A Ukrainian expert assesses the possible impact of a military attack on the Zaporizhzhia nuclear power plant

In a recent Bulletin piece, nuclear power experts assessed that a loss of power supply, a human error, or a military mistake could lead to a disaster at the Zaporizhzhia nuclear power plant in Ukraine. Whereas much has been said about the plant’s repeatedly disconnected from the power grid and the daunting working conditions of the staff still at the plant, little is known about Russia’s military capability in and around the plant and their implications.

As the IAEA conducts its risky mission at the embattled nuclear plant this week, the Bulletin talked with Valeriia Hesse, a Ukrainian non-proliferation and international security expert based in Vienna, Austria. We discussed the possible impact on the Zaporizhzhia plant of a deliberate or accidental heavy artillery shelling or missile strike.

François Diaz-Maurin: Do we know the type of weapons Russia is using in and around the Zaporizhzhia nuclear power plant? And do we know where they are hidden on the plant’s premises?

Valeriia Hesse: According to the Ukrainian Ministry of Defense, Russian troops have used barrel and jet artillery in the Zaporizhzhia region. An engineer at the Zaporizhzhia nuclear power plant [ZNPP] commented that Russian forces placed artillery and missile launchers in and around the plant near the Kakhov reservoir. In this case, not only the types of weapons deployed at ZNPP matter, but more so the types of weapons deployed around that could reach the plant’s premises.

The defense intelligence of the Ministry of Defense reported that the Russian military has brought 2C7 “Pion” artillery units to the Energodar region [the city where the ZNPP is located] and is shelling the plant from the village of Vodyane [located 7 kilometers (4.3 miles) south of the plant]. Batteries of reactive artillery (BM-21 “Grad”) are also located there and have a reaching capacity of up to 20 kilometers (12 miles). British intelligence has shown that Russia maintains an increased military presence at the nuclear power plant with armored personnel carriers deployed only some 60 meters from reactor number 5. [Editor’s note: Since Russia seized the plant in March, only two of the six reactors (units no. 5 and 6) have been operating at the ZNPP. On August 25, Ukraine’s nuclear power company Energoatom reported both units were temporarily disconnected from the external power line which led to the subsequent tripping of the emergency protection. On September 1, because of a mortar shelling, emergency protection triggered again the shutdown of unit 5, and a backup power line was damaged.] Plant employees, on the condition of anonymity, have reported that there are four armored personnel carriers and five to six transportation vehicles under overpasses at the plant and some other equipment in the turbine compartments of power units no. 1 and 2. On top of that, the workers confirmed that Russia shot from the plant’s site at Ukrainian drones and at the industrial site and the city of Energodar, all the while accusing Ukraine’s Armed Forces of conducting these attacks.

Diaz-Maurin: What are the exact capabilities of these weapons? For instance, do they have the capacity to penetrate the containment structures which are approximately a one-meter-thick reinforced concrete wall, and subsequently cause an exposure of the reactor’s core?

Hesse: “Grad” is a Soviet and Russian reactive volley fire system (multiple launch rocket system or MLRS) of 122 millimeter (mm) (9K51) caliber. The most common projectile for “Grad” M-21OF (index 9M22U) weighs 66 kilograms (kg) and is equipped with 6.4 kg of explosive in the warhead. The maximum speed of the projectile is 690 meters per second (about twice the speed of sound). The energy of the projectile explosion is approximately 10 kg of TNT equivalent, or 12 kg of TNT equivalent if we consider the increased energy output of modern artillery shells. For its part, the “Pion,” which is also deployed in the region, is a Soviet-made self-propelled artillery installation equipped with a 203 mm caliber gun (2A44). The Pion’s ammunition load includes OF-43 high-explosive fragmentation shells and an active-rocket projectile. OF-43 shells weigh 110 kg and contain 17.8 kg of explosives and travel at a velocity of 960 meters per second. The explosive energy for this projectile is about 30 kg of TNT equivalent, or 35 kg of TNT equivalent for a more modern explosive.

A reactor containment is designed and built in such a way as to withstand enormous internal and external forces. The wall’s strength also has a safety margin, which means it can withstand greater energy than that of the maximum possible design accident. Typically, a reactor containment is designed to withstand the crash of a commercial airplane of over 300 tons at a velocity of 700 km per hour. This means that the reinforced structure could survive an external force of over 70 x 10⁸ Joules, which is equivalent to almost 1.7 tons of TNT.

