A problem of uranium electrolytical production and refining is considered. Density and surface tension of fused chlorides in the NaCl-KCl-UCl4 system are studied depending on temperature. Molar volumes and their deviations from additive and thermodynamic surface values are computed as related to monomolecular surface layer at 1000 K. The concentration dependences of computed values and surface tension point to complex interaction between components of ternary systems with formation of complex uranium ions.