Feb 25, 2022 7:01 PM

Risks to Ukraine’s Nuclear Power Plants Are Small—but Not Zero

While the Russian military is unlikely to target Ukrainian reactors, a stray missile or a power outage could spark a disaster.

On Thursday, invading Russian forces seized the Chernobyl nuclear plant in northern Ukraine near the Belarus border. The site of the infamous meltdown in the spring of 1986 is the scene of an ongoing environmental crisis. Soil and water remain poisoned by radioactive contaminants, and nuclear material is still being cleaned up inside a containment structure built over the remains of a damaged reactor. But as the fighting continues, there are perhaps bigger nuclear risks emanating from Ukraine: the many active reactors spread elsewhere across the country.

Ukraine’s aging power plants, packed with reactors, cooling systems, turbines, and other key components, require careful maintenance and monitoring that can be disrupted during wartime. They also risk being damaged by a stray missile or artillery shell, especially if the invasion drags on. While experts believe the Russian military would not deliberately target a nuclear plant, a potentially disastrous mistake—one that could harm millions of Ukranians and also neighboring Russians—is not impossible.

“That’s certainly something I think the Russians would make an effort to avoid doing, not only because they don’t want to contaminate the country they’re trying to occupy—but, also, Ukraine needs electricity from those plants,” says Ed Lyman, senior global security scientist at the Union of Concerned Scientists and coauthor of the book Fukushima: The Story of a Nuclear Disaster.

Rafael Mariano Grossi, the director general of the International Atomic Energy Agency, urged “maximum restraint” on Friday to avoid jeopardizing the safety of Ukraine’s nuclear plants. The agency is “gravely concerned” by the unprecedented situation of a large conflict occurring in such close proximity to reactors, according to their statement.

Ukraine has one of the world’s largest nuclear fleets, with four power plants and 15 reactors that produce about half of the country’s power. The massive six-reactor Zaporizhzhya plant in the southeastern part of Ukraine lies just 120 miles from the Donbas region, where the government has been in conflict with Russia-backed separatists since 2014. Energoatom, the utility that runs Ukraine’s nuclear reactors, announced in a statement on Friday that two of those six reactors had been powered down, disconnected from the grid, and put in “reserve.” So far, all are reportedly operating normally.

For nuclear experts, the primary concern is not that missiles are likely to rain down on a nuclear facility, but instead the difficulty of keeping reactors running with adequate staff and safety protocols in the middle of a war zone. Power plants themselves need electricity, and an exploding missile could inadvertently trigger a power outage. Or a cyberattack on the electricity grid could cause one. And if backup generators fail for any reason, that could disrupt a reactor’s cooling system, leading to a meltdown. That’s when the heat produced by the core of a reactor begins to exceed its ability to be cooled. The temperature rises uncontrollably, and eventually components start to melt, leading to the release of radioactive fuel, and possibly fires or explosions.

Those risks could be compounded by staffing problems as the situation in the country grows more chaotic. “Let’s say all the staff say, ‘This is it, we’ve got to get out of here, I’m taking my family to Poland.’ How do you operate the reactor at that point?” asks M. V. Ramana, a nuclear policy expert at the University of British Columbia. (At Chernobyl, the Ukrainian government has accused the Russian military of “detaining” staff who are monitoring the waste site.)

Nuclear power plants rely on a principle of layered safety mechanisms. The risk of any one safety system failing is low—and so the risk of multiple systems collapsing like dominoes is exceedingly low. But an active war zone trips up that system, according to James Acton, codirector of the Nuclear Policy Program at the Carnegie Endowment for Peace.

On Twitter, Acton noted the increased risks of “common mode” failure, where both primary and backup systems simultaneously fail. In one scenario, a Russian attack on Ukraine’s power systems disconnects the nuclear plant from the grid, and then a safety incident, like a fire, occurs. Ordinarily, if the power goes out and the reactors need to be powered down, there are backup systems to keep the power plant cool—the IAEA recommends 72 hours of fuel, Acton noted in an email to WIRED. In peaceful times, that window should be enough time for the grid to come back online, or a fire crew to arrive, or at least for a resupply of diesel to run emergency generators. In wartime, the arrival of those things is not guaranteed. The risk of such an incident remains very low, Acton wrote, but in war, “the unimaginable becomes entirely conceivable.”

