Localized Corrosion of Stainless Steel in a Nuclear Waste Cooling Water System— Part 1: Crevice Corrosion Studies

Parts of a nuclear waste cooling water system, constructed from an austenitic stainless steel, are known to be susceptible to localized corrosion. This is attributed to the presence of chloride ions in the water, albeit only at low concentrations (<10 mg/L), and oxidants produced by water radiolysis. Experiments were carried out using an engineered crevice connected to a large passive stainless steel surface to demonstrate the viability of crevice corrosion. Similar tests were undertaken to investigate the efficacy of nitrate as an inhibitor. In irradiated water containing up to 300 mg/L Cl− and at temperatures of up to 60°C, crevice corrosion of UNS 30403 and 18Cr-13Ni 1Nb was inhibited by nitrate added at molar ratios of approximately 2.9 to 5.7 with respect to chloride. Once corrosion is inhibited, the nitrate/chloride ratio can be reduced to maintain passivity, but a nitrate:chloride ratio of approximately 0.6 or lower is unlikely to be effective.