Water ingress into the primary circuit of HTR-PM (High Temperature Gas-cooled Reactor Pebble-bed Modular) is one of the beyond-design-basis accidents, which will lead to chemical corrosion of graphite and metal material in the reactor, resulting in the generation of combustible gases such as hydrogen and carbonic oxide. Besides, the rise of pressure in the reactor containment caused by the incoming of abundant of gas will threaten to the safety of radioactive material releasing. Therefore, it is essential to analyze the gas behavior in the containment of HTR-PM under the condition of water ingress.
Based on the preliminary design of 250MW HTR-PM, the paper analyzes the transport and distribution of hydrogen, helium and other kinds of gas in the containment under the condition of water ingress accident resulted from a double-ended guillotine break of two steam generator heating tubes which is a typical beyond design basis accident of HTR-PM with the multi-dimensional computational fluid dynamics CFD code GASFLOW. In addition, the density and distribution of hydrogen will be investigated in relation to possible hydrogen explosion.