Kinetic parameters of the oxidation of zirconium alloys in simulated WWER water – Effect of KOH content

The pre-transition oxides formed on two different types of zirconium alloys (Zircaloy 4 and E110) have been characterised in situ using electrochemical impedance spectroscopy (EIS) in high-temperature electrolyte simulating WWER conditions at 310 °C. To obtain a correlation between the oxide film thickness, the oxide growth rate and the impedance parameters, the EIS data have been fitted to a transfer function derived from the mixed-conduction model for oxide films, allowing for the contribution of both an inner, barrier type of oxide and a more defective outer layer. The values of the total oxide film thickness based on the model calculations have proved to be in a good agreement with the values measured from the cross-section micrographs of the specimens using scanning electron microscopy. The main kinetic and transport parameters characterising the oxidation process have been estimated and discussed with regard to the effect of KOH content and alloy type on the mechanism of conduction through the formed oxide.