Off-Gas Generation Rate during Chemical Cleaning Operations at the Savannah River Site - 12499
- Savannah River National Laboratory, Aiken, SC 29808 (United States)
- Savannah River Remediation, Aiken, SC 29808 (United States)
The enhanced chemical cleaning process (ECC) is being developed at the Savannah River Site (SRS) to remove the residual radioactive sludge heel that remains in a liquid waste storage tank. Oxalic acid is the chemical agent utilized for this purpose. However, the acid also corrodes the carbon steel tank wall and cooling coils. If the oxalic acid has little interaction with the sludge, hydrogen gas could conceivably evolve at cathodic areas due to the corrosion of the carbon steel. Scenarios where hydrogen evolution could occur during ECC include the initial filling of the tank prior to agitation and near the end of the process when there is little or no sludge present. The purpose of this activity was to provide a bounding estimate for the hydrogen generation rate during the ECC process. Sealed vessel coupon tests were performed to estimate the hydrogen generation rate due to corrosion of carbon steel by oxalic acid. These tests determined the maximum instantaneous hydrogen generation rate, the rate at which the generation rate decays, and the total hydrogen generated. The tests were performed with polished ASTM A285 Grade C carbon steel coupons. This steel is representative of the Type I and II waste tanks at SRS. Bounding conditions were determined for the solution environment. The oxalic acid concentration was 2.5 wt.% and the test temperature was 75 deg. C. The test solution was agitated and contained no sludge simulant. Duplicate tests were performed and showed excellent reproducibility for the hydrogen generation rate and total hydrogen generated. The results showed that the hydrogen generation rate was initially high, but decayed rapidly within a couple of days. A statistical model was developed to predict the instantaneous hydrogen generation rate as a function of exposure time by combining both sets of data. An upper bound on the maximum hydrogen generation rate was determined from the upper 95% confidence limit. The upper bound limit on the maximum instantaneous generation rate at 5 hours was 6.1 x 10{sup -5} m{sup 3}/m{sup 2}/minute. After two and five days the upper bound limit decayed to 7.9 x 10{sup -6} and 1.3 x 10{sup -6} m{sup 3}/m{sup 2}/minute, respectively. The total volume of hydrogen gas generated during the test was calculated from the model equation. An upper bound on the total gas generated was determined from the upper 95% confidence limit. The upper bound limit on the total hydrogen generated during the 163 hour test was 0.101 m{sup 3}/m{sup 2}. Corrosion rates were determined from the coupon tests and also calculated from the measured hydrogen generation rates. Excellent agreement was achieved between the time averaged corrosion rate calculated from the hydrogen generation rates and the corrosion rates determined from the coupon tests. The corrosion rates were on the order of 0.45 mmpy. Good agreement was also observed between the maximum instantaneous corrosion rate as calculated from the hydrogen generation rate and the corrosion rate determined by previous electrochemical tests. (authors)
- Research Organization:
- WM Symposia, 1628 E. Southern Avenue, Suite 9-332, Tempe, AZ 85282 (United States)
- OSTI ID:
- 22293716
- Report Number(s):
- INIS-US-14-WM-12499; TRN: US14V1372115240
- Resource Relation:
- Conference: WM2012: Waste Management 2012 conference on improving the future in waste management, Phoenix, AZ (United States), 26 Feb - 1 Mar 2012; Other Information: Country of input: France; 6 refs.
- Country of Publication:
- United States
- Language:
- English
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