Abstract
Zinc injection technology (zinc water chemistry, ZWC) was widely applied in pressurized water reactor (PWR) primary circuits to reduce radiation buildup and improve corrosion resistance of structural materials. The simultaneous injection of zinc-aluminium (ZAWC) is a novel implement created to replace part of Zn2+ by Al3+. It was reported ZAWC can improve further corrosion resistance of carbon steels and stainless steels. However, ZAWC sometimes showed even negative effects on Nickel-alloys. In this study, mechanism of formation of oxide film on metals was investigated. The reactions of Fe2+ Ni2+ in oxide films replaced by Zn2+, or Fe3+ replaced by Al3+ in ZAWC were analysed. The thermodynamic data and solubility of mixed oxides (ZnFe2O4, ZnCr2O4, and ZnAl2O4), the products of replace reactions, were calculated. According to the Gibbs free energy difference between products and reactants, values of the formation reaction of ZnFe2O4, ZnCr2O4, and ZnAl2O4 are extremely negative. Solubility of ZnAl2O4 is the lowest among mixed oxide products, which implies the oxide film composites of ZnAl2O4 may show a lower corrosion rate. In addition, the preferential formation of NiAl2O4 on Ni-based-alloy, under ZAWC, was discussed based on crystallographic properties of spinel, which was considered as the cause of negative effects of ZAWC on corrosion resistance of Nickel-alloys. This research provides an analytical basis for the study of thermodynamic stability of oxide films under different chemical chemistry and a theoretical basis for improving corrosion resistance of different metals and optimizing the chemical conditions of PWR primary circuit.
Highlights
Light water reactors (LWR) and pressurized heavy water reactors (PHWR) are the main reactor types of nuclear power plants
The results have proven that this new implement can further improve the corrosion resistance of metal materials on the basis of zinc injection in pressurized water reactor (PWR) primary circuit [20,21]
It is worth noting that the anion preference energy of FeAl2 O4 and NiAl2 O4 are significantly higher than ZnAl2 O4, and as a result, Fe2+ and Ni2+ are easier to combine with the oxygen ions in the spinel, and the stability of bonding is higher
Summary
Light water reactors (LWR) and pressurized heavy water reactors (PHWR) are the main reactor types of nuclear power plants. Stainless steels are the main materials of piping in PWR primary circuit [1,2]. Based on PWR primary coolant water chemistry conditions, it has been reported that iron oxides are the main component in oxide films formed on carbon steels. Oxide films, formed on stainless and nickel-based alloys in high temperature water, had a double-layer structure: a (Ni, Fe)-rich outer layer and a Cr-rich inner layer [3,4,5,6]. 1.0a doufilms, formed on stainless and nickel-based alloys in high temperature water, had.
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