Marangoni migration of rare earth metals during solidification in nuclear fuel rods

This study identifies a mechanism by which the migration of rare earth metals during the solidification of nuclear fuel rods determines their structure and properties. Nuclear fuel rods are designed to contain a small amount of rare earth metals in a matrix of uranium and zirconium, and the rare earth metals should be uniformly distributed in a fine size. However, rare earth metals have been observed to accumulate near the wall during solidification, and the underlying principle remains unclear. In this study, we employ optical and spectroscopic analysis methods to investigate the phenomenon of rare earth metal particles that form and migrate during the solidification process. A significant difference in surface tension exists between the rare earth metal and the uranium-zirconium medium in the molten state at high temperatures, which induces Marangoni migration, and this possibility is verified by fluid simulation. The results of this study can contribute to a fundamental understanding of the inhomogeneous distribution that occurs during the solidification of metallic materials containing small amounts of rare earth metals and ultimately provide guidance for the development of a uniform distribution while studying the hydrodynamic effects of microstructure inhomogeneity during the transition of alloys from liquid to solid phase. • Thermal inhomogeneity during solidification causes composition gradients in U-Zr-RE alloys. • Marangoni flow from surface tension gradients drives rare earth particle redistribution. • Solidification flow patterns control final microstructure in immiscible metallic systems.