Thermal stability investigation technique for uranium nitride

Thermochemical stability of nitride nuclear fuel is an important factor that ought to be considered in fabrication processes, operation and more importantly under accidental conditions. Development of a reliable technique which determines dissociation kinetic parameters and initial temperature of UN disassociation using synchronous thermal analysis apparatus with quadruple mass-spectrometer and SEM investigations was performed. The dissociation process is found to start at temperatures higher than 1500 °С. The process comprises two stages, with a significant increase in mass loss rate at the second stage, which is due to the additional contribution of liquid uranium evaporation. The duration of isothermal exposure before uranium release depends on temperature and the initial N/U ratio and varies from several hours to a few minutes. Intense interaction of the uranium nitride with tungsten crucible was observed after 30 min exposure at 2300 °С.