**UPDATED OCTOBER 25**
By Samuel M. Hickey, Monica Montgomery, Connor Murray and Matthew Teasdale
As the world watches Russia’s illegal invasion of Ukraine, nuclear issues and the risk of escalation are abuzz in the news and on social media. We have received myriad questions about the nuclear implications of this crisis and wanted to share answers to some of the most common questions.
Risk of Nuclear Use
- Is the conflict at risk of “going nuclear?”
- Did Putin threaten to use nuclear weapons?
- Could Putin use a nuclear weapon in Ukraine?
- What is so important about Ukraine to Russia that it would even risk nuclear war?
- What exactly is a “tactical” nuclear weapon?
- Are Russian nuclear weapons being deployed to Belarus?
- Will Russia or Ukraine use a dirty bomb?
Nuclear Power Plants
- How concerned should we be about Chernobyl?
- What happened at the Zaporizhzhia nuclear power plant?
- What are the risks to Ukraine’s nuclear reactors in the current crisis?
Ukraine and Nuclear Weapons
- Could Ukraine have prevented the invasion if it had held onto Soviet nuclear weapons?
- Is there any truth to Putin’s claims that Ukraine seeks nuclear weapons?
- Does Ukraine have the tools to build a nuclear weapon?
- How does the war in Ukraine affect ongoing and future arms control negotiations between the United States and Russia?
- Does the United States have nuclear weapons deployed in Europe?
- Has U.S. nuclear deterrence failed?
- Why is a no-fly zone off the table?
We will update this page as new questions and information arise, and you can submit questions to be answered by tweeting at @nukes_of_hazard.
Is the conflict at risk of “going nuclear?”
The risk of a nuclear war remains low at this moment. Right now, the direct fighting is limited to Russian and Ukrainian forces. Ukraine does not have nuclear capabilities, nor is it a NATO ally or part of the U.S. “nuclear umbrella.”
While Russia does possess a vast nuclear arsenal, it is highly unlikely to use nuclear weapons against Ukraine. Russian President Vladimir Putin has, however, made explicit threats of nuclear use in an attempt to deter Western nations from coming to the aid of Ukraine. What’s more, this conflict borders several NATO allies who benefit from the U.S. nuclear umbrella, providing an all too real reminder that, in the fog of war, an accident or miscalculation could escalate and draw nuclear powers into conflict with one another.
The risk of escalation that could lead to a nuclear war in Europe is real and cannot be understated. This moment shows that a war between Russia and NATO — including the United States — is not inconceivable, but a frighteningly real possibility. While this risk is still extremely low, it is not zero.
Did Putin threaten to use nuclear weapons? (Updated September 21)
Yes. In his speech full of baseless claims and false pretexts for invasion, Russian President Vladimir Putin boasted that “today’s Russia remains one of the most powerful nuclear states” with “a certain advantage in several cutting-edge weapons.” He said, “In this context, there should be no doubt for anyone that any potential aggressor will face defeat and ominous consequences should it directly attack our country.”
This threat is extremely provocative and concerning. It flies in the face of Russian statements going back to the Cold War and as recently as January 2022 that a “nuclear war cannot be won and must never be fought.” Further, it undermines the P5 statement that nuclear weapons were for “defense and deterrence only” and risks providing incentives to potential proliferators.
In February, Putin put his nuclear forces in a “special regime of combat duty.” A great deal of uncertainty surrounds what exactly this posture entails as it is unprecedented, but experts speculate that it at least includes shifting the command and control structure into high alert. However, according to Russian nuclear weapons scholar Pavel Podvig, “it is not something that suggests that Russia is preparing itself to strike first, though.”
UPDATED SEPTEMBER 21: Vladimir Putin’s rare September 21 address to the nation made unambiguous allusions to his willingness to use nuclear weapons. In the speech, Putin warned, “if the territorial integrity of our country is threatened, we will use all means at our disposal to defend Russia and our people. This is not a bluff.” He likewise announced a partial mobilization of up to 300,000 reserve forces.
The reference to territorial integrity is especially concerning given the announcement of sham referenda announced by Russian proxies in Luhansk, Donetsk, and the Russian-controlled areas of Kherson and Zaporizhzhia. These regions are “voting” on whether to become territorial parts of Russia.
The mobilization of additional Russian troops coupled with aggressive language on the use of nuclear weapons, raises the likelihood of their use and miscalculation. Putin justified his comments by making unfounded claims about statements from NATO countries about the “possibility and admissibility of using weapons of mass destruction – nuclear weapons – against Russia.”
Could Ukraine have prevented the invasion if it had held onto Soviet nuclear weapons?
