The sheer scale of nuclear disasters can be difficult to fathom. To that end, the Banana Equivalent Dose is used for context; for example, the fallout after Chernobyl was equivalent to eating 6.48 trillion bananas. When Zaporizhzhia Nuclear Power Plant (ZNPP) was shelled in April 2022, a month after its occupation by Russian forces, Volodymyr Zelenskyy said the potential catastrophe “could have been as bad as six Chernobyls.” In short, that’s a lot of bananas. But how comparable are the two plants, and should there still be concern about ZNPP’s status? 

Chernobyl was built by the Soviets between 1972 and 1977 using RBMK reactors, an archaic model with graphite moderators and water coolants, whereas ZNPP’s modern VVER reactors use water for both purposes. Any reactor employing water as a coolant generates steam, a less efficient neutron absorber than water. In modern reactors, more steam results in less neutron slowing, decreasing reactor power and functioning as an overload prevention measure. RBMK reactors, however, responded to excess steam by generating positive feedback loops, which were partially responsible for the chain reaction at Chernobyl. ZNPP’s VVER reactors, combined with steel-cased concrete reinforcements, make it far less prone to accidental meltdown than Chernobyl, yet instigating one is not out of the question.

Five out of six reactors in Zaporizhzhia are operating in a “cold shutdown” state, which is indefinitely stable if reactors stay cooled. Unit Four, however, remains in “hot shutdown”, a more accident-prone state even when consistently cooled and de-energised. ZNPP relies on water sprinkler cooling ponds connected to each reactor to maintain both states, which were reconstructed after the destruction of the nearby Kakhovka dam. These ponds could still be drained or blocked, destabilising the reactors and causing a chain reaction. Even in a cooled, reinforced state, a direct strike could be catastrophic; opening a reactor in hot shutdown could cause the fuel to slowly melt through its surroundings, causing a Fukushima-type event. 

While alarming, this wouldn’t be realistic unless, as William Alberque of the International Institute for Strategic Studies points out, “they guard it to make sure that no one can do anything about it for a couple of weeks and the fuel builds up and then explodes.” However, Kyrylo Budanov, director of Ukranian intelligence, is not so sure. Russia could gain access to plant controls and manually disable cooling, or power up the reactors and dangerously raise energy levels. “Technical means could be used to speed up the catastrophe,” Budanov states. The two agree that any attempt to engineer a meltdown requires total occupation of the plant.

Currently, though, Ukraine’s level of control over ZNPP is unclear, even to International Atomic Energy Agency regulators placed on site. While technically still operated by Energoatom, Ukraine’s nuclear energy agency, Russia’s counterpart Rosatom has become a de facto joint operator, with Russian troops permanently stationed around ZNPP. Last October, the plant’s Ukranian Director General was briefly detained, and other workers have been detained with increasing frequency. The IAEA’s director has flagged conditions as unsatisfactory, urging Energoatom to install an external boiler that would enable all six units to enter cold shutdown. Even though Ukraine’s national regulator has issued a similar order, construction has still not begun, an indication of Rosatom’s influence.

Though ZNPP is built to withstand accidents, it is not immune to attack. Eight blackouts have already occurred on site, forcing reactors to run on emergency diesel generators. By creating unstable operating conditions, Russia has shown it is not afraid of playing cat-and-mouse with Europe’s largest nuclear power plant. If they did bite, it could cause a disaster far greater than Chernobyl.