This study addresses the physical-chemical processes that might naturally or inadvertently occur and that would lead to a separation of the poisoning nonfissionable actinides (Th-232, U-238) from the fissionable ones (Pu-239, U-235) by selective dissolution and redeposition over a prolonged storage of the waste. Of the various chemistries that were evaluated, carbonate complexation reaction is the most plausible means of achieving the separation of these actinides. Carbonate ions (formed by the dissolution and hydrolysis of atmospheric CO2) can selectively dissolve the actinide oxides through the formation of soluble carbonate complexes, which could result in the separation of poisoning actinides from the fissionable ones. The concentrations of these soluble carbonate species are dependent on the pH, temperature, and other ions; therefore, changes in any of these parameters over time-especially cyclic changes (daily or seasonal)-could cause a selective dissolution and redeposition of the more soluble species away from the less soluble ones. Detailed calculations using the stability constants for the carbonates have shown that the most likely pH range for this process to occur is pH = 10-11. Increased solubility through reaction with organic complexants such as EDTA was also considered, and while it presents a situation similar to carbonate complexation and similar potential for autoseparation of the actinides in the waste tanks, it would require the uncontrolled dumping of large amounts of complexants into the storage tanks.