State-Based peridynamics for thermomechanical modeling of fracture mechanisms in nuclear fuel pellets

This study presents a coupled thermomechanical ordinary state-based peridynamic (OSB-PD) model, including the effects of randomly varying strength parameter and crack gap heat transfer, to investigate the fracture mechanisms in nuclear fuel pellets. The three-dimensional (3D) models of fuel pellets are constructed through irregular non-uniform discretization. The model includes the random variability of the critical stretch of each bond based on normal distribution. The accuracy of the OSB-PD model is validated against the FEM results for the thermomechanical behavior of a fuel pellet without damage. Subsequently, the crack propagation and crack patterns of fuel pellet are studied at different power levels (10 ∼ 40 kW/m). The results show that radial and axial cracks mainly develop during the power rise stage while the circumferential cracks develop during power down stage. These three crack types are verified by comparing with the experimental observations. The number of cracks and fragments of the fuel pellet increases with the increase in power level. Moreover, the fuel pellet can be completely separated at the mid-height cross section when the power level is equal or greater than 25 kW/m.