A Study of Stress Corrosion Cracking and Localized Corrosion of Carbon Steel in Nitrate Based Nuclear Waste

The Hanford tank reservation in Washington State has 177 underground storage tanks that contain approximately 50 million gallons of liquid legacy radioactive waste from cold war weapons production. These tanks will continue to be in operation for at least another twenty years, until further process plans are defined. The work described in this paper was to obtain a comprehensive understanding of the localized corrosion behavior of carbon steel in waste simulants for Tank AP105. While localized corrosion was observed in some other simulants, the work demonstrated that the AP105 simulant is generally benign with respect to localized corrosion when samples were fully immersed in the bulk simulant. Similar to previous findings, nitrite is still the dominant inhibitor that effectively protects the steel from localized corrosion in the simulant. However, severe corrosion attack was observed at the solution/vapor interface. The major effort of this work was to understand the mechanism of the interfacial attack and its relevance to the integrity of the tank.

Key words: nuclear waste, simulant, localized corrosion, nitrite, inhibitor, interface corrosion