Recycling Process for Sinter-Active U₃O₈Powders

Abstract

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.

Uranium carbide oxidation from 873 K to 1173 K

“…Even though the final destiny of the U3O8 powders produced during oxidation treatment of the Dounreay UC pellets is not clear yet, having a powder with higher SSA, using 873 K treatment, could benefit the sintering process of possible recycled fuels in the future. Previous studies by Yang et al [40] on oxidation of UO2 showed that by lowering the temperature from 723 K to 598 K, the U3O8 powder produced had higher SSA and smaller particle size (SSA of 1.50 m 2 g -1 for U3O8 powder oxidised at 598 K and SSA of 0.66 m 2 g -1 for U3O8 powder oxidised at 723 K). Yang et al [40] observed that a finer U3O8 powder was more sinter-active and improved the densification of recycled UO2 pellets compared to high-temperature (723 K) oxidised U3O8 powder [40].…”

“…For all temperatures, as soon as oxygen was inserted into the chamber the sample edges cracked and spallation or exfoliation of small particles occurred. After ~2 minutes from oxygen insertion, what is normally referred to as a "popcorn morphology" of the oxide [40], [41] appeared mostly along sample edges (see Figure 6a to e). In samples oxidised at 873 K, the morphology of the oxide resembling U3O8 homogeneously appeared on the entire surface within 5 minutes of oxygen exposure (see Figure 6a, b and c).…”