Analysis and Modeling of Oxide Reduction Processes for Uranium Oxides

This article describes a kinetic model for the reduction process of used oxide nuclear fuel with molten LiCl at 650°C. In this process, metal oxides, primarily UO2, react to form metallic U and Li2O. As UO2 is gradually reduced, metallic U and Li2O form in molten LiCl, in and through which Li2O dissolves and diffuses. To capture the prescribed chemical and physical phenomena, two classical kinetic models are integrated sequentially to describe Li2O formation, dissolution, and diffusion behaviors. The first part of the integrated model uses a shrinking core kinetics to explain the formation, dissolution, and diffusion of Li2O while accounting for the expanding metallic uranium layer. The second part of the integrated model begins with the completion of Li2O dissolution and deals with the diffusion of excess Li2O in the metallic uranium layer. A Fick's second law without an external source describes the second part of the process behavior. The integrated model explains engineering scale kinetic measurement data from the literature with the effective Li2O diffusion coefficient range between 2 and 6 (10−5cm2/sec).