Chemical interactions between zirconium and free oxide in molten fluorides

The chemical interactions between zirconium and free oxide in FLiNaK melts at different zirconium to oxide (nZr/nO) molar ratios were studied by means of a carbothermal-reduction technique (LECO oxide analyzer) and Raman spectroscopy. ZrO2 precipitates were formed with nZr/nO ≤ 0.5, while ZrO2 was converted to Zr2OFx6−x complexes with nZr/nO > 0.5. The maximum amount of Zr2OFx6−x complexes in FLiNaK melts was found to be 0.020 mol kg−1. With an initial oxide concentration lower than 0.020 mol kg−1 and the required amount of ZrF4, the free oxide in FLiNaK melts could be completely converted to Zr2OFx6−x complexes, which would further prevent the formation of UO2 precipitates.

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