Wargame shows attacks on reactors would cause meltdowns and military paralysis

For more than a year, nuclear experts have wrung their hands about the risk of radiological releases from the Zaporizhzhia nuclear power plant in southeastern Ukraine and how best to prevent them. More than 15 months into the war, though, Russian attacks against Ukraine’s nuclear plants have released no radiation. This may be no accident. So far, Russian President Vladimir Putin has avoided destroying Ukraine’s nuclear power plants. Otherwise, they would have been demolished long ago. Instead, Putin has aimed to damage them and Ukraine’s electrical supply system as part of a larger effort to erode Ukrainian morale.

His strategy is unlikely to be a one-off. North Korea and China also have “wayward provinces”—South Korea and Taiwan, respectively. And they have long-range missiles too. Beijing and Pyongyang have considered targeting reactors. How these countries might, if at all, follow Russia’s example depends on what they make of Putin’s current assaults against reactor sites.

Reactors in warzones. When he launched his full-scale invasion on February 24, 2022, Putin hoped Ukraine would immediately surrender. His initial aim wasn’t to disable Ukraine’s reactors or electrical supply systems but to seize them. And he did: On the first day of the invasion, Russian forces took control of the Chernobyl nuclear plant, and in early March they seized the Zaporizhzhia nuclear plant. Russia’s invasion, however, quickly stalled. As a result, Putin changed his strategy: He directed his military to shell the plant sites and electrical power nodes critical to powering the plants’ coolant pumps and safety equipment. Russian agents also kidnapped and terrorized plant workers, which jeopardized Zaporizhzhia’s safe operation. In addition, Putin stepped-up attacks on the rest of the Ukraine’s electrical supply system to frighten the Ukrainian population further, undermine its will to resist, and possibly destabilize the entire grid, including the nuclear portions of the electrical supply system. So far, these efforts have had mixed results: Some senior officials in NATO countries have been rattled (fearing radiation leaks and military escalation); the Ukrainians, however, have not.

Certainly, Russia’s willingness to take advantage of the military vulnerabilities of nuclear sites in Ukraine has set a precedent. It is unclear if any other nation would make the mistake Russia did in assuming that it could easily seize and hold an adversary’s nuclear facilities at the very outset of hostilities. If not, they might move to Russia’s second stratagem of militarily holding the electrical supply system and its nuclear plants at risk right away. How might such a war proceed? Might Russia aim to knock out the grid, strike Ukrainian nuclear plants, and risk major radiological releases? Might it target NATO reactors (which could include more than 50 US-promised plants in Poland, Romania, and Ukraine by 2037)? How might Ukraine, the United States, and NATO members respond?

To answer these questions, the Washington-based Nonproliferation Policy Education Center (NPEC) designed and hosted a wargame. The game assumed Russia will re-invade Ukraine 15 years from now—in 2037—when both sides will have substantial numbers of long-range, accurate missiles and drones. It also assumed Ukraine and Eastern NATO countries will have new reactors of US design on their territory. In November and December of 2022, NATO officials, American hawks, American doves, Ukrainians, Romanians, nuclear experts, US military officials, and Polish experts were all tapped to prepare, critique, and play remotely over a two-week period.

The game’s play revealed how the uncertainties and dangers of military attacks against nuclear power plants can paralyze decision-making and fundamentally alter the course of wars. The military disruptions these uncertainties introduce may far outstrip the safety issues any reactor radiological release might otherwise present. The game’s play revealed three reasons why.

The US and its allies are unprepared. Overseas adversaries can easily target allied or friendly nuclear power plants in ways that the United States and its allies are unprepared for. What was stunning throughout the game’s play was the reluctance of the players—other than those representing Ukraine and Poland—to act even after Russian military assaults were made against nuclear power plant sites in Ukraine and NATO countries. The United States team, for example, waited and then failed to extract US personnel at reactor sites that Russia had hit in Ukraine and that were leaking radiation. Only after Russian missiles had induced a loss of coolant at one of Ukraine’s Khmelnitsky Westinghouse reactors and threatened to do the same to nuclear power reactors in NATO countries did the NATO team take decisive action. This consisted of supplying the targeted plants in Ukraine, Poland, and Romania with active defenses and auxiliary emergency cooling equipment.

In the game, nuclear expert team members gave contradictory advice to each of their teams about how well any of these reactors would fare against aggressive military assaults. This was unexpected but turned out to be significant. Radiological leaks were detected but assessments of these leaks’ implications for public safety were only hastily made after the reactors were hit. These assessments also varied widely and were responded to quite differently by each team. The Ukrainians ordered a massive evacuation after Russia struck one of its reactors; Poland, whose reactor site also was hit but was releasing no radiation, took no public safety steps until they detected a radiation cloud from Ukraine drifting over Polish territory.