At the ZNPP, the containment is also supposed to survive a shock wave with a compression pressure in the front of 30 kilopascals (about 4.3 pounds per square inch or 0.3 atmosphere). For comparison, the incident pressure of a Grad and Pion projectile blast at 20 centimeters (less than one foot) would be almost 36,000 and 50,000 kilopascals, respectively. The 30-kilopascal pressure threshold would be reached with an M-21OF blast or OF-43 blast happening only 11.5 meters (37 feet) or 16 meters (52 feet) away from the reactor containment building, respectively.

Surface analysis suggests that heavy artillery, like the one deployed in the region, has a possibility of damaging the reactor containment of the nuclear power plant if there is a deliberate effort to pierce it and successive strikes hit the same area. Physicist Ferenc Dalnoki-Veress from the Middlebury Institute of International Studies told me that the exact pressure per unit area will be different depending on the size and shape of the plane and projectile’s front surface. “You can compare it to poking fabric with a finger to doing it with a needle,” he said. However, if less powerful artillery is used, it is unlikely to cause an exposure of the reactor’s core in a single hit.

Let me add that the containment building is not designed to withstand a missile hit, like those from a Kalibr or Tochka-U. Would one of those missiles hit even 47 meters (154 feet) away from the reactor, it would create a shock wave pressure above the containment design limit.

The problem is that many of these weapons, including Grad, Pion, and Tochka-U, are in service in both Russia and Ukraine, making it possible for both sides to accuse each other. But the plant’s workers and Ukrainian officials have since the beginning denounced Russian forces as being responsible for the shelling at the ZNPP.

Diaz-Maurin: Given the confusion around the plant and in the fog of war, what’s the likelihood of a nuclear disaster happening now at the ZNPP? What are, in your view, the most likely scenarios potentially leading to such a disaster? A failed or deliberate launch of a missile, a drone strike, or else?

Hesse: Let me say this first. Everyone should remember that Zaporizhzhia is an operating nuclear facility. So any military intervention is already critical. The ZNPP is the largest in Europe, and a radiation accident there would be a global catastrophe.

Based on the analysis above, a deliberate heavy artillery shelling or missile strike has indeed a significant probability of damaging a reactor containment. Now, if we speak about particular systems, attack drone payloads like those deployed by Russia in Ukraine (Kub, Lancet, Orion, and Forpost), which have the same explosive energy as small-caliber artillery, have little chance to penetrate the containment and expose the core.

Despite the risk of a nuclear accident, it is implausible that a thermochemical explosion like that at Chornobyl would happen at ZNPP. Two factors (flaws in reactor design combined with human error) led to the accident at Chornobyl. But the ZNPP has a different type of reactor. However, there is a high risk that an accident like that of the Fukushima disaster in Japan could occur.

At Chornobyl, a nuclear criticality accident triggered an intensive steam explosion in the core and release of radioactivity directly into the atmosphere. (The RBMK-type reactor did not have a containment structure.) Whereas at Fukushima, a natural disaster led to the shutdown of the reactor cooling system, and there were no in-core explosions. Instead, heating, oxidation, and the meltdown of the cores happened gradually over time, while the radioactive release was partially confined within the containment. (The partial release was necessary to maintain an internal pressure inside the containment below its design limit.)

In my view, the two most likely scenarios threatening the safety of ZNPP are projectiles hitting a spent fuel storage or the plant’s cooling systems being damaged. Another scenario is to blow up the machine room at the working power units, which is outside the containment building. However, the plant’s staff has claimed to be prepared for such a scenario.

On August 6, the Russian forces hit the plant, with an ordnance landing directly next to the spent nuclear fuel storage area and damaging three radiation monitoring sensors around the site. This already created a threat to the plant’s safety because it impairs timely detection and response in case of increased radiation levels. If Russian forces eventually succeeded in hitting the storage area directly, the spent fuel itself would not cause an explosion, but the blast would disperse radioactive materials into the atmosphere. The degree of the subsequent radiological contamination in Ukraine and neighboring countries would then depend on the weather conditions.

