On the oxidation and ignition of uranium carbide fragments in air and comparison with zirconium carbide oxidation

Oxidation of uranium carbide (UC) small fragments from sintered pellets was experimentally tested to better understand UC safe-handling procedures given the renewed interest of non-oxide fuels for high temperature gas or liquid metal cooled reactors. Transformation from UC to U3O8 via a self-ignition reaction was observed at partial pressure of oxygen as low as 10 Pa. The heat output from UC self-ignition in fragments (not-free from UO2 contamination) previously stored in either air atmosphere or inert-atmosphere during a three months period was monitored at 973 K and 1073 K in air atmosphere in a TGA/DTA and no difference could be observed. Residual carbon content, measured as amorphous carbon, carbide or CO/CO2, decreased with exposition temperature in U3O8 resulting oxide, this is in contrast with zirconium carbide resulting oxide, ZrO2. Cracking and stresses accumulated in the oxide were highest for UC to U3O8 compared to UC to UO2 reactions and ZrC to ZrO2 reactions.