Although war planners prefer to devise precise, proportionate diplomatic, political, and military responses, this is difficult to do amid ongoing attacks against nuclear plants. The reason why was made evident in the game: The nuclear experts in the game rendered very different assessments of what was happening and how dangerous the assaults on plants might be to the surrounding population. There was a tendency among NATO members, who wished to stay out of the fight, to downplay the safety implications. It was just the opposite among the countries at greatest risk of being painted with radiation. This suggests that such “differences” in threat perception might not be quickly resolved through some technical nuclear forensic assessments of events. The creation of international norms or nuclear safety zones in war zones, meanwhile, may be desirable but are extremely difficult to attain. As such, the risks and benefits of adding new nuclear plants in high-risk war zones must be reassessed.

Reactor attacks can paralyze allied responses. The hesitation of the United States in responding to military assaults against friendly countries’ reactors can risk near-fatal fracturing of US security alliances. In the game, NATO countries closest to the fighting (e.g., Poland) wanted to join Ukraine in conducting deep strikes into Russia against key staging bases that were launching attacks against Ukraine’s reactors. Initially, some NATO countries were sympathetic to Ukraine striking Russia. All NATO members were concerned that matters might escalate and spill over into NATO territory. As a result, NATO was ready to invoke Article 4 of the NATO treaty, which authorizes NATO members to bring issues of concern to the attention of the organization.

Eager to avoid direct military contact with Russia, however, key members of NATO decided to manage Poland’s desire to back Ukrainian strikes against Russia by invoking Article 5. NATO did this less to support military operations (much less to attack Russia) under Article 5, as to deter any independent action Poland might otherwise take against Russia. In the game, the tactic worked: NATO members, including Poland, were deterred from striking Russia. This tactic, however, failed to deter Kyiv. Ukraine unilaterally struck airbases deep in Russia. This action only further amplified the different concerns of NATO members near the action and those of members located farther back.

Such alliance strains can only be addressed in one of two ways: The reactors either must be defended actively or passively so well that radiological releases and electrical failures appear nearly impossible, or alliance war plans and responses must be devised and agreed to in advance and be sufficiently dramatic to deter such attacks. Neither will be easy. As for developing tailored deterrence strategies, the most relevant analogy here may be “pre-planning” to deal with nuclear weapons attacks—a vexing, dubious undertaking at best.

Legal disagreements about reactor attacks. Attempts to settle the question of whether military assaults against nuclear plants constitute war crimes or if subsequent radiological releases qualify such attacks as nuclear weapons use can themselves become significant wartime distractions. In the game, Ukraine insisted that Russia’s attacks against reactors constituted an actionable war crime under Protocol 1 of the Geneva Convention. Ukraine and others also claimed such assaults constituted first use of nuclear weapons.

These claims divided NATO players. They subsequently not only delayed actions critical to waging the war, but also prompted Ukraine to act unilaterally in an escalatory action, firing missiles deep into Russia without NATO’s support. This is worth avoiding. Both NATO members (except the United States) and Russia have ratified Protocol 1 of the Geneva Convention, which specifically discourages assaulting nuclear power generating stations. Yet current US legal guidance regarding Protocol 1 is murky. Although the United States is obligated as a signatory to Protocol 1 to avoid attacking nuclear power reactors, Pentagon lawyers insist US commanders should ultimately be free to attack these plants if they think it is necessary. It would be helpful if the US view was clarified and brought into line with the strong presumption of US allies against making such attacks.

Yet another divisive issue is what constitutes first nuclear use. In the game, European NATO members sympathized with Ukraine’s contention that Russia’s “intentional” attacks against nuclear plants that consequently released radiation should be considered a “use” of nuclear weapons. The United States ignored this assertion. Yet another unresolved legal question is whether or not radiation that contaminates NATO soil from an intentional Russian attack of Ukrainian reactors should constitute an actual attack on NATO and, therefore, demand an Article 5 response. The players were briefed on this point but chose not to play it. Here, again, some European NATO public officials have supported the idea, whereas the United States has taken no position.

Wargame format. The wargame consisted of three moves. The first began in 2037. Putin’s successor launches a second invasion of Ukraine, and the Russian military assaults and occupies the four-unit Khmelnitsky plant, which now has been expanded to include two US-built reactors in addition to the two Soviet-design VVER reactors. In the second move, the situation escalates and several missiles explode in the parking lots of nuclear power plants in Romania and Poland and hit several supporting emergency diesel generators. The game’s last move was a “hot wash” in which the group discussed the simulation and the players’ key findings.

