Abstract
Fluorination of uranium and plutonium dioxides by fluorine is discussed for the flame tower reactor, which is one of possible reactors in FLUOREX process, a hybrid reprocessing combining a fluoride volatility process and a solvent extraction. A reaction model for a shrinking particle with an un-reacted shrinking core is applied to the fluorination of plutonium dioxide and the reaction rate constants are determined in low temperature range around 400°C using the reported kinetic data [Iwasaki et al., J. Nucl. Sci. Technol., 11, 403 (1974)]. The determined rate equations are used to analyze the fluorination of uranium and plutonium dioxides in the high temperature range (800-1, 200°C), where the flame tower reactor is operated. For uranium dioxides the diffusion of fluorine to the surface of the particle controls the overall fluorination reaction, and the model can predict the recovery of uranium to the product of uranium hexafluoride. For plutonium dioxides, however, the recoveries of plutonium calculated by the presented model do not agree with the experimental recoveries. It is suggested that the reaction mechanism for the fluorination of plutonium dioxide in the high temperature range is different from that in the low temperature range.
