Effects of dissolved zinc and magnesium ions on corrosion of zircaloy-2 in aqueous medium

Abstract

The accumulation of activated oxide corrosion products on the inner wall of the primary heat transport system structural material (carbon steel) of pressurised heavy water reactors causes radiation field build-up around out-of-core areas. In laboratory experiments, it was observed that Mg²⁺ ion injection in water at low concentrations reduces carbon steel corrosion. Similarly, in boiling water reactors, Zn²⁺ ion injection is used to reduce radiation field build-up around the primary heat transport system. Due to metal ion (Zn²⁺ or Mg²⁺) passivation, the corrosion behaviour of the core material of the reactors, zircaloy-2, may be affected. This work describes the modifications of zirconium dioxide films formed on zircaloy-2 in the presence of Zn²⁺ and Mg²⁺ ions in an alkaline aqueous medium under water reactor conditions. The modified zirconium dioxide films were characterised by grazing-incidence X-ray diffraction and field-emission scanning electron microscopy to assess the extent of oxide modifications due to the presence of these cations. Further, the corrosion properties of these modified zirconium dioxide films were analysed by electrochemical methods, and Mg²⁺ ion was found to be a better candidate in terms of improving the corrosion resistance of zircaloy-2.