Oxidative embrittlement (voloxidation, volume oxidation) of both the fuel itself and of Zircaloy fuel claddings shows promise as modification of head-end operations of the PUREX process. The gas-phase conversion of oxide fuel in various atmospheres (O2, air, О3, Н2О vapor, air–СО2 mixture) at 300–600°С ensures almost complete removal of volatile components (3H, 14C, 129I, radioactive noble gases) already before starting the radiochemical reprocessing of the fuel. DEOX process (DEclad via OXidation) has been developed for breaking down strong zirconium claddings. In this process, the fuel claddings are broken down and transform into ZrO2 powder as a result of the reaction of zirconium with oxygen at 1100°С. On the other hand, along with the oxide fuel, other kinds of fuel (e.g., metallic fuel) also require radiochemical reprocessing. This fuel contains not only U, but also other metals (Zr, Al, Mg, etc.). A hydrometallurgical scheme involving the steps of SNF dissolution both in an acid and in an alkali is suggested for reprocessing of this type of SNF.
Our previous studies dealt with the gas-phase conversion of U3O8, MoO3, SrO, ZrO2, and their mechanical mixtures into water-soluble compounds in the NOx–H2O (vapor)–air and HNO3 (vapor)–air atmospheres in the temperature interval from 25 to 150°C show that in the course of gas-phase conversion U3O8 and SrO transform into water-soluble compounds (nitrates, hydroxynitrates), whereas MoO3 and ZrO2 undergo no changes. The principal possibility of separating U from Mo and Zr by gas-phase conversion of the oxides in the NOx–H2O (vapor)–air and HNO3 (vapor)–air atmosphere was established. Therefore, it was interesting to examine the possibility of the gas-phase conversion of metallic U, Zr, and Al in the NOx–H2O (vapor)–air or HNO3 (vapor)–air atmosphere (hereinafter, nitrating atmosphere) into water-soluble compounds. That was the subject of this study.
Gas-phase conversion of metallic U, Zr, and Al into water-soluble compounds in the NOx–H2O (vapor)–air and HNO3 (vapor)–air atmospheres was studied. Monolithic Umet and powdered Zrmet undergo gas-phase conversion to form water-soluble compounds (nitrates, hydroxynitrates), whereas monolithic Zrmet remains unchanged. The degree of conversion of Almet into water-soluble compounds in the examined nitrating media at 25–150°С does not exceed 10%. The principal possibility of separating U from Al and Zr by gas-phase conversion of monolithic samples in a nitrating atmosphere was demonstrated.