A slow-motion crisis has been unfolding at a giant nuclear power plant in Russian-occupied southeastern Ukraine.
The failure of a high-tension power line in an area of combat is raising the risk of an eventual failure of cooling systems that keep nuclear fuel from melting down in the switched-off reactors at the plant, in Zaporizhzhia.
Since Wednesday, the site has operated on backup diesel power to cool the reactors. While external power to the facility has been cut several times during the war, the current outage is the longest yet.
Russia and Ukraine have differing explanations of why electrical power was lost and why it has still not been restored. Russia says Ukrainian artillery severed the line and renders repairs too dangerous. Ukraine says Russia created the crisis as a ploy to justify connecting the plant to the Russian power grid to restart the facility, despite copious wartime risks.
The power loss poses no immediate risk of a meltdown or an explosion. But it removes another layer of safety measures from a plant already operating on a razor-thin margin for error.
“This situation is critical,” Bruno Chareyron, scientific adviser to the Commission for Independent Research and Information on Radioactivity, a French nonprofit, said of the plant’s operation for days on backup diesel power.
“The problem is, with this war, people get used to it,” he said. “It’s very dangerous that people are used to a situation that is absolutely not normal” for the operation of a nuclear power plant.
Why is the site such a risk?
When the Russian Army invaded Ukraine in 2014 and again in 2022, it advanced into a landscape full of Soviet-legacy nuclear sites, including uranium mines, nuclear research laboratories, the Chernobyl disaster zone and active nuclear power plants. All were put at risk by combat.
But the Zaporizhzhia nuclear power plant has caused perhaps the most alarm. Russian troops fought their way into the plant in March 2022, damaging administrative buildings and striking some equipment with small-arms fire. The plant has been on a front line since. All six reactors were shut down in September 2022.
Since early in the occupation of the plant, rights groups say, Russia has arrested employees suspected of having pro-Ukrainian sympathies. Some have escaped and given accounts of torture, raising concerns that high stress levels in the work environment elevate the chances of human error.
In 2023, an explosion in a dam drained the plant’s primary source of cooling water, elevating worries about the risk of a meltdown as the site pivoted to drawing water from a smaller cooling pond and wells.
Fighting nearby severed eight of 10 electrical power lines. Both remaining lines carried power from Ukraine-controlled territory, which Kyiv provides to avoid overheating of the reactors and a radiation release that would contaminate its own territory.
In May, one of those two lines was severed irreparably in fighting. On Wednesday, the Russian authorities said that Ukrainian shelling had cut the other. Ukraine denies firing at locations near the plant where the line failed.
Because all six reactors at Zaporizhzhia have been shut down for at least three years, they generate only a fraction of the heat of an active power plant and require less power and water to cool. Analysts say it would therefore take weeks for the Zaporizhzhia reactors to melt down or explode after pumps stopped circulating water.
The International Atomic Energy Agency has said that the plant has sufficient diesel to circulate water for 10 days.
Why might Russia intentionally cut power?
In May, Aleksey Likhachev, head of Russia’s state atomic energy company, announced a plan to restart the reactors and provide electricity for Russia’s power grid.
Satellite images show Russia has built new pylons for power lines near the plant, in apparent preparation to connect the six reactors to its own grid or to the power system in occupied territory in southern Ukraine.
In this light, Russia’s assertion of damage to the power line tying the plant to Ukraine-controlled territory could be an effort to justify the switch to the Russian grid, said Shaun Burnie, a senior nuclear specialist with Greenpeace Ukraine. Russia could be trying to demonstrate “to the I.A.E.A. and to their own audience” that the Ukrainian power lines are unreliable, he said.
A Russian restart of the plant “is more imminent than we had anticipated,” Mr. Burnie said.
Connecting the plant to Russia’s electrical grid would shift the landscape of peace negotiations that the Trump administration has pushed.
In March, President Trump floated the idea that the United States might operate the Zaporizhzhia plant, with Russia and Ukraine in disagreement on its status after a cease-fire. Ukrainian officials said that the Trump administration may have been eying the site as a source of electrical power for planned postwar mining ventures in Ukraine.
That would not be possible if the plant was restarted to power the Russian, not the Ukrainian, electrical network.
Oleksandr Chubko contributed reporting.
Andrew E. Kramer is the Kyiv bureau chief for The Times, who has been covering the war in Ukraine since 2014.
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