Fluorination Reaction of Uranium Dioxide by Fluorine

Reaction Model for Fluorination of Uranium Dioxide Using Improved Unreacted Shrinking Core Model for Expanding Spherical Particles

“…5,6) In their model, the unreacted core of UO 2 diminishes as reaction (2) proceeds, and the solid particle also shrinks due to gasification by reaction (3). The model successfully represented not only their experiments 7) but also those reported by Yahata and Iwasaki 3) and by Sakurai. 4) The model was also applied to the fluorination of plutonium dioxide (PuO 2 ) to estimate the rate of fluorination.…”

“…4) Although the rate constants have already been determined for the original model, 7) they have to be redetermined for the presented model. The values of the rate constants determined are Figure 2 shows the time-dependent changes in R and r c calculated by the presented model.…”

“…Since the solid intermediate of UO 2 F 2 has been identified by Sakurai 4) at the initial stage, the reaction model of the fluorination of UO 2 can be improved by including the formation of UO 2 F 2 . Ogata et al 7) developed a reaction model for (1) combining the unreacted shrinking core model with the shrinking particle model. 5,6) In their model, the unreacted core of UO 2 diminishes as reaction (2) proceeds, and the solid particle also shrinks due to gasification by reaction (3).…”

“…Although it is difficult to measure particle diameter precisely, the expansion is expected to be observed because the molar density of UO 2 F 2 ARTICLE ( UO 2 F 2 ¼ 20;680 mol/m 3 ) is lower than that of UO 2 ( UO 2 ¼ 40;550 mol/m 3 ). 10) In this study, the original model 7,9) is extended to the situation where the particle swells due to the density difference between the intermediate and the particle itself. While the model is dedicated to the fluorination of UO 2 , the extended model is derived for a general gas-solid reaction consisting of a two-step reaction: the formation of a solid intermediate on the core of an unreacted reactant and the consumption of the intermediate.…”

Nitrogen Trifluoride-Based Fluoride- Volatility Separations Process: Initial Studies

“…It is possible that fluorination of metal and metal oxide surfaces using more aggressive reagents such as fluorine (Ogata et al 2004;Homma et al 2008), bromine pentafluoride (BrF 5 ), ClF 3 (Labaton 1959), etc., follows the "shrinking core" reaction model or similar physical kinetic behavior, but it also could be that the reagent reactivity is such that product barriers, for instance, are fluorinated away with equivalent facility as the starting material. Thermoanalyses of fluorination reaction with aggressive fluorinating agents show little evidence of sequential product formation; rather, volatile production appears to be kinetically favored, and the final process of volatilization likely dominates the observable.…”