An alternative way of reprocessing nuclear fuel by hydrometallurgy could be using treatment with molten salts, particularly fluoride melts. Moreover, one of the six concepts chosen for GEN IV nuclear reactors (Technology Roadmap -http://gif.inel.gov/roadmap/) is the molten salt reactor (MSR). The originality of the concept is the use of molten salts as liquid fuel and coolant. During the running of the reactor, fission products, particularly lanthanides, accumulate in the melt and have to be eliminated to optimise reactor operation. This study concerns the feasibility of the separation actinides-lanthanides-solvent by selectively electrodepositing the elements to be separated on an inert (Mo, Ta) or a reactive (Ni) cathodic substrate in molten fluoride media. The main results of this work lead to the conclusions that:• The solvents to be used for efficient separation must be fluoride media containing lithium as cation.• Inert substrates are suitable for actinide/lanthanide separation; nickel substrate is more suitable for the extraction of lanthanides from the solvent, owing to the depolarisation occurring in the cathodic process through alloy formation.

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a b s t r a c tThis article is focused on the electrochemical behaviour of U ions in molten LiF-CaF 2 (79-21 wt.%) eutectic. On a W electrode, U(III) is reduced in one step to U metal and U(III) can be also oxidised to U(IV). Both systems were studied by cyclic and square wave voltammetry. Reversibility of both systems for both techniques was verified and number of exchanged electrons was determined, as well as diffusion coefficients for U(III) and U(IV). The results are in a good agreement with previous studies. On a Ni electrode, the depolarisation effect due to intermetallic compounds formation was observed. Electrorefining of U metal in a melt containing U and Gd ions was carried out using a reactive Ni electrode with promising results.

The electrochemical reduction of two lanthanides (neodymium Nd and gadolinium Gd) was investigated in the 800-950°C temperature range on nickel and copper electrodes. These materials react with lanthanides (Ln) to form intermetallic compounds. The formation mechanism of the alloys was determined by coupling electrochemical techniques and Scanning Electron Microscopy (SEM) after electrolyses runs; this also allowed the identification of the binary compounds formed. In addition, from the electrochemical results, we calculated the Gibbs energies of Nd/Ni, Gd/Ni, Gd/Cu and Nd/Cu.