Modeling of the thermomechanical behavior of braided SiCf/SiC composite cladding tube during irradiation

Abstract

Silicon Carbide (SiC) is considered a promising candidate for Accident-Tolerant Fuel cladding materials in nuclear reactors. However, existing literature often oversimplifies the heterogeneous geometric characteristics of the braided layers in SiC cladding. This paper presents a detailed modeling of the thermo-mechanical behavior of SiC cladding under light water reactor (LWR) conditions, with a focus on the braiding structure. The yarn, composed of SiC fibers and matrix, is treated as a homogenized orthogonal anisotropic material, and the braiding structure is constructed based on the parametric equations describing yarn paths. The interlayer damage between the yarns and the matrix is modeled using the cohesive zone method. The thermal-mechanical performance of the SiC_f/SiC cladding during reactor startup, power operation and reactor shutdown is evaluated. The results confirm a significant increase in the tensile stress of the braided layer during reactor shutdown. Varying the anisotropic swelling of yarns only have slight effect on the cladding stress. Furthermore, the impacts of braiding patterns, braiding angles and fuel rod gap pressure are also investigated. The findings contribute to a more realistic assessment of SiC composite cladding performance, potentially informing future cladding design and fuel safety assessment.