Above: Molten salt reactors are an active area of nuclear research at INL

NEI: Please give a brief history of INL and the facilities currently available to support the development of advanced reactors and new nuclear fuels?

Idaho National Laboratory (INL) originates from the National Reactor Testing Station, which was established in 1949 to provide a location to develop, test, and demonstrate civilian reactor systems and support the nuclear navy. The site is well known for its first reactor, the Experimental Breeder Reactor-I (EBR-I), which started operations in December 1951. EBR-I was the first nuclear reactor to produce usable amounts of electricity. The reactor was also novel in that it used a liquid metal coolant and operated using a fast neutron spectrum that enabled demonstration of nuclear fuel breeding, a key concept for maximizing uranium resource use. Over the ensuing decades, 52 reactors were operated on the site establishing the technical and scientific basis that underpins the safe operation of our current commercial reactors as well as for the development of future advanced reactor concepts. Four of those 52 reactors are still operating.

There are many research and development facilities at the laboratory that support nuclear energy development, but some key facilities are summarized below:

1) Research fuel fabrication facilities – INL has several facilities devoted to developing and fabricating nuclear fuels for research and development. These facilities can produce metallic- and ceramic-based fuels that support testing in INL’s test reactors and commercial power reactors.

2) Fuels and material irradiation capabilities:

a. The Advanced Test Reactor (ATR) provides steady-state irradiation capabilities for reactor fuels and materials testing, which supports nearly all U.S. reactors in operation or planned, including research reactors, commercial power reactors, naval reactors and future reactors.

b. The Transient Reactor Test facility (TREAT) provides powerful reactor pulses that can test the performance of fuels and materials during power excursions. The TREAT building will also serve as the operational location for the MARVEL reactor.

3) Irradiated fuels examination facilities – INL has three primary irradiated fuels and materials examination facilities:

a. The Hot Fuel Examination Facility (HFEF) is a large hot cell facility that can be used to perform engineering-scale examinations of irradiated fuels and materials. HFEF can accommodate a full range of fuels from TRISO coated particle fuels, metallic fuels and light water reactor fuels. The facility is also used to create samples to be sent to other facilities for more detailed examinations.

b. Irradiated Materials Characterization Laboratory (IMCL) contains a wide range of unique scientific instruments that allow researchers to examine the microstructure of nuclear fuels and materials to gain a fundamental understanding of material performance under irradiation.

c. Sample Preparation Laboratory (SPL) is a new facility still under construction that will provide leading examination capabilities for non-fuel materials that are used primarily for components and structures in nuclear reactors.

4) National Reactor Innovation Center (NRIC) Reactor Demonstration Test Beds – Two reactor demonstration test beds (DOME and LOTUS) are under development.

a. Demonstration of Microreactor Experiments (DOME) is a repurposed and redesigned containment facility, formerly Experimental Breeder Reactor-II (EBR-II), capable of housing Category B nuclear reactors that generate up to 20 megawatts of thermal energy using high-assay low-enriched uranium (HALEU) or low-enriched uranium fuels. The facility provides a location and a supporting ecosystem of systems, equipment, and personnel to shepherd industry partners through a testing program for experimental microreactors to achieve first criticality and validate their design and analytical model algorithms. The DOME is expected to support operations beginning in 2026. Current industry partners engaged in front end engineering and experiment design work in preparation for potential testing are Westinghouse, Radiant and Ultra Safe Nuclear Corporation.

b. Laboratory for Operations and Testing in the US (LOTUS) is a repurposed and redesigned confinement facility, formerly the Zero Power Physics Reactor, capable of housing Category B nuclear reactors that generate up to 500 kilowatts of thermal energy using high-enriched uranium fuels. The facility provides a location and a supporting ecosystem of systems, equipment, and personnel to shepherd industry partners through a testing program for experimental reactors to achieve first criticality and validate their design, fuel characteristics and analytical model algorithms. LOTUS is expected to support operations beginning in 2027/28. A current industry partner engaged in design work in preparation for a potential test program is the Southern/TerraPower Molten Chloride Reactor Experiment (MCRE) project.

5) Collaborative Computing Center (C3) provides state-of-the-art computer systems to perform modeling and simulation of nuclear reactors and fuels to support research on reactor concepts and fuels. C3 currently contains the Sawtooth computer, widely used across the nuclear R&D community. Sawtooth supports the use of advanced simulation software based on INL’s MOOSE framework.

Above: The Collaborative Computing Center (C3) provides state-of-the-art computer systems to perform modelling and simulation of nuclear reactors and fuels

NEI: Describe current research underway at the ATR, both in-house and collaborative

ATR supports the testing of a range of nuclear reactor fuels.

1) Accident tolerant fuels – In support of industry development of accident tolerant fuels for light water reactors, INL is performing irradiations of fuel samples from Westinghouse, General Electric and Framatome to provide fuel performance data to support regulatory approvals for the use of these fuels in commercial power reactors.

2) TRISO fuels – The irradiation program for the Department of Energy’s Advanced Gas Reactor Fuels Program has been completed and the remaining experiments are undergoing post-irradiation examination. Capabilities to support new TRISO fuel irradiations are being developed and irradiation experiments are being designed to support specific advanced reactor developers.

3) High-performance research reactor fuels – Researchers are developing and testing fuels to support the conversion of high-performance research reactors from using highly-enriched uranium to low-enriched uranium.

NEI: What experiments are currently underway at TREAT including latest advances on MARVEL?

