The influence of nuclear graphite oxidation on air ingress accident of HTR-PM

Highlights: •Different bottom reflector graphite oxidation have been compared in the air ingress accident of HTR-PM. •Bottom reflector graphite with high oxidation rate could protect the reactor core from oxidation. •Bottom reflector graphite with high oxidation rate could accelerate the onset of the stable natural circulation. -- Abstract: The high temperature gas-cooled reactor pebble bed module (HTR-PM) has wide potential applications in the development of advanced nuclear energy. The double-ended guillotine break (DEGB) of the horizontal coaxial gas duct accident is a kind of beyond design basis accident of HTR-PM, which will result in air ingress into the reactor core. Even though the rare probability of this accident, it still has got a lot of concerns in the safety analyses of HTR-PM, due to the possible severe consequences of the air ingress accident, which would cause oxidation of the graphite material in the reactor. The oxidation of matrix graphite of spherical fuel elements may lead to the exposure of the TRISO fuel particles and the increase of the radioactivity release. The oxidation of the bottom reflector may cause the decrease of mechanical strength of the nuclear grade graphite. Different kinds of nuclear graphite of the bottom reflector will influence the consequences of the DEGB of the horizontal coaxial gas duct accident. This paper mainly analyzed the influence of the nuclear grade graphite used as the bottom reflector on the consequences of this accident by using the system analysis TINTE code.