During nuclear reactions within the oxide fuel, fission products of hundreds of MeV are generated which cause a considerable damage to the fuel material. The in-pile fuel behaviour and ultimately the life-span of a fuel element depend strongly upon the behaviour of point or extended defect populations created as a combined result of high radiation fluxes and temperatures. Furthermore, the generated fission products are mostly insoluble and in the case of rare gases (Xe, Kr), they can either be released and contribute to an increase of the internal pressure of the fuel rod, or precipitate and lead to the swelling or even the degradation of the fuel.



However, the basic processes through which radiation defects are formed remain unclear at the atomic scale. The proposed thesis aims therefore at studying some of these mechanisms at the atomic scale. It is divided into two distinct sub-tasks. Firstly, it aims at determining the mechanisms of defect formation under irradiation within uranium dioxide, in a nuclear and in an electronic energy loss regime. Secondly, a study of self-diffusion and fission gas diffusion properties will be carried out. In this case, a recently developed accelerated molecular dynamics approach, called metadynamics, will be implemented and applied in collaboration with the Paul Scherrer Institute (PSI, Switzerland). A particular care will be given to the comparison of the obtained results with existing experimental observations, or experiments performed in the laboratory in order to validate the simulation approach.



This research will mainly be carried out at the nuclear fuels department of the French Alternative and Atomic Energy Commission which is a recognized actor in nuclear fuel development. The candidate will be also given the opportunity to interact closely with other leading European institutions in the field of basic materials research for nuclear applications.