Metallurgical characterization of the delta phase formation in uranium-zirconium alloy fuels

Abstract

Uranium – 10 wt% zirconium (U-10Zr) alloy nuclear fuels have been used for many decades and new variations are under consideration ranging from U-5Zr to U-50Zr. As a precursor to studying fission gas behavior using ion implantation, a basic study of U-Zr metallurgy was completed. The initial focus was to clarify literature ambiguity regarding the formation of the UZr<SUB>2</SUB> delta phase. Sample alloys were created containing 0.1, 2, 5, 10, 20, 30, and 50 wt% zirconium. Initial structures were created via “furnace-cooled” and “gamma-quenched” temperature profiles. Samples of each composition and thermal profile were annealed under argon at 600°C for 24, 72, and 168 hours. Quantitative analyses were completed using an electron microprobe. The delta phase formed readily in annealed furnace-cooled samples whereas gamma-quenched samples exhibited sluggish transformations. The rate of cooling U-Zr alloys has a profound impact on the kinetics of delta phase formation.