State of the art of fuel micro-mechanical modelling: From atomic scale to engineering laws in fuel performance codes

This paper presents the state-of-the-art knowledge about the micro-mechanical modelling of the fuel behavior under irradiation with normal and off normal operating conditions. Modelling of fundamental processes can provide key insights in the behavior of the material. Such models target specific phenomena due to the limits of computational resources and scope of theory, necessitating a multiscale approach. This work follows a multiscale paradigm building up in spatio-temporal scale. The micro-mechanical modelling studied addresses all the loading conditions encountered in the reactor with elasticity, plasticity, creep and fracture behavior. Atomistic-scale modelling review reveals mechanisms and physical parameters for elasticity of fresh and irradiated fuel, rupture, dislocation gliding and internal stresses induced by pressurized bubble with fission gases. Simulation techniques proposed at this scale are Density Functional Theory, Molecular Dynamic with empirical potential, Dislocation Dynamics and Phase Field Crystal methodology. At a higher scale, micro-mechanical models are available for the viscoplastic behavior of the material as a continuum from a single crystal to polycrystal systems and the interplay with irradiation and porosity. Crystal plasticity models, homogenisation techniques and FE or FFT full field mechanical simulations give a complete set of tools to achieve the upscaling process from the basic properties up to the engineering mechanical law needed in the fuel performance code. This multi-scale modelling can also address the questions related to fuel rupture properties in order to provide physical basis to the empirical description of the fuel fragmentation process under different types of loading conditions. For this, low scale experiments coupled with micro-mechanical modelling are the keys for the multi-scale characterization of the input parameters of smeared crack models used in fuel performance codes.