When the US cut itself off from Russian energy products, uranium was not on the list. President Joe Biden banned Russian oil, coal, and gas imports in March. The administration reportedly considered sanctioning Russia’s state-owned nuclear power company, Rosatom, too. But industry lobbying and Biden’s plans to include nuclear reactors in a transition to clean energy have left the uranium trade untouched.

Now, Russia’s invasion of Ukraine is forcing the US to grapple with vulnerabilities in its supply chain for uranium. It’s also heating up the long-standing debate over what role nuclear energy might play in the future of the power grid. War has quickly raised the stakes.

The US’s exclusion of uranium from energy sanctions “was very frustrating because we understand that this is part of the Russian war machine,” says Kostiantyn Krynytskyi, head of the energy department at Ukrainian environmental organization Ekodia. Krynytskyi spoke with The Verge on a Skype call from Western Ukraine in a room tinted blue as light filtered through tape covering his windows. The tape was a preventative measure, he explained, to minimize any shards of glass a nearby bomb might send flying.

Putin created Rosatom in 2007, and the state company now produces nearly 20 percent of the world’s nuclear fuel — providing an important revenue stream for Moscow just as fossil fuels do. Rosatom officials have also reportedly been present at two Ukrainian nuclear sites seized by Russian forces, although Russian officials denied allegations that Rosatom would take over permanent management of Ukraine’s largest nuclear power plant.

Ekodia was one of several local and environmental groups that sent a letter to Biden and European leaders this month asking them to cut ties with Rosatom and ban nuclear fuel imported from Russia. It’s not a simple request. Those imports made up about 16 percent of the US’s uranium supply in 2020 (Russian allies Kazakhstan and Uzbekistan provided another 30 percent). That’s a far larger slice than the roughly 7 percent of oil imports that came from Russia that year (the US imports little coal and no natural gas from Russia).

Uranium is a relatively common metal found across the world. But 85 percent of it is produced in just six countries: Russia, Kazakhstan, Canada, Australia, Namibia, and Niger, according to the World Nuclear Association.

Mines produce a solid form of uranium that’s then refined into what’s called yellowcake, which looks sort of like yellow chalk. Then there are a few more steps to take to turn that yellowcake into fuel for a nuclear reactor. First, the yellowcake needs to be turned into a gas, a process called “conversion,” so that it can be “enriched.” Naturally occurring uranium has less than a 1 percent concentration of a specific isotope, U-235. Typical reactors today require uranium with between a 3 to 5 percent concentration of U-235. Uranium enriched to have higher concentrations of that isotope then gets fabricated into fuel rods for reactors.

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The major bottleneck in the supply chain is in the conversion and enrichment processes. There are just a few places in the world to turn to for the conversion step: Russia, France, Canada, and the United States, according to the Nuclear Energy Institute. And again, just a handful of countries — Russia, the US, and a few western European countries — have the capacity to then enrich the uranium.

There are a couple big reasons why this capacity isn’t more widespread. For starters, enriched uranium can be used for either nuclear energy or nuclear weapons. So not having that many of these facilities around the world has been seen as a good security measure. Second, the market for conversion and enrichment services has been pretty saturated — so it hasn’t necessarily made business sense to invest in more capacity globally. At least, until now.

The war in Ukraine is drumming up demand for a more diversified supply chain. In the US, it’s ramped up calls to mine uranium domestically. The Biden administration is rushing to draft requests for proposals for two programs aimed at developing more highly enriched fuel and creating a Strategic Uranium Reserve (similar to the nation’s Strategic Petroleum Reserve), Bloomberg Law reports. Right now, there’s only one operating American uranium mill in White Mesa, Arizona. And in 2020, its production was “too small to report,” according to the World Nuclear Association.

“We can no longer tolerate this nuclear fuel dependence or the flow of U.S. dollars for uranium purchases that prop up the Putin regime. The U.S. has ample uranium resources and the capacity to produce them at the highest global standards,” Scott Melbye, President of the Uranium Producers of America and Executive Vice President of Uranium Energy Corp, said in a press release with Republican senators who introduced a bill to ban Russian imports of uranium.

