Chemical dissolving of sludge from a high level waste tank at the Savannah River Plant

Abstract

The concept for decontamination and retirement of radioactive liquid waste tanks at the Savannah River Plant (SRP) involves hydraulic slurrying to remove most of the settled sludges followed by chemical dissolving of residual sludges. Dissolving tests were carried out with small samples of sludge from SRP Tank l6H. Over 95% of the sludge was dissolved by 8 wt % oxalic acid at 85°C with agitation in a two-step dissolving process (50 hours per step) and an initial reagent-to-sludge volume of 20. Oxalic acid does not attack the waste tank material of construction, appears to be compatible with the existing waste farm processes and equipment after neutralization, and with future processes planned for fixation of the waste into a high-integrity solid for packaging and shipping.

Waste Tank Heel Chemical Cleaning Summary

“…However, a seemingly notable contradiction is that while manganese was readily dissolved in the Poirier and Fink's study, it was the most difficult to dissolve in Bradley and Hill's work. 31 Both sets of tests generally agree that increased temperature, contact time, and oxalic acid concentration yield the best overall sludge dissolution results.…”

“…Bradley and Hill reported on the results of a series of lab scale tests conducted in support of the oxalic acid treatment of sludge heel residue in Tank 16H. 31 They performed three sets of tests:…”

“…32 The experimental procedure for sludge dissolution was the same as outlined for Bradley and Hill's work. 31 The only exception was that in some tests the sludge was dried and rewetted with water before oxalic acid was added. Results are summarized in Table 12.…”

“…The 239 Pu concentration in the sludge solid was about twice (0.14 g/L) that of the original sludge but well below that required for criticality (7 g/L). 2 34 The experimental procedure for sludge dissolution was the same as the one outlined for the Bradley and Hill's work 31 except the amount of sludge dissolved was based on weight instead of volume. All the tests were done at room temperature (~ 23 o C) using 1 M (9 wt %) oxalic acid.…”

“…The use of citric acid as a sludge dissolution agent has been studied in at least two prior comparison sets of research. Bradley and Hill 31 conducted scoping tests with Tank 16H sludge and found citric acid as a lone cleaning agent to be slightly less effective than oxalic acid. Their test with it in a mixture with sulfamic acid yielded significantly reduced results.…”