Pourbaix diagrams for the nickel-water system extended to high-subcritical and low-supercritical conditions

One of the Generation IV nuclear reactor concepts is the supercriticalwater-cooled reactor (SCWR). To assist with plant design and selection of potential construction materials, Pourbaix diagrams for the nickel water-system slightly below and above the critical temperature at a pressure of 25 MPa have been developed. A revised Helgeson–Kirkham–Flowers model with parameters optimized to bunsenite solubility data was used to perform the necessary thermodynamic extrapolations. The third hydrolysis product (Ni(OH)3−) was included in this study after careful review of new data. The diagrams revealed the need for strict water chemistry control to prevent transitioning to regions of active corrosion.

► Pourbaix diagrams for nickel-water are extended to low-supercritical temperatures. ► Thermodynamic properties for use in R-HKF model re-evaluated. ► The Ni(OH)3− anion is included after careful review of NiO solubility data. ► Above the critical point, NiO solubility is low, between 10−14 and 10−13 mol/kg. ► Possibility for NiO dissolution and active corrosion above 350 °C is revealed.