In one of the Chernobyl accident’s most fraught anniversaries to date, the head of the International Atomic Energy Agency paid a wartime safety visit to the plant, which was only recently returned to Ukrainian control by Russia’s invading forces.

In the more than three decades since the plant’s Unit Four reactor exploded and sent radioactive fallout across much of Europe and the Soviet Union, the site of the disaster has never been so vulnerable.

On February 24 when Moscow’s invasion began, the Chernobyl site was overrun by thousands of Russian troops. Their heavy armored vehicles churned up radioactive soil while soldiers dug trenches throughout the exclusion zone, the irradiated 2,800 square kilometer wasteland surrounding the plant that has been uninhabited since the 1986 catastrophe.

With scientists and others watching in disbelief from afar, Russian forces flew over the long-closed plant, ignoring the restricted airspace around it. Chernobyl’s workers were held at gunpoint and forced to work a marathon shift of more than a month, with employees sleeping on tabletops and eating just twice a day.

The Russian presence brough elevated radiation readings throughout plant territory and fears that the site of the world’s worst nuclear accident would produce an encore disaster, courtesy of a Russian rocket or bomb.

Russian forces eventually retreated from the Chernobyl site on March 30 amid reports of soldiers suffering from radiation poisoning.

“The situation was absolutely abnormal and very, very dangerous,” Rafael Grossi, the IAEA’s chief, told reporters this week as he arrived at the New Safe Confinement, the steel dome that covers the radioactive remains of the Unit Four reactor.

Grossi said radiation levels were now “normal.”

“There have been some moments when the levels have gone up because of the movement of the heavy equipment that Russian forces were bringing here and when they left,” he said.

Chernobyl workers told reporters that they had tried to keep the Russians from the most dangerous areas withing the plant’s territory. But in what many called the worst situation they have seen in the decades since the initial disaster, Chernobyl’s power was cut by fighting, leaving them to rely on diesel generators to support the critical work of circulating water for cooling the spent fuel rods.

“It was very dangerous to act in this way,” Maksym Shevchuck, the deputy head of the state agency managing the exclusion zone, told the Associated Press.

Russia’s invasion marks the first time that occupying a nuclear plant was part of a nation’s war strategy, Rebecca Harms, former president of the Greens group in the European Parliament, who has visited Chernobyl several times, told AP. She called it a “nightmare” scenario in which “every nuclear plant can be used like a pre-installed nuclear bomb.”

It is precisely this scenario that the IAEA has been at such pains to avoid since the invasion began, with only mixed success. Aside from Chernobyl, whose first three reactors continued producing power until 2000, Ukraine inherited four operational nuclear power plants from when the Soviet Union dissolved in 1991.

These plants operate 15 Soviet-built reactors between them. One of those plants, the Zaporizhzhya in southeastern Ukraine, is Europe’s largest, and has been in the hands of Russian troops since it was attacked on March 4.

During his Chernobyl visit, Rossi and the Ukrainian government agreed to set up a commission to handle questions of safety at Ukraine’s nuclear plants as the war drags on, the IAEA said in a statement.

Ukrainian nuclear authorities are likewise working with the defense ministry on ways to protect Chernobyl’s most critical areas. At the top of the list are anti-drone systems and anti-tank barriers, along with a system to protect against warplanes and helicopters.

The original disaster

Unit Four at the Chernobyl plant, located 110 kilometers north of Kiev, exploded and caught fire deep in the night on April 26, 1986, shattering the reactor building and releasing more than 400 times more radioactive material into the atmosphere than the Hiroshima bomb.

A view of the New Safe Confinement structure. Photo: - Credit: Nils Bøhmer/Bellona

In the days that followed, nuclear fuel continued to burn, issuing clouds of poisonous radiation and contaminating as much as three quarters of the European continent, hitting northern Ukraine, Russia and Belarus especially hard.

More than 600,000 liquidators – a loose term enveloping police, fire fighters, military, conscripts and other state safety employees – were rushed to the site with minimal protective gear and hardly any plan for extinguishing the carcinogenic blaze.

No word came from the Kremlin as to what had happened. Afraid of losing face, Soviet authorities kept silent as the radiation crawled north. They did eventually evacuate 48,000 residents of the city of Pripyat ­– the workers’ town located 3 kilometers from the site of the explosion – but not until the afternoon of April 27, a whole day later. By early May, Swedish nuclear authorities noticed mysterious spikes in their own radiation monitors and sounded the alarm.

Finally, on May 14, Communist Party Secretary General Mikhail Gorbachev, went on television and admitted to the disaster. Authorities responded by relocating 116,000 people from the 30-kilometer exclusion zone surrounding the destroyed reactor.

In following years, the number of evacuees swelled to 230,000. All the same, 5 million Belarusians, Ukrainians and Russia’s still live in areas tainted by persistently high radiation levels.

The liquidators fought to build a containment structure of cement and steel over the ruined reactor to squelch radiation emissions. The ad-hoc construct trapped 200 tons of uranium, but many liquidators feared at the time that the cement barrier would eventually give way. In 2005 it did.

In November 2016, 30 years after the explosion, the New Safe Confinement, a €1.5 billion, 36,000 ton steel structure, was moved laboriously into place over the wreckage of the Unit Four.

Financed by donations from more than 40 countries coordinated by the European Bank of Reconstruction and Development, the New Safe Confinement is the largest movable land-based structure on earth, with room inside for Paris’s Notre Dame cathedral.

But even so, the molten radioactive debris within the cavernous structure – which is being dismantled by robots – eventually must be stored somewhere, and funding questions surrounding that issue persist.

What impact the radiation had, and how many early deaths it brought about, remains disputed. A UN report from 2005 suggested 4,000 long-term cancer deaths would result among those who received the highest radiation doses.

In the following year, Belarus, probably hardest hit by the radioactive fallout, challenged that, and produced data saying the country alone would see 93,000 cancer deaths stemming from the disaster. Other reports forecast 60,000 deaths in Russia, and a combined death toll in Belarus and Ukraine reaching 140,000.

A clear list of obituaries may never emerge. The massive resettlement means that many who left when Pripyat was evacuated may have already died.

Even with new shelter is in place, the surrounding exclusion zone of around 2,600 square kilometers will remain uninhabitable – and it will take another 20,000 years before people can live near the plant again.

The full extent of Russia’s activities in the Chernobyl exclusion zone is still unknown, especially because the troops scattered mines that the Ukrainian military is still searching for. Some have detonated, further disturbing the radioactive ground. The Russians also set several forest fires, which have been put out.

Chernobyl needs special international protection with a robust United Nations mandate, Harms told the AP. As with the original disaster, the risks are not only to Ukraine but to nearby Belarus and beyond.

“It depends from where the wind blows,” she said.