Abstract
Millions of gallons of high-level radioactive waste are stored in underground carbon-steel storage tanks at the Hanford site. The waste chemistries are alkaline with pH between 11 and 14. Carbon steel is expected to become passive and undergo passive dissolution under the alkaline conditions. Nonetheless, certain corrosive species in the waste chemistries, such as chloride and nitrate, could cause pitting corrosion and stress corrosion cracking (SCC). The risk of pitting corrosion and SCC increases when open-circuit potentials (OCPs) drift in anodic direction compared to the initial values; it is important to determine the extent of drift as a function of waste chemistry and metal surface characteristics. Electrochemical experiments were conducted to determine extent of drift in the OCPs. The tests were conducted with the following three surface characteristics: (i) polished surface by sanding a coupon, (ii) surface with mill-scale plus corrosion product, and (iii) partially removed mill-scale plus corrosion products. Coupons were immersed in a waste simulant for several months and OCPs were recorded. Several other electrochemical techniques were used to measure corrosion-related properties. Experimental data demonstrated that terminal OCPs are independent of surface conditions.
