Pressurized Thermal Shock Analysis with Uncertainty Propagation for the APAL Project Using TRACE and FAVOR

Pressurized thermal shock following a loss-of-coolant accidental scenario has been recognized as a safety concern for the integrity of the reactor pressure vessel since the 1980s. In the context of the recent APAL (Advanced PTS Analysis for LTO) European project, the safety analysis, including coupled thermal hydraulics (TH) and fracture mechanics analyses, has been upgraded to include uncertainty quantification. This paper presents the results obtained by the Paul Scherrer Institute in which the TRACE and FAVOR codes were used. TH uncertainties were estimated and propagated in one-dimensional fracture mechanics models to yield a 95%/95% lower tolerance bound for the maximum allowable adjusted reference temperature. The results are compared for several scenarios (fracture type, fracture criteria, with and without residual stresses) with a conservative base case and a best-estimate case. A sensitivity analysis finally helped determine the most relevant TH uncertain parameters.