High level waste is stored in carbon steel tanks at the Savannah River Site (SRS). The site is currently in the process of waste removal from, and ultimately closure of, these tanks. One of the most time consuming steps in the waste removal process is cleaning the sludge heel from the bottom of the tanks to an acceptable residual quantity. The sludge consists primarily of metal oxides that formed after waste from the canyons was neutralized with sodium hydroxide. Since the canyon waste was originally a nitric acid solution, this acid is a prime candidate for sludge heel dissolution. A series of exploratory tests were performed to investigate the hypothesis that the corrosion rate of carbon steel in nitric acid could be inhibited with oxalic acid. These tests were performed at two nitric acid concentrations (0.3 and 3 M) and three oxalic acid concentrations (4 wt. %, 8 wt. %, and 12 wt. %) and were limited to the expected contact time for sludge dissolution (approximately 3 days). Carbon steels (ASTM A285 and A537) utilized in the construction of Type I, II and IIIA tanks were tested. The general corrosion rate, as well pit depths, were measured and compared.
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