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Numerical simulation of the gas diffusion process during an air ingress accident in the HTR-PM

ZUO Hong-wei1, DONG Yu-jie2, and LIU Bao-ting3
1. State Nuclear Power Engineering Company, Shanghai, 200233 China (
2. Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing, 100084 China
3. China Nuclear Power Design Co., Ltd, Shanghai Branch, Shanghai, 200030 China
Abstract: The consequence of an air ingress accident can be greatly influenced by the gas-diffusion process. It is necessary to study the process of air diffusion in the cavity of the reactor through the rupture of hot gas ducts of the High Temperature Gas-cooled Reactor Pebble-bed Module (HTR-PM) until steady convection forms. The DIFFLOW code was used for the numerical simulation that illustrated the gas-diffusion process inside of the HTR-PM. In the sensitivity analysis, the core temperature, the diffusion coefficient, the frictional resistance coefficient and the surface coefficient of heat transfer proved to be the impact factors. Each factor was evaluated with three levels. The onset time of the steady convection, the velocity in the middle passage under steady convection, and the mass flow in the middle passage under steady convection were observed in the analysis. 32.78 hours after the accident occurs, the steady convection could be established. The flow in the middle passage under steady convection measured 0.32kg/s, while the velocity in the middle passage read 0.56m/s. The sensitivity analysis also showed that the core temperature had a remarkable impact on the onset time, the velocity and the flow of the steady convection.
Keyword: HTR-PM; air ingress accident; gas diffusion
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