A Novel Mesoscale Modeling of Fracture in Nuclear Fuels

Abstract

Nuclear fuels power all the commercial carbon-free energy plants and contribute to the fight against climate change. A comprehensive understanding of the fracture behavior of nuclear fuels during normal and transient conditions is still lacking. In this work, we developed a novel Multiphysics mesoscale model that could predict the fracture in different nuclear fuels under various conditions by employing the phase-field modeling of fracture. This work introduces both (1) An experimental study to understand the fuel fracturing behavior of sintered UO₂ pellets when exposed to thermal shock, and (2) A Multiphysics phase-field fracture model capable of simulating this process. The model could successfully capture the formation and evolution of cracks in UO₂ fuel pellets due to a thermal shock without any ad hoc or a priori assumptions of cracking size, site, thickness, or morphologies. The model was able to capture the overall fracture trends of the corresponding experimental data. Moreover, the model further improved and utilized multi-set order parameters that allowed the simulation of the concurrent crack propagation and microstructure evolution. The new model technique is then validated and employed in an evolved nuclear-grade graphite microstructure to determine the effect of such heterogeneity on the formation and propagation of the cracks along with the variations in the materials' mechanical properties. This new technique advances the fundamental understanding of nuclear fuel behavior under normal and transient conditions and provides a predictive modeling tool for deriving physics-based criteria for the fracture behavior of ₂the current and the new nuclear fuel designs.