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

The supercritical water-cooled reactor (SCWR) is a Generation IV reactor concept that will operate at temperatures and pressures above water’s thermodynamic critical point. Pourbaix diagrams for the iron–water system at temperatures slightly below and above the critical point at 25 MPa have been constructed to aid the evaluation and development of potential construction materials. High temperature data extrapolation was performed using a revised Helgeson–Kirkham–Flowers model and fit to data on magnetite and hematite solubility in high-temperature water. A low-concentration diagram at 350 °C reveals the importance of water chemistry control to avoid transitioning to an active corrosion region.

► Pourbaix diagrams for iron–water are extended to low-supercritical temperatures.
► Thermodynamic properties for use in R-HKF model re-evaluated.
► Above the critical point, magnetite solubility is between 10−11 and 10−10 mol/kg.