Large thermal gradients on structural integrity of a reactor pressure vessel subjected to pressurized thermal shocks

ABSTRACT Pressurized-thermal-shocks (PTSs) are the most severe accidents that impact the structural integrity of a pressurized water reactor pressure vessel (RPV). In general, the one-dimensional thermal-hydraulic analysis results for PTS transients were often used as the loading conditions for structural integrity evaluation of RPV, but may cause over-conservative results. This paper investigates the effects of the cold plume, which is the non-uniform temperature distribution caused by colder water injected separately into the RPV, on the fracture probability of a three loop pressurized water reactor (PWR) vessel subjected to PTS events. The three-dimensional computational fluid dynamics (CFD) technique associated with probabilistic fracture mechanics (PFM) analysis were employed to comprehensively evaluate the structural integrity of RPV under hypothetical PTS accidents. Firstly the model of a PWR pressure vessel in Taiwan was constructed to simulate the thermal-hydraulic phenomena by CFD methodology. Based on the Best Practice Guidelines (BPGs) and ASME V&V guidance, the estimation of mesh uncertainty has been conducted. Then the detailed thermal-hydraulic boundary conditions corresponding to various RPV shell regions were regarded as the loading conditions for PFM analysis. Present results are compared with those which consider the simplified thermal hydraulic analysis system code’s results as boundary conditions.