Influence of Bottom Reflector Oxidation on Air Ingress Accident of HTR-PM

Air ingress accident plays an important role in the safety analyses of the high temperature gas-cooled reactor pebble bed module (HTR-PM). The nuclear grade graphite has a broaden use in HTR-PM and it is usually used as the reflector material, structure material and the moderating material. In the air ingress accident, the oxidation of the matrix graphite increases the risk of the exposure of the fuel particles and the release of radioactivity. Besides, the oxidation of the bottom reflectors may damage the integrity of the reactor bottom structure. The influence of two kinds of nuclear grade graphites on the double-ended guillotine break (DEGB) of the horizontal coaxial gas duct accident was analyzed by using TINTE code. In the premise of ensuring the integrity of the bottom reflector, the nuclear grade graphite with high oxidation rate can obviously decrease the risk of the exposure of the fuel particles and radioactivity release.