Predicting crack patterns in SiC-based cladding for LWR applications using peridynamics

Abstract

SiC continuous fibre reinforced SiC matrix (SiC-SiC) composites are a proposed material for accident tolerant fuel cladding. Thermomechanical models of SiC-based cladding under light water conditions indicate that microcracking in the radial direction of the tubing may lead to a loss of hermicity. SiC-based tubing is known to have anisotropic elastic properties but the effect of this anisotropy have not been incorporated into existing thermomechanical models of clad cracking. This work augments an existing isotropic 2D peridynamic model of cracking and damage in the r-θ plane of a SiC-based cladding to account for the orthotropic elastic properties of SiC-SiC composite tubing. Three SiC-based architectures are modelled under normal operating conditions of a UO2-fuelled pressurised water reactor (PWR). The results of the anisotropic SiC-cladding model are compared with the results of the isotropic model, and the sensitivity of results to material anisotropy, thermal conductivity, and applied linear power rating are analysed.The results of this analysis show that anisotropy has a significant effect on the damage and crack patterns observed in the r-θ plane of SiC-based cladding, if either an inner or outer monolith is present. The anisotropic model predicts more cracks in two layer clad with an inner monolith and higher levels of damage in a two layer clad with an outer monolith than the isotropic model. Under normal reactor conditions the outer monolith clad architecture was found to remain hermetic.