INSIGHTi
Russian Military Actions at Ukraine’s Nuclear
Power Plants
Updated September 8, 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.” Continued shelling during August and September 2022
repeatedly disabled the plant’s connections to the surrounding power grid. The loss of offsite power
forced the two reactors that had been operating since the initial Russian takeover to shut down and then
restart when power lines were repaired. According to IAEA’s September 7 status report, the plant is
currently disconnected from the grid, and one reactor is operating to provide on-site power.
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 from repeated shelling. 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
light water reactors (cooled by ordinary water), using designs from the Soviet Union similar in concept to
Congressional Research Service
https://crsreports.congress.gov
IN11883
CRS INSIGHT
Prepared for Members and
Committees of Congress
Congressional Research Service
2
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 continuing to operate at ZNPP are said to pose the highest risk of radioactive releases at the
site, because the nuclear chain reaction in the reactor core produces heat, pressure, and radioactive
materials. Shutting down all the reactors at the plant—by halting the chain reactions—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
Congressional Research Service
3
reactor core cools while radioactivity decreases, 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, 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
Disclaimer
This document was prepared by the Congressional Research Service (CRS). CRS serves as nonpartisan shared staff
to congressional committees and Members of Congress. It operates solely at the behest of and under the direction of
Congressional Research Service
4
Congress. Information in a CRS Report should not be relied upon for purposes other than public understanding of
information that has been provided by CRS to Members of Congress in connection with CRS’s institutional role.
CRS Reports, as a work of the United States Government, are not subject to copyright protection in the United
States. Any CRS Report may be reproduced and distributed in its entirety without permission from CRS. However,
as a CRS Report may include copyrighted images or material from a third party, you may need to obtain the
permission of the copyright holder if you wish to copy or otherwise use copyrighted material.
IN11883 · VERSION 6 · UPDATED