51314-3754-Stress Corrosion Cracking of Carbon Steel in Nitrate-Based Hanford Waste Simulant Environments

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Product Number: 51314-3754-SG

ISBN: 3754 2014 CP

Author: John Beavers

Publication Date: 2014

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The Hanford tank reservation contains approximately 50 million gallons of liquid legacy radioactive waste from cold war weapons production that is stored in 177 underground storage tanks. Current plans call for treatment and ultimate disposal of the resulting waste. The double-shelled carbon steel tanks presently used for storage will continue in operation until the vitrification plant construction is finalized and waste processing operations are completed.The waste compositions in the storage tanks are grouped according to their main constituents such as nitrite/nitrate-based and carbonate-based chemistries. Most of the wastes are highly alkaline in nature typically with pH values between 12 and 14. Under alkaline conditions carbon steels will tend to be passive and undergo relatively slow uniform corrosion. However carbon steels can become susceptible to localized corrosion (e.g. pitting) and stress corrosion cracking (SCC) in the presence of certain aggressive constituents such as chloride and nitrate even in these passive conditions.Although most wastes stored in these tanks are within specification and are predicted to remain within specification for the foreseeable future there will likely be cases in which the chemistry might become out of specification (e.g. required pH levels above 13). This situation could result from waste chemistries changing over time due to various chemical and radiochemical reactions taking place inside the tanks or could develop during waste transfer and mixing operations. Thus there is concern within U.S. Department of Energy (DOE) oversight groups and regulatory bodies that tank integrity could be compromised given these chemistries change. If tank integrity is threatened there is a need to define mitigation strategies and additional resources might be required to mitigate potential leaks as well as conduct repairs. Thus the objective of the present study was to quantify the risk of stress corrosion cracking under different potential chemistry scenarios. Some of these scenarios were intended to simulate and bound possible chemistries that may develop whereas others were investigated strictly to elucidate the cracking mechanism and its inhibition.