First-principles based computational study on nucleation and growth mechanisms of U on Mo(110) surface solvated in an eutectic LiCl-KCl molten salt

Abstract

We utilize first principles density functional theory (DFT) calculations and ab-initio molecular dynamic (AIMD) simulations to identify underlying mechanisms elucidating the initial stage of electrocrystallization process of U on Mo(110) surface in a eutectic LiCl–KCl molten salt at T = 773 K. Our results clearly unveil surprisingly different principles on the nucleation of U in the media from that under vacuum conditions. U nanoclusters exposed to vacuum completely collapse into flat atomic layers on Mo(110) surface similar to an electrodeposition process. On the other hand, Cl ions in eutectic molten salt thermodynamically drive crystallite formation consisting of UCln(n = 3–6) through agglomeration of U atoms. Those crystallite gradually grows into bigger nuclei by adsorbing on Mo(110) surface. We propose that those behaviors are understandable only with revised conventional theories and that atomic level interactions among U, LiCl–KCl molten salt and Mo(110) surface play a key role to describe the atomic-scale dendrite formation of U in the electrorefining process. Our study can be one of the basic steps to design efficient electrorefining systems by identifying the fundamental cause of the experimentally observed uranium nucleation phenomena. © 2016 John Wiley & Sons, Ltd.