“While there are many things that could go wrong at Zaporizhzhia, “the likelihood of an intentional attack on the [plant] that leads to a major nuclear disaster is low,” Ivanka Barzashka, founder and co-director of the King’s Wargaming Network at King’s College London, told Vox via email. “Moscow would have a lot to lose and nothing to gain from such an outcome, given the reactor’s proximity to Russian forces and population.” Furthermore, the plant is built to withstand direct attacks, as it’s constructed with reinforced concrete.
The real risks to the facility would more likely be due to human error, accidental shelling, or a lack of electricity to cool the nuclear material, according to Matthew Bunn, the James R. Schlesinger professor of the practice of energy, national security, and foreign policy at Harvard’s Kennedy School.
“The biggest concern is [the] cooling of a nuclear power plant,” Bunn told Vox. “In general, to avoid an accident at a nuclear power plant, you need to keep the reactor core under water, and the spent fuel and the spent fuel pool under water so they’re continuously cooled.” That cooling process requires electricity, which now comes from Ukraine’s external power grid. The Fukushima nuclear plant disaster in Japan, for example, occurred because of a tsunami which cut off-site electricity to the plant and destroyed the generators, making it impossible to cool the facility even though the reactor had undergone emergency shutdown.
However, as Bunn told Vox, a number of those lines have already been cut, increasing the possibility that Zaporizhzhia might have to rely on diesel-powered generators to support the cooling process. It’s unclear how much fuel those generators have, given that Russian forces have reportedly been siphoning off the fuel for their own purposes, Bunn said. “Diesel’s a highly sought commodity in any war zone,” he said. “There are supposed to be days of diesel at the site; we don’t know whether that’s still true or not.” The Ukrainian nuclear agency Energoatom said on Friday that Russian forces were seeking diesel to fuel the generators in case of power loss, according to Reuters.
In a worst-case scenario, the plant could lose power and the pumps circulating water to cool the reactor core and spent fuel pool would shut down. The heat that the reactor core and the spent material generate would then boil the surrounding water until it evaporates, exposing the reactor core “within hours,” Bunn said. “The fuel would then start to melt. Even if you shut the reactor down, some people refer to it as ‘the fire that doesn’t go out’ — the fuel still generates a lot of heat from the radioactive decay of the split atoms, what are called the fission products, in the fuel.”
However, a spent fuel fire — what Bunn referred to as the “very very worst case” — is unlikely given that there’s just not as much of it at Zaporizhzhia as there are at other sites; that’s because Zaporizhzhia used to send spent fuel to Russia for storage and reprocessing there. “That really only happens when you have fuel that’s pretty closely packed and really hot, having been released from the reactor fairly recently,” he said.
Even if the electricity supply holds, shelling could damage the facility, causing water to leak out of the plant and upsetting the cooling process. Alarmingly, the ongoing shelling has already done damage to the plant — including near a substation which prompted one of only two operating power lines to shut down on August 5.
As Bunn told Vox, the human element is critical in maintaining the plant’s safety. “The Ukrainian operators have been operating essentially at Russian gunpoint for months,” Bunn said. “[They are under] enormous psychological stress; many of them have sent their families away, they’re exhausted. Under those conditions, the possibility of human error in operating the plant is ever-present. They have been doing a heroic job, but people under stress make mistakes.”
Operators at the plant who have been able to speak to outside sources paint a harrowing picture. “What is happening is horrific and beyond common sense and morality,” plant staff wrote in a Telegram channel, according to the BBC. “The psychological situation is difficult,” a worker called Svitlana told the BBC. “Soldiers are walking everywhere with weapons and everyone is actually kept at gunpoint.””