Fracturing in Ceramic nuclear fuel influences its thermal and mechanical behavior under both normal and abnormal conditions. Empirical models that approximate the expansion of the fractured fuel are typically used in fuel performance simulations, but these models have a limited range of applicability. Two fracture modeling techniques -- the extended finite element method (XFEM) and the discrete element method (DEM) - can model arbitrary fracture and fragmentation. This LDRD project applies those techniques to nuclear fuel performance modeling via the MOOSE-based BISON code. By accounting for fracture using physically-based models, this work will strengthen the ability to predict fuel behavior, particularly in abnormal conditions (project 13-071).
Another project explores how radiation damage leads to swelling, embrittlement and changes in material properties such as elasticity. Researchers are developing a multiscale fuel performance model that bridges atomic and macroscales. To extend an existing multiscale framework (developed under a previous LDRD) to the atomic scale, it implements the phase field crystal (PFC) model into INL's MOOSE-based MARMOT code. That code models intermediate-scale (mesoscale) defect evolution and the resulting change in material properties. Coupling the resulting model to BISON will create a first-of-its-kind multiscale capability that bridges the atomic to the macroscale. By providing a better fundamental uncerstanding of mechanisms occurring during the early stages of irradiation, this project could inform design of nuclear fuels and materials with enhanced accident tolerance.
Simulation data from the BISON fuel performance code can be visualized in a Computer-Assisted Virtual Enviornment (CAVE)