Discrete element method for simulation of early-life thermal fracturing behavior in ceramic nuclear fuel pellets

A discrete element method (DEM) representation of coupled solid mechanics, fracturing and heat conduction processes is developed and applied to explicitly simulate the random initiation and subsequent propagation of interacting thermal cracks in a ceramic nuclear fuel pellet during initial rise to power and during power cycles. The DEM model clearly predicts realistic early-life crack patterns including both radial and circumferential cracks. Simulation results clearly demonstrate the formation of radial cracks during the initial power rise and formation of circumferential cracks as the power is ramped down. In these simulations, additional early-life power cycles do not lead to the formation of new thermal cracks. They do, however clearly indicate changes in the apertures of thermal cracks during later power cycles due to thermal expansion and shrinkage. The number of radial cracks increases with increasing power, which is consistent with the experimental observations.