To investigate the oxidation behavior of UO2pellet in the voloxidation step of reprocessing process for oxide fuel, phase relations of the oxides in the U3O8and Nd2O3system at elevated temperatures in air was studied by XRD method. After the heat treatment of the mixture of Nd2O3and U3O8with a Nd amount of 50 mol% in air at 1273 K for 12 h, the UO2solid solution phase such as NdyU1-yO2+xwas found to be formed in the presence of rare-earths with a small amount of both Nd2O3and U3O8phases. When the 50 mol% mixture was heated at 1273 K in air, the NdyU1-yO2+xsolid solution as a single phase was obtained after 36 h. The effect of heating temperature was also observed; the small peaks for UO2phase at 873 K increased with increasing temperature forming a single phase at 1273 K. When the amount of Nd2O3increased, the amount of solid solution phase increased at the same heating conditions. The lattice parameter of NdyUi-yO2+xsolid solution phase was found to decrease with increasing temperature and Nd amount, compared with that of UO200. The composition of the 50 mol% Nd solid solution, obtained by heat treatment at 1273 K in air for 48 h, was analyzed to be Nd0.482U0.518O1.943by ICP-AES. From these results, the lattice parameter change with x and y values were discussed.
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