In situ electrochemical impedance spectroscopy of Zr–1%Nb under VVER primary circuit conditions

Oxide layers were grown on tubular samples of Zr–1%Nb under conditions simulating those in VVER-type pressurised water reactors, viz. in near-neutral borate solutions in an autoclave at 290 °C. These samples were investigated using electrochemical impedance spectroscopy which was found to be suitable to follow in situ the corrosion process. A –CPEox∥Rox– element was used to characterise the oxide layer on Zr–1%Nb. Both the CPEox coefficient, σox, and the parallel resistance, Rox, were found to be thickness dependent. The layer thickness, however, can only be calculated after a calibration procedure. The temperature dependence of the CPEox element was also found to be anomalous while the temperature dependence of Rox indicates that the oxide layer has semiconductor properties. The relaxation time – defined as (Roxσox)1/α – was found to be quasi-independent of oxidation time and temperature; thus it is characteristic to the oxide layer on Zr–1%Nb.