Inside a laboratory in Kharkiv, Ukraine, sits an experimental device innocuously named the Neutron Source, containing several dozen pounds of enriched uranium — enough, if it were scattered, to contaminate much of the city.
The lab building lies just 14 miles from the front line of Europe’s largest war in eight decades, and Ukrainian authorities say the structure has been damaged by Russian munitions 74 times.
“It’s scary but we are used to it,” said Oleksandr Bykhun, a deputy chief engineer at the Kharkiv Institute of Physics and Technology, Ukraine’s premier nuclear research center, which houses the Neutron Source.
Much of the atomic fear stoked by Russia’s invasion of Ukraine has focused on the Zaporizhzhia nuclear power plant, Europe’s largest, held by Russian forces since early in the war. But Ukraine has a long list of vulnerable nuclear facilities, like reactors for research or power generation — including Chernobyl, where the world’s worst nuclear accident occurred — and storage sites for spent fuel.
The longer the war drags on, the greater the risk of a strike that could spread radioactive material across a wide area. Some of the sites have extensive security measures, but they were not built to take a direct hit from a large bomb.
“It’s a situation which is very dangerous, and we are lucky that no nuclear accident occurred yet,” said Bruno Chareyron, scientific adviser to the Commission for Independent Research and Information on Radioactivity, a French nonprofit group.
The radiation dangers began on the first day of the invasion in 2022, when Russian forces entered Ukraine through the Chernobyl zone, stirring up dust laden with small but detectable traces of plutonium, cesium isotopes and other radioactive elements, and risking a strike on the plant.
In February 2025, a Russian drone blew a hole in the stainless-steel confinement structure over the radioactive ruins of Chernobyl’s No. 4 reactor. While no radiation escaped, the strike broke the hermetic seal around the structure.
The Zaporizhzhia plant has been struck repeatedly, but each time disaster was averted. In 2023, an explosion at a river dam drained the primary source of cooling water for the plant’s six reactors, forcing a pivot to a backup cooling pond. The site now relies on two electrical transmission lines, one of which is periodically severed by fighting.
Russian structures have also been caught in the crossfire. Late last month, debris from a Ukrainian drone shot down by Russian air defenses damaged a transformer station near the Kursk nuclear power plant, forcing its operators to dial back output.
Ukrainian officials have accused Russia of intentionally endangering nuclear sites and raising the specter of a nuclear catastrophe that could contaminate a wide swath of the continent. The drone strike on Chernobyl came the night before the Munich Security Conference opened in Germany, timing that some Ukrainian and Western officials interpreted as a message from Moscow.
The Kharkiv physics institute, which helped design the first Soviet atomic bombs, agreed to stop working with weapons-grade uranium in 2010, sending its stockpile to Russia at the urging of the United States in the name of nuclear nonproliferation. It still stores extremely dangerous materials, like the uranium in the Neutron Source, enriched to be much more radioactive than the fuel used in a nuclear power plant. The institute does not disclose exactly how much uranium is on site.
The device consists of two elements: a core about the size of a school bus together with its metal radiation shields and an attached, about 90-foot-long particle accelerator. The United States partly funded construction in exchange for Ukraine’s surrender of its bomb-grade uranium.
The building housing it has been damaged so many times by drones, rockets and artillery that it could not be an accident, Ukrainian authorities say. They have charged five Russian military officers for targeting it, in an indictment that says a direct hit could contaminate an area where about 640,000 people live. Ukrainian prosecutors accused the officers of “ecocide,” or attempting to damage the environment as a tool of war.
The exterior of the building was not built to withstand attack. Detonations outside rattle the control room daily. Inside, the shock wave from an explosion knocked plaster from a wall near the device.
In 2022, a transformer station was hit, plunging the building into darkness for months. Scientist relied on backup heating to prevent cooling water from freezing and potentially damaging the aluminum coating on uranium fuel rods.
“I just don’t understand what we are dealing with,” Andriy Mytsykov, a chief engineer at the physics institute, said of the attacks. “They do this without any logic.”
After the 2022 invasion, scientists halted experiments and put the Neutron Source into a long-term shutdown mode. But the uranium remained, along with the danger of a release.
Elsewhere at the institute, the scientists continue fusion energy experiments with radioactive hydrogen, despite daily attacks on Kharkiv. They collected sufficient data for a paper they plan to present at a conference this fall, said Mykola Azaryenkov, the institute’s acting director.
“They hit us,” he said, and “we get up and go back to work.”
Andrew E. Kramer is the Kyiv bureau chief for The Times, who has been covering the war in Ukraine since 2014.
David Guttenfelder is a Times visual journalist based in Minneapolis.
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