Development of a Technology for Dissolving a Homogeneous Mixture of Uranium and Plutonium Oxides Obtained by the Plasma-Chemical Method

A plasma technology for the synthesis of mixed uranium and plutonium oxides UO2–PuO2 by denitration of mixed solutions of these metals has been developed at the Siberian Chemical Combine. The production process of U and Pu oxides includes the preparation of mixed initial solutions, their denitration in a plasma reactor with an inductive high-frequency discharge, and isolation of powders from the vapor–gas flow in vortex precipitators or filters with metal–fabric meshes. The particles of the obtained oxide powders possess the features of nanocrystalline and nanoscale materials containing crystalline and amorphous phases in the structure. The equipment for the implementation of this technology has been developed (Zenith plasma plant), on which mixed U and Pu oxides have been produced, and over 60 kg of oxides UO2–PuO2 with the plutonium content of 25 wt % has been synthesized, from which industrial fuel rods for the BN-600 reactor have been fabricated. After the operation of the fuel rods in the BN-600 reactor and corresponding exposure, the cores of the irradiated fuel rods should be dissolved for subsequent radiochemical treatment. The results of the studies on the search for the conditions of dissolution and effective solvents for mixed U and Pu oxides obtained by the plasma technology of decomposition of mixed solutions of uranium and plutonium are presented. It has been found that no complete dissolution of the synthesized oxides occurs in solutions of HNO3 and HNO3 with the addition of the reducing agents for tetravalent plutonium—ascorbic acid and hydrazine. Complete dissolution of the mixed oxides most effectively occurs in solutions of 10 M HNO3 with the addition of 0.25–1.0 g/L HF.