Characterization of the Electrochemical Behavior of a Li-Bi Reference Electrode for the Molten LiCl-Li

Abstract

In order to maximize uranium resources and minimize the need to store radioactive material in geologic repositories, it is necessary to reprocess used nuclear fuel (UNF) to recycle the fissile material and transuranic isotopes that remain. The pyroprocessing operation developed by Argonne National Laboratory as part of the integral fast reactor project was designed to accomplish this goal while minimizing the risk of proliferation (1). Inclusion of oxide based UNF from the current light water reactor fleet into the metallic fuel based fast reactor cycle will require electrolytic oxide reduction in a LiCl-Li2O electrolyte (2). As a side reaction during the electroreduction of U, Li is codeposited on the cathode surface and subsequently dissolves, forming a ternary LiCl-Li2O-Li electrolyte (3, 4). The presence of metallic Li in the electrolyte negates the possibility of using the reference electrodes typically used for molten salt electrochemistry. The Li-Bi couple has been used as a reference electrode previously but has not yet been well characterized (5, 6). This work investigates the stability of the Li-Bi reference couple in varying solution chemistries typical of those found during electrolytic reduction of UO2. Acknowledgements: This work was performed under the auspices of the Department of Energy (DOE) under contracts DE-NE0008262 and DE-NE0008236, and the US Nuclear Regulatory Commission (NRC) under contracts NRCHQ-11-G-38-0039, NRC-HQ-10-G-38-0027, NRC-HQ-13-G-38-0027. W.P. and A.M acknowledge the Fellowship Award from the USNRC. Dr. Kenny Osborne serves as the program manager for the DOE award and Ms. Nancy Hebron-Isreal serves as the grants program officer for the NRC awards. References: 1. J. J. Laidler, J. E. Battles, W. E. Miller, J. P. Ackerman, E. L. Carls, Development of Pyroprocessing Technology. Progress in Nuclear Energy 31, 131-140 (1997). 2. S. D. Herrmann, S. X. Li, M. F. Simpson, S. Phongikaroon, Electrolytic Reduction of Spent Nuclear Oxide Fuel as Part of an Integral Process to Separate and Recover Actinides from Fission Products. Separation Science and Technology 41, 1965-1983 (2006). 3. T. Takenaka, K. Shigeta, H. Masuhama, K. Kubota, Influence of Some Factors upon Electrodeposition of Liquid Li and Mg. ECS Transactions 49, 441-448 (2009). 4. A. S. Dworkin, H. R. Bronstein, M. A. Bredig, Miscibility of Metals with Salts. VI. Lithium-Lithium Halide Systems. The Journal of Physical Chemistry 66, 572-573 (1962). 5. M. Iizuka, Y. Sakamura, T. Inoue, Electrochemical reduction of (U-40Pu-5Np)O2 in molten LiCl electrolyte. Journal of Nuclear Materials 359, 102-113 (2006). 6. X. Ning et al., Self-healing Li-Bi liquid metal battery for grid-scale energy storage. Journal of Power Sciences 275, 370-376 (2015).