No, Ukraine has never actually possessed its own nuclear weapons arsenal. Following the breakup of the Soviet Union in 1991, Soviet strategic bombers and associated bombs and tactical nuclear weapons that were still under Moscow’s command and control were left on Ukraine’s territory. Ukraine did not have the ability to use the weapons nor the facilities to store and maintain them, but, given enough time, Ukraine likely could have reverse engineered the weapons, although at great expense.
Instead, Ukraine then used the Soviet nuclear weapons as a bargaining chip in negotiations for economic aid and security assurances that ultimately led to the 1994 Budapest Memorandum with Russia, the United States and the United Kingdom. In that agreement, Russia and the other signatories pledged “to respect the independence and sovereignty and the existing borders of Ukraine,” which Russia violated in 2014 and now again.
If Ukraine had retained the nuclear weapons, it would have paid a steep price, in terms of the economic and security aid and diplomatic support that Western nations have provided over the years. To say that Ukraine could be the country it is today but with nuclear weapons is false, but it is also true that Putin’s illegal invasion of Ukraine has done serious damage to the credibility of the nuclear non-proliferation regime. Ukraine made the responsible — and only rational — decision to repatriate Soviet nuclear weapons for its own self-interest and collective security.
Are Russian nuclear weapons being deployed to Belarus? (Updated September 9)
On Sunday, February 27, a referendum in Belarus — an effective Russian dependency — approved a new constitution that would remove current language guaranteeing its neutrality and non-nuclear status, and therefore allow Russia to station its nuclear weapons on Belarus’ territory.
Belarusian President Alexander Lukashenko said, “if you (the West) transfer nuclear weapons to Poland or Lithuania, to our borders, then I will turn to Putin to return the nuclear weapons that I gave away without any conditions.” Similar to Ukraine, Belarus inherited nuclear weapons following the breakup of the Soviet Union, but transferred all of them to Russia and codified its nuclear-free status under the Nuclear Non-Proliferation Treaty (NPT).
It remains to be seen whether Russian nuclear weapons will in fact be deployed to Belarus, particularly in light of the fact that NATO has indicated no plan to move any nuclear assets. Russia doing so would come with enormous implications for European security, as Russian nuclear forces in Belarus would not have a deterrent role — that is already filled by strategic forces — but would be there only to threaten Europe with destruction.
UPDATED JUNE 29: On Saturday, June 25, President Vladimir Putin announced that Russia plans to transfer dual-capable Iskander-M short-range missile systems to Belarus in the coming months. The Iskander-M has a range of up to 500 km (~300 miles) and can carry conventional or nuclear warheads. The new nuclear threat is an apparent response to the West’s efforts to enforce European sanctions. Specifically, Lithuania and Poland have prevented goods sanctioned by Europe from traveling across their territory from Russia, through Belarus, to Russia’s Baltic exclave of Kaliningrad.
Russia stores a stockpile of nuclear weapons in Kaliningrad and has been expanding the size and depth of these facilities since 2016. According to Putin, Russia might also help modify Belarusian Su-25 Frogfoot jets so that they could carry nuclear weapons, although he did not see a reason for such a response at the moment. Some analysts argue that if Russia were to train and equip these jets to deliver Russian nuclear bombs — although they would remain under Russian operational control — it would replicate the nuclear sharing arrangement that the United States has with NATO.
UPDATED SEPTEMBER 9: On Friday, August 26, Belarusian President Aleksander Lukashenko announced that Russia upgraded his country’s attack aircraft — Sukhoi Su-25 — to carry tactical nuclear weapons. He warned reporters in Minsk, “[The West] must understand that neither helicopters nor planes will save them if they go for escalation.” Researchers at the International Institute for Strategic Studies questioned the credibility of this announcement and pointed to the Su-25’s role as a support aircraft. The plane could only deliver a nuclear weapon in free-fall mode and would have low-level survivability compared to similar NATO delivery vehicles.
Given longstanding Russian concerns about NATO allies’ capability to deliver nuclear weapons, the announcement of a similar role for Belarus can be seen as an effort to establish an equivalency. In a future arms control negotiation, this could provide a bargaining chip that could be traded away painlessly.
How concerned should we be about Chernobyl? (Updated June 6)
The danger is small. Chernobyl is inside of a large exclusion zone — meaning the space is uninhabited — and its distance from major population centers would mitigate the consequences of a second nuclear accident.
Still, there are two potential areas of concern.
