Nanoscale Characterization of Zirconium Alloy Corrosion: Dissolved Oxygen-Induced Microstructural Transformations

Different nuclear reactor types exhibit dramatically varying dissolved oxygen (DO) concentrations, ranging from less than 10 parts per billion to several parts per million [1].These substantial variations in oxygen environment fundamentally alter the microstructure and corrosion characteristics of zirconium-based fuel cladding materials [2].Secondary phase particles (SPPs), particularly -Nb and Zr(Nb,Fe) 2 Laves phases, play a critical role in the mechanical and corrosion resistance of zirconium alloys.These nanoscale precipitates act as barriers to dislocation movement, enhance material strength, and significantly influence the alloy's oxidation behavior.Our study reveals how dissolved oxygen concentration impacts these crucial microstructural features, potentially affecting the material's long-term performance in nuclear environments.Machine learning-assisted nanopore analysis unveiled microstructural differences across varied dissolved oxygen environments.At high DO concentrations, the oxide layer exhibited approximately twice the nanopore density compared to low dissolved oxygen conditions, with significant variations in pore distribution and interconnectivity.Transmission electron microscopy and electron energy loss spectroscopy (EELS) provided insights into the oxidation of secondary phase particles.The EELS investigation demonstrated how dissolved oxygen concentration alters SPP oxidation.In high DO environments, -Nb particles underwent more complete oxidation, transforming from metallic Nb 0 to fully oxidized Nb 5+ states.This oxidation process releases Nb ions into the oxide layer, potentially modifying its electronic conductivity and protective capabilities.The oxidation of these nanoscale particles directly correlates with changes in oxide layer microstructure, including increased nanoporosity and altered grain structure.Oxide growth kinetics confirmed these microscopic observations, with high DO environments producing significantly different oxide thickness and structural characteristics.The research illuminates how DO concentration induces nanoscale microstructural transformations that ultimately determine the corrosion resistance and performance of nuclear fuel cladding materials.