Phase field model for crack propagation in outer coating layers of TRISO particle fuel

s an advanced fuel form, TRISO particle fuel is relatively reliable due to the excellent capability of its thin coating layers to contain fission products, but it is still prone to cracks or pores in the coatings during production, transportation, and usage. These irregular geometries can significantly impact their ability to maintain structural integrity. Therefore, in order to advance the use of TRISO particles in space reactors, analyzing and predicting the crack propagation in their coatings is crucial. This model introduces the material properties of TRISO particles, irradiation behavior, and fission gas release model, and establishes a phase field model to investigate the crack propagation characteristics of the outer three coatings of TRISO particles. The accuracy of this model for TRISO particle performance was verified through an IAEA benchmark problem and a comparison with BISON program results for TRISO particles. The reliability of the phase field model for crack simulation was validated by analyzing a notched tensile plate and Kalthoff experiment. The effects of a crack in the IPyC layer, a residual pore in the SiC layer, a crack on the outer side of OPyC, and the simultaneous presence of a crack in the IPyC layer and a residual pore in the SiC layer, were studied in succession. The calculation results reveal that cracks in the IPyC layer cause debonding between the IPyC and SiC layers, but they are insufficient to propagate into the SiC layer during the early stages of burnup. Residual pores in the SiC layer lead to the complete fracture of the coating layers, primarily due to excessive gas pressure from the inner IPyC layer rather than the weakening effect of the pores on the structure. Cracks in the OPyC layer cause concentrated tensile stress on the outer side of the SiC layer during the early stages of burnup, which alters the crack propagation path in the coating layers during the later stages of burnup. Therefore, in addition to using material detection techniques to screen out TRISO particles with excessive defects before the production of FCM pellets, it is essential to enhance the ability of coating layers to maintain structural integrity and implement fundamental measures such as expelling accumulated gases from the particles. These actions are crucial for the safe and stable operation of TRISO particle fuel in space reactors.