The first is the shelling of the nuclear reactor that melted down back in 1986, the worst nuclear accident in history. However, in November 2016, the world’s largest movable metal structure was slid over Chernobyl’s nuclear power plant to contain further radiation leaks. It is reported that the containment structure is secure against tornadoes and covers gaps in the initial sarcophagus. The second is the disturbance and dispersion of radiation in the ground. After Russia occupied Chernobyl, higher radiation measurements were taken; likely due to Russian trucks and tanks kicking up radiation in the ground. However, the UN’s nuclear watchdog (the IAEA) confirmed that higher radiation measurements “do not pose any danger to the public.” It is unlikely that Russia would intentionally target any reactors.
UPDATED MARCH 9: On March 9, Ukraine informed the IAEA that Chernobyl station and all nuclear facilities in the Exclusion Zone are without electricity due to the Russian invasion and occupation of the plant. The IAEA quickly responded that the “heat load of spent fuel storage pool and volume of cooling water at #Chornobyl Nuclear Power Plant [are] sufficient for effective heat removal without need for electrical supply” and it “sees no critical impact on safety.”
This development is concerning, but there is still time to mitigate the loss of cooling power.
The key safety issue at nuclear facilities is keeping the reactor core and the spent fuel pool cool and the safe operation of both relies on a constant supply of water. At Chernobyl, the safety emphasis is on the spent fuel pool because the nuclear fuel was removed from its operational reactors as of October 2, 2013. Spent fuel continues to generate heat because of radioactive decay of the elements inside the fuel. If electricity is lost, the water in the pool will eventually boil/evaporate away. Then the fuel would melt, which could potentially lead to a radioactive release, depending on the design of the fuel building and a couple of other factors.
However, there is time to intervene. Since the spent fuel is more than 20 years old, there would likely be many days, not hours, before the fuel was exposed. If the fuel rods become exposed due to boiling/evaporation, then there is a risk of a local radiation release. However, there are backup diesel generators and other temporary equipment and means to keep enough water in the pool to prevent exposure. According to the State Nuclear Regulatory Inspectorate of Ukraine, there is only enough fuel to power the generators for 48 hours, but that is only the timeline until what is called a “station blackout.” Refueling the diesel generators is a possible solution, as is repairing the transmission lines and reconnecting the Chernobyl station to the electricity grid.
It will be more difficult to implement these safety measures, however, during a war. Further, Russian troops have held more than 200 technical personnel and guards at the site for 13 days straight as of March 9 and they are in severe psychological distress.
UPDATED MARCH 17: On March 13, four days after Chernobyl had been cut off from the electricity grid, Ukrainian specialists succeeded in repairing a power line to restore external electricity to the Chernobyl nuclear power plant. Two power lines had been damaged due to Russia’s invasion of Ukraine and, throughout the four day period, the facility was powered by back-up diesel generators. Ukraine’s nuclear regulator and the IAEA noted that the nuclear power plant’s disconnection from the grid last week did not have a critical impact on essential safety functions at the site as the volume of cooling water in its spent fuel facility was sufficient to maintain heat removal without a supply of electricity (see explanation above).
On March 14, the IAEA reported that Chernobyl had again been cut off from the electricity grid, and that the power line had to be repaired. Staff were later able to reconnect the plant to the electricity grid.
Ukraine’s regulator also reported that the more than 200 staff at Chernobyl “who had been working non-stop for nearly three weeks, were no longer carrying out repair and maintenance of safety-related equipment, in part due to their physical and psychological fatigue.” The monitoring and control systems on site do not work, which means the operators will not be aware of possible safety and security problems. Further, the IAEA is still not receiving remote data transmission from its monitoring systems installed at the Chernobyl station, and Ukraine’s regulator has no direct communication with the Chernobyl staff. All of these concerns underscore the continued safety and security risks surrounding Russia’s control of Chernobyl and the urgent need to return the station to regular order with IAEA assistance.
UPDATED MARCH 31: On March 31, the IAEA reported that Russian forces had, in writing, transferred control of the Chernobyl nuclear power plant to Ukrainian personnel. In addition, Russia moved two convoys of troops — previously stationed at Chernobyl — toward Belarus and a third convoy had also left the city of Slavutych, where many of the staff at Chernobyl live, and moved toward Belarus. There are still some Russian forces at the Chernobyl site, but Ukraine presumes “that those forces are preparing to leave.” The IAEA also reported that it was still not receiving remote data transmission from its monitoring systems installed at the Chernobyl site, but such data was being transferred to IAEA headquarters from the other nuclear power plants in Ukraine.
Also, on March 30, it was reported that several hundred Russian soldiers were rushed to a hospital in Belarus from the Chernobyl nuclear power plant after the soldiers dug trenches in the Red Forest, disturbing contaminated soil. Not only does the story rely on bogus sourcing, but reports that Russian soldiers are suffering from “acute radiation sickness” — likely referring to Acute Radiation Syndrome or ARS — have no standing due to nuclear material decay. This is not to say that military operations around Chernobyl are in any way safe, but the specific risk of ARS remains low.
