Russian tanks shelled Europe’s largest nuclear power plant, Zaporizhzhia Nuclear Power Plant near Enerhodar in southeastern Ukraine, on Thursday night, setting off a fire in a training building on the plant’s grounds. That attack, which the U.S. Embassy in Kyiv called a war crime, came just a week after Russia kicked off its invasion of Ukraine by capturing the site of the 1986 nuclear meltdown at Chernobyl.

“The world narrowly averted a nuclear catastrophe last night,” Linda Thomas-Greenfield, U.S. Ambassador to the United Nations, told the U.N. Security Council in an emergency meeting.

This is the first war ever fought in a country with nuclear power plants. Four nuclear plants currently operate in Ukraine, with a combined 15 nuclear reactors and several spent-fuel storage pools divided among them. As the Russian military demonstrates its willingness to attack nuclear plants despite international humanitarian law – and risking a disaster that could spread radiation across the entire continent, including Russia – the war in Ukraine raises a new kind of nuclear threat: not nuclear missiles or bombs, but conventional artillery strikes that could trigger a nuclear meltdown at a power plant under fire.

“Not so many people understand how dangerous nuclear power plants are in the case of war,” Kateryna Pavlova, Chernobyl’s Head of the Department for International Cooperation and Public Relations and former Acting Head of the Chernobyl Exclusion Zone, told the Bulletin of the Atomic Scientists. “I want the world to know that we are one little step—a few millimeters—from destroying our world.”

In a deeply unsettling coincidence, the precedent is being set in the same country that once suffered the worst nuclear disaster on record. A look back at the 1986 Chernobyl meltdown highlights the high stakes of a war where civilian nuclear reactors become targets. It also encapsulates much that hasn’t changed about Russia and its treatment of Ukraine.

Meltdown At Chernobyl

On April 26, 1986, a routine safety test at the Chernobyl Nuclear Power Plant went catastrophically sideways. Instead of shutting down, the Number 4 reactor started an uncontrolled nuclear chain reaction. Unchecked, Reactor Number 4 produced enough heat to melt the uranium dioxide fuel rods in its core. Two explosions destroyed the building that housed the dying reactor, and while the reactor inside burned for 9 days, it sent a plume of airborne radiation across the USSR and Europe.

That’s exactly what experts and world leaders fear could happen again if an attack damages a reactor or the infrastructure that keeps it cool and controls the nuclear fission reactions happening inside.

All four of Ukraine’s current nuclear power plants use reactors of a different type than the one that melted down at Chernobyl in 1986. The newer design pumps pressurized water through the reactor core, where it’s heated by the nuclear fission happening in the reactor, and then to a steam generator. Keeping the water flowing under pressure stops it from boiling away in the reactor core, leaving the fuel rods without coolant. It’s designed to prevent the kind of runaway reaction that happened at Chernobyl in 1986.

Damage to the water pumps, or loss of the electricity that keeps them running, could still cause a catastrophe. That’s what happened at Japan’s Fukushima Daiichi Nuclear Power Plant in the wake of the 2011 tsunami; today, Fukushima and Chernobyl are the only two nuclear incidents rated a 7 on the International Nuclear Event Scale, which only goes up to 7.

“I’m not nearly as worried about Chernobyl as I am about the 15 operating reactors and their spent fuel storage pools elsewhere in Ukraine,” said Edwin Lyman, director of nuclear power safety at the Union of Concerned Scientists, in an email.

The Fog Of War

Back in 1986, Soviet authorities immediately began quietly evacuating people from the area around the plant, including the cities of Chernobyl and Pripyat. But in true Soviet form, those authorities didn’t announce the disaster to anyone else, including the countries downwind of the burning reactor.

Two days after the meltdown, fallout set off alarms at a nuclear power plant in Sweden, 1,000 kilometers west of Chernobyl. The Swedish Radiation Safety Authority investigated and quickly realized the fallout had come from somewhere to the east. Sweden’s government contacted Moscow to ask, very casually, whether anything strange might have happened at one of the Soviet Union’s nuclear plants.

Soviet authorities denied everything. Sweden replied, essentially, that it was too bad the Soviet Union couldn’t clear things up, because that meant Sweden would just have to report the unexplained fallout to the International Atomic Energy Agency. Suddenly, the Soviet officials on the other end of the call remembered that a reactor at Chernobyl might have melted down a few days prior, and it might have been serious enough to cause the evacuation of everyone within a 30-kilometer radius.

Last week, as Russian forces seized control of the Chernobyl facility, Zelenskyy made a not-so-subtle reference to the 1986 exchange when he tweeted, “Reported this to @SwedishPM.”

Although Russian forces haven’t exactly been forthcoming with updates, it now appears that staff at the facility are able to at least keep the pumps running and perform other maintenance duties. That’s become apparently mostly from the fact that nothing has gone sufficiently awry for monitoring systems in nearby countries to detect. But it’s hard for anyone outside Chernobyl to know exactly what’s going on in the now-Russian-occupied facility. The fog of war, in this case, is dense (and possibly also radioactive).

