Experimental Investigations on Stress Corrosion Cracking in High Level Radioactive Waste Tanks

High level radioactive waste (HLW) incident to nuclear weapons production is stored in large underground carbon steel tanks at the Savannah River Site and Hanford Site.  DOE sponsored national laboratories, industry and academia have been investigating corrosion mechanisms that occur in the high level waste tanks for more than fifty years.  As a result, practical and effective solutions for corrosion control of mechanisms such as stress corrosion cracking (SCC) have been implemented.  The types of tests that were employed and the use of the results to predict and ensure mitigation of SCC during storage conditions will be described briefly. Currently there is a desire to optimize the corrosion control programs Savannah River Site and Hanford to address the potential for SCC as the environmental conditions in the waste change over time.  These changing conditions include in-growth of the corrosion inhibitor nitrite during storage due to radiolysis of nitrate, dissolution and removal of aluminum oxides present in solids phases using high temperature caustic, dissolution and removal of soluble salts, and changes in the ambient conditions in the vapor space above the waste.  An overview of the experimental programs that are addressing these issues will be presented.