Materials aspects of SRP waste storage: corrosion and mechanical failure

Studies were made on the causes of observed leaks in mild steel tanks used to store liquid waste from nuclear fuel re processing at the Savannah River Plant. Leaks were observed in the walls of some primary vessels and in some cooling coils. The studies revealed that: wall leaks resulted from nitrate stress corrosion cracking caused by alkaline nitrate solution; and coil leaks resulted from pitting corrosion caused by diluted waste solutions during sludge removal. Stresses that caused wall cracking were residual stresses, primarily those produced during tank fabrication. Pitting of coils was caused by the con-current dilution of nitrite in the waste supernate, and leach-ing of sulfate from the sludge. Results of these studies pro vided the bases for modifications in fabrication and operation of waste tanks. The modifications included:

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