Phase-field simulation study of uranium dendrite growth under pulsed electrodeposition conditions

BackgroundMolten salt electrorefining is a promising technology for nuclear fuel reprocessing, but uncontrolled uranium dendrite growth hinders its stable operation and efficiency. Although several mitigation strategies have been explored, the underlying micro-mechanisms remain unclear; thus, establishing a reliable computational model is essential to elucidate these mechanisms and guide process optimization.PurposeThis study aims to systematically investigate the effects of key pulse electrodeposition parameters, such as voltage amplitude, duty cycle, and pulse width, on the growth behavior and morphological evolution of uranium dendrites in a high-temperature molten salt system, hence to provide quantitative insights into their synergistic control mechanisms.MethodsFirstly, a detailed phase-field model was established to describe the dynamic evolution of uranium dendrites under pulsed electrodeposition conditions. The model incorporated chemical free energy, gradient energy, and electrochemical driving forces. Then, numerical simulations were performed using COMSOL Multiphysics, applying different combinations of duty cycle, pulse width and voltage amplitude. Key morphological descriptors, including dendrite main stem length and the perimeter-to-area ratio, were used to quantify dendrite complexity. Boundary conditions and mesh sizes were carefully defined to ensure numerical accuracy. Finally, ion transport, charge conservation, and interface kinetics were considered in the model to replicate real deposition processes.ResultsThe simulation results indicate that, compared with constant potential deposition, pulsed electrodeposition significantly reduces the growth rate and structural complexity of uranium dendrites. When the duty cycle is set to 0.25 and the pulse width to 3 s, the dendrite length remains within 200 μm, and the perimeter-to-area ratio stays below 0.06 μm-1. In contrast, under constant potential deposition, the dendrite length exceeds 350 μm and the perimeter-to-area ratio rises above 0.1 μm-1, demonstrating more pronounced dendrite elongation and lateral branching. During pulsed electrodeposition, lowering the duty cycle effectively reduces the main stem length and the number of side branches, thus suppressing dendrite growth. Shortening the pulse width helps maintain a smoother dendrite tip morphology by allowing frequent ion replenishment at the electrode interface during the off-time, which mitigates concentration polarization. In addition, the voltage amplitude, as the primary electrochemical driving force, amplifies dendrite growth intensity when increased. The combined adjustment of duty cycle and pulse width demonstrates a clear synergistic effect on controlling dendrite evolution.ConclusionsThis study systematically reveals for the first time the synergistic effects of duty cycle, pulse width, and voltage amplitude on uranium dendrite evolution under pulsed electrodeposition conditions. It is concluded that using a moderate duty cycle with a short pulse width can effectively suppress dendrite formation while maintaining reasonable deposition efficiency. The findings of this study provide valuable theoretical guidance and practical references for optimizing molten salt electrorefining processes, enhancing uranium deposition quality, and mitigating safety risks associated with dendrite-induced short circuits.