4, Illinois Institute of Technology, Chicago, Illinois, United States
3, Modern Electron, Bellevue, Washington, United States
2, Brookhaven National Laboratory, Upton, New York, United States
In order to restrict proliferation of nuclear weapons, highly enriched uranium (≥ 20% 235U) fuel is in the process of being replaced with low enriched uranium (< 20% 235U) fuel in research and test reactors. As the uranium enrichment is decreased, an increase in the uranium fuel density (> 8gU-235/cm3) is required for high performance research reactors. Accordingly, monolithic uranium-molybdenum (U-Mo) alloys, have been studied and considered as a nuclear fuel for these reactors. U-Mo alloy fuel exhibits excellent irradiation performance because the isotropic, body-centered cubic phase (γ-phase) of uranium is stable at the operating temperatures of research reactors (below 250°C). Understanding the effects of radiation damage on the atomic and microstructure of a nuclear fuel is essential to extend fuel lifetime and to enhance the fuel performance. Extended X-ray absorption fine structure (EXAFS) is a useful technique to study radiation damage of materials since it assists in extracting information on the local environment (~5-6 Å away from an absorbing atom) such as atomic distance and coordination number changes after irradiation. Thus, in the present study, low fluence neutron radiation damage of U-Mo alloys is investigated using EXAFS. Synchrotron X-ray diffraction (XRD) is also utilized to examine the microstructural changes in these alloys, including phase identification, phase fractions, crystallite sizes, and lattice parameters. Additionally, pure depleted U and Mo, are analyzed and compared using both techniques. This work will suggest a new approach for understanding radiation damage of not only U-Mo alloy fuel, but also depleted U and Mo.