Ukraine’s Zaporizhzhia nuclear power plant, the largest in Europe, has provoked anxiety ever since Russian troops captured it barely two weeks into the 2022 invasion. But recently, after three years of occupation and frequent near misses that threatened radiological disaster, a promise of sunnier days suddenly popped into view, albeit briefly. In a 19 March call U.S. President Donald Trump and Ukrainian President Volodymyr Zelensky discussed American protection and investment for Ukraine’s nuclear power—or even ownership, according to a White House summary. International Atomic Energy Agency (IAEA) director Rafael Grossi upped the ante one week later, telling Reuters that Zaporizhzhia’s reactors could restart within “months” of a ceasefireand the plant could be fully operational in a year.
The promise of a rapid restart at Zaporizhzhia, which has six 950-megawatt reactors, quickly faded amid daily and deadly Russian attacks on Ukrainian cities. Nevertheless the chief executive of EnergoatomUkraine’s nuclear power utility, essentially endorsed Grossi’s timeline for a demilitarized scenario in an interview this montheven as he acknowledged serious technical challenges including deferred maintenance and a dearth of cooling water.
In fact, according to Ukrainian, European and U.S.-based experts interviewed by IEEE Spectrum, the challenges facing a Zaporizhzhia Nuclear Power Plant (ZNPP) revival could go far deeper. Those experts say that Russia’s operation of the plant may have so badly damaged it that repairs could take years and cost billions of dollars. Particular problems include potential tilting of the reactor buildings, and the integrity of the complex and relatively fragile steam generators for the plant’s pressurized, light-water reactors.
Even if there is a lasting cessation of hostilities, restarting ZNPP’s reactor-generator units may cost more than Ukraine is able to spend. And at least some Ukrainian energy experts say the country should focus instead on building smaller, decentralized power plants.
Volodymyr Kudrytskyithe former director of Ukraine’s power grid operator, said as much last month during a forum at MIT last month. Kudrytskyi said big nuclear power plants concentrate too much power at a few spots in the grid: “We are able to use this Soviet legacy to survive, but this is not the way forward.”
Questionable Operating Practices May Have Damaged the Plant
Since Russia’s full-scale invasion of Ukraine, ZNPP experienced a wide range of unprecedented insults. During its armed seizure in March 2022, Russian forces fired on the plant. That October, Russia began bombing the Ukrainian power system. Those attacks repeatedly disconnected ZNPP from Ukraine’s grid, forcing the use of diesel generators to power the pumps that circulate water over spent fuel, keeping it from overheating and potentially melting down and releasing large amounts of radiation.
Russia’s attacks have destroyed some equipment and placed strain on others, but special concern arises from unprecedented longterm operating modes: hot shutdown and cold shutdown.
ZNPP is the first nuclear power plant in the world to persist in a condition of hot shutdown, in which the plant operates at minimum output. Sustained hot shutdown, for months on end, violated ZNPP’s license. But Russian plant managers insisted that it provided steam needed to sustain critical equipment, such as the water treatment plant, as well as heating for the nearby city of Enerhodar, also under Russian occupation.
Ukrainian and international safety experts argued instead that hot shutdown unnecessarily increased the risk of an accident causing a regional catastrophe, since hot reactors melt down more quickly after cooling systems fail. Ukrainians saw the enhanced risk as a form of nuclear blackmail, arguing that Russian forces could deliberately unleash a radiological incident if they were forced to retreat from the area.
In April 2024 the plant’s Russian management finally relented, placing the last operating generating unit into cold shutdown. Cold shutdown is a safer mode for the plant, but, still, several aspects of the cold shutdown are highly unusual and are provoking concern.
These concerns stem from a complex combination of chemistry and physics. During cold shutdown the cooling flows are low—nearly stationary in some loops—and also relatively cool, in some cases dropping below 35 °C.
The result is a coolant with higher density. Ukrainian nuclear expert Georgiy Balakan says that high-density coolant puts greater mechanical load on the cooling pipes and the delicate tubes within the steam generators. That elevated load, in turn, increases strain on the many welds, as well as on the steel pipes themselves because their metal is less ductile at lower temperatures, according to Balakan.
Low temperature and flow, meanwhile, also impact boric acid that’s added to the primary cooling water to regulate the reactor’s fission reactions, allowing boric acid to crystallize in sensitive areas of the primary circuit pipes and in the steam generators. Efforts to purge crystals can then exacerbate damage. If the damage perforates the steam generator tubes, borated water can leak through and attack the secondary cooling circuits’ steel, which is of a lower grade.