Wargame participants were organized into three teams representing the United States, Ukraine, and NATO-EU nations. The control team oversaw communications, managed the scenario, and represented Russia. Teams responded to the crisis, communicated with other teams to gather information, negotiated, and created a response strategy and contingency plans.

Move one. It is 2037. Putin is dead. His successor, frustrated by the “forced, unjust” armistice reached with Ukraine in 2024, attempts to complete Ukraine’s absorption, launching an attack against Ukraine’s southern and western salients. Westinghouse has completed two of its promised US reactors in western Ukraine at Khmelnitsky, which are operated with the assistance of US technicians. Additional US and South Korean power reactors have been built as promised in Poland and Romania and are now on line.

After several weeks of fighting, Russian forces assault and occupy the Khmelnitsky plant and garrison missile strike forces at the reactor site. The Ukrainians precisely target Russia’s missile units at Khmelnitsky using weapons the United States has shipped to Ukraine. Russia protests publicly, demanding NATO cease supplying such weaponry through Poland and Romania.

Meanwhile, in a repeat of the tactics Moscow used in 2022 against Zaporizhzhia, Russia fires missiles knocking down several power lines into the Khmelnitsky plant. This threatens the continued reliable supply of external electricity to the plant, which is needed to prevent the reactors’ cores and spent fuel pools from overheating and releasing radiation.

Spooked, nearby Romania and Poland (both NATO and EU nations) urge their populations to avail themselves of stockpiled iodine pills. Meanwhile, Russia and Ukraine blame each other for targeting the felled power lines. Then, a missile fells the last external power line connected to the plant, forcing it to run on its emergency diesel generators, which at the time only have enough fuel to operate for ten days.

This sets off international alarms. The director general of the International Atomic Energy Agency (IAEA) warns that the latest attack could result in a Fukushima-like radiological release unless the agency can gain access to the facility and assure proper safety measures are being taken. Fighting near the plant, however, makes it dangerous to access. Nonetheless, in a repeat of 2022, the IAEA manages to send a team of inspectors to help “stabilize” the plant and avert any radiological release.

Unfortunately, the opposite situation unfolds. While the IAEA staff are en route, the Russian military bombs and disables the main paved corridor to the plant. One of the Russian strikes glances an IAEA vehicle, injuring an inspector. Russia indignantly denies any responsibility but joins Ukraine and the IAEA in calling for an emergency meeting of the UN Security Council.

NATO fears Russia will use its military garrison at Khmelitsky to strike the surrounding areas with impunity. The US team cautions that fighting near the plant could cause a radiological release and ultimately a meltdown.

Advisors to the US Energy Department recommend that the US-designed AP1000 and Russian-designed VVER spent fuel be transferred from the pools to dry cask storage. They also warn that further military assaults on Ukraine’s nuclear plants could produce radiological releases that would force the evacuation of communities both within and beyond Ukraine’s borders. Most NATO advisors, however, deem the immediate probability of a major radiological release to be low.

Russia then attacks some of the diesel fuel storage tanks at the Khmelnitsky plant, leaving the plant with only several days’ worth of diesel fuel to run the emergency generators. Shortly after, Ukraine releases a video providing evidence of Russia’s responsibility for the attacks.

Ukraine calls for the IAEA to mediate a shipment of diesel fuel to the plant’s site to prevent a meltdown. The United States and its NATO allies support this request. The United States demands that Russia move its missiles out of the reactor site and create a demilitarized zone around the plant. Ukraine confirms the presence of US Westinghouse personnel at the Khmelnitsky plant, but they are unable to leave the site.

NATO advises the United States that the long-term threat of a radiological release is growing and asks Ukraine and Russia to shut down the last operating reactor at the site. NATO believes that shutting the plant entirely is a reasonable request and suggests enlisting China and the UN Security Council to pressure Russia into doing so. In response to these requests, Russia puts the reactor on normal shutdown mode and demands that the United States de-escalate the situation by ceasing to send arms to Ukraine. When asked to ensure the security of the IAEA inspectors, Russia agrees.

