Ukraine is considering restarting Europe's largest nuclear plant, which is occupied by Russian troops, to ensure its safety just weeks after fears of a radiation disaster prompted its shutdown, the facility operator's head said.

The Zaporizhzhia nuclear power plant has emerged as one of the most worrying flashpoints in Russia's occupation of Ukraine. It has been damaged in fighting, prompting international alarm, and its head was detained by occupying forces through the weekend before his release on Monday.

Ukrainian state nuclear company Energoatom shut down the last of the plant's six reactors on September 11 because Russian military activity had cut reliable external power supplies for cooling and other safety systems, threatening a potentially catastrophic meltdown.

But now the company faces a different problem.

Energoatom President Petro Kotin said the company could restart two of the reactors in a matter of days to protect safety installations as winter approaches and temperatures drop.

Ukrainian state nuclear company Energoatom President Petro Kotin in his office in Kyiv. Photo / Efrem Lukatsky, AP

"If you have low temperature, you will just freeze everything inside. The safety equipment will be damaged," he said in his office at the company's Kyiv headquarters. "So you need heating and the only heating is going to come from the working reactor."

The plant's last operational reactor was placed into what is known as a "cold shutdown" last month, reducing the likelihood of a dangerous meltdown.

But there is still a risk as long as there are nuclear fuel assemblies inside, Kotin explained. Intentional damage to the reactors or the safety and cooling equipment, or a failure of those systems due to cold temperatures, could still lead to disaster.

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Ukrainian emergency rescue teams practise a nuclear disaster drill in Zaporizhzhia in August, 2022. Photo / David Guttenfelder, The New York Times, File

"You have residual heat and you should constantly provide the coolant for these fuel assemblies. If you stop cooling, then you will have meltdown. And that is how it works," he said.

Russian troops occupy the plant and the surrounding area, including the nearby town of Energodar where thousands of Ukrainian workers continue to maintain the facility. The plant is also the only source of heat for the town, Kotin said.

Energoatom could make a decision as early as Wednesday to restart the reactors.
"We at the moment are evaluating all the risks. And this depends on the weather. And actually, we don't have much time to do that," Kotin said.

Russian servicemen guard an area of the Zaporizhzhia Nuclear Power Station, in Enerhodar, Zaporizhzhia region. Photo / AP, File

The plant's director general, Ihor Murashov, was seized and blindfolded by Russian forces on his way home from work on Friday.

Murashov reported that he did not experience beatings or other abuse, but he was forced to make false statements on camera before his release, according to Kotin.

"I would say it was mental torture," Kotin said of the baseless false confessions. "He had [to] say that all the shelling on the Zaporizhzhia Nuclear Power Plant was made by Ukrainian forces, and that he is a Ukrainian spy and he is in contact with Ukrainian special forces."

Murashov was eventually let go at a checkpoint at the edge of territory Russia controls and had to walk about 15km across no man's land to Ukrainian-held areas, according to Kotin.

The power plant sits within one of four regions that Russian President Vladimir Putin has moved to annex. The nearby city of Zaporizhzhia remains in Ukrainian hands.

Members of the International Atomic Energy Agency visited the Zaporizhzhia plant in September, 2022. Photo / Russian Defense Ministry Press Service via AP, File

At the time of the forced shutdown last month, Ukrainian officials had warned it was only a stopgap measure and, as such, unreliable.

Russian forces occupied the nuclear power station, which ranks among the world's biggest, early in the war. Both sides blame each other for shelling that has damaged power lines connecting it to the grid.

Kotin on Tuesday renewed his call for the establishment of a "demilitarised zone" around the plant, where two experts from the International Atomic Energy Agency, the U.N. nuclear watchdog, are currently based. 

— Adam Schreck & Hanna Arhirova, AP