Oak Ridge conducts first neutron scattering measurements on HALEU TRISO fuel

Oak Ridge National Laboratory researchers used the SNAP diffractometer at the Spallation Neutron Source to perform the first-of-its-kind neutron scattering measurements on TRISO fuel particles containing high-assay, low-enriched uranium. Using a tightly focused, 1-millimeter pulsed neutron beam, investigators probed unirradiated HALEU-containing TRISO particles drawn from the same batch later used in the DOE Office of Nuclear Energy AGR Program, establishing a pre-irradiation baseline for uranium carbide content.

As the beam passed through the poppy-seed sized kernels, some neutrons were absorbed by the uranium and others were scattered. A neutron area detector collected the scattered neutrons, yielding data about TRISO properties and composition without destroying the particles. ORNL described the results as “early measurements [that] offer a path for using neutron scattering with reactor‑irradiated TRISO particles,” framing this work as an enabling step rather than a final technical verdict.

The practical value is immediate for researchers and reactor developers. Detailed, non-destructive compositional maps help refine models of phase changes inside TRISO kernels that occur under high temperatures and irradiation. William Cureton summed the potential payoff: “the experiments offer valuable insight and lay the groundwork for more detailed modeling of TRISO fuels. Improved understanding of how kernel composition impacts TRISO behavior can ultimately enable improvements to the economics of TRISO fabrication methods, leading to safer, more efficient, and cost‑effective fuel technologies.”

TRISO fuel is made of uranium-based kernels coated with three protective layers of ceramic and carbon, and it can withstand temperatures above 2,900 degrees Fahrenheit. HALEU enables much higher energy production, known as burnup, and improves reactor performance through better fuel utilization, longer refueling intervals, and reduced waste generation. Neutron scattering at SNS is suited to this work because it can extract atomic-level information under external stimuli such as temperature and pressure, making it possible to follow structural evolution in operando or post-irradiation studies.

Beamline operations included careful alignment: “Beamline scientists at the Spallation Neutron Source align a neutron beam collimator to facilitate the first neutron scattering measurements on tristructural isotropic nuclear fuel containing high assay, low enriched uranium,” Liz McCrory noted in ORNL materials. Laboratory photos show Jasmine Hinton aligning an optical system with a red laser during setup, underscoring the hands-on beamline work required to target millimeter-scale particles.

The data are an early but concrete tool for the TRISO community. Next steps will focus on applying the same neutron scattering technique to reactor-irradiated TRISO particles, characterizing complex phase changes, and integrating the observations into predictive fuel performance models. For follow-up or press inquiries, Oak Ridge National Laboratory is located at 1 Bethel Valley Road, Oak Ridge, TN 37830; phone (+1) 865.576.7658.