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

• Air oxidation of chemically inert IMCs (intermetallic compounds) of uranium and noble metals UM 3 ( M = Ru, Rh, Pd) - potential components of nitride SNF (spent nuclear fuel), has been studied. • Upon IMC oxidation uranium converts to U 3 O 8 , noble metals to PdO, RuO 2 and Rh 2 UO 6 , respectively. • Complete oxidation of IMCs occurs in the temperature range 800–1200 °C, its mechanism is determined by the properties of the noble metal in the alloy composition . • It is advisable to reprocess investigated IMCs as part of SNF using volume oxidation (voloxidation) at temperatures above 1200 °C. 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 UM 3 ( 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 UM 3 ( M = Ru, Rh, Pd) IMCs are completely oxidized in the temperature range 800–1200 °C. UPd 3 and URu 3 oxidation leads to the formation of U 3 O 8 , PdO and RuO 2 . Upon oxidation of URh 3 , the formation of an intermediate phase Rh 2 UO 6 is observed; upon further heating, it decomposes into U 3 O 8 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.