According to a Russian military spokesperson, Ukrainian staff members at Chernobyl “continue to service the facilities in a routine mode and monitor the radioactive situation.” Even if that’s accurate, it’s still not clear whether those staff members are hostages, as Pavlova and U.S. White House Press Secretary Jen Psaki both reported last week. And if that’s the case, the biggest and most immediate danger may be to the maintenance workers themselves.

A day after the attack on, and capture of, the Zaporizhzhia plant, Russian military officials are similarly reticent, saying only that the plant is “being guarded by Russian troops.” The condition of the plant’s staff, or their ability to maintain the reactors and their support infrastructure, remain unclear at this time. It’s easy to imagine, however, that working conditions are tense at best.

“I can’t imagine how it would be in Russia’s best interest to allow any facilities at Chernobyl to be damaged,” Lyman told the AP last week. Then again, it’s also difficult to imagine how it would be in Russia’s best interest to risk catastrophic damage to an operating nuclear reactor, either. And Russian media has already attempted (unsuccessfully) to shift blame for a fire in a training building at Zaporizhzhia to Ukrainian saboteurs – which is among the things Ukrainian officials initially speculated that Russian forces at Chernobyl might do.

Political Fallout From Chernobyl

For the Russian military, the former Chernobyl Nuclear Power Plant was a strategic objective not because of its history or the quantities of radioactive waste still stored at the site (and in the 2,600 square kilometer Exclusion Zone surrounding it), but because of its location. Chernobyl lies along the shortest route from the border between Ukraine and Belarus to the Ukrainian capital city of Kyiv. The former nuclear plant is just 16 kilometers south of the Belarusian border and about 130 kilometers north of Kyiv, where Russian forces hoped to link up with other units moving in from the east.

But for Ukraine, the Battle of Chernobyl (as Wikipedia is already calling it), wasn’t just about protecting a strategic corridor or preventing another nuclear accident; Chernobyl is a powerful symbol of how Ukraine fared under decades of Soviet – Russian, essentially – negligence and exploitation.

Ironically, if things had gone drastically awry at Chernobyl this time, one of the first countries to pay the price (besides Ukraine itself) would have been Belarus, whose border is just 16km from the facility – and which allowed the Russian military to launch the attack on Chernobyl from its soil. Belarus received about 70% of the radioactive fallout from the 1986 Chernobyl disaster.

Much of the political fallout from Chernobyl landed squarely in Moscow, on the other hand. Mikhail Gorbachev, the last president of the Soviet Union, later said that the 1986 nuclear disaster “was perhaps the real cause of the collapse of the Soviet Union.” The year before the disaster, Gorbachev instituted a series of political and economic reforms, including Glasnost: a move toward more transparent government and more open access to information for the average Soviet citizen.

Once the news of the reactor meltdown finally broke, Glasnost let it spread throughout the Soviet Union. People learned not only that a reactor in Ukraine, then a Soviet territory, had melted down and poisoned the surrounding landscape, but that negligence by Soviet officials in charge of the nuclear energy program had caused the problem in the first place. They also learned about the attempts to downplay the disaster, which put lives at risk in Ukraine, Belarus, and elsewhere in the Soviet Union, as well as in the rest of Europe.

Putin is no Gorbachev, however. Under his administration, the Russian government has cracked down heavily on non-state-run news outlets and restricted access to social media in the week since the invasion of Ukraine began.

Kicking Up Dust In The Exclusion Zone

On the evening of February 24, just after Russian forces captured the area around Chernobyl, sensors in the 2,600-square-kilometer Exclusion Zone around the former nuclear plant detected a small spike in radiation levels. Military vehicles driving through the exclusion zone had kicked up plumes of contaminated dust, it turned out.

“The general consensus is that the increase in radiation levels was indeed temporary and due to the resuspension of contaminated dust from the passage of military vehicles,” Lyman said in an email. “Although much surface contamination has been removed and contained (more or less), or blown away, there is still a significant amount of radioactive material scattered about the exclusion zone.”

A look around the Exclusions Zone reveals what could, in a worst-case scenario, become of the area closest to a nuclear plant if an artillery shell or missile struck in exactly the wrong place, or if Russian troops prevent the plant’s staff from operating and maintaining the reactors safely.

Immediately after the reactor meltdown in 1986, Soviet authorities evacuated everyone within a 30 kilometer radius of the Chernobyl plant, creating the military-controlled Chernobyl Exclusion Zone. Today, the Exclusion Zone encompasses about 2,600 square kilometers of dense forest and abandoned cities, all closely monitored for radiation. It’s some of the most heavily radioactively contaminated land on earth – and a regional hotspot of biodiversity.

The Chernobyl meltdown was an ecological disaster; trees and small mammals near the nuclear plant died en masse in the spring and summer of 1986. But over the next few decades, plant and wildlife populations rebounded in the Exclusion Zone once there were no humans around to bother them. At least one fox in the area even figured out how to make sandwiches.

