An earlier version of this article incorrectly gave the distance between the Chernobyl nuclear complex and Kyiv as six miles. It is about 60 miles.
Both sides vied for control of Ukraine’s biggest nuclear power complex Monday. Russia’s Defense Ministry was quoted in state-run media as saying its forces had taken control of “the territory around” the nuclear power complex in Zaporizhia. “The plant personnel are continuing to service the site and control the radioactive situation as usual. Background radiation levels are normal,” the defense ministry said.
However, Ukraine’s state-owned firm Energoatom said the Russian claim was false. The International Atomic Energy Agency said that “additional information” from the operator of the reactors confirmed Russian forces were “operational near the site but had not entered it.”
While a direct attack on Ukraine’s nuclear infrastructure seems unlikely, experts raised the alarm that an inadvertent strike by a missile or air attack could trigger a disaster.
“It is extremely important that the nuclear power plants are not put at risk in any way,” said the IAEA’s director general, Rafael Mariano Grossi. Without naming the catastrophic Chernobyl accident, which took place four decades ago, Grossi said that “an accident involving the nuclear facilities in Ukraine could have severe consequences for public health and the environment.”
The Zaporizhia complex, 140 miles up the Dnieper River from the Black Sea, has six reactors, more than any other location in Ukraine’s nationwide fleet. Three of those are among the reactors disconnected from the grid.
Nuclear experts also said they feared fighting might accidentally damage the pools used for cooling spent fuel, posing a greater danger than any potential threat to the well-constructed vessels designed to protect the reactors’ cores. The open pools, which resemble regular swimming pools, are inside buildings that are not as robust as other structures.
“The largest radioactive inventories remain the spent fuel pools,” said Mycle Schneider, a Paris-based consultant and a member of the International Panel on Fissile Materials.
Operators often disconnect reactors to reduce the amount of heat they generate. Frank von Hippel, a senior research physicist and professor of international affairs emeritus at Princeton University’s program on science and global security, said that “when a reactor is operating, each ton of fuel is generating about 30 megawatts of heat.” Disconnecting it decreases the generated heat to about 300 kilowatts, lowering the required amount of cooling water by a factor of a hundred.
But disconnecting reactors from the electricity grid does not guarantee safe conditions and does not the need for electrical power, experts cautioned. If the grid is damaged or fails, the reactors must turn to standby diesel generators.
“All reactors need power to stay safe. That does not stop with the disconnection from the grid,” Schneider said. “Residual heat remains enormous in the core.”
“We’ve never seen a full-scale war in a country that operates nuclear facilities,” he added. “You can’t just decide to shut them down.”
Edwin Lyman, director of nuclear power safety at the Union of Concerned Scientists, said, “It’s in no one’s interest to have any of those plants damaged, but sometimes things spiral out of control.”
Earlier, Russian forces had seized control of the decommissioned Chernobyl nuclear complex about 60 miles from the capital, Kyiv, and 10 miles from the Belarus border.
A meltdown took place at Chernobyl’s Unit 4 in 1986, spreading radiation across a swath of Belarus, Russia and Ukraine and ultimately leading to 28 deaths in four months and the eventual evacuation of hundreds of thousands of people from an 18-mile exclusion zone. The last of the four reactors there was shut down in 1999.
But the pools are still used to cool Chernobyl’s spent fuel rods, including 20,000 fuel assemblies that are being transferred from storage pools to more protective double-walled dry storage canisters designed to last 100 years, according to the U.S. Nuclear Regulatory Commission. Lyman identified those pools as the area “that would need a relatively high degree of attention.”
Other parts of nuclear reactors can withstand substantial impacts.
The IAEA said Sunday that missiles hit the site of a radioactive waste disposal facility in Kyiv overnight, but there were no reports of damage to the building or any indications of a release of radioactive materials, Grossi said in a statement. Staff members at the facility were forced to take shelter during the night.
The incident came a day after an electrical transformer at a similar facility near the northeastern city of Kharkiv had been damaged, but there were no reports of a radioactive release. “Such facilities typically hold disused radioactive sources and other low-level waste from hospitals and industry,” the IAEA said.
Nonetheless, Grossi said, “these two incidents highlight the very real risk that facilities with radioactive material will suffer damage during the conflict, with potentially severe consequences for human health and the environment.” He said that “once again, I urgently and strongly appeal to all parties to refrain from any military or other action that could threaten the safety and security of these facilities.”
Before Russia’s attack, Ukraine had explored having U.S. firm Westinghouse build four more nuclear reactors. Westinghouse has already been providing some nuclear fuel, previously supplied by Russia.
“The lesson from this is that these facilities are different and more complex than other sources of electricity generation,” Lyman said, “and they do have additional risks.”
An earlier version of this article incorrectly said the International Atomic Energy Association instead of the International Atomic Energy Agency. The article has been corrected.