Multi-scale computational study of the molten salt based recycling of spent nuclear fuels

Abstract

By applying a rigorous computational procedure combining first principles density functional theory (DFT) calculations and statistical mechanics, we acquire thermochemical properties of materials for a pyroprocessing system recycling spent nuclear fuels. Cluster expansions to DFT obtained energies parameterize atomic interaction potentials of Cl-Cl and Cl-U adsorbed on W(110) surface from a molten salt (KCL-LiCl). Using these databases of the long-range and multibody interactions, Monte Carlo simulations identify thermodynamically stable configurations of the adsorbates on the W(110) surface in grand canonical open system at T=773K. Our results indicate that Cl atoms adsorbed at the interface of the molten salt and W(110) surface substantially drive electrochemical deposition of U ions at low chemical potential of Cl. This behavior, however, stops after approximately 1/3 ML coverage of U because the atomic sites on W(110) surface are mostly blocked by adsorbed Cl, which implies that the attractive interactions of Cl-W are stronger than Cl-U as well as the repulsive interactions between U atoms are effective at these coverage ranges. We also predict the solubility limit of U ion in the molten LiCl-KCl phases at T=773K should be about 5 atomic percent, which well agrees with previous reports by experimental measurements. This study indicates that accurate characterization of the stable Cl structure at the interface is vital for understanding the fundamental mechanisms of recycling spent nuclear fuels and for screening high functional electrode materials in the pyroprocessing system. © 2014 John Wiley & Sons, Ltd.