Effect of Molybdate Anion Addition on Repassivation of Corroding Crevice in Austenitic Stainless Steel

In Japan, light water reactors are built on the seacoast because they use seawater as the final heatsink. Leakage of seawater from the condenser section of the reactor could lead to contamination of the reactor coolant, and stainless steels can be susceptible to crevice corrosion in chloride-contaminated water. Therefore, it is necessary to develop counter measures for suppressing the initiation of crevice corrosion and for repassivating the corroding crevice to maintain structural reliability. To accomplish this, first the effect of molybdate anion on suppressing the initiation of crevice corrosion on 316L stainless steel in chloride-contaminated water was evaluated by potentiostatic immersion tests. Next, the effect of molybdate anion addition on the repassivation of corroding crevices was also evaluated through potentiostatic immersion tests as a function of the concentration of chloride anion. Based on the results of these examinations, the beneficial effects of the presence of molybdate anion on the suppression of initiation and propagation of crevice corrosion were quantitatively evaluated in terms of critical potentials.