The electrochemical behavior of thorium and uranium in molten LiF was examined separately and simultaneously at 1173 K using cyclic voltammetry. Inert molybdenum wire served as a working electrode. A platinum wire served as a quasireference electrode. The quality of voltammograms was highly dependent on the degree of dryness of the salt. The experimental results confirmed previous findings for similar salt matrices that thorium is reduced in a single, 4-electron [Th(IV)/Th] step, whereas uranium is reduced in a two-step process, including a 1-electron exchange [U(IV)/U(III)] followed by a 3-electron exchange [U(III)/U]. Diffusion coefficients for thorium and uranium were calculated and plotted as a function of concentration. Calibration curves of peak current density vs. analyte concentration were developed. Separability of uranium from the thorium-rich matrix was confirmed feasible. Satisfactory concentration monitoring of uranium was demonstrated, whereas thorium concentration monitoring in the ternary salt was found problematic. (c) 2015 American Institute of Chemical Engineers AIChE J, 62: 1236-1243, 2016