The thermal performance of fuel matrix material in a CO2 atmosphere

The thermal oxidation performance of a semi-graphitic fuel matrix-material has been compared to two grades of nuclear graphite between 600 °C and 1200 °C in flowing CO2. Fuel matrix material is used to produce compacts or pebbles containing TRISO coated particle fuel for High Temperature Reactors (HTRs). The A3-27 fuel matrix-material grade was compared to NBG-18 and Gilsocarbon nuclear graphite grades. At 1200 °C temperatures A3-27 appears to be more reactive than NBG-18, but less so than Gilsocarbon. At 600 °C the oxidation rate of A3-27 is comparable to that of NBG-18, but both are significantly higher than that of Gilsocarbon. It is concluded that the comparable thermal oxidation behaviour of graphite and fuel-matrix material suggests that operating temperatures in a CO2 cooled reactor fuelled with TRISO coated particle fuel would not need to be reduced below those considered acceptable for the use of nuclear graphite.