(559f) Development of a Rotating Cylinder Electrode for Electroanalytical Measurements in a Used Nuclear Fuel Electrorefiner

Pyroprocessing is an important application of metallurgy to nuclear energy systems as an attractive option for the recycling of actinides from used nuclear fuel. This technology utilizes differences in the electrochemical potentials of metal ions to selectively separate actinides from lanthanides and other fission products found in used fuel. The ability to identify the co-deposition of uranium with other ions (actinides or contaminates) and determine the rate of deposition for each metal would be beneficial to process control and safeguards. DREP (Deposition Rates from Electrode Potentials) was developed to predict the metal(s) depositing at the cathode of an electrorefiner. DREP is an electrorefining model that couples the cell current and cathode potential to determine if multiple metals are depositing and, if so, predict the rate of deposition for each metal. A key assumption to DREP is a constant, well-defined diffusion layer. The diffusion layer at a stationary electrode grows with time until natural convection prevents further growth. Rotating electrode can provide a well-defined, time-independent diffusion layer. Rotating disk (RDE) and rotating ring-disk electrodes (RRDE) have been developed for application in various high-temperature molten salts. However, the RDE and RRDE rely upon an insulator sealing the edges of an electrode to prevent leakage of electrolyte into the electrode-insulator interface. This leakage is exacerbated at high-temperature. Furthermore, many insulators react with molten salts degrading the insulating and/or sealing properties of the selected material. The rotating cylinder electrode (RCE) can circumvent many of these challenges since no insulating material is required. Since no previous work on a molten salt RCE could be found in the literature, a RCE for electrochemical measurements in molten LiCl-KCl eutectic was developed. Electroanalytical measurements made with RCE are also presented. The theory developed for the RCE in aqueous solutions is applied to the electroanalytical measurements in molten LiCl-KCl eutectic to determine its validity in molten salts and to evaluate the experimental setup. Lastly, short-term (<1 min.) electrodeposition test were performed in molten LiCl-KCl eutectic containing UCl₃ and MgCl₂ (surrogate for PuCl₃) in which both uranium and magnesium were deposited at the cathode. The tests were used to validate DREP and evaluate its accuracy in predicting uranium and magnesium co-deposition.