic approach using the NRC/EPRI developed Extremely Low Probability of Rupture software tool (xLPR) to establish a correlation between the approaches. These studies involve two generic nozzle/pipe sizes (large and medium diameters) with dissimilar metal (DM) butt welds susceptible to primary water stress corrosion cracking (PWSCC). First, deterministic fracture mechanics (DFM) analyses were performed consistent with the SRP 3.6.3 methodology. Then probabilistic fracture mechanics (PFM) evaluations with xLPR were performed assuming single circumferential through-wall flaws consistent with that used in the deterministic approach to establish a correlation. Furthermore, for simplicity, the evaluations were based on a single weld location rather than on a whole piping system.
On a preliminary basis, this correlation indicates that although the deterministic LBB approach may not meet the required SRP 3.6.3 margins in certain cases, a probabilistic LBB approach using xLPR may be used to show low probability of rupture meeting the proposed probabilistic acceptance criteria. However, there are several limitations in developing the correlation that have been identified and more studies are needed to address those limitations.
