Research on internal flow characteristics of gas-liquid two-phase flow in reactor coolant pump

The operational performance of the Reactor coolant pump (RCP) is crucial to the safety and reliability of nuclear power plants. During a Loss of Coolant Accident (LOCA), the RCP is subjected to complex gas–liquid two-phase flow conditions, which significantly affect its head, torque, and operational efficiency. In this study, a scaled CAP1400 model is analyzed using a high-fidelity MUSIG model with ten bubble size groups to capture bubble coalescence and breakup. Numerical simulations show that as the inlet gas volume fractions (IGVF) increases from 1 % to 30 %, pump head and efficiency decline continuously, with a sharp performance drop of up to 40 % occurring at IGVF = 5 %–15 %. When IGVF exceeds 10 %, gas accumulation near the impeller suction surface leads to flow separation and channel blockage. The Ω-vortex method is applied to identify distinct flow regimes evolving from bubbly flow to coalescing bubble flow, gas pocket flow, and finally separating flow. This study reveals the changing law of the internal flow in the nuclear reactor coolant pump under the inlet gas-containing condition, analyzes the mechanism of the gas-liquid two-phase flow on the performance of the nuclear reactor coolant pump, and aims to gain a deeper understanding of the specific impact of the gas-liquid two-phase flow on the performance of the nuclear reactor coolant pump.