Idaho Reactor Project Plans to Use Bomb-Grade Uranium

This article is republished with minor changes from the Physics Today website.

Contravening long-standing U.S. nuclear nonproliferation practice, the Department of Energy plans to fuel a new civilian reactor with weapons-grade highly enriched uranium (HEU).

The proposed six-month, 200-kilowatt-thermal Molten Chloride Reactor Experiment (MCRE) at Idaho National Laboratory would employ more than 600 kilograms of HEU, according to a draft environmental assessment issued in March. The document addresses the potential impacts on the environment of the project, which would use components built off-site by TerraPower and Southern Company. But it does not consider the proliferation implications of using HEU for nondefense purposes, despite U.S. efforts to end all such use worldwide.

“The notion that the U.S. government at this point would be building its own HEU-fueled research reactor is a slap in the face to the nonproliferation efforts that the US has been spearheading overseas and at home for decades,” says Edwin Lyman, director of nuclear power safety at the Union of Concerned Scientists. “It’s mystifying and very upsetting.”

The MCRE is slated as a step in the development of TerraPower and Southern Company’s proposed Molten Chloride Fast Reactor, which would both provide electricity and process heat for industries that are difficult to decarbonize, such as chemical and petroleum refining. DOE is providing $90 million of the $113 million MCRE project cost through a 2021 award aimed at developing safe and affordable advanced reactor technologies. The companies have constructed a test facility at TerraPower’s laboratory in Everett, Washington, to help advance the technology.

The companies’ project is separate from a molten salt reactor that TerraPower and the Rocky Mountain Power division of PacifiCorp propose to build near a soon-to-be retired coal power plant in Wyoming. DOE has pledged $2 billion to that project, known as Natrium. Both the Molten Chloride Fast Reactor and Natrium are to operate with high-assay, low-enriched uranium (HALEU) fuel, which is enriched to a maximum of 19.75% in uranium-235. That is just below the 20% threshold delineating HEU, which is acknowledged to be a proliferation concern. Most commercial reactors, including all U.S. power reactors, are fueled with uranium enriched to around 4%.

The proposed MCRE would use weapons-grade HEU, which is enriched to more than 90%. The HEU would be blended into a molten salt that both provides the fuel and cools the reactor core. Unlike light-water reactors, which use water to slow down, or moderate, neutrons to increase fissioning, the MCRE would use unmoderated, or fast, neutrons. The high-energy neutrons would enable the reactor to burn up far more of the uranium fuel than do current reactors, as well as many of the long-lived transuranic elements such as americium, plutonium, curium, and neptunium that end up in commercial nuclear waste.

In a written statement, DOE’s Office of Nuclear Energy did not directly address the MCRE’s inconsistency with U.S. nonproliferation policy. It said that HEU is necessary to reduce the reactor size while ensuring that key phenomena, such as thermal hydraulics and neutronics, will resemble the commercial design. Were MCRE to be fueled with HALEU, the reactor core would need to be roughly three times as large and require 40 times the volume of fuel salt, DOE stated. That would significantly raise the construction cost, the types and amounts of radioactive waste generated, and the volume of irradiated fuel salt requiring storage until reuse. But since the use of HEU in the future Molten Chloride Fast Reactor is out of the question, tests of a HALEU-fueled MCRE presumably would be more directly applicable to the future reactor.

Lately, HALEU has become hard to come by. TerraPower announced last year that its 2028 target for Natrium’s completion will be delayed by at least two years due to the unavailability of HALEU. Russia’s Tenex is the world’s only commercial source of HALEU, and TerraPower cut its ties with the company after Russia’s invasion of Ukraine. DOE has surplus HEU that it could dilute to HALEU, however, for Natrium and other advanced reactors in development.

The HEU to be used for the MCRE is stored in the Idaho lab’s Zero Power Physics Reactor facility (which no longer hosts an operational reactor), and it would not be moved outside the lab boundaries. DOE would retain ownership of the HEU and not make it available for any other reactors. The department noted a difference between MCRE’s anticipated six-month operational life and those of most research reactors, which are designed to perform scientific research for decades.

In a statement, TerraPower said the MCRE, including the use and handling of fuel, would be authorized and operated in accordance with Idaho National Laboratory and DOE requirements. “From its beginnings almost 15 years ago, TerraPower has made reduction of weapons risks a foundational principle,” the company said. TerraPower was cofounded by Bill Gates, who currently chairs its board.

Alan Kuperman, coordinator of the Nuclear Proliferation Prevention Project at the University of Texas at Austin, acknowledges that HALEU-fueled reactors are bigger and more expensive and produce more nuclear waste. But he says the U.S. has consistently maintained to other nations that the nonproliferation benefits of eschewing HEU outweigh the extra cost. “Would the U.S. make an exception for a foreign country that wanted to irradiate 600 kilograms of HEU for six months? Of course not.”

Lyman points to the potential for an insider to divert the HEU during the process of transferring and converting the material from storage. The 648 kilograms of 93%-enriched uranium proposed for the MCRE theoretically could be used to fashion more than 100 nuclear explosive devices, using estimates from a 1995 analysis by Natural Resources Defense Council experts.

No civilian reactors in the U.S. have been built to operate with HEU since the 1970s. The Nuclear Regulatory Commission in 1986 ordered the conversion of all licensed HEU-fueled research reactors, although several still operate with high-enriched material pending conversion to low-enriched fuels. In 1995, DOE canceled plans to build a research reactor, the Advanced Neutron Source, at Oak Ridge National Laboratory, in part as the result of objections to the proposed HEU fuel.

In public comments he submitted on the environmental assessment, Kuperman said that the U.S. in recent decades has allowed HEU only once to fuel a new nondefense reactor: an hours-long test conducted by NASA in 2017 of a microreactor fueled with 30 kilograms of weapons-grade uranium. Three years later, the White House issued a presidential memorandum that all but banned HEU for future space reactors.

The U.S. also declined to provide HEU for Germany’s FRM-II research reactor, which was designed after the U.S. began in 1978 to convert foreign research reactors to low-enriched uranium and take back their U.S.-origin spent HEU fuel. FRM-II, which opened in 2005, initially got by using leftover U.S.-origin HEU from a discontinued German advanced reactor project. Eventually, FRM-II turned to Russia, which has made no effort to discourage civilian use of HEU. In April, the Bavarian State Ministry of Science and the Arts approved a plan to convert FRM-II to HALEU fuel by 2030. Argonne National Laboratory collaborated in the development of the reactor’s lower-enriched fuel.

In December 2021, DOE announced that it had approved the last U.S. shipment of HEU to European reactors for use in the production of the medically important isotope molybdenum-99. That followed years of assistance from DOE to convert those production reactors to low-enriched uranium.

Kuperman has called for DOE to prepare a more comprehensive review, known as an environmental impact statement (EIS), of the MCRE. Such an analysis would consider alternative actions, such as using HALEU in place of HEU. Kuperman says the EIS should include a nonproliferation impact assessment, a process that DOE has carried out in at least six previous projects. He also would like an EIS to verify DOE’s assertion that a HALEU-fueled MCRE would need 40 times as much fuel salt.

The comment period for DOE’s environmental assessment closed on April 14. The agency plans to finalize the assessment this summer. If it deems that the MCRE would have no significant environmental impact, then the project will proceed.