For its part, if the reactor cooling systems come out of order, the fuel will overheat, creating the conditions for a Fukushima-type accident. Even when a reactor is not operational, the fuel components keep decaying, emitting excessive amounts of heat for years after being taken out of the reactor core into a spent fuel storage pool which also requires cooling. In case of the absence of cooling, the overheating damages fuel rods and can cause a meltdown and the release of radioactive isotopes, from short-lived to the ones with very long half-lives, causing immediate as well as long-term damage to people’s health and the environment.

Diaz-Maurin: What about Russia reportedly planning to disconnect the plant from the electrical grid? Would that pose an additional risk?

Hesse: Energoatom’s Petro Kotin warned about Russia’s desire to cut ZNPP off the Ukrainian power grid to connect it to the occupied Crimea and the Russian energy system. The frequencies of the power grids are different, though. Ukraine’s grid uses a frequency that is synchronized with the European grid system. Disconnecting the plant from the Ukrainian grid and connecting it to the Russian one would require a complete—and well-prepared for—shutdown of the plant. It would mean a total cut-off of all power lines connected to the Ukrainian system. Russia has not denied its plan to connect Crimea, and, on August 25, the plant’s workers said Russian forces deliberately damaged the high-voltage power lines that connect the ZNPP to Ukraine’s grid network.

However, for safe operation, a nuclear power plant must continuously transmit the power it generates to the grid system; otherwise, emergency protection systems are activated that shut the reactors down. A blackout also turns the cooling system off, leaving diesel generators as the only system available to continue operating the pumps. This is precisely what happened at the plant on August 25 when all the power lines were cut off due to the ongoing military activity near the plant and automatic safety systems shut down the two reactors (units 5 and 6) that were still operating. After the loss of power, the diesel generators started, and the cooling system continued working, which prevented a nuclear catastrophe. If the generators had failed, without any power supply and thus cooling, the meltdown would have started after only 90 minutes.

Following the incident, Energoatom said both reactors have been reconnected to the Ukrainian grid. However, the generators can run for a limited time in an emergency, and the situation requires restoring the external power supply as soon as possible. The condition of the generators is itself unknown; the IAEA mission will have to check if they are in working condition. There is also a question of how much diesel (fuel) is available on the site.

But a nuclear power plant’s safety also depends on humans to oversee that the automatic systems operate as planned. Let’s not forget that the human factor played a significant role in the Chornobyl accident. Currently, the ZNPP’s staff works under severe Russian pressure on top of almost daily shelling and bombing. Because of this, employees describe the psychological state of the plant’s workers as being critical. This greatly increases the risk of human error.

The ZNPP has been occupied since March 4, and shelling has continued since August 5, creating a multitude of risks at the nuclear facility. On that day, in particular, three projectiles landed right near one of the reactors. There were risks of hydrogen leakage and dispersal of radioactive substances, as well as a high fire hazard. The nitrogen-oxygen station and the combined auxiliary building were seriously damaged. The defense intelligence of the Ukrainian Ministry of Defense also reported that, on August 13, Russian shelling damaged the first unit of a communication workshop of the pumping station and partially destroyed the fire station responsible for the safety of the ZNPP. On top of that, military trucks block access to the turbine areas on the plant, which would impede firefighting in case of emergency. As one can see, the situation at and around ZNPP is volatile and precarious, which poses significant radiation risks due to the militarization of the facility by the Russian occupying forces.

Diaz-Maurin: What can we expect from a UN’s International Atomic Energy Agency mission or a team of outside nuclear experts visit of the ZNPP? To what extent, this could help determine the level of the risks—and reduce those risks—for long as Russia occupies the site?

Hesse: On August 11, Ukraine demanded a declaration from Russia that it accepts the IAEA mission without any preconditions. According to the demand, Russia had to abide not to obstruct the passage of the mission throughout Ukrainian territory, demine the plant, and withdraw its troops, weapons, and equipment from the plant. It took several weeks for Russia to accept the first demand, which it did on August 27. The IAEA mission is currently on its visit to the plant, which is led by IAEA Director General Rafael Mariano Grossi himself.