According to the Centers for Disease Control and Prevention, “ARS (sometimes known as radiation toxicity or radiation sickness) is an acute illness caused by irradiation of the entire body (or most of the body) by a high dose of penetrating radiation in a very short period of time (usually a matter of minutes).” There are very few examples of people who suffered from ARS because of the conditions that need to be met. However, those groups include, “the survivors of the Hiroshima and Nagasaki atomic bombs, the firefighters that first responded after the Chernobyl Nuclear Power Plant event in 1986, and some unintentional exposures to sterilization irradiators.”
The Chernobyl of today is not the same as the Chernobyl of 1986. The most important reason why it is very unlikely that a Russian unit could suffer from ARS is that the “hottest” radiation from the Chernobyl accident has a very short half-life. That means it decays fast and gives off its radiation quickly. Decades later, most of this material is gone and it could take 57 years — thanks to some back-of-the-envelope math by our friend and scientist Cheryl Rofer in a twitter thread — to reach a high enough exposure for ARS. Compared to the month or so that Russian soldiers have been at Chernobyl, this scenario is highly unlikely if not impossible.
This is not to suggest that there are no dangers to Russian units digging trenches, inhaling contaminants from burning firewood or eating food from the forest. The soldiers likely increased their statistical chance of developing cancer. However, reports of ARS can be put to rest. Claire Corkhill, professor of nuclear material degradation at the University of Sheffield, has also said that “There is NO chance of acute radiation sickness from being in the Red Forest. There is also an extremely LOW risk to any person who has spent time there.”
UPDATED JUNE 6: Two months after Russian troops withdrew from Chernboyl, the plant’s staff are taking stock of the damage and looting of the plant’s security systems. While still being cataloged, reports have so far tallied the loss of “Six hundred ninety-eight computers. 344 vehicles. 1,500 radiation dosimeters. Irreplaceable software. Almost every piece of firefighting equipment.”
The Director of Chernobyl’s Exclusion Zone, Yevhen Kramarenko, estimates that more than $135 million worth of equipment is now missing from the power plant, including computer software custom-made for the station. Some of the equipment has GPS trackers that are still pinging their locations and plant staff can see the equipment is moving around Belarus.
During the first week of June, the IAEA concluded its second mission to Chernobyl to provide support to the plant’s staff on radiation protection, safety of waste management and nuclear security. The IAEA team was also able to verify declared nuclear material and activities; check the functioning of the remote safeguards data transmission from Chernobyl to IAEA headquarters which was re-established at the end of April after two months of interruption; and upgrade the installed remote safeguards data transmission systems.
Is there any truth behind Putin’s claims that Ukraine seeks nuclear weapons?
No. In the week leading up to Russia’s invasion of Ukraine, Putin said Ukraine “aspires to acquire” nuclear weapons and “it is only a matter of time” as Ukraine has laid “the groundwork for this since the Soviet era” and “Western patrons may help it acquire these weapons to create yet another threat” to Russia. Russian Foreign Minister Sergey Lavrov repeated these allegations on March 1.
All of these claims are absurd. This is simply the latest pretext in Putin’s web of conspiracy theories to excuse his illegal and unprovoked invasion. Ukraine does not possess nuclear weapons nor any other weapons of mass destruction, is not actively seeking them from allies, nor does it have the domestic technological means to develop nuclear weapons. Ukraine sealed off this pathway in the 1990s (see above). Ukrainian nuclear power facilities are subject to the full scope of IAEA safeguards, and there is no way Kyiv could so much as start down the pathway without the world knowing.
How does the war in Ukraine affect ongoing and future arms control negotiations between the United States and Russia? (Updated September 9)
Talks are on hiatus.
In June 2021, Presidents Joe Biden and Vladimir Putin met in Geneva and released a joint statement on strategic stability, outlining a path forward for nuclear arms control and risk reduction. Several working groups were established that met over the following months to develop a baseline understanding and to facilitate dialogue on security concerns. The most recent round of talks convened in January 2022 to discuss Russia’s military buildup on the Ukrainian border and Russian proposals for security guarantees.
After Putin’s invasion of Ukraine, U.S. Deputy Secretary of State Wendy Sherman confirmed that, “at this stage, I see no reason for a Strategic Stability Dialogue.” A rupture in relations now, however, does not reduce the need for a dialogue on nuclear risks once tensions have decreased. In fact, Russia’s threats to withdraw from the New Strategic Arms Reduction Treaty (New START) and conduct nuclear strikes only heighten the need to determine explicit rules of the road ahead.
