Multi-scale modeling of inter-granular fracture in UO2

Abstract

The brittle fracture behavior of UO 2 fuels is strongly influenced by the porosity and grain size distributions in the underlying microstructure. In service, there is significant evolution of these microstructural features, which can alter the fracture properties and subsequently the thermo-physical-mechanical behavior of the nuclear fuels. To incorporate these microstructural effects on the fracture behavior, a multi-scale modeling framework is developed in the present work. Within this framework, the grain-boundary fracture properties obtained from molecular dynamics simulations are utilized in a phase-field model to investigate the intergranular brittle crack propagation in this material. A sensitivity study with varying porosity, pore and grain size is performed to investigate their influence on the fracture properties. Subsequently, the parameters of an engineering scale fracture model are obtained by fitting the stress-strain evolution obtained from the phase-field simulations. This framework provides a hierarchical coupling of properties evaluated at the atomistic scale to perform more realistic engineering level predictions of fracture in nuclear fuel pellets.