Electrochemical Mitigation of Intergranular Stress Corrosion Cracking in Boiling Water Reactors

The fundamental understanding and practical application of electrochemical mitigation of intergranular stress corrosion cracking (IGSCC) of structural materials in a boiling water reactor (BWR) is described. Controlling the electrochemical property of the surface, e.g., catalytic or insulating nature, alters the electrochemical corrosion potential (ECP) of structural materials and subsequently affects the IGSCC susceptibility in high-temperature water. It is evident that the presence of noble metals on the oxide surface dramatically improves the hydrogen oxidation kinetics and thus enhances the catalytic recombination efficiency of hydrogen (H₂) to oxygen (O₂) and hydrogen peroxide (H₂O₂) to form water (H₂O). The enhancement in the catalytic nature on Type 304 (UNS S30400) stainless steel (SS) surface doped with noble metals results in the thermodynamically lowest ECP value when a stoichiometric or higher amount of hydrogen is present in the water. It is also observed that an insulated protective coating (IPC) layer created with powders of yttria-stabilized zirconia (YSZ), pure zirconium (Zr) or zirconium alloys by thermal spray, chemical vapor deposition (CVD), or physical vapor deposition (PVD) restricts the oxidant transport rate to the metal surface, and decreases the ECP in high-temperature water containing a high concentration of oxidants without the addition or presence of H₂.