Crevice Corrosion Resistance of Alloy 22 in High-Nitrate, High-Temperature Dust Deliquescence Environments

Abstract Alloy 22 (UNS N06022) has been selected as the corrosion-resistant barrier for the nuclear waste containers in the proposed repository at Yucca Mountain. Alloy 22 may be susceptible to crevice corrosion in the presence of hot chloride-containing solutions. The nitrate ion (NO3−) is an inhibitor for crevice corrosion of Alloy 22 in chloride (Cl−)-containing aqueous solutions. The higher the ratio, R = [NO3−]/[Cl−], is in the solution, the stronger the inhibition of crevice corrosion by nitrate. Atmospheric desert dust contains both chloride and nitrate salts, generally based on sodium (Na+) and potassium (K+). Some of these salts may deliquesce at relatively low humidity at temperatures on the order of 150°C. The resulting deliquesced brines are highly concentrated and especially rich in nitrate (Ratios R ≫ 1). Electrochemical tests have been performed to explore the anodic behavior of Alloy 22 in high-chloride and high-nitrate electrolytes at temperatures as high as 150°C at ambient pressure. Tes...