In August 23, the UN’s Security Council determined that it has the “logistics and security capacity in Ukraine to support any IAEA mission to the [Zaporizhzhia] plant from Kyiv, provided Ukraine and Russia agree.”

Diaz-Maurin: What about a call for withdrawing Russian forces from the nuclear power plant or establishing a demilitarized zone around the plant?

Hesse: Clearly, the only way to ensure the safety of the plant is to remove Russian forces from its premises and establish a demilitarized zone in the surrounding area. This would enable the IAEA team to travel safely to the facility, conduct an inspection, and assess the nuclear safety, security, and application of safeguards at the ZNPP.

However, Russia keeps rejecting such a proposal. It is simply not in their interest because they know that the IAEA’s position is that Ukraine has a sovereign right to the station and surrounding territory. First, Russia is concerned that demilitarizing the plant would make it more “vulnerable,” for example, enabling the IAEA to get control over the plant, which then could give the control back over to Ukraine. Second, the militarization of the ZNPP gives Russia powerful leverage since Ukrainian troops will have a hard time retaking the Zaporizhzhia region if Russian troops set up a military base that Ukraine forces cannot target.

On top of that, the leverage is also in creating provocations at the plant and blaming the Ukrainian side for those. There have also been reports of false flag operations, like when Russians brought a Pion with “Z” inscriptions under a Ukrainian flag to Energodar. All of this is supposed to discredit Ukraine in the eyes of partners and make them pressure Ukraine to negotiate as quickly as possible. The threat of an uncontrolled transborder radiation release potentially reaching other European countries creates this sense of urgency. Third, the ZNPP would be a crucial energy source for occupied Crimea and southern Ukraine. The plant is beneficial for Russia while it is occupying those territories. Additionally, depriving Ukraine from 20 percent of its domestic electricity production creates extra pressure, especially with the anticipated energy crisis this coming winter.

Diaz-Maurin: Some have qualified Russia’s actions as “nuclear terrorism.” What do they mean by that?

Hesse: According to the International Convention for the Suppression of Acts of Nuclear Terrorism (2005), the actor falls under the definition of being a nuclear terrorist if it “uses in any way radioactive material or a device, or uses or damages a nuclear facility in a manner which releases or risks the release of radioactive material: (i) With the intent to cause death or serious bodily injury; or (ii) With the intent to cause substantial damage to property or to the environment; or (iii) With the intent to compel a natural or legal person, an international organization or a State to do or refrain from doing an act.” The text notes that the activities of military forces of states are governed outside of the framework of the Convention. However, it emphasizes that it does not make lawful otherwise unlawful acts or preclude prosecution under other laws.

Earlier, the International Court of Justice’s Advisory Opinion of July 8, 1996, provided another explanation for considering existing international treaties and instruments. These included Additional Protocol 1 of 1977 to the Geneva Conventions of 1949, Article 35, paragraph 3, which prohibits the employment of “methods or means of warfare which are intended, or may be expected, to cause widespread, long-term and severe damage to the natural environment;” Principle 21 of the Stockholm Declaration of 1972 and Principle 2 of the Rio Declaration of 1992, which charge states with a duty “to ensure that activities within their jurisdiction or control do not cause damage to the environment of other States or of areas beyond the limits of national jurisdiction.” These principles apply at all times, being war or peace.

If a catastrophe happens at ZNPP, the consequences would be widespread and have transboundary effects. The threat of an accident at Zaporizhzhia arose because of the actions of the Russian Federation which turned the nuclear power plant into a military object. So if an accident happens, according to international law, it would be an act of terrorism carried out by Russia.

Six months into the war, the least we can say is that Russia’s three-day plan to capture Ukraine did not work out. The losses in equipment and manpower are greater than expected, forcing Russia to move old weapons systems out of retirement and increase the size of its Armed Forces to avoid the so-feared general mobilization. On top of that, sanctions are crippling the Russian economy. Consequently, Russian officials have been using negotiation rhetoric more frequently. For now, Putin wants to settle the status quo now that Ukraine’s position has been strong and even pushing to regain territory. But any negotiation on the status quo will only be a temporary solution until Russia regains power and decides to proceed further. That is why the world must hold Russia responsible for committing acts of nuclear terrorism, continue pressing Putin to de-militarize the plant, and avoid making any concessions to the aggressor.