Mechano-electrochemical phase field modeling for formation and modulation of dendritic pattern : application to uranium recovery from spent nuclear fuel

Abstract

Dendrite formation is a critical issue in uranium recovery from spent nuclear fuel (SNF) through a molten-salt electrorefining process. To understand and modulate uranium dendritic formation, we developed a computation model that involves all the complexities in the mechano-electrochemical process, such as diffusion–reaction kinetics, interfacial anisotropy and the variations of electric and stress fields. In particular, the lattice mismatch between deposit and substrate is considered which addressed the importance of cathode material. The model explains various morphologies of dendrites, which in a two-dimensional scenario can be demarcated based on the perimeter-to-area ratio, χ/S. Dendrites can be needle-like, tooth-like, or tree-like when χ/S < 2 mm−1, 2 mm−1 ≤ χ/S < 6 mm−1, and χ/S ≥ 6 mm−1, respectively. With these conditions, the parameter maps for modulating dendritic patterns are drawn to elucidate the effects of interfacial anisotropy, nuclei site geometry, diffusivity, electric and stress fields, which can be employed to design a molten-salt electroplating process to minimize failures caused by dendrite formation.