The aim of the proposed thesis is to develop a phase-field model describing the migration of fabrication porosity in uranium-plutonium mixed oxides under irradiation in sodium fast reactors. The model will take into account evaporation and condensation phenomena as the microscopic driving force moving porosity where the necessary local temperature and temperature gradient conditions are reached to establish this transport mechanism. To provide a consistent estimate of the vapor pressure differences governing the rate of evaporation (and condensation), the phase field model will be coupled to a thermodynamic description of the U-Pu-O ternary system. The candidate will work on the development of the theoretical formulation of the phase field model, as well as its inclusion in the framework of a finite element solver. The computational tool will be applied to study the conditions encountered in prototypical fast neutron reactors, in order to derive new pore migration rate laws for inclusion in the scientific fuel behavior calculation tools (OCS) used at industrial level, such as PLEIADES/GERMINAL V3, the OCS developed in the host department at CEA IRESNE.
The results obtained in the thesis will be the subject of presentations at international conferences (e.g. NuMat - The Nuclear Materials Conference, MMM - Multiscale Materials Modeling Conference, MiNES - Materials in Nuclear Energy Systems, CALPHAD), as well as publications in international scientific journals (Computational Material Science, Journal of Nuclear Materials, Journal of Applied Physics, Acta Materialia).
At the IRESNE institute (CEA Cadarache), the candidate will join a multi-disciplinary materials science community (solid state physics, thermics, mechanics, applied mathematics, thermochemistry, thermodynamics) open to both international research and the industrial world, will have the opportunity to interact with experts involved in the various stages of nuclear reactor design, and will use state-of-the-art numerical simulations on both small and large scales. The candidate will have the opportunity to spend part of his thesis in his thesis supervisor's university laboratory at the Ecole Polytechnique, where he/she will be able to complement the experience gained in an applied research institute such as the CEA with the more academic exposure offered by a university institution. Finally, the candidate will have the opportunity to familiarize himself/herself with and become an expert of two of the most widely used techniques for analyzing the evolution of microstructures in many industrial fields: phase field and thermodynamic calculations using the CALPHAD technique.