The US Department of Energy’s (DOE’s) Savannah River Site (SRS) says the H Canyon facility recently initiated actions to recycle a small amount of used highly enriched uranium (HEU) stored in the Site’s H Area in order to down-blend it into high-assay low enriched uranium (HALEU). “The projected demand for HALEU far exceeds the current supply,” said HALEU Programme Manager Jeff Hasty for Savannah River Nuclear Solutions, the site’s managing and operating contractor.

HALEU is considered key to fuelling many advanced reactors currently in the design phase. Russia is currently the only commercial source of HALEU and accounted for nearly 40% of global uranium conversion services in 2020. The US is now looking to develop its own HALEU production facilities in face of concerns about energy independence. The US Congress directed DOE to establish a HALEU availability programme in the Energy Act of 2020 and the Nuclear Regulatory Commission (NRC) recently approved Centrus Energy’s request to make HALEU fuel at its enrichment facility in Piketon, Ohio. Moreover, in the recently signed Inflation Reduction Act (IRA) some $700m was allocated to develop a domestic supply chain for HALEU.

“Because of H Canyon’s most recent mission of blending HEU into low enriched uranium (LEU) for commercial fuel reactors, H Canyon has stored HEU solutions available for use.” The Savannah River National Laboratory (SRNL) has completed a series of analyses to show downblending of HEU from H Canyon liquid solutions could meet specifications needed for the advanced reactors. Those analyses helped SRS in initiating the planned HALEU project in H Canyon.

“SRNL plays a major role in the research of the Nuclear Fuel Cycle research and development and is always excited to see our efforts applied in real world applications,” said SRNL Environmental & Legacy Management Deputy Associate Laboratory Director Bill Bates. The facility has begun preparations for the pending mission, which will include equipment repair, training, procedure revisions and environmental impact analysis. Support is also being provided by SRNL to complete a detailed set of sample analyses to ensure the HALEU meets reactor material specifications and to certify the shipping containers for material transport.

Downblending is expected to begin in 2025. “This approval is a win-win,” said Hasty. “H Canyon has a useful path for the stored HEU, and at the same time, HALEU availability is increased for the emerging advanced reactors.”

H Canyon, the only operating, production-scale, radiologically-shielded chemical separations facility in the USA, began operations in the early 1950s. The facility’s operations historically recovered uranium and neptunium from fuel tubes used in nuclear reactors at SRS, to produce radioactive materials used in making nuclear weapons. After the end of the Cold War, the facility’s mission changed to one of non-proliferation and environmental clean-up.

The interior of the facility resembles a canyon, giving the facility its name. Most canyon operations are done from a control room using remote control cranes. One side of the canyon is considered "hot" because it has higher radiation levels, while the other side of the canyon is "warm" because it has lower radiation levels. No one has been inside the “hot” side of the canyon since it began operations.

Employees who work in the building are protected from radiation by the thick, steel-reinforced concrete walls. Irradiated spent fuel rods are transported to H Canyon in shielded cask cars from L Area storage. The used fuel rods are dissolved in nitric acid. Uranium liquid, also known as Target Residue Material, is also received from the Chalk River Facilities in Canada. The uranium from these sources is recovered through a complex chemical process, including solvent extraction cycle operations. The cycles remove impurities that are present in the feed. The impurities are then transferred to waste management facilities.

The uranium is mixed with natural uranium in a process called "blend down" and is loaded in shipping containers for shipment off-site. Blending down uranium not only makes it undesirable for use in nuclear weapons, but also makes it able to be converted to fuel rods and used in commercial nuclear reactors operated by the Tennessee Valley Authority to make electricity. H Canyon is also being used as a “test bed” for new technologies, allowing outside parties to test in a real-life operating facility.

Meanwhile, SRNS said the first transfer made under the Accelerated Basin De-inventory (ABD) programme has been completed as part of its ongoing clean-up operations. DOE announced the ADB programme last year. It involves transferring the 29.2 tons of used nuclear fuel stored at SRS to be disposed of via the Defense Waste Processing Facility without recovering the HEU in the material.

Specifically, the plan calls for the material to be processed at H Canyon by using nitric acid to produce a solution of highly enriched uranium, fission products, aluminium and small of amounts of transuranic elements such as neptunium and plutonium. The solution would then be transferred into the high-level waste system and immobilised into canisters at the Defense Waste Processing Facility with a small amount being sent to the Salt Waste Processing Facility and disposed of via the Saltstone Disposal Facility. Once the material has been put into the canisters, it will be stored in S-area until a national used nuclear fuel repository is built.

SRNS programme manager James Therrell said integration between SRNS and Savannah River Mission Completion (SRMC), the liquid waste contractor at the site, and support from DOE was paramount to ensure the processing systems and associated paperwork stay aligned and optimised in support of the mission. “Taken as a whole, the processing and discarding success of ABD material is highly sensitive to technology development timelines, regulatory requirement impacts, and processing schedules throughout the material’s movement through SRS facilities,” Therrell said. “The safe storage of increased amounts of uranium in glass is an example of one of several major technology advancements that has led us up to this initial transfer.”

Matt Arnold, SRNS H Area facility manager, said adding the material to the tank waste represents many months of integration between SRMC and SRNS because H Tank Farm and H Canyon both have highly complex processing schedules that must align. Radioactive liquid waste generated by SRS chemical separations processes is stored in the SRS Tank Farms in both solid and liquid forms. Over 165m gallons of radioactive liquid waste have been generated and concentrated by evaporation to a present volume of approximately 34m gallons. SRS has a total of 51 waste tanks built in the Site's F and H Areas. Eight tanks have been operationally closed. Several of the remaining 43 waste tanks are in various stages of the waste removal, cleaning, and operational closure process.

“The ability to coordinate timing for ABD is essential to prevent extending the mission, avoiding downtime and adding operating expense,” Arnold said. “All of the preparation for this first transfer will set us up for future success. Getting to this point was really a team effort across the different companies, work groups and the DOE. These changes have not only made the ABD mission possible, but have also saved significant lifecycle costs, proving yet again that we are committed to making the world safer.”

Image: The H Canyon chemical separations facility at the Savannah River Site (courtesy of USDOE)