A miscibility gap in LiF–BeF2 and LiF–BeF2–ThF4

Abstract

LiF-BeF 2 and LiF-BeF 2 -ThF 4 are key systems for Molten Salt Reactor fuel. The liquid phase of these systems has been assessed using Redlich-Kister polynomials. The result shows a miscibility gap on the BeF 2 -rich side. This has never been proven experimentally. Nevertheless, evidence for a two liquids region is given by the fact that such a region exists in the analogous MgO-SiO 2 system. Also the ternary system LiF-BeF 2 -ZrF 4 contains such a miscibility gap in the BeF 2 corner.

Thermodynamic evaluation of the (LiF+NaF+BeF2+PuF3) system: An actinide burner fuel

“…Good agreement has been found as shown in figure 3 for a temperature T = 898 K. The LiF-BeF 2 phase diagram is characterized by two eutectic invariant equilibria found at T = 636 K and x BeF 2 ¼ 0:517 and T = 729 K and x BeF 2 ¼ 0:328 in the calculation. Two intermediate phases Li 2 BeF 4 and LiBeF 3 are present in the system as well, the first melting congruently at T = 729 K, whereas the latter decomposing below the solidus at T = 557 K. Similarly to the previous study [23], in which the (LiF + BeF 2 ) system has been assessed using the classical polynomial model for the excess Gibbs free energy description, our assessment indicated a miscibility gap in the BeF 2 rich corner. As discussed in that paper the limiting slope of the liquidus line at BeF 2 side is defined by the fusion enthalpy (or fusion entropy) of pure BeF 2 according to lim…”

Thermodynamic properties and phase diagrams of fluoride salts for nuclear applications

“…Vallet and Braunstein [15] suggested that a miscibility gap may occur at the BeF 2 -rich side of the diagram, based on model calculations. Van der Meer et al [16,17] arrived at the same conclusion based on optimization of the phase diagram data. The assessed phase diagram from that latter study is shown in Fig.…”

“…The phase diagram has been thermodynamically assessed by van der Meer et al [39] based on these data and is shown in Fig. 6.…”

“…The equilibrium diagram of the LiF-ThF 4 system assessed in [39]. Experimental data points are from [38].…”

“…Cantor et al [19] also measured the density, but due to the experimental difficulties derived only an approximate value, 1960 kg m À3 at 1123 K. The value of MacKenzie is recommended and taken as a constraint in our estimation. The obtained density for liquid BeF 2 as a function of temperature is shown below: r ðkg m À3 Þ ¼ 3190:5 ðAE58:1Þ À 1:1589 ðAE0:0468ÞT ðKÞ (16) Using the Eq. (16) together with the selected data for the LiF and ThF 4 densities taken from [46] we have calculated the expected density function of temperature for the LiF-BeF 2 -ThF 4 (71.7-16.0-…”