Frequently Asked Questions: Ukraine Nuclear Power Plants

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This page will be updated regularly as new information is gathered.

Last updated: April 29, 2022

1. Status of Ukraine’s operational nuclear power plants

The IAEA and Ukraine safety regulator said eight of the country’s 15 reactors remained operating, including two at the Zaporizhzhya nuclear power plant (NPP), three at Rivne, one at Khmelnytskyy, and two at South Ukraine. The radiation levels at all NPPs remain in the normal range.Update 21 – IAEA Director General Statement on Situation in Ukraine

2. What is the status of the Zaporizhzhya nuclear power plant?

Of its six reactors, two are currently operating. The operating reactors decreased their power generation to about half of their maximum capacity after a break in an on-site power line on March 17th.Update 24 – IAEA Director General Statement on Situation in Ukraine The onsite power line is now operational and power has been increased to 600 MWe in both units.Update 25 – IAEA Director General Statement on Situation in Ukraine The Ukranian regulator did not say what had caused the break in this internal line at the site.

The NPP has four high voltage (750 kV) power lines plus one on standby. Two of the four were damaged earlier. A third line was lost on March 16thUpdate 24 – IAEA Director General Statement on Situation in Ukraine and is expected to be repaired March 22.Update 25 – IAEA Director General Statement on Situation in Ukraine The two remaining lines are sufficient to ensure the safe operation of the plant. Back-up diesel generators are onsite and available in case they are needed.

Site radiation levels remain normal, and spent nuclear fuel remains safely stored on the premises. A more detailed assessment of safety and security concerns is provided below:

  • Safety of plant personnel – medium safety concern
    The primary concern at the Zaporizhzhia has always been, and remains, the health and wellbeing of the plant operators. Operations at the Zaporizhzhya site are under the control of a Russian military commander.
  • Fatigue of plant personnel – medium safety concern
    Although plant workers are now allowed to rotate in shifts and are less susceptible to fatigue, the mental stress of working under the command of the Russian military since March 3, 2022, is of concern. Moreover, plant workers also cope with the immediate threat of Russian aggression against themselves, their families, and their communities. Human error is a high contributor to risk in any industry. Hostile working and living conditions can increase human error rates.
  • Safeguards monitoring – very low security concern
    The objective of safeguards monitoring systems is to deter the spread of nuclear weapons through early detection of the misuse of such material. The February 27, 2022, loss of offsite power to this monitoring capability at Zaporizhzhia degrades the ability to control and account for nuclear material.Update 16 – IAEA Director General Statement on Situation in Ukraine Electrical power to this system has been intermittent since Russian forces have occupied the site.
  • Spent fuel pools – very low safety concern
    If electricity from the grid is lost, cooling pumps are powered by onsite emergency diesel generators. Should those generators be lost, the pools have sufficient inventory to maintain cooling for an extended time. In the unlikely event that cooling is lost for a sufficient amount of time that the spent fuel is uncovered, it is still located inside the containment building.
  • Radiation from site – very low safety concern
    At present, safety systems are operating normally and radiation levels are normal.

3. What is the status of the Chernobyl site?

Chernobyl Units 1, 2, and 3 were all shut down by 2000 and remain permanently shut down for decommissioning. Site radiation levels remain normal, and spent nuclear fuel remains safely stored on the premises. However, safeguards monitoring is degraded, which presents challenges to monitoring and accounting for nuclear material.

Russian forces took control of the site on February 24th and held the staff on site for 26 days. On February 25th, the Ukrainian regulator reported “elevated radiation levels at the Chernobyl site, possibly caused by heavy military vehicles churning up contaminated soil, but the IAEA assessed that the radiation readings remained low and did not pose any danger to the public.”Update 2 – IAEA Director General Statement on Situation in UkraineReports of Russian soldiers receiving high doses or suffering effects of radiation sickness are unlikely to be true and cannot be confirmed by the IAEA.Update 38 – IAEA Director General Statement on Situation in Ukraine