Putin is using his nuclear weapons as a shield to perpetrate a conventional invasion by keeping those who want to come to Ukraine’s aid at bay. Russia’s international isolation is a consequence of Putin’s reckless invasion of Ukraine, but eventually, the parties must come back to the table. Nuclear blackmail cannot be used to establish precedents like a “sphere of influence,” and the way to achieve sustainable guarantees is through hard-nosed diplomacy.
UPDATED SEPTEMBER 9: In early June 2022, President Biden expressed his desire to continue strategic stability talks with Russia despite the war in Ukraine. Mallory Stewart, Assistant Secretary of State for the Bureau of Arms Control, Verification, and Compliance further clarified that, “it’s very hard to figure out how we can sit and think that our diplomacy will be taken seriously on that side.” President Putin similarly made overtures in late June which were promptly contradicted by his press secretary. Thus, dialogue on a new arms control agreement is stymied by political realities.
On August 8, Russia suspended the travel of American inspectors to visit Russian nuclear weapons sites as agreed under the New START treaty. On-site inspections, a critical component of the treaty’s verification’s mechanism, had been suspended since March 2020 due to the Covid-19 pandemic but the United States and Russia had been working to restart inspections in recent months. The Russian foreign ministry claimed that U.S. sanctions impeded the ability of their own inspectors to conduct on-site inspections in the United States. The State Department responded to say that discussions on treaty implementation are kept confidential.
Does the United States have nuclear weapons deployed in Europe?
Yes. The United States currently maintains an estimated 100 tactical or non-strategic nuclear weapons at six NATO air bases in Italy, Turkey, Belgium, Germany and the Netherlands, for use by U.S. and allied aircraft. The weapons are not armed or deployed on aircraft, but instead are kept in underground vaults and the codes to arm them remain in American hands.
The weapons are a part of the U.S. pledge to support the collective defense of allied NATO nations with its own armed forces and, critically, nuclear weapons. U.S. nuclear weapons have been deployed in Europe since the mid-1950s and reached an all-time peak of 7,300 during the height of Cold War tensions in 1971. Although these weapons have minimal effect on U.S. deterrence, they are seen as vital evidence of U.S. commitment to collective security by many allies.
Russian officials, including Foreign Minister Sergey Lavrov on March 1, have long criticized the United States’ deployment of nuclear weapons in Europe as a violation of the NPT. In the negotiations preceding the invasion of Ukraine in December 2021, Russia included the removal of U.S. deployed nuclear weapons in Europe on their list of proposed security guarantees, to which the United States responded that it was prepared to discuss this disagreement.
Has U.S. nuclear deterrence failed?
No. Ukraine is not part of NATO, so the United States is not treaty-bound to intervene militarily on Ukraine’s behalf and does not guarantee to use the U.S. nuclear deterrent to defend Ukraine. The United States does maintain positive security assurances with its NATO allies, in that it promises to come to the aid of one of them, even possibly with the use of nuclear weapons, if they are attacked.
With that in mind, U.S. nuclear deterrence was never on the line in Ukraine, so Putin’s invasion, though abhorrent and illegal, did not somehow crack or subvert the U.S. nuclear deterrent. Likewise, it is false to suggest that if the United States had more nuclear weapons, either in Europe or at home, then Putin would have been deterred from invading Ukraine. Both the United States and Russia currently have enough nuclear weapons to inflict catastrophic harm, so more nuclear weapons would be irrelevant to the United States’ ability to deter Russian aggression in Ukraine.
What happened at the Zaporizhzhia nuclear power plant? (Updated September 9)
No nuclear reactor is designed to operate in a war zone. With indiscriminate use of high explosives in proximity to reactors, as we are currently seeing in Ukraine, there is a serious risk that some of the nuclear infrastructure could be damaged, possibly resulting in radiation releases. Fortunately, such a disaster was averted at Zaporizhzhia.
The shelling of Zaporizhzhia — Ukraine’s largest nuclear power plant with six reactors — is the first time that a civilian nuclear reactor has ever come under military assault. Late March 3 or early March 4, a projectile from Russian forces hit a building within the plant site—not a reactor, but a facility adjacent to the reactor. The shelling caused a fire that was eventually extinguished, although firefighters were shot at trying to get to the facility. The plant is currently under Russian control and reportedly, operators are working at the nuclear power plant at gunpoint. It is important to note that the safety systems of the six reactors at the plant were not affected at all by the fire, and there has been no release of radioactive material. Also, radiation monitoring systems are fully functional.
