Viscosity of LiF–NaF–KF eutectic and effect of cerium trifluoride and uranium tetrafluoride additions

Kinematic viscosity of the 46.5LiF–11.5NaF–42KF eutectic (mol%) has been measured in the temperature range 727–1144 K by the method of torsional oscillations damping of a cylinder with the liquid under study. Found that the kinematic viscosity of this eutectic has some deviations from the exponential law, that may be explained by the existence of clusters in the melt. The volume fraction of the clusters in the eutectic as a function of its temperature was estimated. The kinematic viscosity of the 46.5LiF–11.5NaF–42KF eutectic (in mol%) with additions of (1) 5 and 10 mol% CeF3 as well as (2) 20 mol% UF4 and 10 mol% CeF3 was also measured. It is experimentally proved that the addition of 5 mol% CeF3 significantly reduces the viscosity at low temperatures and slightly increases it – at high temperatures. Reduction of viscosity at low temperatures can be explained by the fact that the molecules of CeF3 destroy clusters. Additions of 20 mol% UF4 also decreased kinematic viscosity of the molten salt mixture compared to pure 46.5LiF–11.5NaF–42KF eutectic (in mol%). Note, that all additions used significantly increased the liquidus temperature of the molten salt mixture. Particularly, additions of 20 mol% UF4 without and with 10 mol% CeF3 increased the liquidus temperature up to 923 and 1023 K, respectively.