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

Abstract

SUMMARY 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 = 773 K. 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 = 773 K 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. Copyright © 2014 John Wiley & Sons, Ltd.

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

“…Our DFT results clearly indicate that U ions favor clustering into various crystallite as UCl n ( n = 3–6), mediated by chemical bonding with Cl ions in the eutectic LiCl–KCl molten salt. It is well agreed with the finding of our previous papers that U and Cl ions have strong chemical interactions. The overall topology of the U nanocluster does not change with only marginal modification around the outmost shell by the interaction with Cl ions nearby.…”

A study of uranium adsorption to single-crystal tungsten

“…Moreover, it should be pointed out that our results are consistent with the ones recently reported by Kwak et al [12]. In that work, the authors used the coupled cluster expansion of Cl/U/W(100) surface to develop a potential surface which was consequently used in Monte Carlo simulations using the grand canonical Hamiltonian.…”

“…We choose to study uranium adsorption to tungsten for many reasons. First, uranium adsorption to tungsten has been studied both experimentally and theoretically in the past [12][13][14] and this gives us a point of reference. Second, tungsten is used as a working electrode candidate in cyclic voltammetry studies and uranium adsorption to the tungsten electrode has been known to complicate the interpretation of cyclic voltammetry measurements and models.…”

First principles computational studies of spontaneous reduction reaction of Eu(III) in eutectic LiCl-KCl molten salt

“…20 First principles-based computational chemistry can be useful for this objective because it is largely free from empirical assumptions and easy to decouple effects of entangled experimental variables. [21][22][23][24][25][26] For example, computational coordination chemistry for radioactive ions in high-temperature molten salt 21,[27][28][29] shows good consistency with experimental validations. Recently, due to dramatic advances in computational architectures and software engineering, empowered first principles computational approaches with accurate and fast prediction of key properties of complex materials exposed to vacuum, gas phase, or even liquid solution environments can be possible.…”

“…First principles‐based computational chemistry can be useful for this objective because it is largely free from empirical assumptions and easy to decouple effects of entangled experimental variables . For example, computational coordination chemistry for radioactive ions in high‐temperature molten salt shows good consistency with experimental validations.…”