(214d) Evaluating Metallic Nd and Pr Interactions with Molten Chloride Salts Using Spectroscopy and in-Situ Electrochemical Spectroscopy.

After the nuclear fuel (i.e., UO₂) is used inside the reactor, the fuel matrix is characterized by a variety of fission products (FP). Many of the FP (i.e., rare earth elements, alkali/alkaline earths, actinides) in the used nuclear fuel can be recovered via nuclear reprocessing technologies. In pyroprocessing, the used nuclear fuel is electrochemically dissolved into a molten chloride (LiCl-KCl) eutectic salt mixture in the electrorefiner. Due to the different applied potentials, uranium is initially reduced onto an inert cathode. However, many of the remaining FPs accumulate in the melt and are challenging to recover by an inert electrode, especially the rare earth elements (Nd, Gd, Pr, Sm) due to their multivalent oxidation states, disproportionation reactions (Nd³⁺+Nd⁰=Nd²⁺) and undergo dissolution in the electrolyte. Due to these challenges, FP recovery is inefficient and leads to the constant discarding of the molten chloride salt which in turn generates more waste. Additionally, the presence of rare earth elements and other fission products in the molten salt electrolyte changes the physical and chemical properties of the electrolyte, which impacts the efficiency of the recovery of uranium, and the lifespan of the molten chloride salt. To improve the recovery efficiency of the FP, specifically rare earth elements, the fundamental interactions between rare earth elements in the molten chloride salt and their metallic form: LiCl-KCl-NdCl₃, LiCl-KCl-PrCl₃ with pure Nd and Pr metals were investigated at 773–873 K. The kinetics pathways of the disproportionation/dissolution reactions occurring at the interface between the rare earth metal and the molten chloride salt were investigated via UV-Vis and Raman spectroscopy. The electrochemical transitions of Pr³⁺/Pr(s), Nd^2+,3+/Nd(s) were evaluated using an inert W electrode at 773–873 K using cyclic voltammetry, chronoamperometry techniques coupled with in-situ UV-Vis spectroscopy to characterize their kinetic pathways and contrast the results obtained by chemically reacting the metallic rare earth and the molten chloride salts.