The TREAT facility is performing experiments to support a range of fuels development activities. In 2023, the first Transient Water Irradiation System for the TREAT (TWIST) calibration test demonstrated the ability to conduct experiments that simulate the first phase of a loss of coolant accident in a light water reactor to support fuel safety testing. This addresses a key gap since the Halden reactor shut down.

As part of a joint project between the U.S. and Japan to perform the first transient tests on fast reactor fuels in more than two decades, INL developed the Temperature Heatsink Overpower Response capsule. The device houses fuel experiments in TREAT that mimic conditions of fast reactors during postulated accident conditions.

The MARVEL team completed an updated 90% final design package for the microreactor that included resolving hundreds of technical comments, followed by the final design review. A contract has been signed for cask recertification to support transporting the Training, Research, Isotopes, General Atomics (TRIGA) fuel from France, and the lab procured high-assay low-enriched uranium for fuel fabrication in February 2023 and a contract has been finalized to produce the MARVEL fuel.

NEI: When do you expect DOME and LOTUS to be available to researchers and how will these new test beds be used?

The NRIC DOME facility will be available in 2026 to support reactor experiments. In 2023, NRIC announced the selection of three companies for front-end engineering and experiment design (FEEED) process that will support activities before performance experiments within DOME. The outcome of the FEEED process will determine the specific timing of the microreactor experiments. The companies chosen for the FEEED process includes Radiant, Ultra Safe Nuclear Corporation and Westinghouse.

The LOTUS test bed will be available in 2027 for installation of the first reactor experiment, which is anticipated to be the Molten Chloride Reactor Experiment.

NEI: What research, in-house and collaborative, is currently underway on molten salt reactors?

INL is performing a range of research and development on molten salt reactors and to support Advanced Reactor Demonstration Program projects. INL has established a capability to perform irradiation of molten salt fuels and in 2023 performed the first uranium-fueled chloride salt irradiation in history at the lab’s Neutron Radiography Reactor. Through NRIC, INL is establishing the Molten Salt Thermophysical Examination Capability to perform key property measurements on irradiated fuel salts.

In partnership with Southern and TerraPower on the Advanced Reactor Demonstration Program MCRE project, INL has made significant progress to produce fuel salts. In 2023, INL achieved a ~98% yield during a fuel salt synthesis scale-up run, exceeding project requirement of a 90% yield, and performed a full-scale fuel salt synthesis demonstration using 9 kilograms of depleted uranium to produce 17 kg of fuel salt.

NEI: Is INL looking to restart development of fast reactors – how are plans for the VTR developing?

INL has never stopped working on the development of fast reactors, with the primary focus over the years being the development of advanced metallic fuels based on similar concepts that were proven in the operation of the Experimental Breeder Reactor II. Current work is primarily in collaboration with Advanced Reactor Program Projects including the TerraPower Natrium project and the Advanced Reactor Concepts project.

All work on the Versatile Test Reactor (VTR) has stopped due to the lack of Congressional funding for the project. There is a strong need for VTR to support nuclear reactor and fuel development given the lack of such a facility in the U.S. and partner countries.

NEI: INL has offered to site advanced reactor experiments. How many companies have undertaken to build their reactors/fuel facilities at INL and how has the cancellation of the UAMPS-NuScale experiment affected this?

Oklo will site its first Aurora microreactor and initial fuel fabrication facility for Aurora at INL. Other companies have expressed interest in siting both reactor and fuel facilities at INL and are pursuing site access. Several companies have expressed interest in testing reactors at INL as well.

The Department of Energy launched the Cleanup to Clean Energy initiative and released a request for information in 2023 to get input on siting carbon free energy sources, including nuclear reactors, on the INL site. DOE is reviewing the submissions.

The cancelation of the UAMPS Carbon Free Power Project, which intended to deploy a NuScale VOYGR small modular reactor commercially (not as an experiment) has had no impacts on the activities to site other reactors at INL.

NEI: What progress is being made on the development of HALEU fuel?

INL continues work to recover HALEU from used EBR-II driver fuel to provide feedstocks to support reactor demonstrations, including the Oklo reactor mentioned earlier.

In the fuel development area, INL continues work on a range of fuels using HALEU. Specific activities include continuing the post-irradiation examination of TRISO fuel, development of irradiation experiments of TRISO fuels to support reactor developers, fabrication and irradiation of metallic fuels, and producing roughly two dozen HALEU uranium dioxide pellets for testing as light water reactor fuel.

NEI: What work is being done on TRISO fuel?

Several aspects of TRISO fuel development were outlined in answers above. Here’s a summary of those answers and a few additional items:

  • Performing post-irradiation examination of the advanced gas-cooled reactor TRISO fuel that provides data to support reactor developer use.
  • Expanded modeling and simulation capabilities for TRISO fuel in the R&D 100 award-winning BISON fuel performance code.
  • Continued development of capabilities at ATR to support TRISO fuel testing.
  • Direct work with reactor developers on design of irradiation experiments to be irradiated at ATR to support their specific fuel qualification needs.

NEI: What do you consider to be the main priority going forward in terms of reactor and fuel development?

1) Complete the three near-term reactor experiments and demonstrations that establish the ability to start up and operate new nuclear reactors for the first time in nearly 50 years. These projects are MARVEL, Project Pele and MCRE.

2) Develop and maintain key experimental capabilities to support fuels development. This includes capabilities for experimental fuel fabrication, irradiation, and examination and key facilities including ATR, TREAT, HFEF, IMCL and SPL. Continued development of infrastructure to support these areas is needed.

3) Complete NRIC DOME and LOTUS test beds and the first industry partner experimental reactor tests in those facilities, establishing capabilities to support reactor testing and demonstrations.