Electrochemical separation using molten salts is a promising technology for recycling uranium and transuranic metals from used nuclear fuel. As used nuclear fuel is processed in the molten salt electrolyte (LiCl-KCl), alkaline-earth fission products (Sr and Ba) that are more active than uranium are oxidized and accumulate in the molten salt as dissolved ions, which must be periodically removed to reuse the process salt (LiCl-KCl) and minimize nuclear waste generation. The recovery of alkaline-earth elements from the molten salts is challenging due to the higher stability of Sr and Ba ions relative to the Li and K ions in the chloride solution. This work will present that the recovery of Sr and Ba from molten salts can be achieved using liquid metal electrodes by leveraging the strong chemical interactions between alkaline-earth and liquid metals. The principle of alkaline-earth recovery into liquid metals will be discussed by comparing the thermodynamic properties (redox potentials) of alkaline-earth/liquid-metal alloys to those of alkali/liquid-metal alloys. The experimental approaches to determine the thermodynamic properties of binary alkaline-earth/liquid-metal alloys of (Sr, Ba)-(Bi, Sb, Pb, Sn) will be presented, including (i) electromotive force measurements using solid electrolytes, (ii) thermal characterization using differential scanning calorimetry, and (iii) structural analysis by X-ray diffraction. The feasibility of separating alkaline-earth elements into liquid metals will be demonstrated, which could be employed as a critical step for reusing the process salt in order to minimize the generation of additional nuclear wastes.

Recovery of alkaline-earth fission products from molten salts

2019 Fall National Meeting

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