Mixtures of alkali fluorides with uranium tetrafluoride are of potential importance in moltensalt reactors and in the reprocessing of nuclear fuels. In this paper detailed phase diagrams are presented for the binary systems KF-UF4 and RbF-UF4. Data for the determination of phase boundaries were obtained in large part by quenching after equilibration. Thermal analysis and visual observation were used as supplementary methods. Phase identifications were made by X-ray powder diffraction and by optical microscopy. In the system KF-UF4 four compounds have been identified. Two of these, 3KF.UF4 and 7KF .6UF4, melt congruently at 957°C. and at 78Q°C., respectively. The compound 2KF .UF4 melts incongruently to 3KF.UF4 and liquid at 755"C., and the compound KF.2UF4 melts incongruently to UF4 and liquid at 765°C. There are three eutectic points in the system: 15.0 mole yo UP4, 735OC.; 38.5 mole ' % UF4, 740°C.; and 54.5 mole % UF4, 735°C. The compound 2KF.UF4 decomposes during cooling to 3KF.UF4 and 7KF. 6UF4 at 608OC. Two other compounds, KF.3UF4 and KF.6UF4, have been described by another investigator. One of these, KF.3UF4, was not obtained at all in the present investigation. The other, KF.6UF4, was not obtained under equilibrium conditions and was found only in KF-UF4 mixtures that had been exposed to the atmosphere while molten. Seven solid compounds are present in the system RbF-UF4. All of these melt incongruently with the exception of 3RbF.UF4 and RbF-UF4, which melt at 995°C. and at 735"C., respectively. The incongruently melting compounds and their melting points, peritectic compositions, and melting products are: ZRbF.UF4, 81S0C., 38 mole ' % UF4,3RbF-UF4 + liquid; 7RbF.6UF4, 693"C., 44 mole % UF4, RbF.UF4 + liquid; 2RbF.3UF4, 722"C., 56.5 mole % UF4, RbF.3UF4 + liquid; RbF.-3UF4, 73OoC., 57 mole yo U F 4 , RbF.6UF4 + liquid; and RbF.6UF4, 832"C., 70.5 mole yo UF,, UF4 + liquid. The three eutectic temperatures and compositions in the system are: 10.0 mole % UF4, 71OOC.; 43.5 mole ' % UF4, 675°C.; and 55.0 mole % UF2, 714°C.
Oak Ridge National laboratory, Oak Ridge, TennesseeThe phase equilibrium diagram of the ternary system NaF-LiF-UF4 described in this paper is based on evidence from thermal analysis and from microscopic and X-ray analyses of samples obtained from thermal gradient quenching experiments. Temperature-composition relations were established through the temperature interval between the liquidus and a lower limit of about 300OC. All the stable compounds in the binary systems LiF-UF4 and NaF-UF, (including the subsolidus compound NaF .2UF4) display primary phase fields in the ternary system. No ternary compounds of NaF-LiF-UF4 occur. The following eutectics are to be found in the ternary system: 60 NaF, 21 LiF, 19 mole yo UF,, 48OOC. ; 35 NaF, 37 LiF, 28 mole % UFI, 48OOC. ; 24.3 NaF, 43.5 LiF, 32.2 mole % UFI, 445OC.;and 24.5 NaF, 29 LiF, 46.5 mole yo UP,, 602OC.The compounds 7NaF.6UF4 and 7LiF.6UF4 display limited solubility in each other. The exact limits of the miscibility gap in the 7NaF.6UFr7LiF.6UF4 join have not been determined.
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