Microstructural characterization and growth kinetics of the reaction layer in U-10wt.%Zr/Zircaloy-4 diffusion couples

Abstract:

U-Zr alloys cladded with Zircaloy-4 alloy are being developed as metallic fuels for water-cooled reactors. The fuel-cladding compatibility is key to the safe operation of the reactors, however, there are few studies on the interfacial reaction and diffusion of U-Zr alloys and Zircaloy-4 alloy. To investigate the compatibility and the diffusion behavior between U-Zr alloys and Zr-4 alloys, solid-to-solid U-10wt.%Zr/Zr-4 diffusion couples were assembled by vacuum hot pressing and then vacuum annealed at the temperatures range from 580 ℃ to 1100 ℃ for various time. Both scanning and transmission electron microscopy were employed for analysis of the microstructures and composition profiles at the interfaces of the couples. The compatibilities between the two alloys were systematically investigated. δ-UZr₂ and ~20nm-thin U-rich layers existed in vacuum hot pressed samples. The interdiffusion coefficient constant and the activation energy were measured, which are 4.23(±0.63)×10^-6 m²/s and 160.73(±1.67) kJ/mol, respectively. The interdiffusion coefficients of U-10wt.%Zr/Zr-4 alloys couples are higher than that of U-Zr alloys, especially for low temperature.

Key words:metallic fuel; cladding; interface; interdiffusion; hybrid reactor