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

LiF-BeF2 and LiF-BeF2-ThF4 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 BeF2-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-SiO2 system. Also the ternary system LiF-BeF2-ZrF4 contains such a miscibility gap in the BeF2 corner.