Stress-diffusion coupling in UO2

Full text of publication follows: In this paper we study the oxidation of UO2 pellets from point of view of mechanical stresses induced by the UO2/U3O7 interface. A thermodynamic model of coupled stress-diffusion is presented leading to a diffusion coefficient depending of stresses. At the same time the diffusion of O2- in UO2 involves mechanical stresses due to the chemical expansion. A FEM simulation of a multi-domain U3O7 connected to a UO2 substrate shows that the maximal stress in the U3O7 layer depends of its thickness, as observed experimentally. More generally, this approach can be used in order to explain phenomena as chemical fragmentation experimentally observed for several types of materials