Alloying Effect on the Stability and Diffusion Behavior of Intrinsic and Xe-incorporated Defects in U-Zr Metallic Fuel: A First-Principles Study

Defect evolution and atomic diffusion in U-Zr solid solutions impact advanced nuclear fuel performance, particularly irradiation stability and fission product retention. First-principles calculations are conducted to examine alloying effects on the thermodynamic stability and migration mechanisms of intrinsic and Xe-incorporated defects in α- and δ-(U, Zr) phases. The V U and V Zr vacancies are the predominant defects due to their lower formation energies. Zr alloying reduces vacancy formation energies in the U-Zr system compared to pure U, indicating enhanced defect accommodation. The predicted migration barriers for stable vacancy defects range from 1.03 to 1.14 eV in α-(U, Zr) phase and from 0.96 to 2.20 eV in δ-(U, Zr) alloys, higher than those in the pure α-U phase, suggesting that Zr alloying suppresses their diffusion under irradiation. Moreover, Xe substitutional defects (Xe U and Xe Zr ) are more energetically favorable than Xe interstitials (Xe i ) in α- and δ-(U, Zr) alloys. Zr additions stabilize the Xe substitutional and interstitial defects in the α-(U, Zr) phase. The migration barriers for Xe U and Xe Zr defects are higher than those for Xe i in α- and δ-(U, Zr) phases, indicating a preferential migration of the latter. Zr alloying hinders the diffusion of Xe i in the α-(U, Zr), but may accelerate that of Xe U in this phase. This study uncovers the effect of Zr alloying on defect behaviors in the U-Zr solid solution, contributing to the understanding of its impact on nuclear fuel expansion performance and the pore morphology formation across the α- and δ-(U, Zr) phases.