Electrochemical Impedance Spectroscopic Study of Passive Zirconium

The development of deterministic models for predicting the accumulation of corrosion damage to zirconium and Zircaloys in pressurized water reactor (PWR) coolant environments requires the acquisition of values for various model parameters. In the present work, 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 at by optimization. The results indicate that the corrosion resistance of zirconium in high-temperature, hydrogenated aqueous solutions is dominated by the outer layer, as was found to be the case for nonhydrogenated solutions where a defective oxide barrier layer forms. 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.