NSUF 25-5303: Influence of Carbon Stoichiometry and Microstructure on the Irradiation Performance of Uranium Carbide Fuels
Uranium carbide (UC) is a candidate fuel for advanced reactors due to its high density and thermal conductivity. A key fabrication challenge is maintaining precise control over carbon stoichiometry, particularly in the carbothermic reduction (CTR) process, which can lead to the formation of secondary carbide phases such as U₂C₃ and UC₂. These phase variations—and their associated microstructures—are hypothesized to significantly impact fuel performance metrics such as fission gas release (FGR) and swelling. However, prior irradiation campaigns have not been able to isolate these effects due to overlapping variations in temperature and burnup. This project leverages irradiated UC fuel kernels from two MiniFuel vehicle targets (GA-FOA-201 and GA-FOA-202) to investigate the role of carbide phase and morphology on UC fuel performance. The kernels, approximately 460 µm in diameter, were irradiated at nominal temperatures of 700°C and 800°C to burnups between 1.8% and 3.1% FIMA. Two distinct carbon levels in the as-fabricated fuel resulted in microstructural variants containing UC/UC₂-y or UC/UC₂ platelets. Bimodal performance was observed at 800°C: subcapsules GA222 and GA223 exhibited high FGR and asymmetric swelling, while GA224 showed low FGR and uniform swelling. Subcapsule GA225, irradiated at 700°C, provides a comparison point for temperature-driven effects. Post-irradiation characterization— electron microscopy, EBSD, and image analysis—will be used to identify crystallographic orientation, grain morphology, and phase fraction evolution. The goal is to correlate microstructural features with observed performance trends and isolate the influence of phase morphology, particularly the platelet-forming UC₂ phase. Results from this study will inform improved UC fuel specifications and contribute to a mechanistic understanding of carbide fuel behavior under irradiation conditions relevant to advanced reactor deployment.
Additional Info
| Field | Value |
|---|---|
| Awarded Institution | Oak Ridge National Laboratory |
| DOI | 10.46936/NSUF/60015341 |
| Embargo End Date | 2027-09-10 |
| Facility Tech Lead | Kory Linton |
| NSUF Call | FY 2025 RTE 2nd Call |
| PI | Denise Adorno Lopes |
| PI Email | [email protected] |
| PI Phone Number | 8656170743 |
| PIE Facilities | Irradiated Materials Examination and Testing Facility |
| Project Member | Dr. Jason Harp, Group Leader - Oak Ridge National Laboratory (https://orcid.org/0000-0002-5345-8440) |
| Project Member | Dr. Christian Petrie, Group Leader - Oak Ridge National Laboratory (https://orcid.org/0000-0003-1167-3545) |
| Project Member | Dr Denise Adorno Lopes, Senior R&D Staff Member - Oak Ridge National Laboratory (https://orcid.org/0009-0002-3705-9877) |
| Project Type | RTE |