In close collaboration with the process simulation and systems analysis laboratory (LSPS) and in a model-mechanistic approach, the trainee will start with CFD/DEM and FE calculations using software such as Open FOAM for fluid mechanics. or LIGGGHTS for granular dynamics. This is a crucial step for the construction of predictive models necessary for the optimization of the processes used. The comparison with experimental measurements will adjust the parameters of the model and at each moment will allow us to address questions and issues on: The position, movement, speed of each sheath and the intensity of the solid-solid interaction forces in the rotary kiln Aeraulics and thermodynamics in fluid-structure and fluid-solid interactions, The kinetic approach of oxidation and transformation of UO2 into U3O8 by germination and Avrami-Erofeev type growth. This internship aims to develop modeling around the oxidation of UO2 fuel under cladding and under air at temperature and to incorporate different issues of multiphysics phenomena to guide either new settings or technological adaptations.