Radioactive waste primarily containing sodium nitrate, nitrite, and hydroxide is stored in underground storage tanks at
the Department of Energy (DOE) Savannah River Site (SRS). A comprehensive structural integrity program which includes chemistry controls, is in place to preclude any consequential corrosion in these waste tanks to maintain safe storage of the waste. The current chemistry control program places temperature limits on solutions containing low levels of nitrate (expected to prevent caustic stress corrosion cracking (CSCC) when hydroxide is present. However, during a sludge mass reduction campaign, these limits will be challenged with high hydroxide concentrations and corrosion testing has been completed to support control during the operations. The results of electrochemical testing and mechanical U-bend testing are presented here.