Development of a 2D axisymmetric SiC cladding mechanical model and its applications for steady-state and LBLOCA analysis

Abstract

A 2D axisymmetric SiC cladding mechanical model with anisotropic material properties based on finite difference method was developed. The developed model was used to analyze the behavior of SiC clad fuel (double-layer and full SiCf/SiC composites structure) in steady-state and large break loss of coolant accidents (LBLOCA) by coupling with the thermal-hydraulics simulation code MARS-KS (Multi-dimensional Analysis of Reactor Safety-Korean Standard). The multi-axial pseudo-ductile deformation model considering the characteristics of SiCf/SiC composites was employed, and the Weibull statistical failure model was applied to assess the failure probability of the cladding. Using anisotropic elastic properties, stronger tensile stress was induced in the outer monolith layer than in the isotropic case, which greatly increased the failure probability. In steady-state operation, this study shows that the failure probability of a double-layer SiC cladding is sensitive to the rod internal pressure. In-line with other studies, it was also found that the irradiation induced swelling accumulated in the refueling stage is a challenge to the structural integrity of the SiC cladding concept. The LBLOCA analysis demonstrates that the SiCf/SiC composite layer can maintain the coolable geometry of the fuel rod for both duplex and full composite cladding. Hermeticity is shown to depend on the arrestment of matrix cracks developed by pseudo-ductile deformation. Experimental support and validation on matrix crack propagation, pseudo-ductile behavior of SiCf/SiC composite under multiaxial loading, and rod-scale thermal shock with reflood quenching are necessary to further improve the model.