On the Post-Irradiation Mechanism of Cracking Initiation in Dispersion Fuel Plate Edges: A Global-Local Modeling Approach

In research and test reactors, a prevalent cause of fuel plate failure is the formation of blisters due to temperatures exceeding critical thresholds. This phenomenon compromises the safe operation of reactors. Out-of-pile annealing tests indicate that blisters in post-irradiation dispersion fuel plates predominantly form in the edges, particularly at the fuel meat/cladding interface. A global-local modeling approach is developed to conduct three-dimensional numerical simulations of the thermo-mechanical coupling behaviors within a representative fuel plate slice during irradiation and post-irradiation annealing. This approach provides significant insights into the influencing factors and mechanisms underlying the cracking initiation and the subsequent bubble formation observed during annealing. The global model supplies the local model with realistic, far-field boundary constraints, which is the most critical coupling to ensure that the local model operates within the authentic mechanical environment of the entire fuel plate rather than in isolation. The results clearly demonstrate that: (1) The mechanical interactions between the meat and cladding are intensified in fuel plate edge regions due to cladding constraints; during annealing, the highest normal stress of fuel skeleton in the fuel particles near the plate edges reaches 254.5 MPa—8.56 times higher than that in central regions, aligning with experimental observations of preferential cracking in these zones; (2) To mitigate severe tensile stresses in the meat edge during annealing and enhance blistering resistance, a particle-free matrix-only buffer zone is designed around the meat edge, resulting in much lower normal stress of fuel skeleton in near-edge particles to 32.32 MPa. This study provides a mechanistic basis for predicting post-irradiation cracking initiation and offers design guidelines for fuel plate optimization.