Oxidation studies of UM3 (M = Ru, Rh, Pd) intermetallides

Abstract

Mixed uranium and plutonium nitride (U,Pu)N is a promising candidate fuel for fast reactors. Fission of U and Pu during reactor operation is accompanied by the formation of chemically inert compounds of uranium and noble metals - intermetallides (IMCs) with the general formula UM3 (M = Ru, Rh, Pd). One of possible steps in reprocessing of spent nitride nuclear fuel is voloxidation - oxidation in an oxygen-containing environment aimed at removal of gaseous components of SNF. In contrast to well-studied oxidation of uranium nitride in air at high temperatures, the oxidation of intermetallic compounds of uranium and noble metals has not been studied in sufficient detail. In the present work, it is shown that UM3 (M = Ru, Rh, Pd) IMCs are completely oxidized in the temperature range 800–1200 °C. UPd3 and URu3 oxidation leads to the formation of U3O8, PdO and RuO2. Upon oxidation of URh3, the formation of an intermediate phase Rh2UO6 is observed; upon further heating, it decomposes into U3O8 and metallic Rh. It is shown that peculiarities of oxidation of the studied IMCs are determined by reactivities of relevant noble metals with respect to oxygen. This study demonstrates that voloxidation of IMCs from nitride SNF should be performed at temperatures above 1200 °C.