A phase-field investigation of factors affecting the morphology of uranium dendrites during electrodeposition

The growth of uranium dendrites has been one of the critical issues in the electrorefining of spent nuclear fuel for several decades. However, a comprehensive description of uranium dendrites, including the contribution of electrodeposition and the interface property, remains unavailable. In this paper, the phase-field method is applied to assess the effects of applied voltage, exchange current density, interfacial energy, interfacial anisotropy, interfacial noise, initial electrodeposit size, and initial electrodeposit density on the uranium dendrites. Furthermore, an approach for precisely estimating the phase-field parameters is developed to capture more details of dendrites, such as interfacial mobility, reaction constant, barrier height, and gradient energy coefficient. The results reveal that high applied voltage, high exchange current density and low interfacial energy stimulate the growth of dendrites with complex structures. The dendrites are dominated by the tip-controlled mechanism regardless of the applied voltage, exchange current density and interfacial energy, but for high interfacial energy, the growth of some side branches follows the thermodynamic suppression mechanism. Strong interfacial noise can enhance the anisotropy of the system, making it difficult to distinguish the principal branches from the side ones, which are intertwined with each other. Moreover, a parameter map is drawn to quantitatively predict the uranium dendrite patterns, which vary as a function of the densities and sizes of the initial electrodeposits. The cause of tip splitting is analyzed as either insufficient interfacial anisotropy or a large initial electrodeposit size. The numerical results are in good agreement with the experimental data and the current theory. Overall, this work provides a theoretical basis for controlling the morphology of uranium dendrites.