Activation Energy for Isotope Exchange Reaction between ²³⁵UF₅ Nanoparticles and ²³⁸UF₆ Gas

Abstract

The temperature dependence of the rates for two kinetic processes involved in the isotopic exchange reaction between 235U-enriched UF5 nanoparticles and natural UF6 gas was experimentally examined using our kinetic model that includes the fraction of high-reactivity molecules of UF5 on the outermost layer of the particles. The activation energies obtained from the Arrhenius plot for the fast process and the slow process were similar, 36.1 and 39.3 kJ/mol, respectively. This indicates that the two rate processes are mainly caused by the difference in the preexponential factor of the Arrhenius equation. It was suggested that such a difference in the reactivity of the UF5 molecules was caused by the difference in the adsorption configurations of UF6 molecules on the surface of UF5 molecules due to the steric hindrance of neighboring fluorine atoms.