This study focused on the electroreduction process of uranium cations in molten fluorides. It involved cyclic voltammetry, chronopotentiometry with and without current reversal, and square wave voltarnmetry. The results indicate a two-step reduction process for uranium(IV). The first step U(IV)/U(III) exchanging one electron corresponds to a soluble/soluble system and is limited by U(IV) diffusion with D-U(IV) = 1.25 +/- 0.35 x 10(-5) cm(2) s(-1) in LiF-NaF at 720 degrees C. In order to perform a thorough study of the second step U(III)/U(0) in the reduction process, the melt was chemically reduced in U(III) with U metal as reducing agent. Alternatively to the use of LiF-NaF where U metal is unstable at 720 degrees C, the chemical reduction of U(IV) in U(III) was performed in a LiF-CaF2-UF4 solution containing U metal at 810 degrees C. It has been confirmed that the reduction of U(III) proceeds in one step exchanging three electrons and by a diffusion controlled process with D-U(III) = 2.2 0.7 x 10(-5) cm(2) s(-1) in LiF-CaF2 at 810 degrees C. (c) 2006 Elsevier Ltd. All rights reserved.