Modification of oxide film on Zircaloy-2 by magnesium ions in high temperature aqueous solution

Abstract

Inorganic metal ion additives are being explored for controlling the corrosion and deposition of activated corrosion products on out of core surfaces in Pressurized Heavy Water Reactors (PHWRs). Mg2+ ions can modify the oxides on heat transfer surfaces like Zircaloy and thus influence its corrosion properties. Zircaloy-2 coupons were exposed to simulated Primary Heat Transport (PHT) system environment in the presence and absence of Mg2+ ions and were characterized to understand the surface morphology, defect density and the corrosion protectiveness. Incorporation of Mg into the oxide was confirmed by XPS. GIXRD and Raman spectra showed presence of predominantly monoclinic zirconia with traces of tetragonal phase. GIXRD on Mg-doped films showed that, the monoclinic ZrO2 fraction increased by 2% from 7d to 42d exposure. The films formed in presence of Mg always had higher impedance and lower passive current density than that formed in the absence of Mg for the same duration. This study shows that the Mg doped oxide imparted corrosion protectiveness and the doping is not detrimental to the material.