Numerical Simulation on the Thermal Hydraulic Characteristics in Pool-Type Fast Reactor Based on the New-Designed Passive Dynamic Residual Heat Removal Valve

Abstract The passive features of the Emergency Heat Removal System (EHRS) is a crucial component of the reactor’s safety design, and its passive safety features has a significant impact on its performance during accidents. The coolant in the new sodium-cooled fast reactor enters the core directly through the control valve and heat transfer pipe during accident conditions. Because the decay heat exchanger (DHX) is equipped with a check valve at the outlet position. This valve can be opened automatically in the event of an accident, improving the reactor’s passive safety features. For the new design model of sodium-cooled fast reactor, a calculation model of new residual heat removal system calculation model is established with a new ball check valve by CFD software. The UDF program was used to simulate the opening and closing of the check valve by jointly simulating FLUENT dynamic mesh technology and transient dynamics. This allowed the spool of the new ball valve to move freely with the fluid. Simulation calculations were conducted to determine the thermal and hydraulic characteristics of the ball check valve under normal operation and accidental shutdown conditions. Additionally, the dynamic process of temperature change was analyzed after opening the passive safety system under accidental conditions to evaluate the effect of the control valve. The results indicate that the new control valve is passively opened due to the temperature difference and buoyancy force. Additionally, the fluid in the DHX undergoes natural circulation throughout the entire core, gradually recovering from standby power to full power operation. When the flow rate of the pump gradually decreases, it would take over the task of cooling the core. This not only enhances the passive safety features of the EHRS but also efficiently conducts the heat of the reactor, and effectively discharges the residual heat of the core.