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Denise Adorno Lopes1 Tashiema Wilson1 Theodore Besmann1 Elizabeth Sooby Wood2 Joshua T. White3 Andrew Nelson3 Simon Middleburgh4

1, University of South Carolina, Columbia, South Carolina, United States
2, The University of Texas at San Antonio, San Antonio, Texas, United States
3, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
4, Westinghouse Electric Sweden AB, VasterĂ¥s,, VasterĂ¥s, Sweden, Sweden

Uranium nitride-silicide composites are being considered as a high-density, high thermal conductivity fuel option for Light Water Reactors (LWRs). During development chemical interactions were observed near the silicide melting point which resulted in formation of an unknown U-Si-N ternary phase. In the present work, U-Si-N samples were produced by arc-melting under a N2 atmosphere. The resulting samples were characterized by SEM/EDS and XRD, and demonstrated an equilibrium between U3Si2, UN, USi and a U-Si-N ternary phase with a distinct crystallographic structure. DFT+U calculations were performed to evaluate the thermodynamic stability of various ternary structures from the analogous system U-Si-C. The combined results provided a good fit to a proposed structure for U20Si16N3 obtained using U=1.1 eV, where the phase was also found to be energetically stable. The results support the thermal stability of this ternary phase and should lead to further exploration of the U-Si-N system.

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