Five ways HFIR can advance nuclear fuel innovation

The U.S. is ready to build more nuclear reactors, but a dwindling network of research reactors capable of testing new nuclear fuels for commercial use presents a major bottleneck.

With a long record of success in innovation and fuel experimentation, the Department of Energy's (DOE) High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory (ORNL) is one of the few research reactors equipped to clear the backlog and support accelerated fuel development and qualification.

A new paper in Nuclear Engineering and Design outlines how HFIR, one of the world's highest-flux steady-state research reactors, is essential to developing the data needed to qualify new fuels that can extend reactor lifetimes, improve efficiency and enable the deployment of new reactor technologies.

HFIR can accommodate a broad range of test conditions and experimental platforms

HFIR's famously intense neutron flux allows researchers to test materials across a range of neutron energies, making it a flexible test reactor that can accommodate many types of experiments. With three primary irradiation regions, HFIR can accommodate small and simple "rabbit" capsules that can be rapidly designed, built and deployed in the flux trap, or center of the reactor, where samples receive the highest amount of neutrons. The reactor's removable and permanent beryllium reflector regions can host larger and more complex irradiation experiments, including those with instrumentation and sensors or thermal neutron shields to tailor the flux spectrum.

HFIR is a leader in novel nuclear fuels experimentation

ORNL has led fuel development and testing efforts for decades, using HFIR to perform the separate-effects and integral tests that have supported fuel development and qualification. The reactor was foundational in developing the architecture of high-temperature gas reactor fuels like TRISO fuel particles, and performed targeted, high-throughput tests on new fuel and cladding concepts. Recent testing campaigns leveraging the MiniFuel concept have irradiated a broad range of fuels, including Accident Tolerant Fuel concepts, coated fuel particles, and metallic fuels. This campaign complements extensive fuel cladding irradiations in HFIR's flux trap.

HFIR's modernization is enabling instrumented experiments

HFIR has undergone major modernization efforts throughout its operational history to improve the speed, flexibility, and accuracy of its capabilities. Through the development of the Materials Irradiation Facility, ORNL enabled more precise control of instrumented experiments. The MIF regulates temperatures using controlled sweep gas mixtures and can independently control multiple temperature zones within a single experiment. Further, automated monitoring systems continuously track temperature, pressure and gas composition while allowing researchers to remotely monitor and adjust experiments in real time. These experiments were instrumental in detecting fission gas release from tri-structural isotopic, or TRISO fuels, during irradiation in HFIR, demonstrating HFIR's role as a high-throughput testing platform capable of simultaneously supporting multiple sophisticated experiments.

HFIR can provide the technical basis for fuel qualification

Fuel experiments performed at HFIR can support technical reports used as basis for nuclear fuel qualification by the U.S. Nuclear Regulatory Commission. The reactor can provide high-quality data on key fuel performance factors including fission gas release, microstructure evolution, and how a fuel reacts with its cladding. In addition to validating fuel performance and informing safety analyses, the data that HFIR can provide is well-suited to inform the NRC technical reports that support qualification of new fuel forms.

HFIR is the nexus of ORNL's fuel testing ecosystem

HFIR sits on the ORNL campus within a comprehensive infrastructure for examination and analysis of nuclear fuels. The lab's integrated facilities, including the Coated Particle Fuel Development Laboratory, the Low Activation Materials Development and Analysis laboratory, the Irradiated Fuel Examination Laboratory, and the Irradiated Material Examination and Testing Facility, paired with ORNL's decades of knowledge in fuel development, represent a comprehensive testbed for fuel testing and experimentation.

HFIR is a critical asset among the nation's nuclear research facilities, with myriad capabilities to rapidly deliver high-quality data needed to move fuels from early-stage concepts to regulatory qualification. As utilities pursue longer reactor lifetimes and developers work to commercialize advanced reactor technologies, using HFIR's capabilities more strategically can keep the pace of industry demand.

This research was supported by the U.S. Department of Energy Office of Nuclear Energy Advanced Fuels Campaign.

ORNL is committed to supporting U.S. energy needs by pursuing strategic research that advances a wide variety of affordable, abundant and competitive nuclear technologies, and strengthens national security. The lab's scientific expertise and world-class facilities are often the first step in advancing nuclear energy innovations.

HFIR is a DOE Office of Science user facility.

UT-Battelle manages ORNL for the DOE's Office of Science, the single largest supporter of basic research in the physical sciences in the United States. The Office of Science is working to address some of the most pressing challenges of our time. For more information, please visit energy.gov/science. -Liz McCrory