UPDATED JUNE 6: The situation at Zaporizhzhia is very dangerous. Petro Kotin, Acting President of Ukraine’s state nuclear agency Energoatom, warned that Russia has deployed more than 500 troops, as well as tanks and other military vehicles at the plant, and that they have fired on Ukrainian workers and damaged the facility. Russia is also allegedly storing explosives and weapons on the premises of the facility, and if they were to explode, even accidentally, they could create a nuclear disaster.
In late May, IAEA Director General Grossi warned about the amount of nuclear material at the plant, which reportedly contains 30,000 kilograms of plutonium and 40,000 kilograms of enriched uranium. At the IAEA Board of Governors meeting on June 6, Grossi also expressed concern about the supply of spare parts to the facility and that data on nuclear material at Zaporizhzhia was still not being transmitted to the IAEA.
Russia maintains control of Zaporizhzhia, and the IAEA has been unable to visit the site since the outbreak of the war. The Ukrainian government does not want the IAEA to visit the facility while it is under Russian control because that could be interpreted as international recognition of Russian annexation.
Control of Zaporizhzhia is not just about oversight. While Energoatom has dismissed the idea as “wishful thinking,” Russia plans to connect Europe’s biggest nuclear power plant to its electricity grid. It is theoretically possible for Russia to do so but it would take several years to build a power line and to make effective use of the plant. Zaporizhzhia is currently connected to Ukraine’s electricity grid and at full capacity, it provides about 25% of Ukraine’s electricity. Only two of its six reactors are presently operating.
UPDATED SEPTEMBER 9: The conditions around the Zaporizhzhia nuclear plant remain precarious. After weeks of negotiations and discussions, IAEA Director General Rafael Mariano Grossi led a delegation of IAEA inspectors to the plant on September 1. The inspectors described grave concerns in their report to the UN Security Council which also detailed ongoing issues with the two of six reactors currently operating at Zaporizhzhia.
Ukrainian sources and IAEA inspectors report that shelling continues to affect the plant and the area around it. Both sides continue to blame the other. In August, military activity affecting Zaporizhzhia included strikes that damaged the plant’s fire station (August 11), transitional galleries and laboratory and chemical facilities (August 20-22), and ongoing reports of Russian military units being stationed at the plant. On September 5, the Zaporizhzhia plant again lost its connection to Ukraine’s power grid after the backup power line was disconnected to extinguish a fire. Repairs on the regular power lines are ongoing. The overall effect of military action near the plant seems to be aimed at breaking its connection to the Ukrainian power grid and depriving Ukraine of up to 20% of its electricity.
The uncertainty surrounding the plant’s power supply is extremely concerning. Zaporizhzhia is Europe’s largest nuclear power plant. Interruptions to the reactors’ power supply significantly increases the risk of a nuclear accident. In this context, IAEA inspectors and UN Secretary-General Antonio Guterres called for a demilitarized security perimeter around the Zaporizhzhia plant and called on both Russia and Ukraine to refrain from military activity toward the plant.
What are the risks to Ukraine’s nuclear reactors in the current crisis?
The fuel inside of a nuclear reactor is very radioactively hot. It has to be cooled continuously and the kinds of actions you see in a war can disrupt the cooling of the reactor or even the spent fuel pool. Even if the reactor is shut down, there is tremendous heat. The primary means of getting energy to cool the reactor — the electricity grid, which Russia is presently attacking — is off-site, so the war can impact a reactor without touching the site. Electricity grid attacks are a common tactic in a war and are a possible outcome of uncontrolled missile strikes. Any attack that would cut a reactor off from the grid would raise the risk of a meltdown.
All reactors have on-site diesel generators as a backup, since electricity goes down from time to time, and batteries that can last for a few hours. These generators are not meant to work for long periods of time and would eventually require refueling, which could be difficult in a warzone. More immediately though, in the midst of shelling, there can be a “station blackout” if both the off-site and on-site power goes down. Then, according to Harvard University Professor Matthew Bunn, “the reactor’s cooling would fail and the reactor would melt down, and a radioactive release would be quite likely (though the specifics depend on how well the building holds in the steam pressure and whether hydrogen released from the reaction of the zirconium fuel cladding with high-temperature steam detonates and causes an explosion that shatters the building, as happened at Fukushima, etc.).”
The spent fuel pool also poses a danger because if it loses electricity, the water will eventually boil away and the fuel would melt. The conditions under which radiation would be released really depend on the confinement chamber, how full the pool is and the positioning of hot fuel assemblies. However, the dangers do not simply come from shelling or a direct military assault on the power plant. There could also be something as routine as a fire that could damage back-up cooling systems. These dangers are heightened when firefighters trying to put the fire out are driving through a warzone and are being fired upon, as happened at Zaporizhzhia. A minor nuclear safety threat under normal conditions can be magnified during a war and there is little room for error at a nuclear power plant.
