Electrochemical Impedance Spectroscopic Study of Passive Zirconium in High Temperature Hydrogenated Aqueous Solutions

The Point Defect Model (PDM) was further developed to account for the properties of passive films comprising hydride barrier layers and porous oxide outer layers that form on zirconium and Zircaloys in high temperature, hydrogenated aqueous solutions. The model parameter values were extracted from electrochemical impedance spectroscopic data for zirconium in hydrogenated, borate buffer solution (pH 6.94) at 250{degree sign}C by optimization. The results indicate that the corrosion resistance of zirconium in high temperature, hydrogenated 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 described above, and the extracted model parameter values might be used, for example, for predicting the accumulation of general corrosion damage to Zircaloy fuel cladding in PWR operating environments.