When Russia first occupied the Zaporizhzhia nuclear power station in early 2022, the Ukrainian operator Energoatom reported that Russian forces had likely mined the compound. After the nearby Kakhovka dam was destroyed in early June — purportedly by Russian military forces — Kyiv announced that Russia had also placed land mines in the power plant's cooling ponds.

Now, military staff in Ukraine have warned that Russian soldiers have supposedly also affixed "objects resembling explosives" to two blocks of the power plant.

In late June, the International Atomic Energy Agency reported that it had found no indication of mines or other explosives at the power stations. IAEA Director General Rafael Mariano Grossi has announced that agency experts now require access to further parts of the power plant to conduct a more thorough inspection and rule out the presence of any explosives.

Cooling system is Zaporizhzhia's weakest spot

Olha Kosharna, a Ukrainian nuclear safety expert, has emphasized that placing land mines in the most important cooling segments poses a direct threat to the power station. She added that the water in the cooling pond played a decisive role by cooling the fuel rods within the reactor, thus preventing them from melting by overheating.

The Zaporizhzhia nuclear power plant is made up of six blocks, which have been out of operation since last fall. Five blocks are in "cold shutdown" — a state in which they no longer generate electricity.

Dmytro Humeniuk of Ukraine's State Scientific and Technical Center for Nuclear and Radiation Safety explained that while the reactors must still be cooled, as the fuel rods are still emitting heat, the water cannot be vaporized. If the cooling system were to be destroyed, water could escape, and the expert estimated a nuclear accident would occur within eight days.

According to experts, the sixth reactor is still in "hot shutdown," in which power units generate thermal power — although the IAEA had ordered its cold shutdown four weeks ago. If this is the case, the cooling water can reach 280 degrees Celsius (536 degrees Fahrenheit) and would evaporate in the event of a leak. This would leave experts just 27 hours to prevent radiation from escaping.

"I think all this blackmail and all these threats are happening to halt Ukraine's counteroffensive in the region," said Kosharna.

Is a disaster like Fukushima possible?

Experts believe a detonation in any part of Zaporizhzhia's cooling system could lead to a disaster such as the one in Fukushima, Japan. In 2011, an earthquake and subsequent tsunami interrupted the cooling sequence of three reactors of the Fukushima Daiichi Nuclear Power Plant, resulting in a core meltdown that released radiation.

"Following this, an evacuation zone was established which people had to leave. Three years later, they returned due to the low radiation, and now, the zone has been reduced to one-third,” said Mark Zheleznyak, a visiting professor with the Institute of Environmental Radioactivity at Fukushima University.

Zheleznyak believes the risk potential at Zaporizhzhia is smaller than it was in Fukushima. "There wouldn't be a radiation disaster, because a shutdown block cannot emit radioactive iodine," he said, advising against succumbing to panic and buying iodine tablets meant to protect the thyroid gland against radioactive iodine.

How much of the surrounding area is at risk?

Ukraine's Center for Nuclear and Radiation Safety has developed two possible scenarios in case of a nuclear accident at the Zaporizhzhia plant.

In the first scenario, the 1-meter-thick (3.2-foot) protective encasing of the reactor stays intact, while the facility beneath it melts. This could be the case if the power went out completely, or the cooling systems were damaged. Experts estimate that in such a scenario, an area of about 2.5 kilometers (1.6 miles) surrounding the power plant would be contaminated with radiation.

"Basically, this would only affect the staff working at the power station," the center said in a recent statement, adding that these people would have to leave the area. "Iodine prophylaxis is not necessary."

The other scenario considers a nuclear accident accompanied by a damaged protective shell. "In this scenario, radiation would affect a much wider radius and have far more serious consequences. The contaminated area would depend on weather conditions," the center explained.

Ivan Kovalets is an expert in environmental modeling at the National Academy of Sciences in Ukraine. He has calculated that, depending on wind force and direction, an area of up to 20 kilometers (12.5 miles) surrounding the nuclear plant could be heavily affected.

"In this case, immediate evacuation would be required," said Kovalets. Even people living as far as 550 kilometers away from the power plant could face certain health risks. "At such distances, however, there is no need for immediate countermeasures or evacuations," he added.