The high level waste storage double-shell tanks at the Hanford site are highly basic. The high basicity is a key factor in controlling the chemical behavior of different components of the waste and in influencing the corrosion rate of the carbon steel primary tanks. However, the introduction of atmospheric CO2 can act to reduce the pH of the tank wastes over time and possibly alter the corrosion rate of the carbon steel tanks. In order to at least partially address this issue for waste tank 241-AN-107, thermodynamic modeling calculations were performed to predict the changes in pH and carbonate concentration that could occur as CO2 is absorbed from the atmosphere. The calculations extended to complete equilibrium with the partial pressure of CO2 in the atmosphere (i.e. pCO2 = 10-3.5 atm). Simulations were performed for both the “upper” segments of tank 241-AN-107, which have been influenced by the introduction of high concentrations of NaOH to the supernatant, and for the “lower” segments where the salt cake/interstitial liquid have not been substantially altered by the introduction of base concentration.
Revised: September 29, 2008 |
Published: September 7, 2005