CFD Simulation Of Hydrogen Migration And Water Vapor Condensation With Accidents Happened In The Containment

The containment was the third security barrier in the nuclear power plant,mainmenting its integrity was very important to alleviate the severity of the accident.When the reactor was damaged,the hydrogen gathered in the containment would cause local hydrogen risk,adopting appropriate measures could reduce hydrogen concentration;when LOCA happened,the temperature and the pressure of the containment would exceed the limit,but the PCCS could solve this problem,which could prevent further increase in temperature and pressure.In this paper,the software Fluent was selected to simulate the flow and distribution of hydrogen in the accident to study the movement of it,at the same time,the effect of the wall condensation was to be studied.The simulation of the hydrogen flow showed that,in the accident,after it flowed out from the break location,it would flow upward along the compartment,when it reached the dome,the hydrogen would flow downward to the contralateral space;under the effect of the turbulence,the airflow would form swirl in the steam generator compartment and the dome space;in the mainstream areas,the change of the hydrogen concentration was offected by the turbulence diffusion,where the concentration would enrich at the early stage and then decrease;in the layering process of hydrogen concentration,the transverse diffusion caused by the concentration difference of different height played a major role,in addition,the concentration of the hydrogen is higher at the top of the dome and the turbulence there is stronger.Research on the factors affecting the flow of hydrogen showed that the hydrogen production rate had great influence on the turbulence of the gas at the dome and the steam generator compartment;moreover,it could also affect the distribution of the hydrogen in the containment: the greater of the hydrogen production rate,the intenser of the hydrogen turbulence,the greater change of the hydrogen concentration.The proportion of the vapor in the mixture gas had influence on the flow and distribution of the hydrogen,with the improving of the vapor's proportion,the range of the high concentration of the hydrogen decreased,the hydrogen in the containment was more evenly distributed.Simulation results of water vapor condensation on the wall surface indicated that the change of the concentration of the air and water vapor caused by the water vapor condensation would be influenced by the geometry structure of the containment and the gravity: the structure near the compartment had influence on the gas diffusion effect,the concentration of the air near the wall surface of the compartment is high;compared with the air,the density of the water vapor is smaller,so condensation would cause the concentration of the air which at the lower position of the containment high.At last,the results of the simulation found that the ability of the wall heat conduction influenced the heat transfer of the containment wall,and by improving the ability of the wall heat conduction,the water vapor condensation efficiency could be effectively improved.Simulating the flow of the hydrogen in the accident could better grasp its liquidity and distribution in the containment,at the same time,this could provide a reference for the location of the hydrogen elimination device;the effects of the wall on water vapor condensation was examined by the simulation and the measures were proposed to improve the condensing efficiency.