Pitting Factor Criteria for localized corrosion inhibition of liquid radioactive waste stored in Hanford double shell tanks

摘要

Liquid radioactive waste stored in carbon steel double shell tanks (DSTs) at Hanford has a comprehensive chemistry control program to prevent general corrosion, stress corrosion cracking (SCC) and other types of localized corrosion. Currently, the chemistry control program inhibits general corrosion and localized corrosion due to nitrate concentrations using sodium hydroxide to raise pH over 12. However, future streams may increase the concentration of aggressive species (e.g., chloride, fluoride, and sulfate) and may decrease the pH of the waste. Using a statistically designed matrix of cyclic potentiodynamic polarization (CPP) tests, the chemistry control program is being optimized. Additionally, immersion tests were performed to measure open circuit potential (OCP) and weight change corrosion rates for partially and completely immersed coupons. Pitting factor criteria of 1 to 2 representing borderline conditions were studied to provide limits for the chemistry control program.