An Initial Study of Uranium Morphology in Fused LiCl-KCl

Molten salt electrorefining is one method by which reusable constituents within used nuclear fuel can be recovered for recycle and especially radiotoxic isotopes removed for incorporation into tailored waste forms. In these processes, irradiated metallic uranium or uranium alloys are dissolved at an electrochemical anode and crystals of purified uranium are collected at a cathode. The morphology of the deposited crystals can impact a variety of important factors, including the adhesion characteristics of the deposit to the cathode surface and the amount of salt which is macroscopically and microscopically occluded with the deposit. In addition, future applications such as direct creation of nuclear fuels by electrochemical deposition might be enabled if the science and fundamentals of uranium deposition morphology were thoroughly understood. A reasonable amount of experience has been collected from uranium electrorefining within the range of typical plant conditions. However, only limited laboratory study has been performed to define and understand the range of uranium crystal morphologies under repeatable laboratory conditions. The present study was an initial step to define these morphologies and transitions. The deposit from each deposition potential was primarily composed of a different morphology with little crossover of that morphology into the other deposition potentials. The spacing of these experiments (overpotentials of 25, 150 and 450 mV) is wide enough that additional dominant morphologies could exist. In addition, while the majority of the deposit from each potential was comprised of a particular morphology, minor morphologies were also found within the deposit. This may indicate the presence of an additional dimension of complexity, namely uranium concentration. Additional experimental and theoretical studies would be valuable to elucidate this subject. Additional results will be presented and discussed. (authors)