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DOE OSTI2020

Materials Data on U2N3 by Materials Project

U2N3 crystallizes in the cubic Ia-3 space group. The structure is three-dimensional. there are two inequivalent U+4.50+ sites. In the first U+4.50+ site, U+4.50+ is bonded to six equivalent N3- atoms to form a mixture of distorted edge and corner-sharing UN6 octahedra. The corner-sharing octahedral tilt angles are 59°. All U–N bond lengths are 2.27 Å. In the second U+4.50+ site, U+4.50+ is bonded to six equivalent N3- atoms to form a mixture of distorted edge and corner-sharing UN6 octahedra. The corner-sharing octahedra tilt angles range from 59–61°. There are a spread of U–N bond distances ranging from 2.25–2.33 Å. N3- is bonded to four U+4.50+ atoms to form a mixture of edge and corner-sharing NU4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U2N3 by Materials Project

U2N3 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. U+4.50+ is bonded in a 7-coordinate geometry to seven N3- atoms. There are a spread of U–N bond distances ranging from 2.23–2.55 Å. There are two inequivalent N3- sites. In the first N3- site, N3- is bonded to six equivalent U+4.50+ atoms to form NU6 octahedra that share corners with twelve equivalent NU4 tetrahedra, edges with six equivalent NU6 octahedra, and edges with six equivalent NU4 tetrahedra. In the second N3- site, N3- is bonded to four equivalent U+4.50+ atoms to form NU4 tetrahedra that share corners with six equivalent NU6 octahedra, corners with six equivalent NU4 tetrahedra, edges with three equivalent NU6 octahedra, and edges with three equivalent NU4 tetrahedra. The corner-sharing octahedra tilt angles range from 16–57°.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Dislocation Loops in Proton Irradiated Uranium-Nitrogen-Oxygen System

Here in this study, we investigated the dislocation loop types formed in the proton-irradiated uranium-nitrogen-oxygen (U-N-O) system, which involves uranium mononitride (UN), uranium sesquinitride (a-U2N3), and uranium dioxide (UO2) phases. The dislocation loop formation is examined using specimens irradiated at 400°C and 710°C. Based on the detailed transmission-based electron microscopy characterization with i) the morphology-based on-zone and ii) the invisibility-criterion based two-beam condition imaging techniques, only a single type of dislocation loop in each phase is found: a/2?110?, a/2?111?, or a/3?111? dislocation loops in UN, a-U2N3, and UO2 phases, respectively. Molecular statics calculations for the formation energy of perfect and faulted dislocation loops in UN phases indicate a critical loop size of ~ 6 nm, above which perfect loops are energetically favorable. This could explain the absence of faulted loops in the experimental observation of the irradiated UN phase at two temperatures. This work will enhance the understanding of irradiation induced microstructural evolution for uranium nitrides as advanced nuclear fuels for the next-generation nuclear reactors.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