Effects of pyrochlore content on the phase, structure, and properties of uranium-rich glass ceramics

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In this study, the effects of the pyrochlore content on the phase, structure, and properties of uranium-rich glass ceramics were studied by modifying the mass ratio of the uranium pyrochlore in the glass ceramics. The results indicate that U has a high occupancy rate of approximately 0.7 f.u. at the A position of pyrochlore, and the crystal pyrochlore phase in the glass matrix can increase or decrease according to the U amount in the waste. Specifically, at a high occupancy rate and crystallization amount, the U loads reach 20 wt% in the sample, which exceeds the reported 16 wt% maximal U loads of pyrochlore-based glass ceramics. Furthermore, all the samples have excellent mechanical properties and chemical stabilities. The bulk density of each sample is more than 90% the theoretical density, which is 10–20% higher than those of the glass ceramics prepared by pressure sintering. Moreover, the Vickers hardness values of all samples exceed 6 GPa, and the U leaching rate after 21 days is only 6.7 × 10−5 g m−2 d−1, which is an order of magnitude lower than those of brannerite glass ceramics under equal leaching conditions.