Abstract
The phenomenon of siphon break is a passive physical process. It is important for the safety design of pool type Liquid Metal Fast Breeder Reactor (LMFBR) and spent fuel pool of the nuclear power plant adopted Light Water Reactors (LWRs). It can affectively mitigate the Loss of Coolant Accidents of LMFBR and spent fuel pool of LWRs. In the present study, the system thermal hydraulic code RELAP5/MOD3 is used to simulate the experimental results of siphon break apparatus of Beijing Tsinghua University. The simulated results of flow rate in main pipe, pressure drop in downcomer and water level in upper tank over time are compared with the experimental results. The simulated results are also compared with the results of CFD (Computational Fluids Dynamics) analysis. The results have demonstrated that the general trends of the experimental results can be caught by RELAP5 code. Nevertheless, the time duration of siphon break phenomena as predicted by the code is significantly less than the experimental results. A detail analysis of the code simulation results has shown that the two phase multipliers as predicted by the code is about an order of magnitude smaller than the experimental results. It is believed that the difference is due to the assumption of fully developed flow in the code calculation. Sensitivity studies of the different downcomer pipe diameter and outlet valve opening show that the instability of the flow is stronger when the resistance is larger.