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Jun 08, 2023

U.S. planning test reactor to run on weapons

The U.S. Department of Energy (DOE) is planning a small test reactor that would

The U.S. Department of Energy (DOE) is planning a small test reactor that would burn a large amount of weapons-grade uranium, according to the project's draft environmental assessment. The experiment, to be built in a cost-sharing arrangement, would provide data for a new type of power reactor being developed by TerraPower and Southern Company Services. But the use of highly enriched uranium, first reported by Physics Today, would contravene the U.S. policy of removing HEU from civilian reactors around the world to keep it from being made into bombs.

The decision is "discouraging," says Edwin Lyman, a physicist and director for nuclear safety at the Union of Concerned Scientists. "When the U.S. preaches the nonproliferation gospel, it should practice what it preaches." Alan Kuperman, a political scientist at the University of Texas at Austin, says, "There was not by any means adequate public disclosure by the department that they were planning to contradict 5 decades of U.S. nonproliferation policy."

Neither DOE nor Idaho National Laboratory (INL), where the test reactor will be built, would comment on the issue.

The Molten Chloride Reactor Experiment (MCRE) would differ dramatically from conventional power reactors. They consume uranium fuel enriched to roughly 4% uranium-235, the fissile isotope, and encased in metal rods. Some uranium atoms split or fission to release energy and neutrons, which then split other uranium atoms in a chain reaction. Pressurized water flows around the rods both to slow the neutrons so that they split atoms more effectively and to carry heat to steam generators that ultimately drive turbines to generate electricity.

The MCRE would instead be cooled by molten salt, into which the uranium would be dissolved. In theory, a molten salt reactor could burn used fuel from conventional reactors and generate less long-lived radioactive waste, Kuperman says. Because the salt would not slow the neutrons, the reactor would need fuel with higher enrichment, which would generate more neutrons.

TerraPower's commercial reactor would use fuel enriched to as much as 19% uranium-235, so-called high-assay, low-enriched fuel. But the MCRE will run on HEU enriched to greater than 90%—630 kilograms of it. That's hundreds of times more than some research reactors use and enough to make dozens of bombs, Kuperman estimates. The uranium is leftover from another research reactor that ran at INL from 1969 to 1990, he says.

Running on HEU should enable the MCRE to produce the data needed to design and license the molten-salt power reactor while remaining relatively small and inexpensive, Lyman says. DOE would cover $90 million of the MCRE's $113 million cost, and the reactor would start up in a few years. But its thrifty design would cost the United States credibility, says John Tierney, executive director of the Center for Arms Control and Non-Proliferation. "This is going to be seen as hypocritical by many, many people."

In the 1950s and ’60s, the U.S. helped build research reactors around the world, providing HEU for many of them. In the 1970s, it changed course and led efforts to remove HEU from those reactors and repatriate it. Of the 171 research reactors that ran on HEU, 71 have switched to low-enriched fuel and 28 have shut down, according to the International Atomic Energy Agency—although five U.S. research reactors still use HEU.

The issue highlights a tension between DOE's Office of Nuclear Energy, which is eager to develop new reactors, and its National Nuclear Security Administration, which controls nuclear weapons and works for nonproliferation, Kuperman says. He and others have drafted a letter to DOE and President Joe Biden's administration to encourage them to reconsider the plan. "If they make the wrong decision, I think they’re going to undermine much more of the nonproliferation regime than they realize."