On March 20th, the Russian occupying force allowed some Chernobyl site workers to leave the site and other staff to replace them. The remaining staff were allowed to rotate on March 21st (except 13 who chose to stay and most of the Ukrainian guards).Update 28 – IAEA Director General Statement on Situation in Ukraine The Ukrainian nuclear regulator and Russian forces reached an agreement on how to organize future staff rotations; however, there has not been a shift change since March 20-21.Update 34 – IAEA Director General Statement on Situation in Ukraine

On March 31st, Ukraine informed the IAEA that the Russian forces that have been in control of Chornobyl Nuclear Power Plant (NPP) since 24 February had, in writing, transferred control of the NPP to Ukrainian personnel.Update 38 – IAEA Director General Statement on Situation in Ukraine Russian forces withdrew from Chernobyl on March 31.Update 46 – IAEA Director General Statement on Situation in Ukraine

On April 26, 2022, the IAEA and Ukraine agreed to establish a working group to coordinate IAEA assistance and support workers at Ukraine’s nuclear sites to maintain safe and secure operations.Update 64 IAEA Director General Statement on Situation in Ukraine On April 28, 2022, IAEA Director General Grossi presented results of an IAEA mission to Chernobyl to deliver equipment and measure radiation levels around the Chernobyl site. Measurements confirmed that radiation levels around the site, including locations inhabited by Russian forces, remain well below radiation dose limits for plant workers.Update 66 IAEA Director General Statement on Situation in Ukraine

A more detailed assessment of safety and security concerns is provided below:

  • Safety of plant personnel – medium safety concern
    The primary concern at the Chernobyl has always been, and remains, the health and wellbeing of the plant operators. Operations at the Chernobyl site are under the control of a Russian military commander. Plant personnel are forced to operate under hostile working conditions and do not have the freedom to communicate effectively with plant management, or with the Ukrainian regulator, or to conduct routine activities.
  • Fatigue, mental and psychological stress of plant personnel – medium safety concern
    On April 10 the Ukrainian regulator informed IAEA that a new shift of plant workers was allowed to relieve plant personnel that had been on shift since March 20-21.Update 48 – IAEA Director General Statement on Situation in Ukraine Shifts are normally rotated every 12 hours to prevent worker fatigue. It is not clear why normal shift rotations did not resume after March 31, when control of the Chernobyl facility was returned to Ukrainian personnel and Russian forces withdrew from the site. The mental stress of duty under duress since February 24, 2022, also remains a concern. Human error is a high contributor to risk in any industry, and the prolonged mental and psychological stress of Russia’s hostile invasion of Ukraine and five-week occupation of the site will have taken a toll on plant workers. Prolonged mental and psychological stress can increase human error rates.
  • Safeguards monitoring – medium security concern
    The objective of safeguards monitoring systems is to deter the spread of nuclear weapons through early detection of the misuse of such material. A February 27, 2022, loss of offsite power to this monitoring capability at Chernobyl degrades the ability to control and account for nuclear material.Update 16 – IAEA Director General Statement on Situation in Ukraine Electrical power to this system has been intermittent since Russian forces occupied the site.IAEA Nuclear Safety and Security in UkraineDuring the week of April 25, 2022, inspectors from IAEA “verified nuclear material present, thus re-establishing continuity of knowledge regarding nuclear material at the site. In addition, IAEA technicians upgraded the unattended monitoring systems installed at the site and deployed new transmission channels based on satellite technologies. Since then, the remote data transmission has been partially re-established.”Update 66 IAEA Director General Statement on Situation in Ukraine
  • Spent fuel pool – very low safety concern
    Safety considerations are limited to the cooling of used fuel from the Chernobyl reactor units 1, 2, and 3. In 2000, unit 3 was the last unit to permanently shutdown. After so many years, the heat load from this fuel is very low. Electricity from the grid was lost on March 9th and restored on March 14th according to the IAEA.Update 21 – IAEA Director General Statement on Situation in Ukraine | IAEA If electricity from the grid is lost, cooling pumps are powered by onsite emergency diesel generators.Update 16 – IAEA Director General Statement on Situation in Ukraine Should those generators be lost, the pool has sufficient inventory to maintain cooling. The temperature of the fuel, if dry, is still sufficiently low for the fuel to be air-cooled.
  • Radiation from site – very low safety concern
    At present, the primary source of radiation exposure to the public is the used fuel in the spent fuel pool. The potential for used fuel damage is very low.

