Substantiation and Choice of Am and Cm Imitators for Electrochemical Measurements in a LiCl–KCl Melt

Abstract—Spent nuclear fuel (SNF) processing is strongly difficult because of high radioactivity of its actinides including the most active americium and curium. Primary experiments on their extraction using nonradioactive imitators are preferable, but the choice of them is impeded by a necessity to obey a broad range of physicochemical properties with imitated elements. In this work, the choice is substantiated and the most appropriate imitators are proposed on the basis of literature data to study the separation of americium and curium in chloride melts. Europium and gadolinium can serve as imitators for chemical processes in the molten LiCl–KCl eutectic, but a high difference of potentials of americium and curium does not allow their use for studying the electrochemical kinetics. The arbitrary potentials and electroreduction kinetics of a series of metals (Mg, Sc, Sr, Ba, Pr, Nd, Ce, Eu, and Gd) in the chloride melts at various temperatures are analyzed. A high convergence of the reduction potentials of magnesium and scandium with those of the imitated elements assumes their application as electrochemical imitators for studying separately americium and curium (without their simultaneous presence in the solution). In spite of the resembling reduction potentials, the combined use of the Mg/Sc pair for the study of this process seems doubtful, since the electrochemical kinetics of these elements differs strongly from the kinetics of the target actinides. The Nd/Ce pair can serve as a more suitable pair for the combined study of the electrochemical kinetics of americium and curium due to the high affinity of both chemical and electrochemical properties to the imitated elements. A comparison of the electrochemical kinetics of cerium and curium reduction in the chloride melts shows that both elements exist in the melt in the oxidation state 3+ and are reduced in one step. In turn, both neodymium and americium are reduced in two steps, and the transition from the oxidation state 3+ to 2+ begins for both elements in a potential range of –1.5 V versus the silver chloride reference electrode.