Vapor Space Stress Corrosion Cracking of Radioactive High Level Waste Tanks

Radioactive waste is stored in underground storage tanks at the Department of Energy (DOE) Savannah River Site (SRS). The waste tanks store supernatant liquid salts, consisting primarily of sodium nitrate, sodium nitrite, sodium hydroxide, and sludge. Controls on the solution chemistry (minimum nitrite and hydroxide concentrations) are in place to prevent the initiation and propagation of pitting and stress corrosion cracking in the tanks.  However, recent experience has shown that steel not in contact with the bulk waste solution or slurry, but exposed to the “vapor space” above the bulk waste, may be vulnerable to the initiation and propagation of stress corrosion cracking.  Experiments have been performed to predict the vapor space SCC vulnerability