Primary loop study of a VVER-1000 reactor with special focus on coolant mixing

The intention of this work is to demonstrate the ability of modern computational fluid dynamics (CFD) tools like ANSYS CFX to model technical facilities with complex geometry such as a reactor pressure vessel with its primary loops over all relevant scales from a range of approximately 1 mm up to a largest dimension of about 50 m. For this purpose, a detailed model of a VVER1000 reactor pressure vessel (RPV) and an extended model with simplified primary loops (Loop model) are presented. The primary loop components like steam generators and pumps are modelled by the outer shapes and additional source terms for energy and momentum exchange. The RPV model part is tested without primary loops; results are compared with former results obtained with a coarser model. The improved model shows less sensitivity on the discretization scheme, and recalculated hot leg temperatures transients are improved. As an example case for the Loop model, the swirl of flow patterns at the core inlet derived from experimental data obtained at the Kozloduy Nuclear Power Plant (Unit 6) is simulated. As progress to the RPV model the Loop model is able to predict a swirl, but due to the lack of technical details, like the pump impellers, the swirl is overestimated.