Electrochemical impedance spectroscopic study of passive zirconium - I. High-temperature, dearated aqueous solutions

The development of deterministic models for predicting the accumulation of corrosion damage to zirconium and Zircaloys in boiling water reactor 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 oxide barrier layers and porous oxide outer layers that form on zirconium and Zircaloys in high-temperature, deaerated aqueous solutions. The model parameter values were extracted from electrochemical impedance spectroscopic data for zirconium in deaerated, borate buffer solution [0.1 M B(OH)(3) + 0.001 M LiOH, pH 6.94] at 250 degrees C by optimization. The results indicate that the corrosion resistance of zirconium in high-temperature, deaerated aqueous solutions is dominated by the porosity and thickness of 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 sheath in BWR operating environments. (c) 2006 The Electrochemical Society.