For weeks, Russian troops occupied the damaged Chernobyl nuclear power plant. An insider report now describes these weeks between two dangers: enemy soldiers and radioactive waste. The fourth part describes how the Ukrainians worked together after the blackout in Chernobyl to keep critical supplies running.

Even decades after the explosion, Chernobyl still harbors risks. The molten nuclear lava inside the destroyed reactor remains unstable. The concrete sarcophagus protecting the reactor was designed to last no more than 30 years – now it’s 35 years old and showing the first cracks and fractures. His condition is constantly monitored. According to Olena Parenyuk, a researcher at Chernobyl, it’s unlikely, but not impossible, that a shift in the elemental composition could set off a chain reaction as the lava continues to break down.

Other risks are also present. About 22,000 spent fuel rods, left over from when the reactors were still in operation, are still hot. If not properly refrigerated, they can burn through their containers and release nuclear radiation. The fuel rods were previously stored underwater and are now being moved to a different location where they can be stored more safely under helium. So far only 12% has been withdrawn.

Another danger comes from the radioactive waste that Chernobyl recycles, to put it mildly, from its own decommissioned reactors and Ukraine’s four remaining nuclear power plants. Most of this waste is stored in metal drums buried in concrete. If the kegs are moved, there is a risk that they will be damaged and leak. A “dirty bomb” could even be made from the contents.

Three high-voltage lines supply Chernobyl. The technicians need power to monitor and cool the nuclear debris. If the power fails, the risk of a leak increases. I asked Parenyuk about the greatest of all possible dangers. She shakes her head: “It’s like asking which organ in your body is most at risk when you stop breathing.”

On March 9, the power went out in the power plant. Nobody knows why. Perhaps there was damage from the fighting or from sabotage. Although emergency power generators were available, the fuel was only enough for 24 hours. The Russians were informed by the Ukrainian side that the supply would last 12 hours. “If an accident occurs,” Semenow told an officer, “you are responsible for it.”

Vitaly Tymofeev is a good-natured former liquidator in his 60s who worked with four colleagues in the liquid nuclear waste reprocessing department. In a windowless building, they mixed radioactive water with cement and hardened it in steel drums. The most dangerous thing, he told me, was cleaning the cement mixers.

On the day the Russians occupied the facility, a batch of 16 barrels was ready to be taken away. The ventilation system used to cool the nuclear waste was shut down when the power went out. It took three days to figure out how to connect it to a generator. Radiation levels are believed to have increased during this period, but this could not be detected because, four weeks later, the Ukrainians were still unable to replace the dosimeters used to take the measurements.

Electricians were sent to fix the power line. The territory outside the exclusion zone was difficult to cross: Russian and Ukrainian checkpoints alternated; occasionally there were fights. Misunderstandings reigned between the Russian soldiers and the Ukrainian electricians. The electricians first refused a Russian military escort, then they demanded one.

Several attempts were made to fix the problem, but the damage could not be located and reached; it was unclear whether it was one or more disorders. On the third day of the blackout, power was restored for two and a half hours around noon. Just 15 minutes after Ukrainian television announced the news that the power plant was back online, the power went out again.

Employees were forced to prioritize electricity supply: electric heaters and superfluous appliances were switched off. Kutenko’s team slept in their parkas. “We were unlucky that it was very cold at the time, down to minus eight degrees at night,” he says. They “smelt very badly because we worked hard and sweated,” but hot showers were considered an unnecessary luxury.

The hungry generators had to be refilled almost constantly – every three hours during the day and every five hours at night. The Russian troops sent for diesel tankers, but their nozzles were too wide for the generators, so the fuel had to be transferred to 200-litre oil drums before it could be filled. “We pumped by hand, which kept us a little warm,” reports Kutenko.

There was also no electricity in Slavutych, where the families of Chernobyl workers live. But the city is a place of engineers, and an old gas station was quickly restored to provide energy. Cables were connected to solar panels on the museum’s roof, allowing people to charge their phones and connect – albeit slowly – to the internet. Local residents chopped firewood and built barbecue areas in their gardens. “In this war, all our people were united, we became one family,” Father Ioan, the town’s Orthodox priest, told me.

The article first appeared in The Economist entitled “The inside story of Chernobyl during the Russian occupation” and was translated by Charlotte Zink.