Solubility of Uranium and Plutonium in Alkaline Savannah River Site High Level Waste Solutions

Abstract

Five actual Savannah River Site tank waste samples and three chemically-modified samples were tested to determine solubility limits for uranium and plutonium over a one year time period. Observed final uranium concentrations ranged from 7 mg U/L to 4.5 g U/L. Final plutonium concentrations ranged from 4 µg Pu/L to 12 mg Pu/L. Actinide carbonate complexation is believed to result in the dramatic solubility increases observed for one sample over long time periods. Clarkeite, NaUO₂(O)OH · H₂O, was found to be the dominant uranium solid phase in equilibrium with the waste supernate in most cases.

Keywords:

• actinide
• clarkeite
• precipitation
• x-ray diffraction

Notes

*Hydroxide measured as free or uncomplexed.

*DWPF ˭ Defense Waste Processing Facility.

*Indicates altered concentrations resulting from added solids.

*Initial uranium spike level: 2400 mg/L, additional 3000 mg/L spike after 250 days.