We have developed a probabilistic fracture mechanics (PFM) analysis code PASCAL4 for evaluating failure frequency of reactor pressure vessels (RPVs) considering neutron irradiation embrittlement and pressurized thermal shock events. It is well-known that flaw distributions such as flaw size and density have an important role in failure frequency calculation by PFM analysis. NUREG-2163 provides a methodology to obtain more realistic flaw distributions based on Bayesian update reflecting non-destructive examination (NDE) results, which is applicable for the case when there are flaw indications through NDE. However, there may be no flaw indication as the inspection results of some RPVs. Therefore, we proposed likelihood functions to be applicable for both case when flaws are detected and when there is no flaw indication as the NDE results. In these Bayesian update methods, likelihood functions are applied to independently obtain posterior distributions of flaw depth and density using the same NDE results. In this study, we further improve the likelihood functions to enable them to update flaw depth and density simultaneously. Based on the improved likelihood function, several application examples are presented in which flaw distributions were estimated by reflecting NDE results through Bayesian update and PFM analysis. The results indicate that the improved likelihood functions are useful for estimating flaw distributions.


Improved Bayesian Update Method on Flaw Distributions Reflecting Non-Destructive Examination Result

Division / Sponsors: 
Pressure Vessels & Piping (PVP)


Paper Proceedings: https://asmedigitalcollection.asme.org/PVP/PVP2020/volume/83815

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