A CALPHAD-informed approach to modeling constituent redistribution in Zr-based metallic fuels using BISON

Highlights: • A new constituent redistribution model was added to the BISON fuel performance code. • The model is applicable to uranium-zirconium and uranium-plutonium-zirconium fuels. • It leverages pycalphad thermodynamic calculations to improve performance. • Its binary predictions are acceptable but ternary predictions require improvement. • The model has been coupled to BISON thermomechanics at the engineering scale. A CALPHAD-informed (Computer Coupling of Phase Diagrams and Thermochemistry) constituent redistribution model was developed for Zr-based metallic fuels and incorporated into the BISON fuel performance code. Three uncertain model parameters associated with $\beta$ and $\gamma$ phase kinetics were calibrated using integral test data from U-Zr fuel elements irradiated in Experimental Breeder Reactor II. The calibrated constituent redistribution model was shown to predict the behavior of U-Zr fuels with excellent accuracy. Model predictions for U-Pu-Zr fuels were physically reasonable but less accurate. Reduction of uncertainties in the ternary phase transition temperatures and collection of kinetic data for the $\zeta$ phase are expected to improve the model's ternary predictions. Finally, the new model was coupled to existing thermomechanics models in BISON to simulate irradiation of an entire U-Zr fuel element, demonstrating its ability to accurately predict the behavior of U-Zr fuels with realistic geometries and mesh resolutions at the engineering scale.