Ukraine asks the United States and NATO to issue a joint press release stating that Russia’s actions were an intentional effort to trigger a meltdown of one of the Khmelnitsky nuclear reactors, that Russia’s attacks of the plant constitute a war crime, and that the allies view any event involving radiological dispersal as an intentional use of a “nuclear weapon” by Russia against Ukraine. Washington is hesitant to grant Ukraine’s request and confers with key NATO members regarding its position. NATO consensus, however, was impossible to achieve. A key concern was that backing Ukraine’s position would undermine any opportunity to negotiate with Russia.

Disappointed, Ukraine issues its statement independently and makes its own military plans to regain control of the plant. For this purpose, Kyiv asks the United States and NATO for precision missiles, drones, electronic warfare equipment, and satellite intelligence—to which they both agree. Ukraine also asks the United States and NATO for tools and transformers to restore external electrical power to the plant, as well as Western experts to monitor the plant’s safety and the security of the plant’s staff. The United States and NATO demur and instead suggest the IAEA assume this role and that UN peacekeepers and the Red Cross be placed in and around the nuclear plants.

Washington, then suggests a hedging strategy. First, it asks NATO to pressure Russia to demilitarize a zone around the plant. Second, it asks NATO for help positioning troops, diesel fuel, and emergency generators at the border with Ukraine. NATO agrees and positions counter-battery radar, counter-battery missiles, and troops near the Ukrainian border in Southern Poland. NATO also puts troops on a 24-48-hour recall alert system to allow them to quickly deploy where needed. It also puts its Combined Biological Radiological Nuclear (CBRN) forces on standby.

Several NATO members believe Russia’s aggression against the Khmelnitsky plant constitutes a significant security risk. They raise this issue but defer to the United States on whether to invoke Article 5. Washington is not ready to do so.

Move Two. Fighting in and around the Khmelnitsky plant continues. Russia warns Ukraine’s reckless targeting of Khmelnitsky risks a Chernobyl-like radiological release.

Meanwhile, Ukraine’s counteroffensive against Crimea gains ground. As Ukrainian forces close in on Sevastopol, Ukraine discovers that Russia intends to launch a false flag attack against a small research reactor at the Sevastopol National University of Nuclear Energy and Industry. Russia fires a missile damaging the reactor, prompting a limited, local release of radiation. Moscow immediately accuses Ukraine of having attacked the reactor with NATO-supplied weaponry and again demands that Romania and Poland close their borders to any further deliveries of US and NATO-supplied offensive weapons. Moscow further warns that failure to seal the border will result in Russia taking “proportionate” action against Poland and Romania.

Before NATO or the UN can meet, several missiles explode in the parking lots of the US NuScale reactor in Romania and of the Westinghouse AP1000 and Korean KEPCO APR-1400 reactors in Poland. Poland and Romania temporarily shut down these plants. Meanwhile, Ukrainian forces push Russian troops out of key positions in Crimea. Panicked, Moscow announces it will target Poland and Romania further unless they immediately stop all military equipment transfers into Ukraine. The United States, NATO, and Ukraine try to confirm Russia’s culpability for the strikes in Poland and Romania as a majority of NATO members are unwilling to attack Russian forces until there is proof of an imminent attack.

While NATO awaits definitive intelligence, Ukrainian technicians at the Khmelnitsky nuclear plant worry that they may soon run out of diesel fuel needed to run the emergency electrical generators. To replenish their diesel stocks, Ukraine asks NATO to deliver fuel to Khmelnitsky. The United States, concerned about US Westinghouse employees unable to leave the Khmelnitsky plant, plans to use the extraction of its personnel as an opening to also bring fuel to the generators.

Ukraine again calls for the United States and other NATO member countries to condemn Russia’s attack against nuclear power reactors as a war crime under Protocol 1 of the Geneva Convention and insists it constitutes a first use of nuclear weapons. Shortly thereafter, overhead surveillance confirms that the missiles that struck Romania and Poland were fired from Russian-occupied Crimea. European NATO members, sensing Washington’s general reluctance to invoke Article 5, are uncomfortable doing so but fear Poland, who is closest to Ukraine geographically and politically, might now strike Russia unilaterally. They want to invoke Article 5 to prevent this and the expansion of the war that might follow if Russia is struck.

Ukrainian leaders, meanwhile, feel NATO has abandoned them. They begin planning a retaliatory strike against Russia. Initially, some Ukrainian officials privately advocate striking Russian nuclear reactors, natural gas infrastructure, and urban and political centers. They drop this suggestion, though, for two reasons. First, it is unclear how hitting these targets will bring victory. (Ukraine had too few long-range strike systems to take this expansive target set on.) Second, striking them would undermine Ukraine’s position that striking power reactors is a war crime. For these reasons, any Ukrainian strike against Russia is limited to military targets.

