Numerical simulation of temperature heterogeneity inside the AP1000 upper plenum and hot leg

The high-fidelity simulation for nuclear reactor has attracted more attentions recent years and it could provide much deeper understanding of the thermal hydraulic features in the reactor pressure vessel, promoting the reactor design optimization or operation guidelines making. The temperature heterogeneity in hot legs induces the deviation of reactor core power level estimation. In order to investigate the lateral flow at the reactor upper plenum and temperature heterogeneity in the hot legs of AP1000, a multi-scale coupling method was proposed with the computational fluid dynamics (CFD) and sub-channel analysis in this paper. The sub-channel analysis code, COBRA-EN, was used to calculate the coolant temperature distribution at core outlet and provide the accurate boundary conditions for CFD simulation. A detailed CFD analysis model from the core outlet to hot leg outlet was established. The main internal components including control guide tubes with eight large opening windows on it and support columns were kept, while other little components including control rod assemblies were omitted to decrease the total mesh quantity. Compared with the temperature field at core outlet, the maximum temperature difference at the entrance of the hot leg drops 10.0 K after the strongly mixing in the upper plenum. The hotter coolant from central fuel assemblies remains at the upper part of the hot leg, while the cooler coolant from peripheral fuel assemblies stays in the lower part of the hot leg. The temperature heterogeneity and its evolvement along the hot leg were analyzed. © 2020 Elsevier B.V.