INSIGHTi
Russian Military Actions at Ukraine’s Nuclear
Power Plants
Updated September 12, 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 potential damage to the plant that
could cause large radioactive releases to the environment. Russian forces 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.” Continued shelling during August and September 2022
repeatedly disabled the plant’s connections to the surrounding power grid. Whenever offsite power was
lost, the two reactors that have been operating since the Russian takeover would usually shut down for
safety reasons and then restart when power lines were repaired. According to Ukraine’s nuclear safety
agency, the plant was reconnected to the grid as of September 12, 2022, but all six of the plant’s reactors
were in cold shutdown because of ongoing shelling in the area.
After months of negotiation, an IAEA expert team arrived at ZNPP on September 1, 2022, to assess the
conditions at the plant. IAEA’s report on the mission, issued September 5, 2022, described extensive
damage to plant facilities and surrounding infrastructure. The report warned that continued military action
“represented a constant threat to nuclear safety and security because critical safety functions (containment
of the radioactivity and cooling in particular) could be impacted.” The report called for “establishment of
a nuclear safety and security protection zone around the ZNPP.” It also noted that the plant’s operating
staff is “subject to constant high stress and pressure” which “could lead to increased human error with
implications on nuclear safety.” Russian forces have seized control of ZNPP and its management, but the
plant’s operational personnel have remained on duty. IAEA experts will remain at the plant to monitor
safety conditions.
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
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light water reactors (cooled by ordinary water), using designs 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. 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.
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 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.
Any reactors that were to continue operating at ZNPP would be considered to pose the highest risk of
radioactive releases at the site, because of the heat produced by their nuclear chain reactions. The current
shutdown of all the plant’s reactors has reduced that risk. When a reactor is shut down, the nuclear chain
reaction stops and no longer generates heat, immediately reducing the reactor’s total heat output by about
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94%. The remaining 6% of the heat comes from the radioactive decay of nuclear materials in the reactor
core. As the reactor core cools because of falling radioactivity (with heat output dropping by 99.5% after
one day), there is less decay heat that must be removed by plant cooling systems. The risk of overheating
could be further reduced by transferring nuclear fuel from the plant’s six reactors into adjoining storage
pools, although they also must be constantly cooled, such as by adding water.
Reactor Safety Risks from Russian Attacks
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
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