Why danger still looms at Ukraine’s nuclear power plants
The science, strategy and risks behind Russia’s takeover of a Ukrainian nuclear facility.
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Russian forces have seized one of Ukraine’s four nuclear power plants — and while their actions have not produced any radioactive catastrophes, they have put the entire world on edge. The takeover of the Zaporizhzhia nuclear complex last week led to a fire on the site but did not harm the reactors or other radioactive material. Forces were also advancing on the Yuzhnoukrainsk, or South Ukraine, plant as well, Ukrainian President Volodymyr Zelenskyy told U.S. senators on March 5. Occupying the two plants would mean they control nine of Ukraine’s 15 nuclear reactors. The Russians have also assumed control of the defunct Chernobyl nuclear plant where operations focus on safe storage of nuclear waste.
The International Atomic Energy Agency, along with the Ukrainian nuclear regulator and power company, has said that no significant damage has occurred. Radiation levels at the plants are normal. But the director general of the IAEA, Rafael Mariano Grossi, has emphasized that the current state of affairs is not sustainable.
“There is nothing normal about what is going on,” he said during a news conference on March 7 “There is safe operation, but there are many, many questions on the ability to sustain this for much longer.”
This is the first time that nuclear power plants have been targeted by military operations, which some, including the U.S. embassy in Kyiv, have called a “war crime.” Nuclear power accounts for half of Ukraine’s electricity generation, and along with the radioactive threat, these major parts of the power grid are now in Russia’s hands.
Russia’s actions around nuclear facilities in Ukraine are unprecedented and dangerous, though no radioactive materials have been released to this point. The ongoing safe operations of the plants depend on how they are managed — and who is managing them — from this point forward. For Russia, controlling such a large source of Ukraine’s electricity is strategically valuable to disrupt Ukrainian military and government operations as well as civilian life.
The cooling system is key
The Zaporizhzhia plant is home to six individual reactors installed between 1984 and 1995, while the Yuzhnoukrainsk has three reactors installed between 1982 and 1989. All nine of them are pressurized water reactors (PWR) — the most common type of reactor design globally, accounting for about 80 percent of all the world’s reactors. The Zaporizhzhia plant’s reactors are from the Russian-designed VVER series of PWRs. VVERs of varying generations have been used or are currently under construction in at least a dozen countries.
The reactor cores, where the energy-producing fission reactions occur, are contained within thick concrete structures capable of withstanding significant physical shocks — a direct hit from a 20-ton airplane, according to some VVER design specifications. The reactors use the nuclear fission reactions to heat up water, producing steam that turns a turbine and generates electricity; importantly, the water also acts as a coolant, keeping the reactor core stable.
The coolant must be maintained while the reactors are running in order to prevent disasters. A cooling system failure was the root of the 2011 disaster at the Fukushima Daiichi plant in Japan: After the massive Tohoku earthquake caused the plant’s reactors to automatically shut down, the subsequent tsunami inundated backup diesel generators that were responsible for continued cooling.
The Ukrainian situation is also completely distinct from that seen in the 1986 Chernobyl disaster. The design of that plant was fundamentally different; as the reactor began to lose stability, a combination of design flaws and operator errors led to an uncontrolled nuclear chain reaction. That design, according to University of Rhode Island Professor of Mechanical, Industrial and Systems Engineering Bahram Nassersharif, is “very much unlike these VVER reactors or the reactors that we have here in the United States.”
The VVERs and other modern reactors are much easier to control. If steam begins to accumulate in the coolant, the reactor will slow its output rather than increase it.
Nuclear Risk Lens
Confusion over who’s in charge
There has been no release of radioactive material at Zaporizhzhia, the IAEA and Ukrainian officials have said. During the battle, a fire broke out in a training building, some distance from the reactors themselves; officials said that one structure associated with the reactors did sustain some minor damage, but nothing that was considered of particular risk. More recently, the IAEA said it was investigating “reports that Russian forces have carried out munition explosions” on the grounds of the Zaporizhzhia plant. The organization said that Ukrainian regulators had previously said they would dispose of unexploded munitions at the site following the Russian takeover on March 4.
As of Monday, two of the six Zaporizhzhia reactors were running at or near full capacity. Two others were in “cold shutdown,” another was cooling down and another was offline for planned maintenance. David Woods, an Ohio State University emeritus professor of integrated systems engineering and an expert on safety in highly complex systems like nuclear power plants, told Grid that as long as the operators can continue running the plant, then no problems should arise.
“Are competent people in charge?” he asked. “Because if they’re in charge, everything’s going to be OK.”
The answer to this, however, is not entirely clear. According to the IAEA, while Ukrainian plant managers at Zaporizhzhia are still at their posts, they are now answering to the commander of the Russian forces, who have been joined by “at least 11″ representatives of the Russian state nuclear company Rosatom. This, according to IAEA director general Grossi, is a violation of one of the seven pillars of nuclear safety: “The operating staff must be able to fulfill their safety and security duties and have the capacity to make decisions free of undue pressure.”
Woods told Grid that the reactors themselves are not the likely cause of any problems with a military takeover of a nuclear facility. Instead, spent fuel pools (and the active cooling they require) and dry cask storage on the sites could more easily be damaged by shelling or other military action. This is still a low-probability event, he stressed, and it would likely result in radioactive releases that are confined to the local area or the adjacent river, rather than the continentwide effects of a Chernobyl-sized catastrophe.
