Kinetic study of the UO2/C interaction by high-temperature mass spectrometry

Developing uranium dicarbide–graphite porous materials for the SPES project

“…A confirmation of the proposed reaction sequence, leading to the formation of a minor amount of UC besides the main product UC 2 , can be found in the work of Gossé and co-workers [31], who recently reported the effects of kinetic limitations concerning the interaction between UO 2 and C. Their high temperature mass spectrometry experiments performed on UO 2 + C pellets (in stoichiometric ratio) confirmed the strong interaction between these two compounds at T > 700°C. When UO 2+x reached an almost stoichiometric composition, a carbide phase began to form and a three phase domain was attained, where UO 2 , C and UC coexist.…”

“…The presence of hyper-stoichiometric oxide, namely UO 2+x , in the UO 2 C sample can partially explain the production of carbon monoxide at these temperatures, as the consequence of the reduction of uranium dioxide to hypo-stoichiometric UO 2Àx [31][32][33].…”

From uranium(IV) oxalate to sintered UO 2 : Consequences of the powders' thermal history on the microstructure

“…Such compounds could still exist in some of the samples fired at the lowest temperatures (typically below 600 • C), and are expected to delay and/or hinder the sintering processes [39]. However, the residual carbon content is more likely to be present in an amorphous state as the formation of defined oxycarbide species could be excluded considering the carbon amount in the samples (typically less than 10 wt.%) [40]. On the other hand, it is most likely that the carbon present in the samples initially heated in air remained as elemental and amorphous carbon, that could be located either in solid defects (such as boundaries between crystallites) or directly inserted in the fluorite-type lattice of UO 2 .…”

Progress in understanding fission-product behaviour in coated uranium-dioxide fuel particles

“…At high burn-up (>9% FIMA, that is foreseen in the design of the actual VHTR), the CO and CO 2 pressures may become an unacceptable loading regarding the mechanical integrity of the particle. It has been recently shown experimentally that the kinetics of formation of CO could limit the build up of the internal pressure of the particle [22]. For this reason, the CO and CO 2 pressure values determined from the equilibrium calculations presented here have to be considered as conservative.…”