Abstract:Zirconium alloys are extensively utilized as cladding materials for fuel elements in water-cooled nuclear reactors due to their low thermal neutron absorption cross-section, high thermal conductivity, excellent corrosion resistance, and good compatibility with UO2. Small Modular Reactors (SMRs) represent a significant direction for future nuclear energy. However, the simplified design of small water-cooled reactors, which often lack hydrogen addition and oxygen removal facilities or have limited deoxygenation capacity, leads to an elevated concentration of Dissolved Oxygen (DO) in the primary circuit coolant. This increased DO level can adversely affect the corrosion resistance of zirconium alloy cladding. Sn is an important alloying element for zirconium. Nevertheless, research on the influence of DO on the corrosion resistance of zirconium alloys with varying Sn content is scarce. Therefore, this study investigates the corrosion behavior of zirconium alloys with different Sn contents in water at 360 °C/18.6 MPa with different DO concentrations, aiming to provide a theoretical basis and guidance for developing zirconium alloy cladding materials for water-cooled SMRs. To explore the effect of Sn content on the corrosion behavior of zirconium alloys in oxygen-enriched water, corrosion tests were conducted on three Zr-xSn-0.35Fe-0.15Cr (x=0.5, 1.0, 1.5, wt%) alloys and a Zr-4 alloy in a dynamic autoclave at 360 °C/18.6 MPa with a DO concentration of 1000 μL/L. The microstructure and phase composition of the alloys and their oxide films were characterized using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Raman spectroscopy. The results indicate that the second-phase particles (SPPs) in the Zr-xSn-0.35Fe-0.15Cr alloys are primarily composed of two types: fcc-Zr(Fe,Cr)2 and hcp-Zr(Fe,Cr)2. With increasing Sn content, the size and the Fe/Cr atomic ratio of the SPPs increase, while their area fraction decreases. During the 290-day corrosion period, the corrosion kinetics transitioned from a cubic rate law to a parabolic or power-law rate law. An increase in Sn content led to an earlier transition time in the corrosion kinetics and a higher post-transition corrosion rate. The corrosion kinetics shifted from parabolic to power-law behavior, indicating a degradation in corrosion resistance. However, all the Zr-xSn-0.35Fe-0.15Cr alloys exhibited significantly superior corrosion resistance compared to the Zr-4 alloy in the 1000 μL/L DO water environment. This paper discusses the underlying mechanism of how Sn content influences the corrosion behavior in oxygen-enriched water from the perspectives of SPPs oxidation and the microstructural evolution of the oxide film.