Evaluation of U₃Si₂ fuel pellets sintered in an argon vs. vacuum environment

A comparison study on the effects of sintering U₃Si₂ pellets under vacuum (~1x10-6 mbar) vs in argon has been carried out as part of a pellet fabrication process for potential light water reactor fuel application. A cross section of pellets sintered in each environment was examined using scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS). The average density of pellets sintered under vacuum and argon was 11.90 g/cm³ (97.5% theoretical density (TD)) and 11.37 g/cm³ (93.2% TD), respectively. SEM micrographs and EDS revealed the grain structure of pellets sintered under vacuum (vacuum samples) to be angular with a Si rich phase, U₅Si₄, along the grain boundaries, while grain structure of pellets sintered in argon (argon samples) reveals smaller average grain size and higher porosity with two separate Si rich phase inclusions: U₅Si₄ and USi. EDS confirmed the main phase in each pellet to be U₃Si₂ with an O rich phase inclusion. The estimated area percent of U₃Si₂ and the O rich phase in the samples from SEM image analysis was: argon samples 83.9% and 5.9% and vacuum samples 81.8% and 4.6%, respectively.