Title: Uranium nitride (UN) pellets with controllable microstructure and phase – fabrication by spark plasma sintering and their thermal-mechanical and oxidation properties

Abstract

Dense uranium mononitride (UN) pellets with controlled microstructures and tailored grain size from large-grained to a few microns are synthesized by spark plasma sintering (SPS) combined with high energy ball milling. The impacts of the sintering conditions on fuel microstructure, grain size, physical density, and phase behavior are systematically investigated, and the thermal-mechanical properties and oxidation behavior of the SPS densified UN pellets are characterized. Higher sintering temperatures and longer ball milling durations and thus finer starting UN powders promote sintering and densification, and dense UN pellets above 95% theoretical density can be achieved by SPS at 1873 K for 10 min. UN phase purity is maintained in the SPS-densified pellets sintered at a lower temperature and short duration. A phase heterogeneity with secondary UO₂ or uranium sesquinitride (U₂N₃) occurs for the UN pellets sintered at higher temperatures using finer UN powders. The hardness and fracture toughness of the SPS-densified UN pellets increase with smaller grain sizes and higher densities to 7.9 GPa and 3.5 MPa m^1/2, respectively. Furthermore, both small (1–2 μm) and large grain-sized (30–50 µm) UN pellets exhibit good thermal conductivity. Dynamic oxidation testing by a thermogravimetric analyzer in air shows that the onset temperature for oxidationmore » varies with microstructure and phase heterogeneity of the SPS densified UN pellets. Particularly, the smaller-grained (micron-sized) UN pellets containing uranium oxides and U₂N₃ display lower weight gain and significantly-reduced oxidation kinetics, and full oxidation completes at a temperature above 1173 K when tested with a ramp rate of 10 K/min.« less

Authors:

Yang, Kun ^[1]; Kardoulaki, Erofili  ^[2];

• Search DOE PAGES for author "Kardoulaki, Erofili"
• Search DOE PAGES for ORCID "0000-0002-0982-5127"

Zhao, Dong ^[1]; Gong, Bowen ^[1]; Broussard, Andre ^[1]; Metzger, Kathryn ^[3]; White, Joshua Taylor  ^[2];

• Search DOE PAGES for author "White, Joshua Taylor"
• Search DOE PAGES for ORCID "0000-0002-4409-2264"

Sivack, Michael ^[3]; Mcclellan, Kenneth James  ^[2];

• Search DOE PAGES for author "Mcclellan, Kenneth James"
• Search DOE PAGES for ORCID "0000-0002-3503-6754"

Lahoda, Edward J. ^[3]; Lian, Jie ^[1]

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+ Show Author Affiliations

1. Rensselaer Polytechnic Inst., Troy, NY (United States)
2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
3. Westinghouse Electric Company LLC, Cranberry Township, PA (United States)

Publication Date:

Sat Aug 28 00:00:00 EDT 2021

Research Org.:

Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

Sponsoring Org.:

USDOE Office of Nuclear Energy (NE)

OSTI Identifier:

1819162

Report Number(s):

LA-UR-21-25305
Journal ID: ISSN 0022-3115; TRN: US2214609

Grant/Contract Number:  

89233218CNA000001; NE0008947; NE0008824

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Nuclear Materials

Additional Journal Information:

Journal Volume: 557; Journal ID: ISSN 0022-3115

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; uranium nitride; phase heterogeneity; microstructure control; oxidation resistance