Investigation of the Quasi-Binary Phase Diagram FLiNaK-NdF(3)

The NdF(3) solubility in molten eutectic FLiNaK, which is a conceivable medium for a molten salt reactor (MSR), was determined by the quasi-binary phase diagram FLiNaK-NdF(3). The eutectic mixture FLiNaK was prepared by direct melting of components LiF, NaF and KF·HF. The acidic anhydrous salt (KF·HF) was used instead of the hygroscopic KF. The NdF(3) was sintered by hydrofluorination of Nd(2)O(3). The oxygen impurity in the prepared eutectic FLiNaK, determined by an oxygen analyzer LECO OH836, was 0.036 wt.%, whereas the NdF(3) contained 0.04 wt.% of oxygen. A part of the FLiNaK-NdF(3) quasi-binary phase diagram was obtained using two thermal analysis techniques: differential thermal analysis (DTA) and differential scanning calorimetry (DSC). The FLiNaK-NdF(3) phase diagram in the region of 0–30 mol.% NdF(3) contains one eutectic at 2 mol.% NdF(3) and 450 °C and two peritectic points: 8 mol.% NdF(3) at 500 °C and 22 mol.% NdF(3) at 575 °C. The region of the FLiNaK-NdF(3) phase diagram below the liquidus line is rather complicated due to the complex structure of the multicomponent system in its molten state, as in its solid state. The NdF(3) solubility in FLiNaK is about 5 mol.% at 490 °C and 29 mol.% at 700 °C; this means that the process of the MA transmutation in the MSR can be carried out in molten FLiNaK with a content of actinides as high as 15–20 mol.% in the temperature range of 550–650 °C.