Thermodynamic assessment of the LiF–NaF–ThF4–UF4 system

Thermodynamic assessment of the (LiF+UF3) and (NaF+UF3) systems

“…While repeating several measurements the solidus temperatures decreased whereas the liquidus temperatures stayed constant. Between 740 K and 775 K we observed over the full measured composition range signals in the DSC analysis which correspond exactly to the transition temperatures of the compounds U 6 Li 7 F 31 and ULi 4 F 8 in the LiF-UF 4 phase diagram [14]. This can be visualized very well by the superposition of the LiF-UF 4 phase diagram with the measured data of the (LiF + UF 3 ) system (see figure 1).…”

“…At temperatures of (772 AE 2) K, (823 AE 2) K, and (868 AE 2) K we found indications for transitions over almost the whole measured composition range which are not explained by the NaF-UF 3 phase diagram. It is conspicuous that also the data of Barton show the transition at 868 K, which is close to the lowest eutectic temperature in the (NaF + UF 4 ) system found at 881 K [14]. Figure 6 shows a superposition of the NaF-UF 3 and NaF-UF 4 phase diagrams.…”

“…This phase diagram was used together with the data of the (LiF + UF 4 ) system [14] and a preliminary version of the (UF 3 + UF 4 ) system based on results of Thoma et al [15], which was assessed by our group, to calculate pseudo binary LiF-UF 3 -UF 4 phase diagrams with constant amounts of UF 4 between 0 mol% and 15 mol% as shown in figure 3. The calculations show that with an increasing UF 4 content in the (LiF + UF 3 ) system the solidus temperatures are decreasing continuously and the solidus line follows a shape similar to the measured solidus temperatures.…”

“…For this reason the thermodynamic description of the (NaF + UF 4 ) system [14] and the preliminary assessment of the (UF 3 + UF 4 ) system were used to calculate the pseudo binary NaF-UF 3 phase diagrams with different amounts of UF 4 to analyze the effect on the NaF-UF 3 phase diagram. As Table 4 gives the phase labeling.…”

Thermodynamic assessment of the LiF–ThF4–PuF3–UF4 system

“…The ThF 4 -UF 4 system forms a continuous solid solution [12,13] as described by the following relation:…”