A REVIEW OF KINETIC DATA ON THE RATE OF U3O7 FORMATION ON UO2

Kinetic data on the rate of U3O7 formation on UO2 have been critically reviewed. Oxidation of UO2 powders displays diffusion-controlled (par abolic) kinetics, whereas sintered UO2 pellets display approximately l inear kinetics, presumably because the rate of oxidation in the latter is limited by a combination of cracking, intragranular and grain-boun dary oxidation. The activation energy for the formation of U3O7 on UO2 is estimated to be 96 kJ mol(-1) for powders and 99 kJ mol(-1) for si ntered pellets. Analysis of kinetic data suggests that the formation o f U4O9/U3O7 may have a significant impact on a,eight-gain oxidation ex periments with used nuclear fuel and should thus be considered when es timating the rate of U3O8 formation.