4. What happened at Zaporizhzhia?

On March 3, 2022, Russian military operations and shelling around the Zaporizhzhia nuclear power plant resulted in fire damage to a training building. The fire was extinguished. Security footage supports claims by Ukraine's nuclear regulator of damage at three other locations: the Unit 1 reactor building, the transformer at the Unit 6 reactor, and the spent fuel pad which is used to store nuclear waste. The integrity of the used fuel storage canisters was maintained, evidenced by plant radiation levels, which remained normal.Update 10 – IAEA Director General Statement on Situation in Ukraine Security video footage also shows ordnance striking a high-voltage line outside the plant. According to the IAEA, two offsite transmission lines were damaged in the attack. The plant operator also reported shelling damage to an administrative building and a power transformer located on-site but separate from the power plant. No damage to any of the reactors or essential safety equipment was reported.

There are reports of further explosions at the Zaporizhzhia nuclear power plant on March 14th. Indications are that Russian forces carried out disposal of unexploded munitions at the site of the Zaporizhzhya NPP, and IAEA is seeking information about the situation from Ukraine.Update 21 – IAEA Director General Statement on Situation in Ukraine The regulator had previously informed the IAEA about ongoing work to detect and dispose of unexploded munitions found at the damaged training center and elsewhere around the NPP site following the events of March 4, 2022, when Russian forces took control of the Zaporizhzhia nuclear power plant site.

5. How much damage could the attack on the Zaporizhzhia plant have caused?

Concerns that shelling and other munitions might have compromised containment and the reactor core were unfounded and implausible. The nuclear reactors are housed within thick, steel-reinforced containment structures. After September 11, 2001, aircraft impact tests for similarly designed and constructed containment structures in the US revealed that these structures are highly resistant to damage from a direct hit by large aircraft. The reactors were never physically vulnerable to the military shelling. Absent an intentional effort to destroy the plant with bunker-buster munitions or similar weaponry, standard artillery and rocket-launched grenades were incapable of damaging the plant’s containment.

The primary safety concern from military operations was a loss of electrical power to cooling and safety systems, which did not occur. Electrical power was continuously available to all safety systems. If that power had been lost, redundant emergency diesel generators would have supplied power to safety systems, ensuring safe shutdown and core cooling for operating reactors and the spent fuel pool, which are housed in containment structures.

6. What was the potential worst-case scenario?

Even in a worst-case scenario, there would be no release of radiation to the public. All reactors would have been shut down and ceased generating electricity, power would have been lost from the electrical grid, and all six emergency diesel generators would be either disabled or destroyed as a result of the battle to take control of the plant. Alternatively, the emergency generators would have eventually depleted their seven-day fuel oil reserves if grid power could not have been restored.

In this scenario, active cooling systems to the reactors would be lost, similar to the events that resulted in the meltdown of reactor cores at Fukushima Daiichi in 2011. Absent offsite or backup power for safety systems, which is highly unlikely, water in the reactors would eventually boil off and uncover the fuel within approximately 3-4 hours.https://doi.org/10.1016/j.anucene.2019.02.006 If, in addition to the loss of all power, the reactor operators are unable to intervene to replenish coolant losses and continue other safety functions, the water would have boiled off and uncovered the fuel rods in approximately 1-2 hours.

In this event, recently off-loaded, irradiated (hot) fuel in the spent fuel pool would begin to heat up and, over time, fuel cladding would partially melt. In contrast to Fukushima Daiichi, however, where fuel melt resulted in build-up and explosion of hydrogen inside the containment structures and reactor buildings, the reactors at Zaporizhzhia feature a passive hydrogen safety system that does not require external power. Unlike the containment features at Fukushima Daiichi, the containment structures of VVER-1000 plants like Zaporizhzhia are leak-tight. As a result, even in a worst-case situation, any releases of radioactive gas from failed nuclear fuel cladding would be retained within the containment structure, preventing release to the public.

Five of the six reactors were already shut down when the firefight around the plant broke out, and heat loads were very low.

