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DP-MS-77-94 (Rev 4/30/78) SLn:ss c.orro::Jion of carbon stAP.l storage ta.nks containing alkaline nitrate radioactive waste, at the Savannah River Plant is controlled by specification of limits on waste composition and temperature. Actual cases of cracking have occurred in the primary steel shell of tanks designed and built before 1960 and were attributed to a combination of high residual stresses from fabrication welding and aggressiveness of fresh wastes from the reactor fuel reprocessing plants. The fresh wastes have the highest concentration of nitrate, which has been shown to be the cracking agent. Also as the wast.e soluLiuns age and are reduced in volume by evaporation of water, nitrite and hydroxide ions become more concentrated and inhibit stress corrosion. Thus, by providing a heel of aged evaporated waste in tanks that receive * The information contained in this article was developed during the course of work under Contract No. AT(07-2)-1 with the U.S. Department of Energy. fresh waste, concentrations of the inhibitor ions are maintained within specified ranges to protect against nitrate cracking. Tanks designed and built since 1960 have been made of steels with greater resistance to stress corrosion; these tanks have also been heat treated after fabrication to relieve r~sidual stresses from construction operations. Temperature limits are also specified to protect against stress corrosion at elevated temperatures.

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