An office building at the Zaporizhzhia nuclear power plant in southern Ukraine was photographed on 14 June, 2023, 15 months after the facility was captured by Russian troops. Olga Maltseva/AFP/Getty Images
Steam Leaks or Groundwater Extraction Could Doom Plant
Russian officials controlling ZNPP have reported a series of leaks to IAEA observersincluding steam generator leaks in half of its power units. Balakan, a former special advisor to the president of Energoatom, the Ukrainian nuclear utility, calls those telltale signs of the physical and chemical assault on the plant’s equipment. “The Russians acted as if they could operate the water-chemical regime for an unlimited time,” he says.
Independent experts contacted by IEEE Spectrum affirmed Balakan’s analysis. They include a senior U.S. nuclear engineer familiar with Soviet-design reactors, who spoke to Spectrum on condition of anonymity because they feared retribution from national authorities, and a Ukrainian engineer who is not authorized to speak to the press.
Steam-generator issues can shutter a nuclear plant for good. That scenario played out in California in 2013 when utility Southern California Edisonscrapped its only nuclear power plant after botched steam generator repairs that cost nearly $2 billion ($2.7 billion in 2025 dollars).
Another set of potentially costly issues stem from the operators’ shift to groundwater for cooling following the demolition of the Kakhovka Dam in June 2023. Potential implications include impairment a critical safety system: the reactor control rods.
After the draining of the Kakhovka Reservoir eliminated ZNPP’s original source of cooling water, Rosatomthe Russian nuclear generation and technology conglomerate, drilled 11 wells on site. Withdrawing of groundwater is cause for concern, according to Aybars Gürpinara former top safety official at the International Atomic Energy Agency (IAEA). “Especially when there is significant ground water extraction, settlement is always a possibility,” wrote Gürpinar, now a consultant based in Vienna and Brussels, in an email to Spectrum.
Subsidence has caused multiple expensive headaches for Soviet-designed VVER-1000 reactors, including ZNPP’s. Nearly 20 years ago Energoatom had to attach counterweights to arrest tilting of several reactor buildings settling into the site’s sandy soil, according to a 2024 LinkedIn post by Balakan. In 2011, Rosatom told then-President Dmitry Medvedev it had plans to fix the “progressing tilt” at the Balakovo and Kalinin power plants.
Gürpinar says tilting could crack ZNPP’s concrete base and interfere with reactor control rods, slowing their gravity-driven drop into the reactor to squelch fission reactions during station blackouts. He says the rods could even get “stuck,” forcing operators to rely on boric acid to control the reactor and leaving them without backup control.
In a statement to Spectrum, Rosatom asserted that: “No ground level changes or signs of subsidence have been observed.”
Restarting the Reactors Would Require Solving Multiple Problems
Addressing structural damage is only one of many challenges to safely restarting ZNPP’s reactors. Last month, ZNPP’s Russian-appointed director Yuriy Chernichuk said in an interview for Rosatom’s corporate magazine that job one is shoring up the cooling water supply, because restarting reactors will generate thousands of times more heat. Rosatom says it plans to tap the Dnieper River for this purpose.
Chernichuk went on to provide a laundry list of additional challenges, including:
•Repairing or replacing upgraded Western equipment subject to international sanctions;
•Securing operating licenses from Russia’s nuclear regulator, since Ukrainian unit licenses begin to expire this year;
•Rebuilding personnel from ZNPP’s current skeleton staff; and
•Building transmission links to Russia’s grid.
Chernichuk said that “the most realistic option” is to launch Units 2 and 6 first. Their reactors are loaded with Russian-produced fuel, whereas other reactors contain fuel produced by U.S.-based Westinghousefor which Rosatom has neither license nor experience.
If Ukraine reclaims the plant, Energoatom might more easily address its issues. It could start with Units 1 and 3, which have fresher fuel. Energoatom also better understands ZNPP’s equipment, and it has access to Western gear and expertise.
Similar advantages could flow to the U.S. if it could pressure Russia to give up the plant. However, Zelensky has rejected U.S. ownership.
Balakan projects that Energoatom would need one year to restart just one power unit in a best-case scenario where ZNPP is “under full control of Ukraine” and equipment damage is not severe.
But show-stoppers could still emerge. If the steam generators need extensive parts or replacement, it might not make sense to proceed—new steam generators could cost over $1-billion per unit, judging by the experience of Southern California Edison. “They’re not only expensive. They’re very complicated gadgets and they’re hard to fix,” says the U.S. expert who spoke with Spectrum.
Unfortunately, only Russian firms manufacture the steam generators employed at ZNPP. And those might not be available at any price.
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