Aqueous chemistry of metals under supercritical water conditions

To minimize corrosion and corrosion product transport in nuclear power systems the chemistry control strategy for the primary coolant of pressurized water and heavy water reactors (PWRs and PHWRs) involves the addition of lithium hydroxide. It is not clear whether this treatment will provide adequate chemistry control in the operation of the prospective supercritical water-cooled reactor (SCWR). Application of LiOH for the pH control of the coolant at the SCWR operating conditions is examined in this study. The association constant and pH of dilute aqueous LiOH solutions near and above critical point of water are calculated via Molecular Dynamics (MD) simulations. Corrosion testing is also performed on stainless steel tubing for different pH values under SCWR pressurized flow conditions at 25 MPa. The results indicate that addition of LiOH to the coolant will provide adequate pH control up to 500 °C. At temperatures above 650 °C the pH control becomes progressively more difficult as the dielectric constant and density of water decrease, leading to the association of LiOH.