The post-doctoral work concerns the mechanism of mass transfer induced by evaporation-condensation under a thermal gradient. In nuclear fuels, the presence of porosities, the very high temperatures combined with the strong thermal gradient activate this evaporation-condensation phenomenon. This results in a displacement of porosities towards the central hot part and a transfer of material in the opposite direction towards the external cold part. This phenomenon is currently modeled by a 2D homogenized approach at the fuel pellet scale in which the material transfer is computed by solving the advection equation coupled to the heat equation by the finite element method.
The post-doctoral fellow will have to set up a microscopic modeling of the vapor phase transfer phenomenon. This work will allow to improve the simulation of free volumes associated to cracks and thus, to justify the assumptions of the velocity law of porosities migration used in the 2D homogenized model.
The work to be carried out is decomposed in two main steps which are on the one hand, the formulation and the numerical implementation of the constitutive equations of the microscopic model, and on the other hand, the justification of the homogenized model. The post-doctoral fellow will work at the CEA Cadarache site in the framework of a collaboration between the research teams of the Department of Fuel Studies and the IUSTI of Aix-Marseille University on the simulation of material transfer in the vapor phase under a thermal gradient. A major advance expected from this work is to take into account the evolution of the geometry of porosities, induced by the material transfer, with techniques for tracking the movement of solid-gas interfaces. The results will be valorized by publications in scientific journals and participation in conferences.