Reactive hot pressing of nonstoichiometric uranium dioxide

High density UO2+x pellets have been produced by reactive hot pressing uranyl oxalate at temperatures up to 700°C. Rapid densification occurred during the decomposition reactions resulting in densities in the range 90 to 92 pct of the theoretical. A density of 98 pct of the theoretical value was achieved by further hot-pressing at 650° to 700°C for 30 min. This densification behavior can be related to the nonstoichiometry and submicron sized particles of UO2+x produced in the decomposition reactions. The kinetics of hot-pressing of powder compacts of this UO2+x were studied in the temperature range 500° to 700°C. The results were analyzed utilizing models proposed by Fryer. The activation energy of 53 kcal per mole, obtained from this analysis is the same as that for creep of nonstoichiometric urania in the temperature range 975° to 1400°C, suggesting that the mechanism controlling the rate of the final stage of densification may be a creep process.