What exactly is a “tactical” nuclear weapon?
Tactical nuclear weapons, included in the category of “non-strategic nuclear weapons,” are generally lower-yield nuclear weapons designed for use on the battlefield or in a “limited” nuclear strike. Nuclear mines, artillery, torpedoes, some gravity bombs and shorter-range ballistic and cruise missile warheads are considered non-strategic nuclear weapons. The United States possesses hundreds of such nuclear gravity bombs while Russia maintains a diverse stockpile of up to 2,000 tactical nuclear weapons.
Because these weapons often come with lower yields and thus less nuclear fallout, they could be perceived as being more “usable.” Regardless of yield, however, the use of any nuclear weapon would come with devastating humanitarian and environmental costs. For context, the bombs the United States dropped on Hiroshima and Nagasaki would be considered “low-yield” nuclear weapons in today’s arsenals. Further, the use of a tactical nuclear weapon risks escalation to a full-blown strategic nuclear war with even wider death and destruction. For many of these reasons, successive administrations reduced the U.S. stockpile following the Cold War. The non-strategic weapons still in the U.S. inventory are primarily to ensure a shared NATO nuclear commitment.
In the current crisis, tactical nuclear weapons have often been mentioned in the context of Russia’s “escalate to de-escalate” strategy in which Russia could consider using a low-yield tactical nuclear weapon in a conventional war to gain a local advantage or stave off an imminent battlefield defeat. Any use of a nuclear weapon by Russia, even a tactical one, remains unlikely at this current moment though, as it would result in severe universal condemnation and risk escalating the conflict beyond Ukraine.
Why is a no-fly zone off the table?
A no-fly zone could place U.S. and NATO aircraft into direct conflict with Russian air forces and possibly escalate into an all out war or nuclear conflict between NATO and Russia. Ukrainian President Volodymyr Zelensky has repeatedly urged President Biden and NATO to impose a “no-fly zone” over “significant parts” of Ukraine. However, the White House, the Pentagon, and NATO quickly dismissed the proposal because of its nuclear implications. Whatever advantages a no-fly zone could convey are more than offset by the risk associated with catastrophic conflict.
Does Ukraine have the tools to build nuclear weapons?
First off, Ukraine does not currently possess the nuclear material for a bomb. During the Obama-era Nuclear Security Summits, six joint cooperation operations between the United States, Ukraine, Russia and the IAEA successfully removed 234 kilograms of Soviet-era produced highly-enriched uranium (HEU) from Ukraine and returned it to Russia where it was downblended to low-enriched uranium (LEU). While HEU can be used to make a nuclear weapon, LEU cannot. All of Ukraine’s HEU was removed by 2012.
Second, Ukraine does not have any enrichment facilities, so it cannot turn its civilian LEU fuel, which it uses to fuel its existing nuclear reactors, into weapons-grade fuel. It would take years and billions of dollars to construct the facilities and to build up the necessary expertise.
Third, Ukraine does not have any reprocessing facilities, so it cannot separate plutonium from the spent fuel of its reactors. While there is plutonium in spent fuel, it is around one percent by weight of the material found in the pool and would need to be chemically separated from the undesirable isotopes, and Ukraine does not have the facilities to do so.
Fourth, Ukraine’s nuclear power facilities are subject to the full scope of IAEA safeguards. Ukraine signed an Additional Protocol with the IAEA in 2006, which means that nuclear inspectors get to visit all nuclear-related facilities to determine that there is no indication of undeclared nuclear material or activities. It is extremely unlikely that Ukraine could divert any material to a clandestine program while the IAEA is so heavily involved in the Ukrainian program, and none of the world’s intelligence agencies have spotted any evidence to support this claim. Ukraine is also a member of the Nuclear Non-Proliferation Treaty, meaning that it has pledged not to pursue nuclear weapons and the IAEA is able to verify this pledge.
Fifth, Ukraine has no missiles or aircraft designed to deliver nuclear weapons. The Soviet nuclear missiles left behind after its collapse were destroyed, so Ukraine would need to either modify existing missiles and aircraft or build entirely new ones to fit such a mission, which would take years.
None of this means that it could not be done in the long term. As is the case for many countries, the obstacles to building a nuclear weapon are high but not insurmountable. However, the world has multiple layers of assurances that Ukraine is not pursuing a nuclear weapon nor does it have the ability to reconstitute its ability to do so quickly. Russia’s >disinformation efforts to fit its pre-war narrative are undermined by the facts.
