Transient flow analysis of pool-type reactor coolant pump under flow coast-down

Abstract

When power is off, the flow rate of coolant in the RCP decreases rapidly and irregular phenomena appear. However, the inflow coolant tends to be uneven and unsteady due to the design of coolant pool. To simulate the actual situation of pool-type RCP under flow coast-down, Circulation-loop model and Open-border model were established. It provides two prediction methods of the power-off condition of pool-type RCP. The flow rate of Open-border model drops synchronously with rotation speed, and that of Circulation-loop model is dynamically fed back through calculation. Variation trends of external characteristics of the two models are similar. However, it is found that a large-scale and low-speed vortex appears at the horizontal suction part of the pool in Circulation-loop model, blocking the coolant transport channel. Thus, there is obvious fluctuation and hysteretic nature phenomenon in the decline of flow rate compared to the decline of rotation speed in Circulation-loop model.