CFD analysis of coolant flow in the nuclear reactor VVER440

Abstract

The paper introduces results of computational fluid dynamics (CFD) simulations of water flow at the reactor pressure vessel (RPV) outlet and under the RPV head. Several CFD calculations of the steady-state and dynamic processes involving forced and natural circulation of coolant are presented in the paper. In the steady-state regime, several calculations were performed for various number of the reactor coolant system (RCS) loops connected to the reactor and the results have been used to analyse the effect of the RCS configuration to the coolant flow at the reactor outlet and under the reactor vessel head. General flow patterns are described in the outlet part of the reactor and under the reactor vessel head and, also, the influence of a lower flow rate through the reactor on thermal homogeneity of coolant under the vessel head. Simultaneously, we discuss the influence of the coolant flow rate at the core outlet on the heat transfer from the under-head space. Unsteady calculation was also done for a reactor cool-down in the regime of natural circulation. The calculation conditions correspond with the data obtained from the experiments led in the frame of the cool-down process of VVER440 reactor at Mochovce nuclear power plant in 2003. In the calculations, the main attention was applied to establishing the basic trends in the cool-down of water content at the outlet part of the reactor and under the head of the reactor vessel.