By 2019, the outskirts of the Exclusion Zone had cooled enough that Ukrainian authorities considered shrinking the zone’s boundaries. But the heart of the Exclusion Zone remains so contaminated that even the dust kicked up by a military convoy is still radioactive. And the melted remains of Reactor Number 4 still squat in the darkness of what’s left of the old reactor building.

By the end of 1986, workers had completed a steel and concrete structure meant to contain the radioactive remains of Reactor Number 4. At least 31 of them died of radiation poisoning in the effort. Engineers boasted that the structure – now known to most Americans as the “sarcophagus,” although its official name is much less evocative: Shelter Structure – could withstand an earthquake of at least 6.0 on the Richter scale without cracking.

But as many lives as it cost, and as remarkable as it is, Shelter Structure was only a temporary solution to a horrifyingly permanent problem. It was designed to last just 20 to 30 years – long enough to buy engineers time to devise and build a more permanent confinement for the deadly nuclear waste left over from the meltdown of Reactor Number 4. The eventual solution, financed by a 30-country international effort, took the form of a much larger steel structure called the Chernobyl New Safe Confinement, whose construction wrapped up in July 2019. A century from now, the New Safe Confinement will need another replacement.

Ukrainian officials briefly entered the remains of the old reactor building, and photographed the surreal corium formations inside, in 1996; by then, the material had “cooled” enough that it was safe to visit, at least for a little while. By now, it’s even less of a threat. But the corium, along with about 30 tons of radioactive dust and contaminated soil, still isn’t something that anyone wants released into the world.

The Importance Of Keeping Cool

The bigger concern at Chernobyl is stored nuclear waste from three other reactors at Chernobyl (the ones that didn’t melt down), which kept operating until 2000.

“There are about over 21,000 fuel assemblies stored at Chernobyl. Most of them are in a wet storage pool, but some have been transferred to a dry storage facility that started operating last year,” said Lyman in an email. “There is of course lots of other radioactive waste in various forms and storage condition throughout the exclusion zone.”

And none of those storage facilities were built to withstand artillery shells.

In particular, Interim Storage Facility 2, or ISF-2, holds spent fuel rods from Chernobyl Reactors 1 through 3. They fuel rods are still radioactive even after their working life is over, so they’re kept in a pool of water to keep their temperature down; the water also provides some shielding against escaping radiation. After 20 years or more, the spent fuel rods can be stored in dry facilities, like the new one at Chernobyl.

Some cooling pools use electric pumps to keep the water cool.

“If active cooling is required, it is provided through electrically powered pumps,” explained Lyman in an email. “If their operation is disrupted – or if there is damage to the pool that causes the water to drain – the spent fuel could heat up and potentially reach a temperature where the zirconium cladding on the fuel rods could ignite, causing fuel damage and a radiation release.”

But even in a worst-case scenario, a radiation release from the Interim Storage Facility at Chernobyl is an unlikely risk, according to Lyman.

“The spent fuel in the pool has cooled for more than 20 years, and I would expect the risk that a cooling disruption could occur and not be mitigated before fuel damage occurs to be very low,” he said in an email. “Of course, if there were a major battle at the site and facilities were indiscriminately bombed, then all bets are off – but that doesn’t appear to be a likely possibility.”

Attack On Zaporizhzhia Nuclear Power Plant

Thursday night’s fire at Zaporizhzhia underscored the reasons Lyman worries about Ukraine’s operating reactors. Zelenskyy reported that Russian tanks had fired at the nuclear plant, and a security video feed from the plant shows incoming shells, including one that exploded in a parking lot. For a tense few hours, most of the world had no way to know whether the fire would affect the plant’s reactors or its radioactive waste storage.

Rafael Grossi, the IAEA director-general, called it a “close call” in his comments to CNN.

The fire, which Ukrainian firefighters extinguished once the shelling stopped, was confined to a five-story training building on the plant’s grounds. Auxiliary buildings for one of the plant’s six reactors were damaged, according to a statement from Ukraine’s State Nuclear Regulatory Inspectorate, but the reactors themselves are undamaged and all but one has been safely shut down.

Russian forces now have control of most of the plant, which means keeping it operating safely – or allowing staff members to do so – is now up to them.

War In The Nuclear Age

“No country besides Russia has ever fired upon an atomic power plant’s reactors,” Zelenskyy said in a Facebook post.

Historically, countries at war have often targeted major infrastructure like power plants and dams, although at other times, warring nations have made a point to spare civilian infrastructure. Nuclear plants obviously raise a much greater potential problem if they’re bombed or damaged. That’s why international humanitarian law considers nuclear plants off-limits.

Russia’s military even admits that:

A 1990 Russian Federation military manual prohibits Russian forces from attacking “works or installations containing dangerous forces in the knowledge that such attack will cause excessive loss of life, injury to civilians or damage to civilian objects.” The manual includes nuclear power stations on its list of “especially dangerous objects,” even if they’re otherwise military objectives.

That manual appears to have been tossed out the window on the way to Ukraine.

As of 6:41 P.M. on Friday, Russian military units in southern Ukraine had advanced to within 32 kilometers of the Yuzhnoikrainsk Nuclear Power Station, Ukraine’s second largest.