Oxidation Behavior of Carbide Fuels

Oxidation of UC: An in situ high temperature environmental scanning electron microscopy study

“…The presence of both U3O7 and U3O8 in the oxide at the end of the experiment, and the fact that Equation 3 is said to happen after carbon transforms into CO and/or CO2 28 suggests that gases are released during sample explosive expansion. However, a direct correlation between the CO2 release and sample explosion cannot be drawn as it was not possible here to monitor the gas evolution.…”

“…Iyer et al 28 proposed a mechanism of oxidation for UC which involves: first the diffusion of oxygen into the uranium carbide matrix with the precipitation of carbon, reported to be highly reactive. The resulting oxycarbide is converted into uranium dioxide with subsequent precipitation of carbon as a second phase.…”

“…The resulting oxycarbide is converted into uranium dioxide with subsequent precipitation of carbon as a second phase. This oxide acts as a diffusion barrier for oxygen transport through the carbide matrix 28 . It is unclear whether the oxide product readily spalls off or stays adherent to the carbide core, as contradictory results have been reported 11,12,13 .…”

“…Reactions (1) and (2) occur at the same time, however reaction (3) is believed to occur when all the carbon is oxidised to CO2 28 . Slightly different reactions have been reported 7 where the intermediate products of oxidation are UC2, UO2, UC1-xOx, UO3 or directly U3O8 and carbon could be oxidised either to CO or CO2 14 depending on temperature and oxygen availability 29 .…”

“…The presence of carbon increases the complexity of the oxidation mechanism of UC in comparison with oxidation of UO2 or metallic U as carbon can be found in the oxide as either free carbon, as carbide, as oxycarbide, as carbon monoxide or dioxide 14 . UC is well known to be pyrophoric 3,28 and its ignition temperature is system dependant and is affected by several parameters such as heating rate, partial pressure of oxygen, and at least ten other factors including mass and specimen geometry 2 . The proposed UC ignition reaction 28 is:…”