[en] In this study a mathematical model is developed in order to simulate fluorination reaction of uranium dioxide leading to produce uranium hexafluoride. The model considers homogeneous reaction for intermediate solid and heterogeneous one for unreacted shrinking core. Also, this study tries to clearly show the shortcoming of those foregoing models that take surface reactions for both solids. In fact, one may not trust the accuracy of those models due to ignoring the importance of the diffusion phenomena into the intermediate solid and taking place the reaction within it. On the other hand, by neglecting the undeniable effects of operating conditions, including temperature and particle size on gas concentration distribution and reaction rates may introduce large deviations. For this mentioned purposes, the governing equations are derived on the basis of the mass conservation law and have been solved numerically. Besides, for the first time, some dimensionless equations and groups are introduced to predict the reaction rates and the amount of the main and the intermediate products for using numerical procedure. Comparing the results with the corresponding experimental ones represents the desirable accuracy of the model. After validation of the model, the effect of some operational variables such as temperature and initial particle size have been investigated on the reaction rates and the conversions