Starting from the pioneering work of Beremin, the classical Beremin-Weibull fracture probability’s model was extended recently to tackle with non-monotonic thermomechanical loadings. As a result of temperature effect on mechanical fields’ heterogeneity, an apparent temperature dependence of tile cleavage stress was also introduced to fit correctly the fragile to ductile transition. Considering the classical expression of the fracture probability, this extension consists in substituting the instantaneous opening stress by the maximum of the instantaneous opening stress versus cleavage stress ratio, this maximum being searched for previous active plastic time. This extended Beremin model was successfully applied to WPS tests experienced on low alloy ferritic steel compact tension specimens. Through this work, we aim at applying this approach to assess RPV structural integrity, assumed to be affected by a subclad flaw, during a simulated PTS event. The pressurized vessel is submitted to a thermal transient applied on the inner cladded surface. Considering a circumferential flaw, a two-dimensional elastic-plastic Finite Element calculation is performed. Therefore, the time evolution of elastic-plastic stress intensity factor KJ at the crack tip in base metal is calculated. Then, the time evolution of the cumulative fracture probability, as predicted by the extended Beremin model, is derived to evaluate the vessel integrity.

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