Pyrochemical technology is one of promising methods for reprocessing fast neutron reactors spent fuels after short cooling time. Working temperatures can be lowered by employing low-melting eutectic mixtures of alkali chlorides.  Ternary lithium-potassium-cesium chloride eutectic has the lowest melting point (529 K) of all known alkali chloride systems. The main objective of the present work was therefore studying the behavior and determining main electrochemical and thermodynamic properties of uranium (E*U(III)/U(0), E*U(IV)/U(III), ?G of formation, DU(III), DU(IV)) in LiCl-KCl-CsCl eutectic melt. The measurements were performed at 573�1073 K employing potentiometry, cyclic and square wave voltammetry. Uranium concentration in the melt and the average oxidation state were determined by chemical analysis after each experiment.Uranium formal standard electrode potentials in LiCl-KCl-CsCl eutectic melt were determined using electromotive force method. E*U(III)/U(0) linearly increases with temperature and between 576-1067 K is described by the following equation:E*U(III)/U(0) = -2.901 + 6�10-4 � T (� 0.029) VFrom the results of the electrochemical measurements change of Gibbs free energy of the formation of uranium trichloride in LiCl-KCl-CsCl melt at 576-1067 K was calculated:?G*UCl3  = -839.8 + 161.7�10-3 � T (� 2.6) (kJ/mol)Uranium(IV)/(III) electrochemical reduction was studied using cyclic and square wave voltammetry.  Analysis of the experimental data showed that U(IV) ? U(III) reduction is a reversible one-electron diffusion controlled process.Information concerning diffusion of ions of the same metal in different oxidation states is important for explaining the mechanism of diffusion of polyvalent metal ions in molten salt media.  In the present work the diffusion coefficients of uranium(III) and (IV) ions were determined between 573-1073 K employing cyclic voltammetry.  The experimental results are satisfactorily described by the following equations:lgDU(III) = -4341.809/T + 0.199 (�0.088) cm2/slgDU(IV) = -3002.613/T � 1.541 (�0.047) cm2/s

Uranium electrochemical behavior and properties in LiCl-KCl-CsCl eutectic melt

247th National Meeting (2014)

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