Study of flow behavior in APR1400 safety injection tank with fluidic device

Abstract

Safety Injection Tanks (SIT) of APR1400 have Fluidic Devices (FD), which control mass flow passively. Due to the structure of the FD, nitrogen can enter the system before emptying the full tank. Since the current methodology of SIT/FD modeling does not consider the nitrogen entrainment, the conservativeness of the system analysis code cannot be guaranteed. Therefore a Computational Fluid Dynamics (CFD) analysis was conducted to capture the flow of water and nitrogen in the SIT/FD. The Volume Of Fluid (VOF) model was first used and successfully calculated the mass flow rate. However, the nitrogen entrainment cannot be modeled accurately, so the Multiphase Segregated Flow model was implemented. Despite the concern, nitrogen entrainment amount was found to be too small to cause any significant difference. Therefore, it was concluded that the accumulator model in the system analysis code is sufficient to describe the current SIT/FDs of APR1400s.