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 7mgU/L to 4.5gU/L. Final plutonium concentrations ranged from 4 mu gPu/L to 12mgPu/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 center dot H2O, was found to be the dominant uranium solid phase in equilibrium with the waste supernate in most cases.