Abstract
Pressurized thermal shock (PTS) may cause a quick, catastrophic cleavage fracture in a reactor pressure vessel (RPV) of a pressurized water reactor (PWR). Low temperatures, thermal strains, and radiation embrittlement can all combine to create dangerous situations for structures, specifically thick-walled reactor pressure containers with fractures and welds as weak areas. A thorough picture of the temperature and stress intensity is required to determine the likelihood of the onset and spread of a cleavage crack. The ductile to brittle transition temperature affects the critical stress intensity for brittle cleavage fracture. This complicated combination of loads, absolute temperatures, and temperature gradients is combined with radiation damage to evaluate the likelihood that cleavage fracture will occur. In earlier works, simulations were carried out using combined computational fluid dynamics (CFD) and finite element method (FEM) simulations to get the most realistic picture of this issue. However, due to the complexity of the problem, the thermal mixing of the fluid and its effects on the RPV wall are simulated by models that are simplified in terms of geometric complexity and physics. This study investigates the effect of the interaction between multiple emergency core cooling (ECC) plumes on the thermal response of the RPV wall by considering a full (360 degree) RPV geometry with two loops for the ECC fluid injection. We first perform a transient conjugate heat transfer CFD simulation to compute the spatial and temporal evolutions of RPV wall temperature. The unsteady Reynolds-averaged Navier-Stokes equations are solved on the fluid side, and the unsteady heat transfer equation is solved on the solid side.
Next, a static structural analysis using FEM is conducted using the temperature profile obtained from CFD analysis on a one-loop reactor as input. The goal of the FEM analysis is to investigate the link between the depth, length, and ratio of the crack and the probability of failure. A probabilistic approach is used to evaluate the possibility of failure. The ultimate goal of these studies is the generation of a code that can implement hydraulic models that replace the time and resource-demanding CFD and FEM analysis.