Corrosion Considerations for Life Management of Hanford High-Level Waste Tanks

Abstract

Abstract(1) The potential for corrosion-related aging mechanisms to be active in the Hanford Site waste tanks is frequently questioned and there are related uncertainties. This paper considers surveillance and analyses for evaluating the potential influence of corrosion processes such as stress corrosion cracking, pitting, crevice corrosion, uniform corrosion, microbiologically-induced corrosion, embrittlement, and corrosion of the reinforced concrete steel on the useful life of Hanford radioactive waste tanks. There are two types of Hanford Site underground reinforced concrete, carbon steel lined waste tank structures. They primarily store caustic nitrate wastes, some at elevated temperatures, from defense reprocessing of spent nuclear fuels. Some of the Hanford waste tanks have leaked radioactive liquid waste to the soil. These leaks are possibly due to nitrate-induced stress corrosion cracking. Major efforts prescribed to avoid nitrate-induced stress corrosion cracking in newer tank designs appear successful. A potential for pitting and crevice corrosion cracking in the carbon steel liners exists. There has been no evidence of significant uniform corrosion of the carbon steel liners and there has been no evidence of waste tank degradation caused by corrosion of the concrete reinforcing steel. As much as practical, surveillance for evidence of active corrosion is conducted. This surveillance primarily consists of leak detection and monitoring today. Remote closed-circuit television examinations of one type of Hanford waste tank were recently completed and a remote (robotic) ultrasonic testing (UT) system is under development for quantitative examination of the same type of tanks that received the closed-circuit television examination. A waste tank life management program is being developed to qualify the Hanford waste tanks for continued safe storage of these wastes. Corrosion evaluations, structural analyses, and surveillance are required to qualify the tanks and to promptly detect evidence of possible distress.