Farther to the west, Ukraine continues its plans to retake the Khmelnitsky plant. As fighting intensifies near the plant, all power to the plant is lost when unidentified missiles hit these reactors’ dedicated emergency diesel generators. Within hours, battery backup power for the reactors’ instruments is also lost.

Fire trucks are not available to provide emergency cooling. Ukrainian experts have no access to the plant, but they assess there is now only enough convective cooling to prevent meltdowns for a day or so at the VVER reactors and perhaps a bit more for the AP1000 units. As for the spent fuel pools, these should remain stable for at least a week.

The United States moves backup power generators and diesel fuel to Ukraine’s border. US troops accompany these shipments. Russia warns that if NATO troops enter Ukraine, it would constitute an act of war against Russia. The US troops and power backup equipment do not cross the border. The US plan to rescue the Westinghouse employees also falls by the wayside as the crisis escalates, leaving US citizens trapped at Khmelnitsky.

After three days, meltdowns occur within all the reactors. However, at one of the two the AP1000 reactors, things spin even further out of control. Not only does the automatic, passive water-cooling reserve system runs out and radioactive steam and hydrogen build up; but because there is no external electricity flowing into the plant, the AP1000 reactors’ electric hydrogen igniters cannot be used to “burn” off the hydrogen. An accidental spark at one of the AP1000 units prompts an explosion. This produces a major breach of the reactor’s concrete containment and a significant atmospheric radiological release. Ukraine calls for a ceasefire to allow evacuation. Russia does not respond to this request.

The AP1000 reactor’s radiological release upsets Ukraine’s military plans to retake the Khmelnitsky plant. Frustrated, Ukraine decides to retaliate against Russia with a major long-range missile strike against Russian Black Sea fleet bases, including the base at Novorossiysk, well within Russian territory. Ukraine’s objective is to make a “proportionate” military strike against valued Russian military bases.

At the Khmelntisky plant, shifting winds push the plant’s leaking radiation towards Poland, prompting some officials to recommend evacuating Rzeszow and Lubin. Ultimately, this course is rejected and instead Polish authorities ask the citizens to stay-at-home. NATO also considers delivering air defense systems, including Patriot and THAAD units, to Ukraine. These would protect its nuclear plants and act as a first-line defense for the rest of Eastern Europe. Ukraine, though, is unaware of these NATO deliberations. Ukraine, still believing NATO has abandoned it, asks Poland to conduct joint military operations against Russia.

Russia learns about NATO’s plan to send air and missile defenses into Ukraine and warns that, if these systems cross the border, they will become a legitimate military target. At this time, unidentified missiles hit diesel generators at the Polish plant and at the Romanian CANDU reactors. Russia claims again that this is Ukraine’s doing. NATO, including the US team, decide to go ahead with the deployment of air defense units to Ukraine, despite Russian warnings. NATO and the US team also deploy air and missile defenses, fire trucks, emergency electric generators, and diesel fuel stocks at all the nuclear plants in Poland and Romania. Washington forward-bases B-21 bombers to Poland and Romania to deter further Russian aggression, invokes Article 4, and asks NATO to invoke Article 5.

From this point on, events unfold rapidly. The players have difficulty managing what ensues.

Ukraine asks NATO for additional intelligence, missiles, and drones so Ukraine can strike the Russian staging bases that attacked Poland and Romania. Some frontline NATO countries are sympathetic, but the United States and several legacy NATO members refuse to support such attacks.

Meanwhile, NATO-provided air and missile defense systems cross the border into Ukraine. In response, the Russians target them. Russia hits most of these air and missile defense systems after they cross the border. Russia hits one, however, while it technically is still in NATO territory. Further to the south, the radiation spewing from the Khmelnitsky plant forces Russian troops to begin to evacuate the site. At this point, Ukrainian forces decide to move in to open up a corridor for fire trucks to reach the reactors. However, their progress is stalled by Russian forces.

Eager to take action, even without US or NATO support, Ukraine then launches a missile strike against the Russian strategic bomber airbase at Engels, which intelligence shows is a source of many airstrikes against Ukraine. Ukrainian missiles disable the air base’s runways, fuel farms, and long-range bombers.

Per its previous warning that any strike against its territory would constitute cause to place its nuclear forces on high alert, Russia does so. The United States, United Kingdom, and France respond in kind and NATO formally invokes Article 5 but does not take immediate military action. Instead, the United States proposes providing support to a Ukrainian offensive against Crimea, leaving open the option of direct US military involvement if that offensive is unsuccessful.

Game play ends at this point.