The dissolution step of uranium and mixed oxide uranium-plutonium spent nuclear fuel is a key initial step of a new alternative hydrometallurgical method—the CARBEX process. The study considers carbonate oxidizing systems NaHCO 3 /Na 2 CO 3 –H 2 O 2 /2Na 2 CO 3 ·3H 2 O 2 /М 2 S 2 O 8 , where M = Na, K, or NH 4 + , for dissolving actinide oxide powders. The chemical and physical factors that determine the rate of oxidative dissolution of powdered individual oxides UO 2 , U 3 O 8 , PuO 2 and NpO 2 in carbonate media were found. The results obtained are important for the development of the oxidative and sonochemical options of dissolution of highly calcined crystalline samples of uranium, plutonium and neptunium oxides, as well of spent nuclear fuel in carbonate media.