The Chernobyl plant, known as a “first-generation” reactor, used graphite as a “moderator,” to slow neutrons down and facilitate fission chain reactions. But graphite burns, and when the graphite began to smolder, it helped spread radioactive material into the air. After the catastrophe, that design was phased out worldwide. Now, in the Ukraine and elsewhere, most nuclear plants have “pressurized water reactors,” which use water rather than graphite. But while the newer water reactors are safer, risks remain if plant operators can’t keep the coolant system going, since water heated by the fuel rods needs to be replaced by cool water.

“If the cooling system doesn’t work, that is a prescription for disaster,” says Bob Rosner, a physicist at the University of Chicago and former chair of the Bulletin of the Atomic Scientists’ Science and Security Board. He recalls the 2011 Fukushima Daiichi disaster in Japan, when the reactors there were cut off from the electric grid by a 9.0-magnitude earthquake offshore. Then the subsequent tsunami knocked out emergency diesel generators. Some backup battery power remained, but eventually that ran out too. With the reactors no longer able to run their coolant pumps, much of the uncovered nuclear fuel then melted.

It doesn’t help that Ukraine’s nuclear plants are getting old, Rosner says. Most were built in the 1980s, dating back to the Soviet era; the only reactors the country has closed are Chernobyl’s. In particular, the Rivne reactors northwest of Kyiv are close to or past the typical 40-year age limit. (In the US, plant operators can often get their license extended for another 20 years, following inspections and any necessary maintenance.) When considering a plant’s safety risks, the critical thing to pay attention to is a reactor’s containment vessel, which contains the nuclear fuel. That’s usually made of steel, but after many years of neutron bombardment, the steel becomes brittle and can crack. Older reactors, like most of those in Ukraine, need constant surveillance for that reason, Rosner says.

Refueling Ukraine’s reactors could also be challenging. Nuclear plants never keep new fuel onsite; they need to plan a brief shutdown for when the fuel arrives. Ukraine gets most of its nuclear fuel from Russia, but over the past few years, the country also made agreements to acquire fuel from Pittsburgh-based Westinghouse Electric, making it less dependent on Russian supplies.

While it’s been 36 years since the Chernobyl disaster, the Russian seizure of the defunct facility still poses unique challenges and risks, Lyman says. The remains of the damaged reactor lie buried under a concrete “sarcophagus,” which was built in the aftermath of the disaster and is now surrounded by the New Safe Containment facility, built in 2016. Engineers designed the structure to withstand earthquakes, tornadoes, and high-speed winds. Chernobyl’s three other reactors kept operating for years; the last one shut down in 2000. Some of those reactors’ spent nuclear fuel is stored in swimming-pool-like wet storage ponds, while some of it has been transferred to dry casks, large steel or concrete cylinders that are designed to last for years.

According to the State Nuclear Regulatory Inspectorate of Ukraine, on Friday, new readings from the automated radiation monitoring system in the Chernobyl area detected higher gamma ray radiation measurements than normal, up to 9.46 microsieverts per hour. The gamma rays could be the emissions from radioactive materials, Rosner says. They may have been caused by heavy military vehicles stirring up contaminated soil, according to the IAEA statement released Friday. Still, agency officials wrote in their statement, the radiation levels “are low and remain within the operational range measured in the Exclusion Zone since it was established, and therefore do not pose any danger to the public.” In contrast, the SNRI statement says that “control levels of gamma radiation dose rate in the Exclusion zone were exceeded.”

Ukraine faces plenty of nuclear risks even if Russia never deploys nuclear weapons, as Vladimir Putin has threatened. “What’s going on horrifies me,” Rosner says. “I’m not so worried about the reactors; I worry about the people, the Ukrainians.”