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

Oxide layers were grown on tubular samples of Zr-l%Nb under conditions simulating those in VVER-type pressurised water reactors. viz. in near-neutral borate solutions in an autoclave at 290 degreesC. These samples were investigated using electrochemical impedance spectroscopy which was found to be suitable to follow in situ the corrosion process. A -CPE(ox)parallel toR(ox)- element was used to characterise the oxide layer on Zr-l%Nb. Both the CPEox coefficient, sigma(ox), and the parallel resistance, Ro(x), 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 R., indicates that the oxide layer has semiconductor properties. The relaxation time defined as (R(ox)sigma(ox))(1/x) was found to be quasi-independent of oxidation time and temperature; thus it is characteristic to the oxide layer on Zr-l%Nb. (C) 2002 Elsevier Science B.V. All rights reserved.