INSIGHTi

Russian Military Actions at Ukraine’s Nuclear
Power Plants
Updated August 29, 2022

Russia’s ongoing military occupation of Ukraine’s six-reactor Zaporizhzhia nuclear power plant
(ZNPP)—the largest in Europe—has raised widespread alarm about the potential for damage to the plant
that could cause large radioactive releases to the environment. Russian forces attacked and captured the
plant on March 4, 2022, with reported “heavy fighting and artillery shelling.” Shelling around the plant
resumed on August 5, 2022, prompting the International Atomic Energy Agency (IAEA) to warn, “Any
military firepower directed at or from the facility would amount to playing with fire, with potentially
catastrophic consequences.” Shelling on August 25, 2022, disabled the plant’s connections to the
surrounding power grid. The loss of offsite power forced the two reactors that had been operating to shut
down. The connections were restored and the units restarted the following day. Some analysts argue that
attacks on nuclear power plants could be considered a “war crime” under international law.
IAEA is negotiating with Russia and Ukraine to send an expert mission to ZNPP “in the next few days” to
“assess the physical damage to the ZNPP’s facilities, determine whether the main and back-up safety and
security systems were functional and evaluate the staff’s working conditions,” according to an August 28,
2022, IAEA statement.
The two reactors operating at ZNPP are said to pose the highest risk of radioactive releases at the site,
because they are running at full or nearly full pressure and heat output to generate electricity. Shutting
down all the reactors at the plant would reduce that risk. When a reactor is shut down, its heat output
immediately drops by about 94%, with the remaining heat continuing to be produced by the radioactive
decay of nuclear materials in the reactor core. As the reactor core cools, it becomes less vulnerable to
disruptions in plant cooling systems. Decay heat, even at reduced levels, must be constantly removed
from the reactor core to prevent the nuclear fuel from melting. Such risks could be further reduced by
transferring nuclear fuel from the plant’s six reactors into adjoining storage pools, although they still must
be constantly cooled.
Russian military action at Ukrainian nuclear facilities has drawn high-level congressional concern. Senate
Foreign Relations Committee Chairman Bob Menendez sent a letter on March 28, 2022, asking that “the
IAEA take decisive actions to mitigate the risks from the Russian Federation army’s incursion, attacks,
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and occupation of Ukraine’s four nuclear power plants, national nuclear labs, and the Chernobyl
Exclusion Zone.”
The four-unit Chernobyl nuclear plant, whose last operating reactor permanently closed in 2000, was
occupied on the first day of the Russian invasion of Ukraine, on February 24, 2022. Russian troops left
the plant by April 1 as part of a general withdrawal from northern Ukraine.
Nuclear Power Plants Operating in Ukraine
Ukraine has four operating nuclear power plant sites with a total of 15 reactors, which in recent years
have provided about half of Ukraine’s total electricity generation. All the operating Ukrainian reactors are
light water reactors (cooled by ordinary water), using designs from the Soviet Union similar in concept to
most of the world’s commercial power reactors. Ukraine’s operating nuclear plants are located throughout
the country, as shown by the following IAEA map:

Source: IAEA, 2020

The operable Ukrainian reactors are fundamentally different from those at the Chernobyl plant, which
suffered a major explosion in 1986.
Reactor Safety Systems
The core of a light water reactor consists of about 100 tons of highly radioactive nuclear fuel producing
tremendous heat through a nuclear chain reaction.
To slow or shut down the chain reaction, control rods are inserted into the reactor core. Although
shutdown happens very quickly during an emergency, substantial amounts of heat continue to be
produced from radioactive decay of the nuclear materials in the reactor core after the chain reaction stops.
If water does not continue to circulate through the core, decay heat can build up enough to melt the

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nuclear fuel and breach the steel pressure vessel that holds the core. The heat and pressure could also
eventually escape the concrete containment structure that surrounds the pressure vessel and associated
pumps and piping. This occurred during the Fukushima Daiichi accident in Japan at reactors built with a
different type of containment from those in Ukraine.
Reactor Safety Risks from Russian Attacks
Russian forces have seized control of ZNPP and its management, but the plant’s operational personnel
have remained on duty “under constant psychological pressure,” according to the Ukrainian nuclear
regulatory agency.
The ongoing Russian military action poses a range of potential threats to Ukrainian nuclear plant safety:
 Direct military damage to one or more reactors. Nuclear power plants are not designed to
withstand military munitions, which could directly penetrate the concrete reactor
containment and steel pressure vessel, allowing release of highly radioactive material.
 Military damage to reactor safety systems. Even if a military attack did not damage the
reactor containment, explosions and fires could disable safety systems vital to avoiding
core overheating.
 Station blackout: loss of electric power. Nuclear plants rely on electricity to run cooling
pumps and control systems. If power from the electric grid is lost, diesel generators
produce backup power and are intended to operate long enough for grid power to be
restored. Loss of power from both the grid and the diesel generators results in station
blackout, the condition that caused the radioactive releases at Fukushima, even though
the reactors there had shut down.
 Disruption of plant personnel. Plant safety could be at risk if military action hindered or
blocked the hundreds of workers needed to operate, maintain, and manage a nuclear
power plant.
 Damage to spent fuel pool or cooling systems. If damage to a spent fuel pool allowed its
water to drain, or if its cooling systems were disabled, the spent fuel could overheat and
release large amounts of radioactive material to the environment.


Author Information

Mark Holt
Mary Beth D. Nikitin
Specialist in Energy Policy
Specialist in Nonproliferation







Disclaimer

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