Electrochemical study of corrosion behavior of Zr-1%Nb in LiOH and KOH solutions

Zirconium alloys are widely used for fuel cladding and in pressure tubes in most water-cooled reactors, because of its low neutron absorption cross section and high corrosion resistance. Theprimary coolant in pressurized water reactors (PWR) contains lithium hydroxide (LiOH), which is used for pH control since it has been recognized that a more constant pH is desirable to reduce radiation field and fuel depositions. But it has been known that LiOH accelerate corrosion ofnuclear fuel cladding [1-4]. Therefore, in this work the potential of KOH instead of LiOH for PWR application was investigated.Corrosion properties of the Zr-1%Nb alloys were assessed by Autolab potentiostat/galvanostat (model 302N, Netherlands), in naturally-aerated 1 M LiOH and 1 M KOH solutions at roomtemperature. A conventional three-electrode cell was employed for the measurements, with an Ag/AgCl electrode and a platinum counter electrode. Zirconium plates with ~1 cm2 area that used as working electrodes were immerged 90 minutes prior to the tests in the solution to allow thestabilization of open-circuit potential. The electrochemical impedance spectroscopy (EIS) tests were carried out at a frequency range of 10 mHz to 100 kHz at the open circuit potential and the perturbation amplitude was 10 mV. The scan rate and perturbation for potentiodynamicpolarization (PDP) were 1 mV/s and ±10 mV, respectively. The polarization curves of the zirconium electrode in the 1.0 M LiOH and KOH solutions wereshown in figure 1-a, and the electrochemical parameters that are obtained from the polarization curves are summarized in table 1. The experimental impedance plots altogether with simulated spectra by equivalent circuit were shown in figure 1-b. The electrochemical parameters of theequivalent circuit elements are listed in table 2.

Keywords:

Zirconium , corrosion behavior , LiOH , KOH , potentiodynamic polarization , EIS