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U.S. to Use Weapons-Grade Uranium in Reactor Experiment
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December 2023
By Shizuka Kuramitsu

The U.S. Energy Department is expected to begin work in the coming months on a civilian research project that relies on weapons-grade highly enriched uranium (HEU), a fuel type that the United States and other countries have long sought to phase out for such energy uses.

Researchers at Idaho National Laboratory work on synthesizing and irradiating a molten chloride salt fueled with enriched uranium. The experiment is attempting to validate the safety and reliability of a simple reactor type that could efficiently provide electricity and heat for communities and industry. (Photo via Idaho National Laboratory)The project has raised concerns among nuclear nonproliferation experts, who say it conflicts with long-standing U.S. nonproliferation efforts to minimize the civilian use of HEU, which can be converted more easily than low-enriched uranium (LEU) for use in nuclear weapons.

A group of 20 experts, including university professors, heads of think tanks, and former U.S. government officials, urged the Energy Department to reconsider alternatives to HEU. But department officials rejected such appeals in September and said the project is consistent with U.S. policy.

The U.S. plan is to have government-funded civilian research reactors use more than 600 kilograms of HEU in a six-month experiment to prepare the design of a new type of reactor. Critics say the fuel to be used would be enough for dozens of nuclear weapons.

The project got underway in December 2020, when the Energy Department selected a civilian energy company, Southern Co., to conduct the new research reactor experiment, called the Molten Chloride Reactor Experiment, at the Idaho National Laboratory. The experiment is aimed at advancing the new TerraPower LLC Molten Chloride Fast Reactor technology.

Specific project details were revealed in March. On Aug. 1, the Energy Department issued a draft assessment that analyzed the potential environmental impacts associated with the project and concluded there would be “no significant impact.”

A 30-day public comment period in August generated expressions of opposition to the use of HEU fuel, concern about the project’s “potential effects on the U.S. nuclear nonproliferation efforts,” and laments about “lack of consideration of environmental concerns.”

But after the Energy Department’s Office of Nuclear Energy considered the comments, it affirmed its original support for the project, according to a department document released on Oct. 19.

The 20 nuclear proliferation experts who wrote to the department on May 30, including Alan Kuperman, an associate professor at the Lyndon B. Johnson School of Public Affairs at the University of Texas, and Frank von Hippel, a Princeton University physicist, urged the department to suspend work on the project until it considers an alternative design and prepares an assessment of the nonproliferation impact.

If the department “were to proceed with an HEU-fueled [Molten Chloride Reactor Experiment], the damage to national security could exceed any potential benefit from this highly speculative energy technology,” the experts wrote.

They argued that using HEU “would be a convenience rather than a necessity” and that the “reactor does not require HEU fuel.” Converting the project design to LEU fuel would “increase significantly the size of the facility and the amount of fuel, thereby incurring a delay and increasing some costs. However…other costs for security could be reduced,” they added.

In a written response on Sept. 5, the department said this experiment “requires the use of higher enrichment fuel to keep the size of the experimental reactor small.”

It reaffirmed the U.S. policy “to refrain from the use of weapons-usable nuclear material in new civil reactors or for other civil purposes unless that use supports vital U.S. national purposes.” But it also argued that using HEU is fully consistent with this policy because “the experiment will provide vital data to the U.S. national interests assuring the safety and security of this advanced nuclear energy technology” and emphasized that the later commercial operation of the new reactor would not use HEU.

“This experiment does not pose a security or nonproliferation risk akin to the use of HEU in a civilian reactor that operates for decades, continually refuels, and requires production or transport of HEU across distances,” the department letter stated.

Since the 1970s, the United States has led international collaboration to reduce and minimize the use of HEU for civilian purposes. It has converted a total of 71 reactors domestically and abroad from use of HEU fuel to LEU fuel. Over five decades, such diplomatic and financial efforts have contributed to the nonproliferation regime by strengthening HEU minimization norms.