Electrochemical Impedance Spectroscopic Study of Passive Zirconium in High Temperature De-aerated Aqueous Solutions

The Point Defect Model (PDM) was further developed to account for the properties of passive films comprising oxide barrier layers and porous oxide outer layers that form on zirconium and Zircaloys under simulated boiling water reactor operating conditions. The model parameter values were extracted from electrochemical impedance spectroscopic data for zirconium in de-aerated, borate buffer solution (pH 6.94) at 250C by optimization. The results indicate that the corrosion resistance of zirconium in high temperature, de-aerated aqueous solutions is dominated by the outer layer. The impedance model based on the PDM provides a good account of the growth of the bi-layer passive films, and the extracted model parameter values might be used, for example, for predicting the accumulation of general corrosion damage to Zircaloy fuel sheath in BWR operating environments.