Could Putin use a nuclear weapon in Ukraine?
Yes, he could, but the likelihood remains extremely low, absent escalation to a wider NATO conflict.
Russia’s formal nuclear doctrine allows for nuclear use only when there is an existential threat to the state. In theory, Putin might authorize nuclear use in response to a nuclear attack or a perceived imminent use of nuclear weapons or other WMDs on Russia and/or its allies. Russia might also authorize nuclear use in response to a strike that would incapacitate its nuclear force structure, potentially hampering its ability to counterattack or to communicate with its nuclear forces. Most concerningly, Russia appears to reserve the right to use nuclear weapons in a conventional conflict “when the very existence of the state is in jeopardy.”
Currently, none of these conditions have been met nor has Russia made any changes to its deployed nuclear weapons on the ground to prepare for nuclear use.
The threshold for nuclear use is not the same for all exotic weapons. While Putin has already employed chemical weapons against political enemies and has used thermobarics and other non-WMD instruments of terror against civilian populations, the calculus for using nuclear weapons is much more complicated.
Using a nuclear weapon in Ukraine, even a so-called “low-yield” or “tactical” nuclear weapon, would be seen as a clear crime against humanity and would cement a place for Putin among the great mass murderers of history. Any leader mindful of his legacy would hesitate at this. The sanctions enacted since Putin’s invasion have already triggered panic in the Russian economy; universal condemnation and far more serious pushback, possibly even militarily, would likely ensue following nuclear use. Putin remains a rational actor, and, unless under existential threat — which he is not currently — should want to avoid a general nuclear exchange.
What is so important about Ukraine to Russia that it would even risk nuclear war?
The reasons behind Russia’s fixation over and invasion of Ukraine are complex and rooted in the Russian government’s own view of its history and role in the world. Simply put, a Ukraine that falls within the Russian sphere of influence is central to Russia’s post-soviet self-definition and represents a critical test of Putinism.
According to the way Russians are taught their history, Ukrainians are a sub-class of Russian, as are Belarussians. The terms Russians use to describe their neighbors (somewhat offensively to Ukrainians) are “people from our border” or “little Russians.” In fact, history’s first identifiably Russian state was centered on Kyiv in the Middle Ages. While the political center shifted north and east, many Russians still see Ukraine’s territory as part of their cultural sphere and are easily convinced that drive for Ukrainian nationhood and national identity is, at least in part, an outside effort to divide and weaken historic Russia. Similarly, Moscow’s preconception that it remains the natural leader of the former empire enhances the priority placed on dominating the former Soviet space.
Moreover, Ukraine’s separation from Russia challenges the post-Cold War narrative that Putin promotes. During the 1990s, Russia’s leadership could have taken a European orientation and moved, as did most other formerly communist states, but instead chose to reinforce a narrative of Russian exceptionalism. European integration would have meant embracing western democratic and social values, which first the Yeltsin government, then that of Putin, chose to define as somehow anti-Russian.
Were Ukraine to join Euro-Atlantic institutions and become more prosperous than its neighbor, its success would not only destroy the myth that Ukraine needs Russian leadership, but would also directly undermine the idea that the former Soviet states are better off without the West.
Putin has also strengthened his own grip on power by embracing the idea that only strong leadership works with Russians, a narrative that imagines their history with the growth of the Russian state paralleled by the growth of autocratic control. According to this view, the 1990s provide proof that democratic governance does not work in the Russian context, and the country has benefited from the subsequent Putin dictatorship.
Given Putin’s view that Ukrainians and Russians are more or less the same people, Ukraine becoming a successful democracy would pose a direct threat to the narrative on which Putin relies to remain in power. Putin had greater tolerance for previous Ukrainian governments that were corrupt and ineffective, but a democratically-elected Zelensky moving his country toward Europe is a danger.
Will Russia or Ukraine use a dirty bomb? (Updated October 25)
There is zero evidence that either Russia or Ukraine will detonate a dirty bomb. These bombs utilize conventional explosives to disperse radioactive material over a given territory. Neither Russia nor Ukraine would benefit from irradiating territory they hope to occupy and/or retain. Similarly, Russia possesses the largest nuclear arsenal in the world. Dirty bombs are both less advanced and less reliable than weapons already in Putin’s possession, and therefore would introduce more risk into his already precarious calculations.
Presently, both sides have accused each other of planning to use such a device as a pretext for escalation. Russian officers at the Zaporizhzhia nuclear plant, which houses spent fuel from nuclear reactors that could be used in a dirty bomb, have not permitted IAEA inspectors and Ukrainian officials to monitor the full range of operations since taking control.