[en] Uranium nitride-silicide composites are being considered as a high-density and high thermal conductivity fuel option for light water reactors. During development, chemical interactions were observed near the silicide melting point which resulted in formation of an unknown USiN ternary phase. In the present work, USiN composite samples were produced by arc-melting U₃Si₂ under an argon-nitrogen atmosphere to form the ternary phase. The resulting samples were characterized by SEM/EDS-EPMA and XRD, and demonstrated an equilibrium between U₃Si₂, UN, USi and a USiN phase with a distinct crystallographic structure. Rietveld refinement of the ternary structure was performed, considering the ternary structures existent in the analogue USiC system, and a good fit was obtained for the hexagonal U₂₀Si₁₆N₃ phase. DFT + U calculations were performed in parallel to evaluate the thermodynamic and dynamic stability of the ternaries U₂₀Si₁₆N₃ and U₃Si₂N₂. The calculated enthalpy of formation and phonon dispersion support the existence of stable U₂₀Si₁₆N₃ and U₃Si₂N₂, although some soft modes in the U₂₀Si₁₆N₃ phase phonons are observed. The results presented here thus demonstrate the occurrence of at least one ternary phase in the USiN system.