High hopes and safety fears for next-generation nuclear reactors

Next-generation nuclear reactors are heating up the debate over whether their fuel could be used to make bombs, undermining efforts to prevent the proliferation of nuclear weapons.

The uranium in the fuel could theoretically be used to develop a nuclear weapon. Older reactors use concentrations as low as that they do not actually pose a weapons proliferation threat. But advanced reactors would use higher concentrations, making them a potential target for terrorist groups or other countries that want to use the fuel to develop their own nuclear weapons, some experts warn.

They argue that the US has not prepared enough to protect itself against this worst-case scenario and call on Congress and the Department of Energy to evaluate potential safety risks with advanced reactor fuel.

Other experts and industry groups still think it is unlikely that this worst-case scenario will materialize. But the issue is beginning to come to a head as nuclear reactors become a more attractive energy source, garnering a rare show of bipartisan support in Congress.

Nuclear reactors generate electricity without producing the greenhouse gas emissions that cause climate change. And unlike solar and wind power, which fluctuate depending on the weather and time of day, nuclear reactors provide a constant source of electricity similar to gas and coal-fired power plants. Earlier this month, President Joe Biden signed bipartisan legislation into law intended to accelerate the development of next-generation nuclear reactors in the US by streamlining approval processes.

Next-generation reactors are smaller and more modular, making them cheaper and easier to build than older nuclear plants. In addition to generating electricity, small reactor designs could also be used to produce high temperature heat for industrial installations.

The US Nuclear Regulatory Commission (NRC) certified an advanced small modular reactor design for the first time last year. And we’re probably years away from seeing commercial plants in action. But if the US wants to get there, it will also have to build a supply chain for the fuel these advanced reactors would consume. The Inflation Reduction Act includes US$700 million to develop this domestic fuel supply.

Current reactors generally run on fuel made with an isotope of uranium called U-235. Naturally occurring uranium has quite low concentrations of U-235; it has to be “enriched” – usually up to a 5% concentration of U-235 for a traditional reactor. Smaller advanced reactors would run on more energy-dense fuel enriched with 5 to 20 percent U-235, called HALEU (short for high-grade low-enriched uranium).

This greater concentration is what worries some experts. “If the usability of HALEU’s weapons is confirmed, then even a single reactor would pose serious safety concerns,” says one political analysis written by a group of nuclear proliferation experts and engineers published in the journal Science last month (including an author credited as one of the architects of the first hydrogen bomb).

Fuel with a concentration of at least 20 percent is considered highly enriched uranium, which could potentially be used to develop nuclear weapons. With HALEU projects reaching 19.75% U-235, the authors argue, it is time for the US to think seriously about how safe the next generation of nuclear reactors would be against malicious intent.

“We need to make sure we don’t mess up here and make sure all safety and security arrangements are in place before we go and start shipping [HALEU] across the country,” says R. Scott Kemp, associate professor of nuclear science and engineering and director of MIT’s Nuclear Security and Policy Laboratory.

That 20 percent threshold dates back to the 1970s, and bad actors apparently have more information and computational tools at their disposal to develop weapons, Kemp and his co-authors write in the paper. It may even be possible to make a bomb with HALEU well below the 20 percent limit, the paper claims.

Fortunately, this would still be incredibly difficult to do. “This is not a minor theft,” says Charles Forsberg, principal research scientist at MIT and formerly a corporate fellow at Oak Ridge National Laboratory. A group might have to steal a few years’ worth of fuel from a small advanced reactor to make the kind of bomb described in the paper, he says.

Even with a working weapons project, he says it would take a sophisticated team of at least several hundred people to go through all the steps to turn this fuel into uranium metal for a viable weapon. “Unless they are much better than me, and the colleagues I work with, a subnational group [like a terrorist group] There’s no chance,” he says. On the edge.

An opposing nation would have more capacity than a small group. But he still doesn’t think it would be worth it for them. With their resources, they could go ahead and build a factory to produce weapons-grade uranium, typically enriched above 90% U-235.

A more credible risk, he says, would be if another country started producing and storing HALEU for future reactors – but actually had more nefarious intentions in mind. After enriching uranium for HALEU, they have already begun to develop their capacity to obtain military-grade uranium. “That’s the concern we have with any nation-state that decides to produce HALEU,” says Forsberg. “They’ve taken a few steps…they’re getting to the racing line.”

In addition to asking Congress for an updated safety assessment of HALEU, the document suggests setting a lower enrichment limit for uranium based on new research or increasing safety measures for HALEU to more closely match to fuels usable in weapons.

Unlike the authors of Science paper, Forsberg believes that appropriate precautions are already in place to keep next-generation nuclear reactors and HALEU safe in the US. Security risks have been well understood and discussed for decades, he says, although much of this is confidential information. This is part of what makes it difficult to assuage fears.

“The views of the authors of this study do not present any new information that should discourage the development and deployment of HALEU in accordance with the already stringent requirements established by U.S. and international regulatory bodies,” Jennifer Uhle, vice president of technical and regulatory services at the Nuclear Energy Institute, said in a statement emailed to On the edge.

Some of the fears surrounding nuclear energy following the catastrophes of Chernobyl in 1986 and Fukushima in 2011 have disappeared with the need to find energy sources that do not contribute to climate change and with promises of more advanced technologies. But not everyone is convinced, and the safety concerns that arise with HALEU dovetail with other issues that critics raise with nuclear energy.

“Unless there is a really good reason to switch to fuels that pose greater risks of nuclear proliferation, then it is irresponsible to pursue them,” says Edwin Lyman, director of nuclear energy safety at the Union of Concerned Scientists and another author of the paper. Lyman also raised concerns on radioactive waste from nuclear reactors over the years. “There is no good reason.”