Ukraine warned the European Union last month it needed imminent help protecting nuclear plants from a potential Russian assault that could strand the country in frigid darkness and cause  “catastrophic consequences” across Europe.

In a letter sent to EU energy chief Kadri Simson and seen by POLITICO, Ukrainian Energy Minister German Galushchenko said that Moscow may be preparing a series of strikes on Kyiv’s nuclear energy facilities.

If those strikes take out key electrical infrastructure like substations and switchyards, it would cause major problems for Ukraine's atomic plants, he warned. Nuclear facilities may lose the backup electricity needed during outages, or be forced into emergency shutdowns. Generators might be left reliant on last-resort diesel backups.

Ultimately, such damage could cause “serious harm” to Ukrainians and even trigger a nuclear accident with devastating implications for Europe, Galushchenko argued, urging Simson to help push the issue with EU countries. 

The letter comes as concerns mount that Ukraine’s nuclear power plants lack the needed protections to rebuff a Russian missile barrage. Kyiv currently controls three atomic plants, while a fourth, Zaporizhzhia, is under Russian occupation and in shutdown mode.

Speaking at the United Nations General Assembly last month, Ukrainian President Volodymyr Zelenskyy warned that “any missile or drone strike, any critical incident in the energy system could lead to a nuclear disaster.”

“Moscow needs to understand this, and this depends in part on your determination to put pressure on the aggressor,” he told delegates in New York. “These are nuclear power plants, they must be safe.”

With only one-third of Ukraine’s prewar power-generation capacity left online after unyielding Russian air attacks, the country “is increasingly dependent on the three remaining operational nuclear power plants,” the International Energy Agency cautioned last month.

“Nuclear [power] stations now are the cornerstone of power supply in Ukraine,” said Oleksandr Kharchenko, managing director at the Energy Industry Research Center think tank and an adviser to Ukraine’s government, estimating that they provide 60 percent of Kyiv’s current generation capacity.

“If they’re out, it's a big problem,” he said, noting that any successful missile attack could lead to “up to two weeks” of just four to six hours of electricity supply each day for the country when the weather is cold.

With a “focused attack,” it would be “rather easy” for Russia to “damage [Ukraine’s nuclear plants] to the point that they cannot provide electricity and heat,” said Leon Cizelj, a professor of nuclear engineering at the University of Ljubljana.

Still, the atomic plants have enough layers of protection to make a radioactive incident “not very probable,” he added.

The subject is on the EU’s radar. The bloc’s energy ministers are set to discuss Ukraine’s energy security for the winter at a meeting in Luxembourg next week.

The European Commission declined to respond to a request for comment from POLITICO.