Comparison of oxidation behaviour of nuclear graphite grades at very high temperatures

In this study, the oxidation characteristics of nuclear grade graphites IG-110, IG-430, Type A(MA), Type B (MB), PGA, ATR-2E, G347A and G458A in air environments at temperatures ranging from 700 to 1600 °C were investigated. The oxidation rates and activation energies were determined based on mass loss measurements in a series of oxidation tests. Significant increases in oxidation rates above 1200 °C were observed at very high temperatures for all graphite grades. Isotropic graphite grades were found to have higher oxidation resistance than anisotropic graphite PGA, but the differences for fine grained graphite were small. In Regime III, pitch-based graphite has better oxidation resistance than petroleum-based graphite, and the isotropic graphite grades with larger filler particles had lower oxidation rate than the graphite grades with smaller filler particles at temperatures higher than 900 °C. The bulk oxidation rates were found to be sensitive not only to experimental conditions but also any change in the testing system in Regime III. In order to reliably compare oxidation rates among graphite grades, all tests should be conducted in the same system and using the same test procedures.