Comparison of Oxidation Behaviors of Different Grades of Nuclear Graphite

The oxidation behaviors of different grades of nuclear graphite - PAEB, PCEB, PPEA, and IG-11 - were studied thermogravimetrically at 400, 800, and 1200°C as a part of work to select one grade of nuclear graphite for use in a gas turbine-modular helium reactor (GT-MHR). The results showed that all grades of nuclear graphite resist oxidation at 400°C. The difference in oxidation between different grades of nuclear graphite was greater at 800°C than at 400°C and 1200°C. At 800°C, for the same grade of nuclear graphite, when the centerline of the specimen is parallel to the axis of extrusion (with grain), the oxidation rate is greater than that of the graphite specimen with the centerline perpendicular to the axis of extrusion (against grain). The experimental results revealed that PPEA had the best oxidation resistance, and IG-11 had the worst due to high impurities. Moreover, the oxidation experiment exhibited that there were some oxidizable materials in unclear nuclear graphite.