Electrochemistry of uranium in molten LiCl-LiF

Sylvain Geran (1, 2) , Pierre Chamelot (1) , Jérome Serp (2) , Mathieu Gibilaro (1) , Laurent Massot (1)

1 LGC - Laboratoire de Génie Chimique
2 CEA - Commissariat à l'énergie atomique et aux énergies alternatives

This work is focused on the electrochemical behaviour of uranium in molten eutectic LiCl–LiF (70–30 mol%) in the 550–650 °C temperature range. On tungsten electrode, U(III) ions were reduced in one step to U metal exchanging 3 electrons and oxidized also in one step to U(IV) exchanging one electron. Both systems were studied by cyclic and square wave voltammetries and chronopotentiometry. The re- duction and oxidation mechanisms of U(III) ions were found to be diffusion controlled processes. The diffusion coefficient of U(III) was measured at different temperatures, and it followed an Arrhenius “type law”. Apparent standard potentials were measured in chloride-fluoride (LiCl-LiF eutectic) and pure chlo- ride media (LiC-KCl eutectic). The addition of fluoride ions into a chloride salt leads to the formation of more stable complexes reduced at more negative potentials. This shift of reduction potentials is more pronounced for the U(IV)/U(III) transition (~ 500 mV) than for the U(III)/U system (~ 100 mV).

Mots clés: Molten chloro-fluoride media; Electrochemistry; Uranium; Fluoride stabilizing effect; Electrochemical reaction mechanism

Domaines: Génie des procédés

Sylvain Geran, Pierre Chamelot, Jérome Serp, Mathieu Gibilaro, Laurent Massot. Electrochemistry of uranium in molten LiCl-LiF. Electrochimica Acta, 2020, 355, pp.136784. ⟨10.1016/j.electacta.2020.136784⟩. ⟨hal-03118790⟩