Modeling of Zirconium Atom Redistribution and Phase Transformation Coupling Behaviors in U-10Zr-Based Helical Cruciform Fuel Rods under Irradiation

Abstract

Uranium–zirconium metal-based Helical Cruciform Fuels (HCFs) have shown a promising prospect for their use in advanced nuclear reactors. However, during irradiation, dual-phase coexistence and the spatial heterogeneous distribution of zirconium atoms occur at higher powers, affecting the thermo-mechanical coupling behaviors and safety of fuel elements and assemblies. In this study, based on the phase-field approach, the coupled multi-field governing equations to describe the zirconium diffusion and phase evolution for U-Zr metallic fuels are improved. Furthermore, the corresponding numerical algorithms and procedures for multi-field coupling calculations are developed. The numerical predictions of zirconium atom fraction are in good agreement with the relevant experimental results, validating the developed models, algorithms and programs. The zirconium atom redistribution and phase transformation coupling behaviors in high-power U-10wt%Zr-based HCF rods are also obtained. Moreover, the complex evolution mechanisms of multi-field variables are analyzed. The results indicate the following: (1) the irradiation enhancement of the thermal mobility and chemical mobility plays a critical role in the redistribution of Zr atoms; (2) the multi-field results of HCF rods have helical symmetric characteristics; (3) the contribution competitions of the temperature gradient and chemical potential gradient within the α phase and γ phase significantly influence the zirconium-atom redistribution, with the zirconium-rich zones formed in the elbow region and the zirconium-poor zones appearing inside. These research efforts supply a foundation for the further involvement of mechanical fields in multi-field coupling computation.