Effects of Nb2O5 and oxygen potential on densification of simulated U3O8 powder compacts

The effects of Nb2O5 and oxygen potential on the densification of simulated U3O8 powder compacts have been studied. The simulated U3O8 compacts with and without 0.5wt% Nb2O5 additions were sintered at 1700 .deg. C in the oxygen potentials ranging from -520kJ/mole to -390kJ/mole. It was found that the simulated UO2 pellet had a density of about 7.5 g/cm3 and was independent of oxygen potentials. However, with 0.5wt% Nb2O5 addition, the density was increased up to 10.37 g/cm3, dependent on the oxygen potentials. This enhancing effect of Nb2O5 is supposed to be related with the increase in concentration of uranium vacancy, because NbO2 is interstitially dissolved in UO2. The simulated U3O8 compact with Nb2O5 which had been annealed at 900 .deg. C for 1 hour in argon before sintering, achieved a higher density of 10.53 g/cm3 and small grain size after sintering