NSUF 26-5680: High-Resolution Microscopy of Uranium Mononitride MiniFuel to Quantify Lower-Length-Scale Parameters
Uranium mononitride (UN) is a promising fuel for advanced reactor concepts because of its high uranium density, excellent thermal conductivity, and favorable irradiation behavior. However, its licensing is limited by a sparse experimental database, particularly at the lower length scale (LLS), where defects, grain boundaries, and local chemistry control swelling and fission gas release (FGR). Current mechanistic fuel performance models, including the UN-SIFGRS module developed under the NEAMS program, rely on loosely constrained LLS parameters that are often inferred from UO₂ or UC analogs, introducing significant uncertainty.
To address this gap, University of Texas at San Antonio, Los Alamos National Laboratory, Oak Ridge National Laboratory, and Westinghouse Electric Company LLC jointly designed the ROADRUNNER MiniFuel irradiation campaign, the first well-documented UN experiment conducted under iso-thermal and iso-burnup conditions. ROADRUNNER was explicitly developed to support accelerated fuel qualification and mechanistic modeling. The campaign includes four UN variants with tightly controlled density and impurity content (carbon and oxygen), all fabricated with full process traceability and comprehensively characterized prior to irradiation. Carbon and oxygen impurities are historically linked to enhanced swelling and FGR, making their systematic evaluation critical for expanding the qualified compositional space of UN.
This proposal focuses on a Rapid Turnaround Experiment to perform the first systematic, high-resolution LLS characterization of as-fabricated ROADRUNNER UN specimens. Using SEM/EBSD and high-resolution TEM, the study will quantify grain structure, grain-boundary character, dislocation density, nanoscale defect populations, and impurity-associated chemical heterogeneities. These measurements will be translated directly into LLS input parameters to inform fuel performance codes.
The resulting pre-irradiation dataset will enable one-to-one comparison with post-irradiation ROADRUNNER samples following HFIR discharge in 2026, providing the first controlled defect evolution data for UN. This work will close a critical knowledge gap, improve mechanistic model fidelity, and strengthen the scientific basis for accelerated UN fuel qualification.
Additional Info
| Field | Value |
|---|---|
| Awarded Institution | Los Alamos National Laboratory |
| DOI | 10.46936/NSUF/60017654 |
| Embargo End Date | 2028-04-22 |
| Facility Tech Lead | Kory Linton |
| NSUF Call | FY 2026 RTE 1st Call |
| PI | Anton Schneider |
| PIE Facilities | Low Activation Materials Design and Analysis Laboratory |
| Prep Facilities | Low Activation Materials Design and Analysis Laboratory |
| Project Member | Dr. Joshua White, Research Staff - Los Alamos National Laboratory (https://orcid.org/0000-0002-4409-2264) |
| Project Member | Dr. Maria Kosmidou, Postdoctoral Research Associate - Los Alamos National Laboratory (https://orcid.org/0000-0002-3599-408X) |
| Project Member | Dr Denise Adorno Lopes, Senior R&D Staff Member - Oak Ridge National Laboratory (https://orcid.org/0009-0002-3705-9877) |
| Project Member | Dr. Anton Schneider - Los Alamos National Laboratory (https://orcid.org/0000-0001-7750-4547) |
| Project Type | RTE |