Simulations for cooling effect of PCCS in hot leg SB-LOCA of 1000 MW PWR

Abstract

The passive containment cooling system (PCCS) for reactor containment is a security system that can be used to cool the atmosphere and reduce pressure inside the containment in case of temperature and pressure increase caused by vapor injection, which requires no external power since it works only with natural forces. This article aims to establish a CFD simulation model for the Passive Containment Cooling System of 1000MW PWR using Code_Saturne and FLUENT software. The comparison of 4 different models based respectively on mixture model, COPAIN test, Uchida correlation and Chilton-Colburn analogy are used to simulate the condensing effect, the improvement of source code are based on a 3D simulation of PCCS system. To simulate the thermal-hydraulic condition in the containment after LOCA accident caused by a double-ended main pipe rupture, a high temperature vapor with the given mass flow rate are supposed to be the source of energy and mass. Meanwhile the surface of three condensing island use the wall condensation model.The simulation results obtained from the 4 models show similar transient process, the difference between the steady-state analysis of three models is less than 3%. Meanwhile, the large mass flow rate of water loss inside the containment induce a high flow rate of steam which could be uniformly mixed with air in a short time, the impact of steam injection to different directions on the simulation results is not obvious. For the self-condensing efficiency of 3 groups of PCCS system, the non-centrosymmetric injection position resulting that the condensing efficiency is slightly higher for the two heat exchanger groups nearby. During the first 2400s of simulation time, more than 75.69% of the steam is condensed, the occurrence of condensation at the wall mainly driven by natural convection, the effect of thermodynamic siphon could improve the flow rate of gas mixture inside the tubes when the velocity of mixture is not large enough. The steam could smoothly enter the tube and reach the internal cooling surface then to be condensed. Besides, PCCS ensure that the containment internal pressure is maintained below 2bar and the temperature is maintained below 380K during 3600s.