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The Nuclear Energy Institute, a trade group that includes utilities, says more conversion and enrichment capacity is needed — and still pushes back against an all-out ban on Russian uranium. “We see bans or sanctions really having a trickle-down impact to the world, to global utilities,” says Nima Ashkeboussi, NEI’s senior director of fuel and radiation safety. “That disruption and a potential scramble amongst US utilities and global utilities could, in the near term, threaten some nuclear plants from being able to find fuel,” he says.

Nuclear power plants in the US typically refuel every 18 to 24 months, so it would take a little more time before shocks to the uranium supply chain would affect people’s power supply. Longer-term, however, the loss of Russian uranium could interrupt plans to tackle climate change by turning to new nuclear technologies.

Next-generation nuclear reactors generally require fuel that’s enriched with up to 20 percent U-235, called HALEU. (This is short for high-assay low-enriched uranium. The fuel older reactors use is called LEU, short for low-enriched uranium.) With higher enrichment, nuclear power plants can go longer before refueling. The more energy-dense fuel also allows for smaller reactor designs. But the only major supplier of HALEU is in Russia, experts tell The Verge.

“Any prospects of Russian supply of HALEU basically went down the drain after they invaded Ukraine,” says Alan Ahn, a senior resident fellow for the think tank Third Way.

Two Department of Energy-funded demonstration projects for advanced reactors will need HALEU by the end of 2024, according to Ashkeboussi. The DOE does have some HALEU stockpiled. But getting a new production facility up in the US would take at least four years, Ashkeboussi says.

Biden’s budget proposal for 2023 includes a funding boost for the DOE that includes money to help “​​secure the availability” of HALEU. It’s part of a broader push to speed up the development of technologies that can transform the US economy into one that runs entirely on carbon-free electricity.

Biden wants to get that done by 2035. That feat would be a massive lift, and axing nuclear energy would arguably make that even harder. At the moment, nuclear energy supplies just under 20 percent of the nation’s electricity — but about half of the US’s carbon-free energy.

The urgency comes from another existential threat, the climate crisis. Climate scientists have found that the world has just a few decades to virtually eliminate greenhouse gas emissions from fossil fuels or careen into a catastrophic climate crisis. The relatively short timeline to completely makeover the world’s energy systems has made nuclear energy more palatable to some environmentalists, who say reactors are needed to provide consistent power as wind and solar power ebb and flow with the weather.

There are clear risks with nuclear energy, especially at the beginning and end of the fuel’s lifecycle, which make it a no-go for other advocates. The US is still cleaning up a legacy of Cold War-era uranium mining on Navajo land that has been tied to kidney disease, cancer, and a neuropathic syndrome in children. The federal government has also struggled to find a permanent storage solution for nuclear waste, leaving it in limbo at power plants.

New calls to ramp up uranium production in the US have already raised a red flag for tribes and activists that have pushed back against nearby uranium mines and waste sites, The Guardian reports. While the US’s sole uranium mill’s production of yellowcake has dwindled, the site in Arizona still stores leftover radioactive waste. And if the US does move to ramp up its domestic uranium supply, uranium production at the mill could start to really churn again. Members of the Ute Mountain Ute Tribe have pushed for the site’s closure; its tribal council also passed a resolution last year opposing the creation of a national Strategic Uranium Reserve.

Photo by Zaporizhzhia Nuclear Power Plant/Anadolu Agency via Getty Images

Even before the current conflict in Ukraine, Krynytskyi, the Ukrainian activist, was wary of nuclear energy. His environmental group has historically pushed to phase out both fossil fuels and nuclear energy. Ukraine is more reliant on nuclear power than nearly any other nation in the world. But the nuclear power plants that supply about half the nation’s electricity are now at unprecedented risk. Its largest plant, Zaporizhzhia, has already survived Russian shelling. Fires have reportedly also broken out at Zaporizhzhia, and Chernobyl, already the site of the worst nuclear power plant disaster in history — both of which have been seized by Russia.

“When the whole country and the whole world is shaking, thinking about what will happen in Ukraine with nuclear power plants,” Krynytskyi says. “Look what can happen here. You need to phase it out.”