Electrorefining is an important unit operation for the pyroprocessing of spent nuclear fuel; however, the uncontrolled growth of uranium dendrites traps molten salt into the deposited uranium, increases the short-circuit risk, decreases the current efficiency, and thus hinders the engineering application of the electrorefining technology. In this study, the finite element method is applied to the study of the electrorefining dynamics subjected to convection, diffusion, electromigration, and electrode reaction. The velocity field, concentration field, electric field, and flux density field are evaluated. The local current density on the cathode is evaluated under different overall current densities, overpotentials, cathodic shapes, and positions for the evaluation of dendritic growth. Finally, it is concluded that the uranium will be deposited first onto the cathode tip and the frontside of the cathode facing the anode, the position of the electrode and the shape of the cathode tip will not have significant influence to the priority of deposition, and a glass insulated tip can effectively improve the uneven growth of uranium dendrites on the cathode surface as proposed by Srihari et al. (Sep. Sci. Technol. 51, 1397).

No abstract

Electrorefining is an important unit operation for the pyroprocessing of used nuclear fuel; however, the uncontrolled growth of uranium dendrites on the cathode is hindering its engineering application. In this study, the phase-field modelling is applied to the study of the growth of uranium dendrites using the finite element method, and the fractal dimension and the perimeter-to-area ratio are employed to classify quantitatively the morphologies of uranium dendrites. It is shown that uranium dendrites can form sprout-like, fishbone-like, and tree-like morphologies, and the effects of anisotropic strength, symmetry index, overpotential, and temperature to the morphologies of uranium dendrites are discussed. It is concluded that the diffusion of uranium cations (diffusion rate-controlling) in molten salt and the electrode kinetics (kinetic rate-controlling) are the two rate-controlling steps for the electrodeposition of uranium, and the diffusion rate-controlling mechanism is responsible for the growth of complicated dendritic morphologies.

No abstract