Three-dimensional fracture of UO₂ ceramic pellets by phase field modeling

Fracture is the primary failure type for the UO₂ ceramic pellets, which are operated under irradiation and thermal processes, and physically confined by the cladding. In this work, by combining closely coupled physical processes of heat conduction, heat transfer, and mechanical deformation with the cohesive phase field framework, we proposed a high-precision modeling of quasi-static cracking of three-dimensional (3D) UO₂ ceramic fuel pellets under high temperature and irradiation. The simulation results agree well with the experimental results, indicating that the proposed method has the potential to capture 3D crack modes in the interested time range. Further, we studied the relation of the 3D fracture patterns of fuel pellets with the peak power densities. It was found that the power level plays a critical role in determining the competition between radial and circumferential cracks, as well as transverse penetrating cracks.