Electrochemical corrosion of zircaloys under irradiation and different water chemistry conditions

Shadow corrosion is observed in BWRs either on fuel cladding in contact with Inconel spacers or on channel in close proximity to 304 SS control blades. In order to understand the shadow corrosion mechanism, electrochemical corrosion behavior of Zircaloy-2, Alloy X-750 and 304 SS were previously investigated under UV radiation and published previously. In this study, effects of radiation (up to 300 keV photons) and water chemistry on the electrochemical corrosion behavior of Zircaloy-2, Alloy X-750, and 304 SS were investigated. Measurements of corrosion potential, galvanic corrosion and electrochemical impedance were carried out in 0.01M Na₂SO₄ at 25degC under UV illumination at 5 eV or photon energies from 2.5 keV to 300 keV using synchrotron radiation. Also, similar measurements were performed in high purity water under various water chemistry conditions at 290degC - 300degC by using UV illumination. The results show that the presence of radiation shifted the corrosion potential of Zircaloy-2 and Alloy X-750 in the anodic or cathodic direction, respectively, and increased anodic currents when Zircaloy-2 was galvanically coupled with Alloy X-750 in 0.01M Na₂SO₄ at 25degC, may cause accelerated corrosion of Zircaloy-2. In addition, the results showed that hydrogen peroxide increased the electrochemical kinetics at Zircaloy-2 surface in high temperature water under UV irradiation. (author)