Effect of zinc injection on the oxide film structure and corrosion release behavior of Alloy 690TT in high temperature pressurized water

To elucidate the inhibition mechanism of zinc water chemistry on the corrosion product release from key materials in pressurized water reactor (PWR), this study systematically investigates the evolution of oxide films and the release kinetics of elements (Ni, Cr, Fe) from Alloy 690TT under both basic (Zn-free) and zinc-injected (50 ppb) conditions in simulated primary water at 325 °C for up to 3336 hours. Oxide film analysis reveals that zinc injection promotes the transformation of the outer oxide layer from a porous, needle-like NiCr₂O₄ spinel to a dense, granular (Zn,Cr,Fe)₃O₄ composite spinel, while the inner compact Cr₂O₃ layer remains stable. Analysis of the release kinetics shows that zinc injection significantly reduces the corrosion release rates of the main metallic elements. Nickel is the primary released element, and its initial release rate is reduced by approximately 71% with zinc injection. Furthermore, based on the corrosion release rate data from various time points, a quantitative predictive model describing the evolution of the average release rates of Ni, Cr, and Fe over time has been established. • Oxide film structure of Alloy 690 in zincated water is characterized. • Release kinetics of Alloy 690 in PWR water with and without Zn are quantified. • Mechanism for mitigating corrosion release of Zn-injection is revealed. • A predictive model for release kinetics of Ni, Cr, and Fe is established.