7. How does this incident compare to other major nuclear accidents?

  • Chernobyl
    The situation and safety concerns associated with the shelling of Zaporizhzhia are substantially different from the Chernobyl accident. Unlike the Chernobyl reactor, the Zaporizhzhia reactor units are pressurized water reactors that use the same light-water technology as operating power reactors in the US. By contrast, the Russian-designed RBMK Chernobyl reactors feature graphite-moderated designs. The Unit 4 accident at Chernobyl was caused by an uncontrolled nuclear chain reaction and steam explosion in the reactor, which had no containment structure to prevent release of radioactive material. The failure mechanism that resulted in the accident at Chernobyl is physically impossible with the Ukrainian VVER reactor designs.
  • Fukushima Daiichi
    The Fukushima Daiichi accident was also substantially different from the situation in Ukraine. The Daiichi nuclear accident was caused by a massive tsunami following a major earthquake off the coast of Japan on March 11, 2011. The tsunami overwhelmed offsite and onsite electrical distribution to all safety systems for all three operating boiling light-water reactors. The Daiichi reactors were of an early 1960s design, and each reactor was housed in a Mark I containment. Unlike the pressurized water reactors used in all Ukrainian reactors, the Mark I containments offer significantly less volume for steam and hydrogen, which is produced during a chemical reaction between steam and zircalloy cladding around the uranium fuel. The low-volume containments are housed within reactor buildings, which are not hardened, steel-reinforced concrete structures like the containment structures at Zaporizhzhia.

To date, military operations and shelling around the Zaporizhzhia plant have not caused a loss of power to the reactor or spent fuel pool cooling systems or to other safety equipment. But even if a sustained loss of power were to occur, a release of radiation even comparable to that which occurred at Fukushima Daiichi would be extremely unlikely, given the Zaporizhzhia plant’s differing design and more recent vintage. An intentional and deliberate attempt to blow up the plant and cause a major radiological event, with munitions far more powerful than those utilized by Russian troops as they seized control of the plant, would still fall far short of what is necessary to produce a release of radiation comparable to that which occurred at Chernobyl.

8. How does this compare to other catastrophes in war zones?

Military conflict frequently damages major infrastructure of all sorts, often with substantial public health consequences. Major industrial infrastructure, from refineries and petrochemical plants to dams, bridges, and roads, are frequently damaged in military conflicts, intentionally and unintentionally, and often have substantial public health and environmental consequences. Oil wells set afire during the first Gulf War, for instance, are estimated to have caused as much as $40 billion in environmental damage and as many as 1000 fatalities from respiratory ailments. In addition, many thousands of civilians have perished in dozens of commercial aircraft unintentionally shot down in military conflicts. Those consequences, however, are almost always vastly less significant than the suffering and damage associated with the conflicts themselves.

Virtually no civilian infrastructure is designed to operate in a war zone. But modern light-water nuclear power stations, sheathed in concrete containment structures, supported by multiple redundant electrical and cooling systems, surrounded by large exclusion zones, and guarded by security forces, are better engineered to withstand military operations and attack than any other class of civilian infrastructure.


9. What are the potential risks of other nuclear plants in Ukraine?

Eleven of the fifteen operational nuclear reactors in Ukraine are of the same model as Zaporizhzhia. Two reactors at the South Ukraine site are variations of the reactor design used at Zaporizhzhia. Two reactors at the Rivne site are older, smaller reactors that have confinement buildings instead of leak-tight containment buildings. These reactors provide less robust but adequate protection from radiation release than the larger models at other sites, and significantly more protection than the Chernobyl design.

10. What are the potential risks of non-power nuclear facilities in Ukraine?

On March 7, 2022, the State Nuclear Regulatory Inspectorate of Ukraine (SNRIU) reported shelling damage to the National Scientific Center “Kharkiv Institute of Physics and Technology” (KIPT), a nuclear research facility in Kharkiv, that produces radioisotopes for medical and industrial purposes.Updated information on the neutron source site | State Nuclear Regulatory Inspectorate of Ukraine (snriu.gov.ua) The research facility housed very low quantities of nuclear material, and damage did not result in radiation exposure to the public. SNRIU reported the radiological situation at the KIPT site is normal.