In-Situ Density Measurement for Enhanced Electrorefining Material Accountancy

To further enhance the proliferation resistance of electrorefining (ER) processes, precise and reliable analytical methods are essential for determining the inventory of fissile material. This can be achieved by electrochemically measuring the salt concentration and converting it to mass using its density. However, the density within the refiner is not fixed, and small variations in salt composition can significantly impact its thermophysical properties. While an ideal mixing model provides reasonable density estimates (with errors up to 2-3%), such errors are unacceptable when precise material accountancy of fissile material is crucial. This study developed a methodology to measure density in situ without relying on crucible calibration curves, enabling simultaneous density and electrochemical measurements when the density of the salt cannot be accurately modeled. This approach utilizes a precision-machined crucible, a single tungsten electrode, and a multimeter to measure the open circuit potential for direct density calculation. This methodology has been validated in a pure LiCl-KCl eutectic salt with a relative error of 0.3% compared to literature values. Future work will focus on measuring the density of varying concentrations of synthesized UCl3 to determine the concentration of uranium dissolved in the salt. Additionally, the diffusion coefficient and standard potential of the U(0/III) redox couple in the molar standard reference state can be measured with high precision. The aim of this project will benefit the ER process due to its simplicity and ability to provide accurate concentrations in a molar reference state, thus improving the reliability of diffusion coefficients and standard potentials.