The US Department of Energy (DOE) has completed an environmental assessment, issued on 17 January, which determines that there will be no significant impact on the environment from using DOE-owned high-assay low-enriched uranium (HALEU) fuel.

The HALEU is stored at the Idaho National Laboratory (INL)  and possibly also at the Idaho Nuclear Technology and Engineering Center (INTEC) and could be used to fabricate fuel at INL's Materials and Fuels Complex (MFC) to support US companies in the development and deployment of new reactor technologies. The determination followed the publication in October 2018 of a draft environmental assessment, under the National Environmental Policy Act (NEPA), which was open for public comment until 30 November. DOE said the process would not have a significant impact on the environment and would be an important tool for advancing safe, economical, and low carbon nuclear energy.

The  HALEU is from used fuel from the Experimental Breeder Reactor-II (EBR-II), which operated at INL from 1964 to 1994 and is now decommissioned. Since 2000, DOE has used an electrometallurgical treatment process at MFC to refine and down-blend sodium-bonded used nuclear fuel containing highly-enriched uranium material generated  in the Experimental Breeder Reactor-II (EBR-II).  A product of this process is a limited amount – approximately 10t – of  HALEU  that is currently stored at INL.  DOE plans to utilise the capabilities at MFC and INTEC to convert this metallic HALEU into fuel for research and development purposes.  

Many advanced reactor designs being developed will require HALEU fuel, enriched to between 5% and 20% in fissile uranium-235 (U-235), which is greater than the less than 5% U-235 used in today's nuclear plants. The USA currently has no commercial facilities capable of producing HALEU. The environmental assessment means the federal government can now fabricate HALEU fuel at INL from existing HALEU feedstock. "This is a finite amount of HALEU with limited applications for specific advanced reactor designs but is one of several efforts undertaken by DOE to help ensure the availability of HALEU in support of the US nuclear power industry," DOE said.

DOE's activities will support near-term research, development and demonstration needs of private-sector developers and government agencies, including advanced reactor developers.

The proposed action identified in the environmental assessment calls for establishing the capability at INL to fabricate HALEU ceramic and metallic fuels from the HALEU produced through the electrometallurgical treatment process currently operating at INL, and by using other small quantities of HALEU stored at INL.  Construction and operation of any reactors that propose to use the HALEU fuel will require additional review under NEPA. DOE this month announced plans to award a contract to a subsidiary of Centrus Energy Corp to demonstrate the production of HALEU using US-origin enrichment technology at the American Centrifuge Plant site in Piketon, Ohio.  

DOD looks to HALEU-fuelled SMR

Meanwhile, the US Department of Defense (DOD) on 18 January issued a Request for Information (RFI) for a small mobile reactor using HALEU fuel to provide electrical power in rapid response scenarios. "At a time when military operations are more energy-intensive than ever before, it is crucial that the [DOD] seek out game-changing technologies such as nuclear energy, which is a safe, reliable, and nearly unlimited resource," the RFI, issued by the Office of the Under Secretary of Defense for Research and Engineering said. "Small mobile nuclear reactors have the potential to be an across-the-board strategic game changer for the DOD by saving lives, saving money, and giving soldiers in the field a prime power source with increased flexibility and functionality," it noted.

The mobile nuclear reactor is required to produce a threshold power of 1-10MWe for at least three years without refuelling. It must weigh less than 40t and be suitable for transportability by truck, ship, and C-17 aircraft. Designs must be "inherently safe", ensuring that a meltdown is "physically impossible" in various complete failure scenarios such as loss of power or cooling, and must use ambient air as their ultimate heat sink, as well as being capable of capable of passive cooling.

The reactor must be capable of being installed to the point of "adding heat" within 72 hrs and of completing a planned shutdown, cool down, disconnect and removal for transport in less than seven days. It should operate semi-autonomously and demonstrate minimisation of added proliferation risk. The RFI also specifies that the core design must use HALEU advance gas reactor tri-structural isotropic fuel.

The RFI will be the basis for a decision on whether to issue a Request for Solutions, for what is anticipated will be a multi-phase prototype project. Up to three different reactor design efforts could be awarded under Phase I, which will include a full-scope reactor prototype engineering design study that taking 9-12 months. In Phase II, the chosen design would be constructed and tested as a system prototype. Interested parties have until 8 February to respond to the RFI.

Photo: Test Cascade at the American Centrifuge Plant (Centrus Energy)