The effect of the oxidation temperature of UO 2 pellets on the powder properties of oxidized U 3 O 8 powders has been investigated. The powder morphology, crystalline size, and BET surface area of recycled U 3 O 8 could be modified by controlling the oxidation temperature of the UO 2 pellets. Recycled U 3 O 8 powder with a high BET surface area and a small particle size could be obtained by lowering the oxidation temperature. It was also found that this low-temperature-oxidized sinter-active U 3 O 8 powder is effective in mitigating the density drop of the UO 2 pellets when the recycled U 3 O 8 powder is added. Moreover, the recycled powder acted as a grain-size-enlarging promoter in the UO 2 pellets.

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Powder morphology evolution of recycled U 3 O 8 according to the thermal treatments has been studied. The defective UO 2 pellets are oxidized to U 3 O 8 powders at a conventional temperature of 350 or 450 C in air. Those powders are pressed into green pellets and then sintered at 1,500 and 1,730 C in H 2 gas flow. Final reoxidized U 3 O 8 powers are obtained by reoxidizing those sintered pellets at 450 C in air. This paper shows that the reoxidized U 3 O 8 powder morphology and the BET surface areas are greatly dependent on the density of sintered UO 2 pellets before reoxidation. Reoxidized U 3 O 8 powders are added to virgin UO 2 powders to fabricate UO 2 pellets and the effect of such addition on the UO 2 pellet properties is investigated. The reoxidized U 3 O 8 powders having a certain range of BET surface area significantly promote the grain growth of UO 2 pellets.

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