Oxidation behavior of fine-grained isotropic nuclear graphites

In high temperature gas-cooled reactors (HTGRs), graphite has been widely used as a moderator, reflector and fuel block for its excellent moderating power, mechanical properties and machinability. The graphite structures may be oxidized due to oxygens from the leakage in the heat-exchanger tube and graphite outgassing. Therefore, the oxidation of graphite is very important for analyzing the safety of the reactors and assessing the operational life of core structures. All the nuclear graphites are being manufactured from the two kinds of cokes, i.e., petroleum and coal-tar pitch coke, and the impurity levels are different among the fuel block, reflector and supporting structure so that the type of coke and level of impurity should be considered to analyze the oxidation behavior of nuclear graphite. In this study, to investigate the effects of coke types and impurity levels on the oxidation behavior, the thermogravimetric experiments were performed on three kinds of fine-grained isotropic nuclear graphites