Oxidation and Temperature Effects on the Fracture Toughness of Nuclear Graphite at VHTR

Understanding the effects of oxidation and temperature of nuclear graphite are important for the design and safety analysis of the very high temperature gas-cooled reactor (VHTR), because the graphite experiences structural degradation via oxidation during normal reaction operation or accident. At present, the most critical event expected in this type of reactor is an air-ingress accident, which is caused by a pipe break. When air is ingressed into the reactor due to an accident, the graphite materials in the moderator and reflector suffer from a chemical reaction with oxygen. Until recently, several researchers have investigated the effect of oxidation on mechanical properties of nuclear graphite. For example, a 50% tensile strength reduction by about 10% weight loss was reported. In the present study, we tested and estimated the fracture toughness of nuclear graphite in various temperature(25 .deg. C - 700 .deg. C) after uniform oxidation by 0 to 15%