Computer simulation of the processing of uranium mononitride with an argon-oxygen gas mixture

Abstract

Uranium mononitride (UN) appears to be one of the most efficient fuels for nuclear reactors. The creation of a closed fuel cycle requires the reprocessing of spent nuclear fuel (SNF). The spent fuel reprocessing cycle includes the conversion of nitride fuel into actinide oxides. The oxidation of UN in an oxygen-argon environment at a temperature of 923 K was studied using the molecular dynamics method. A significant difference in the rate of oxide formation for crystalline and amorphous UN particles was revealed. The structure of these particles during the transition from nitride to uranium oxides was studied in detail based on the calculation of partial radial distribution functions and the construction of hybrid polyhedra. For a particle with an amorphous structure, the amount of U–O bonds created significantly exceeds the corresponding characteristic for a crystalline particle. This is facilitated by more intense fragmentation of the amorphous particle in the gaseous Ar–O mixture. Temperature is a more important regulator of the oxidation process than the oxygen concentration in the gas mixture. The destruction of U–N bonds leads to the formation of nitrogen gas, and when U–O bonds are formed, clusters of uranium oxides are created, tending to agglomeration.