Analysis of Siphon-Breaker Systems for Nuclear Reactors Using RELAP Codes and CFD Simulations

Abstract

The development of siphon-breaker systems is crucial for controlling core uncovering in the event of a loss-of-coolant accident (LOCA) in nuclear reactors. Although they are primarily used in openpool reactors, there is growing interest in their use in pressurized SMRs to mitigate drainage following an auxiliary system failure. In a previous study, we presented the validation of an experimental rig and CFD simulations (OpenFOAM-10 with VOF) against high-speed imaging. In this work, we extend that research by evaluating two new siphon-breaker designs and alternative operating conditions with CFD. We also develop a reduced model in RELAP5 to reproduce the experiment and compare liquid-level dynamics and siphon-break times. The results show good agreement between RELAP and CFD in the overall level evolution, while CFD simulations capture the air-liquid interface in greater detail. The new designs reduce overshooting, providing additional criteria for optimizing safety systems in SMRs.