The Russian assault on the Zaporizhzhia nuclear power station in Ukraine two weeks ago unleashed a destabilizing cocktail of events that, in the worst case, could still lead to a severe nuclear accident. And as Russia’s violence continues and spreads, it may threaten Ukraine’s other nine nuclear power plants, including older units in western Ukraine that may be less protected against some extreme hazards.

At Zaporizhzhia, Russian troops fired ammunition, including grenades and perhaps artillery shells, at the station, which is Europe’s biggest. Ukrainian national guard forces, tasked to defend the six power reactors, returned fire. An auxiliary building was set ablaze, invaders prevented access by firefighters, and attacks may have damaged a transformer at one of the reactors. Russian troops ignored pleas from the plant operators to withdraw, forced their way into reactor buildings, and took command of the staff.

Mark Hibbs
Hibbs is a Germany-based nonresident senior fellow in Carnegie’s Nuclear Policy Program. His areas of expertise are nuclear verification and safeguards, multilateral nuclear trade policy, international nuclear cooperation, and nonproliferation arrangements.
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Last week, Russian occupiers brought in personnel from Rosatom, Russia’s state-controlled nuclear power company, to “consult” with Ukrainian operators. Ukrainian regulators contested Russian claims that Rosatom had taken control of the station’s management. A senior nuclear security official told Carnegie that the Russians threatened to dismiss Ukrainian personnel unless they declared their loyalty, and land mines were planted on the site. Two of the four main power lines linking the station to Ukraine’s power grid have been damaged; one line must be functional to assure supply of power to the plant.

Since the attack, Ukrainian operating personnel have been working under great pressure, and nuclear safety at the plant has been challenged or degraded in critical areas. The effectiveness of plant personnel may be reduced, and clear lines of authority and communication involving operators, management, and regulators have been weakened. The reliability of the electric power supply system has been reduced, and Russian troops may inhibit effective response by plant personnel should an emergency arise.

Prior to these events, governments and the nuclear power industry—including in Ukraine—had intervened to improve the chances that what is unfolding at Zaporizhzhia will not result in a nuclear disaster. They took actions on both essential fronts: nuclear security and nuclear safety.

Partly in response to growing awareness of terrorist threats over the past two decades, more attention has been paid to potential hostile incursions. Encouraged by the United States government, which held a series of nuclear security summits beginning in 2010, Ukraine identified and addressed weaknesses in nuclear stations’ physical protection and security. Ukraine reported significant progress, especially after Russia occupied Crimea and interfered in eastern Ukraine beginning in 2014.

In nuclear safety parlance, an armed attack on a power reactor is an “extreme external event,” a category that also includes tornadoes, earthquakes, and airplane crashes. A turning point was the 2011 destruction of three reactors at Japan’s Fukushima Daiichi nuclear power plant after a tsunami. Experts recognized that had Japan’s government and industry taken specific precautionary measures before the tsunami occurred, the reactors’ demise could have been prevented. Since then, governments and industry have improved the protection of nuclear installations against extreme natural events. The Ukrainian government and industry systematically investigated all of Ukraine’s nuclear power plants to find weaknesses, with the intention to stiffen plants’ defenses in part through modern upgrades of the plants’ original engineering systems.

For all extreme external events—armed attacks as well as severe storms—the ultimate initiators of a dire nuclear safety crisis may be the same: a station blackout, loss of off-site power, and/or loss of emergency cooling capacity. Between 2011 and 2021, Ukraine designed and implemented 80 percent of a comprehensive upgrading program for all fifteen nuclear power plants, encompassing critical areas such as black-out conditions, emergency power and coolant supplies, and qualification of plant equipment for extreme conditions.

One critical line of defense at a nuclear power plant is the outer structure surrounding the reactor and its fuel. Most reactors are outfitted with concrete-steel containments designed to withstand extreme impacts, such as a collision with fighter jet aircraft aimed directly at the reactor, or attacks by targeted explosive charges. But not all reactors are equal. A few older units, including two at Rivne in Ukraine, were built without concrete-steel containments. Measures to improve the robustness of confinement equipment for such reactors are limited. 

Governments and industry will doubtless investigate and assess nuclear safety and nuclear security risk in light of events at Zaporizhzhia and other nuclear installations in Ukraine, including by revisiting the significance of actions carried out before the invasion to defend against an array of external threats. But how they respond to the first-ever military incursion against an operating nuclear power plant will depend above all on how Ukraine’s nuclear power stations weather the invasion of Russian forces.

Ukraine took steps to defend its nuclear plants against threats from sabotage, cyberattacks, and terrorism, but the Zaporizhzhia station was not prepared to withstand an onslaught from an invading foreign army. Likewise, despite efforts in Ukraine to systematically incorporate emergency preparedness and accident management principles, if operators are intimidated, stressed, deterred from taking sound actions, or replaced by outside personnel unfamiliar with an installation whose safety systems have been modified, including with Western technology and equipment, advance preparation may not suffice. 

Barring a catastrophe at any of Ukraine’s fifteen nuclear power plants, the events of the past few weeks won’t likely prompt most other states to reconsider or abandon existing and planned nuclear power investments. Will Russia’s attack now rekindle safety fears in Europe and blunt the prospect of more nuclear power to mitigate global warming? Probably not. Russia’s behavior will likely mean instead that Europe will welcome fission reactors as a counter to dependence upon imported Russian fossil fuels. Countries currently building nuclear plants with Russian cooperation—Turkey and Finland, for example—might reconsider these long-term commitments, partly because Russia may not be able to finance them but also for national security reasons. On balance, it is more likely that European governments will respond to greater concern for their nuclear plants not by shutting them down or canceling plans for new ones but by stiffening their overall national defense against a Russian invasion of their territory.

The most effective direct response to perceived greater nuclear security threats will be at the technical expert level. Governments and industry will again review the preparedness status of nuclear installations in light of new information about what transpires in Ukraine. They may reconsider decisions and plans to extend the lifetimes of older plants with greater vulnerabilities including concerning containment integrity, and they may more deeply investigate how personnel should respond in real time to de-escalate risks should armed forces overwhelm a nuclear power plant site.

The International Atomic Energy Agency (IAEA) has urged that safety at Ukraine’s nuclear power plants be maintained in seven specific areas—a message that might serve as the basis for future multilateral negotiation to address threats of war to nuclear power plants. The IAEA has made recurring efforts to discourage attacks against nuclear installations, and protocols of the Geneva Convention outlaw military incursions against nuclear power stations; nevertheless, Iraq, Israel, and the U.S. have attacked adversaries’ non-power nuclear assets, and last week Russian forces shelled a nuclear research installation in Kharkiv. Governments may respond to events in Ukraine by reinforcing their nuclear facilities’ defense against adversaries’ aggression, but Russia’s invasion will not raise their expectations that future belligerents will act with restraint.

After publication, this piece was updated to reflect the final version of the text.