ORNL Completes Critical Post-Irradiation Testing on HALEU TRISO Fuel
The U.S. Department of Energy's Oak Ridge National Laboratory (ORNL) has announced a major milestone in advanced nuclear fuel development. On September 4, 2026, ORNL researchers successfully completed post-irradiation mechanical property measurements on TRISO fuel particles containing high-assay low-enriched uranium (HALEU). This critical work is a core component of the Advanced Gas Reactor (AGR) Fuel Development and Qualification Program.
Quantifying Radiation Effects on Fuel Layers
To understand the structural changes induced by the harsh reactor environment, researchers utilized advanced instrumented indentation testing. This technique allowed them to precisely measure the mechanical properties of the inner pyrolytic carbon (IPyC), outer pyrolytic carbon (OPyC), and silicon carbide (SiC) layers of the irradiated HALEU TRISO particles.
The results confirmed a measurable decrease in both the elastic modulus and hardness of the SiC layer, alongside significant property changes in the PyC layers.
These empirical findings are indispensable. They provide the vital data needed to validate fuel performance models and ensure the reliability of fission product containment under extreme operating conditions.
Ongoing Safety Testing and AGR Experiments
Beyond mechanical measurements, ORNL is actively conducting ongoing post-irradiation examination (PIE) and high-temperature safety testing for the AGR-5, AGR-6, and AGR-7 experiments. Recent safety testing conducted at extreme temperatures of 1600°C and 1800°C has successfully confirmed the structural integrity of the TRISO coating and its fission product retention behavior.
This builds upon earlier 2026 neutron scattering measurements of HALEU-containing TRISO particles. Together, these comprehensive tests de-risk the deployment of next-generation advanced gas reactors by proving that HALEU TRISO fuel can withstand the rigorous demands of commercial operation.
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