Effect of a Thermal Oxidation on the Compressive Strengths of Selected Nuclear Graphites

In a very high temperature gas-cooled reactor (VHTR), graphite structures may be exposed to oxidative impurities contained in the helium coolant gas during a normal operation and/or air that ingresses into the coolant in the event of a depressurization. In both cases, they are believed to be oxidized at various temperatures corresponding to their locations, i.e. core, core support, moderator and reflector, in the reactor. The degradation of a compressive strength of nuclear graphite caused by a thermal oxidation is one of the most serious problems for the safety analysis and design of the VHTR. The effects of an oxidation on the compressive strength have been extensively studied, however the results were dependent on not only the oxidation conditions but also on the structures of the graphite so more studies are needed to thoroughly understand the subject. In this study, we examined the change of the compressive strengths of five candidate nuclear graphites for the VHTR