Raman spectroscopy of uranium nitride kernels

Uranium nitride is an advanced fuel candidate for a wide variety of advanced nuclear reactors. This work summarizes the first characterization of UN kernels by Raman spectroscopy. First-principles density functional theory calculations were performed to predict the Raman spectra of uranium sesquinitride (U₂N₃), uranium dinitride (UN₂), uranium mononitride (UN), uranium monocarbide (UC), as well as U-N-C (UN_1-xC_x) and a U-N-C-O mixture. A core–shell structure was identified by scanning electron microscopy and Raman spectroscopy imaging. A signal at ∼500 cm⁻¹ was identified on the periphery of the core-shell structure, possibly corresponding to U₂N₃ and/or UN₂. This signal broadens and shifts to 470 cm⁻¹ because of the formation of UNC, UNCO or U₂N_3+x structures. The culmination of this work demonstrates the feasibility of using Raman spectroscopy to identify variations in composition and phases in UN kernels.