The oxidation behaviour of uranium in air at 50–300°C

The oxidation behaviour of adjusted uranium in air at 1 atm pressure has been examined at 50–300°C, with emphasis on the influence of water vapour at concentrations up to 3×104 vpm. The work also covered the effects of prior irradiation of the metal. Temperature had the most pronounced effect and increased the rate of oxidation by a factor of over 106 from 50 to 300°C. Water vapour also increased the attack at 100–200°C by up to a factor of 7.5, but was without significant influence at 50, 75 and 300°C. The enhanced attack could be explained by the incorporation of hydroxyl ions in the oxide lattice or by the transitory formation of uranium hydride. Support for the latter explanation was provided by tests in wet air with defected cans containing uranium powder, where oxidant access was limited. The influence of irradiation, to a burn-up of 5600 MWd/t, was governed mainly by the magnitude of the associated swelling. It only became significant for the most swollen (17–21%) material examined, when it increased the attack by factors from 4–90. The mechanism involved the break-up of the uranium surface during oxidation.