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On Sunday, for the first time since November 2022, the Ukrainian nuclear power plant in Zaporizhzhia, in the south-east of the country, was at the center of a military operation: a downed drone crashed into the building that houses one of the six reactors of the plant . The news immediately caused concern from the International Atomic Energy Agency (IAEA), which recalled that any military operation near a nuclear power plant could cause a serious radioactive leak.
The risks of an accident in a power plant like the one in Zaporizhzhia are, however, extremely limited, although comparisons are very often made with the Chernobyl disaster, which occurred in Ukraine in 1986. The chances of a disaster of a similar magnitude occurring in Zaporizhzhia too are ruled out by virtually all experts, but the possibility of a minor accident cannot be ruled out.
The Zaporizhzhia Nuclear Power Plant (often abbreviated to ZNPP, an acronym for Zaporizhzhia Nuclear Power Plant) is the largest in Europe. It has six nuclear reactors, which before the war produced half of all Ukraine’s nuclear energy and about a fifth of the entire country’s electricity needs. The power plant is on the banks of the Dnipro River, near the town of Enerhodar and 50 kilometers as the crow flies from the city of Zaporizhzhia, the capital of the region of the same name. Between the city and the power plant passes the front line that divides the Russian troops from the Ukrainian ones: the ZNPP is therefore under the control of Russia, but it is very close to the front line.
Since September 2022, the plant has stopped producing electricity, and five of its reactors have gradually been put into “cold shutdown”, a state in which the number of reactions within the radioactive fuel is reduced to a minimum and the temperature in the reactor drops below that of boiling water at ambient pressure, typically around 90°C.
One of the reactors, number 4, was instead maintained throughout the winter in “hot shutdown”, to guarantee heating to the nearby town of Enerhodar. When a reactor is in this state, the nuclear reactions that take place inside it are still capable of heating the water to boiling temperature: consequently it is more important that the cooling system remains operational.
In his latest reportpublished on April 4, the IAEA said that with the end of the cold season, reactor number 4 could also soon be put into operation cold shutdown. “It is a favorable choice from a safety point of view, but it does not eliminate the fact that the ZNPP remains in a highly precarious situation,” IAEA Director Rafael Grossi said.
A Russian soldier guarding the plant in May 2022 (AP Photo, File)
One of the main security weaknesses in the power plant is the cooling system. Without the electrical energy necessary to circulate water in the systems, uncontrolled steam production and therefore an explosion could occur. Since the power plant no longer produces electricity, the cooling system is powered by two external power lines, which are in turn connected to the Ukrainian electricity grid (this is because, although the power plant is controlled by Russia, connecting the power plant to the Russian system active in Crimea would first require a complete shutdown of the system, a long and complex operation).
Since the beginning of the war, the power plant has suffered eight partial or complete blackouts due to the interruption of these lines during fighting on the front or Russian bombing. The result has been to cause new alarm among Ukrainian and international authorities each time. However, the plant is equipped with modern safety systems, including emergency diesel generators, which make the risk of an explosion remote. Even the permanence of the reactors in “cold shutdown” greatly limits the dangers.
Another accident possibility is one caused by an intentional attack leading to a breach in the containment structure and thus the exposure of a reactor and the radioactive material it contains. The reactors, as well as part of the spent radioactive fuel depots, are protected by imposing concrete structures capable of withstanding even the crash of a medium-sized aircraft.
Several experts, however, they doubt that these structures can resist attacks from the most modern weapons, such as ballistic missiles and large-caliber artillery, especially if these attacks were repeated. But even in the worst case scenario, it is almost impossible that an attack or accident on the power plant could generate continental-scale effects, as happened in Chernobyl.
In the case of Chernobyl, a series of human errors and design flaws caused the complete destruction of the reactor and the building that contained it and produced a fire that lasted for eight days, a major factor in the spread of radioactive material over great distances.
In the case of the ZNPP, the exact extent of contamination would depend on the type of accident, the size of the breach and atmospheric conditions, such as whether or not there was wind. In case of an episode particularly seriousthe city of Zaporizhzhia, which before the war had 750 thousand inhabitants, could also end up involved.
While Ukrainians and Russians blame each other over the latest attacks, it is unclear who would have an advantage in willfully causing a nuclear accident with unpredictable consequences. But the possibilities of a mistake cannot be ruled out.
The plant has already been at the center of chaotic fighting. On March 4, 2022, the complex was occupied by Russian troops after a firefight involving only the administration buildings. In the following summer, the Ukrainians attempted to liberate the power plant and the nearby town of Enerhodar by initiating several amphibious attacks from across the Dnipro River.
In the autumn of 2022, several witnesses reported the presence of Russian heavy weapons within the perimeter of the plant. During that period, the most intense bombing of the facility occurred, and there were the latest episodes of damage to the reactor containment buildings, as in Sunday’s attacks.
Since then, the situation seems to have improved. A group of IAEA technicians is constantly present at the plant and the access they have to the various buildings in the complex has steadily increased over the months. The director of the agency, Grossi, often goes personally to inspect the plant, and in his latest visit he said that there was no evidence of the presence of heavy weapons in the complex.
But Grossi also reminds us that the situation remains precarious and can easily get worse. One of the most widespread fears among experts is that of an accident caused by the precarious conditions in which the plant operates. Not only because of the air raid alerts, bombings and frequent blackouts, but also because of the pressure to which the Russian occupiers subjected the plant’s staff. Only a part of the Ukrainian workers who worked at the plant at the time of the occupation retained their jobs. Many fled due to interrogations, threats and the requirement to accept a Russian passport. Technicians who have left the plant and some of those who still work there describe a climate of constant pressure that complicates their work.
Russia’s nuclear energy company, Rosatom, has sent numerous employees to fill gaps in ZNPP’s workforce. But according to its Ukrainian counterpart, Energoatom, the staff in charge of the plant is insufficient and does not have the adequate training to manage the modern safety systems installed in recent years.
In this context, some experts are more concerned about a slow degradation of the power plant caused by poor maintenance, with unpredictable long-term consequences, than by an immediate accident which, deliberate or not, seems relatively unlikely for the moment.