Determination of oxidation rates and volatile oxidation products for HTGR graphite matrix material exposed to steam atmospheres

[摘要] High-temperature gas-cooled reactors (HTGRs) in operation use tristructural isotropic (TRISO) particles embedded in graphite and carbonized resin matrix to form the fuel element. This graphite matrix material serves as a supportive structural element, heat transfer medium, and neutron moderator. In HTGR designs, fuel compacts are exposed to helium coolant, which facilitates high outlet temperatures (750 degrees C<950 degrees C) and subsequently greater thermal efficiency than current commercial power reactors. However, data pertaining to the oxidation resistance of graphite matrix material in HTGR accident or off-normal conditions (<50k kPa pH(2)O, 800 degrees C<1600 degrees C) is limited. In this study, both the oxidation behavior of matrix graphite material and its gas-phase products, including CO, CO2, and H-2, are quantified in varied oxidant atmospheres using a coupled thermogravimetric analyzer and mass spectrometer. Oxidation rates reported here for varied steam (H2O [g]) atmospheres are predominantly linear and comparable with literature values in the range of tested temperatures (800-1200 degrees C). Changes in dominant matrix oxidation products from primarily CO to a mixture of CO, CO2, and H-2 were observed at higher temperatures (>= 1000 degrees C) and steam atmospheres (>= 5 kPa pH(2)O). Kinetic data indicates that there was no shift in oxidation regime with chemical oxidation occurring at all temperatures and H2O (g) atmospheres tested. These data provide insight into the oxidation behavior of graphite matrix material and will inform future testing conditions, notably mixed atmospheric conditions, of HTGR fuel elements. (C) 2021 Elsevier B.V. All rights reserved.

[发布日期] 2021-12-15

[关键词] Graphite matrix material;High-temperature oxidation;Matrix oxidation products;High-temperature gas-cooled reactors;Nuclear materials