Notably, the Chernobyl site itself was also seized by Russia forces and remains under their control. Though monitors did observe a brief spike in radiation levels there, this was due to heavy military equipment kicking up some contaminated dust and poses no long-term risk. Experts have said the Chernobyl site, which has not had a functioning nuclear reactor in more than two decades, poses little threat to the public.
There is, however, old nuclear fuel still stored at Chernobyl, and Ukrainian authorities reported that a power line to the area had been cut. On March 9, Ukraine’s Minister of Foreign Affairs Dmytro Kuleba said on Twitter that backup generators would last 48 hours, after which the lack of power and cooling would make “radiation leaks imminent.” Experts pointed out that very little leftover heat remains in the Chernobyl waste, though, suggesting the risk may be overblown. The IAEA acknowledged the power cut and noted it violated one of the key pillars of nuclear safety — an uninterrupted power supply — while adding that the agency “sees no critical impact on safety.”
On Sunday, IAEA said that power had been restored to the Chernobyl site; one day later, it reported that Ukraine’s transmission system operator, Ukrenergo, said that one of two power lines into the facility had again been damaged “by the occupying forces” before it could be fully restored. Hours later, the Ukrainians told IAEA that the repairs were complete and the plant was being reconnected to the national power grid.
In the meantime, the radiation monitoring system at the Chernobyl site has stopped sending data to the IAEA. Similar systems at other Ukrainian nuclear facilities continue to operate normally. International groups are also monitoring for radioactive releases, including the Department of Energy’s Nuclear Incident Response Team, and no changes to radiation levels or radioactive material have been detected.
Notably, the nuclear risks have not been confined to the power plant sites. Grossi also confirmed that shelling in the eastern Ukrainian city of Kharkiv had destroyed a neutron generator used in scientific experiments at the Kharkiv Institute of Physics and Technology. “What we can say is that … this place has a very small inventory of material — very small. It is a subcritical facility,” he said.
Still, because it did contain some nuclear material, the facility was under IAEA safeguards, Grossi acknowledged. “It was actually part of a cooperation between the United States and Ukraine, the Obama administration,” he said. “It is a scientific institution. It is very regrettable what happened.”
There is no indication of danger from the incident, but it demonstrates again the somewhat cavalier approach to nuclear facilities across Ukraine.
Military Strategy Lens
Russia’s nuclear focus is unprecedented — and brazen
Experts said Russia’s focus on capturing Ukrainian nuclear power plants reflects a broader military strategy. But many were surprised by the brazenness of the fighting around the Zaporizhzhia plant.
The IAEA said that the damage to the plant was caused by the Russian forces, but experts were unsure how to interpret it.
“Either Russian leaders ordered the attack, which would indicate a level of recklessness and brinkmanship that we had not anticipated, or Russian troops on the ground fired on the plant without orders — or even possibly in contravention of them,” wrote Jon Wolfsthal, a senior adviser at Global Zero and former National Security Council senior director, in a Washington Post commentary.
David Shlapak, a senior defense researcher at the Rand Corporation, told Grid, “Were I the Russians, I would have tried to take that power plant offline. Now, whether I would have gone in there guns blazing is another story.”
While the risk of fighting around a nuclear plant is hard to fathom, there are a number of reasons why controlling Ukraine’s nuclear power plants would be a strategic priority for Russia.
Controlling or damaging an enemy’s power grid is a common tactic in modern warfare, and Russia has been a key perpetrator. As Grid’s Tech Reporter Benjamin Powers recently wrote, Russia has carried out significant cyberattacks on Ukraine’s grid in the past.
“From 2014-2018 there were ten attacks by pro-Russian separatists and others on energy infrastructure in Ukraine alone,” Anu Narayanan and Jonathan Welburn, experts at the Rand Corporation, wrote in an email to Grid.
But in the current conflict, Russia has opted for conventional weapons instead of hackers to exert control over Ukraine’s power system.
By taking over Zaporizhzhia, Russia has now seized one-fifth of Ukraine’s electricity generation. Before the invasion, Ukraine was preparing to connect its grid to neighboring European nations by 2023. For now, though, the grid is isolated, meaning Ukraine cannot easily access new power sources. If Russia occupies all four plants, it would control 50 percent of the nation’s electricity generation.
“Gaining control of an electrical power grid aids the enemy in causing chaos in the population but also disrupts defense and strategic planning for Ukrainian governance,” said Elizabeth Buchanan, a lecturer in strategic studies at Deakin University in Australia who focuses on energy security issues.
Another advantage of controlling the nuclear power plants is that they can serve as bases for the Russian military, as it is unlikely Ukrainian soldiers would try to regain the plants and risk further damage to the facilities.
A final motivation for Russia may extend beyond the war, Buchanan said. “It is likely the capture of [Zaporizhzhia] is related to long-term post-conflict plans on Russia’s part, in which the infrastructure remains and is used to power the eastern republics (should a bargain be struck),” she wrote in an email to Grid. “This is after all, the largest nuclear power plant in all of Europe — a key strategic asset the Kremlin would no doubt be eyeing.”
Russia’s invasion of Ukraine has thrown the international order into chaos, sent shocks through European and global energy markets, and produced nearly 2 million refugees. The takeover and damage of civilian nuclear facilities, whether done with the goal of controlling the power grid or other strategic aims in mind, adds yet another layer of risk and uncertainty to the situation. With the Yuzhnoukrainsk plant potentially targeted next, and two other nuclear power plants under Ukrainian control still, danger remains.
“It’s a war zone,” said Woods, of Ohio State. “You can’t exclude anything.”
This story originally ran March 8 and has been updated.