| Abstract Scope |
We present a robust multiscale modeling framework for investigating fracture behavior in nuclear fuels, with uranium dioxide (UO₂) and TRISO fuel particles serving as representative systems. The framework couples molecular dynamics (MD) simulations with an advanced phase-field model that integrates phase transition theory and variational fracture mechanics. This formulation captures the stochastic and size-dependent nature of fracture and explicitly links the crack length scale to the critical stress using a generalized Griffith criterion. Microstructural heterogeneity and sub-mesoscale imperfections are incorporated. For UO₂, the model reproduces brittle fracture behavior observed in MD and experiments, including porosity-induced strength degradation. As void aspect ratio decreases, fracture strength degrades more rapidly than stiffness due to localized stress amplification. The framework also provides insight into the variability in experimentally measured fracture strengths of nuclear fuels by accounting for sample size, porosity level, and pore morphology. |