- Ukrainian officials warned of an "ecological threat" after Russian troops seized Chernobyl.
- Nuclear experts said they weren't concerned about a major release of radiation at the site.
- Chernobyl has been largely decontaminated and its nuclear reactors are no longer running.
"Our defenders are giving their lives so that the tragedy of 1986 will not be repeated," Ukrainian president Volodymyr Zelensky tweeted Thursday.
In 1986, the core of a reactor opened at the Chernobyl Nuclear Power Plant in Ukraine, sending plumes of radioactive material into the air. The toxic fumes not only contaminated the local vegetation and water supply, but they also poisoned nearby residents, some of whom went on to develop cancer.
Ukrainian officials said Friday on Twitter that radiation levels in the 20-mile exclusion zone, which restricts access to visitors, had risen above normal levels. They added that they couldn't determine the cause of the spike "because of the occupation and military fight in this territory." But experts at Ukraine's state nuclear agency told Reuters that heavy military equipment in the area may have stirred up radioactive dust.
The International Atomic Energy Agency said Friday that the site's radiation levels "remain within the operational range measured in the exclusion zone since it was established, and therefore do not pose any danger to the public."
Nuclear experts told Insider they aren't particularly concerned about a major release of radiation at Chernobyl.
Most of the site has been decontaminated, so foot traffic probably wouldn't release enough radiation to threaten people outside the exclusion zone. Even if Chernobyl were attacked, experts said, its nuclear reactors are no longer running, meaning a conventional weapon couldn't ignite the same kind of explosion witnessed there in 1986.
"There's always the risk of contaminating that zone further, but is it going lead to this large-scale radiological release over a wide area? That's not too likely," Edwin Lyman, director of nuclear power safety at the Union of Concerned Scientists, told Insider.
"I would probably be, at this point in time, more concerned about the conventional weapons dropping on somebody's head rather than an extremely extended footprint of radioactive contamination," said Kathryn Higley, a professor of nuclear science at Oregon State University.
Fire or an explosion would be far less destructive since Chernobyl is no longer an active power plant
Experts said they worried more about an accident in the Chernobyl Exclusion Zone than a direct attack. Russia's presence in the zone is likely strategic, Lyman said, to ensure the safe passage of troops advancing toward Ukraine's capital, Kyiv.
But if a military weapon accidentally struck Chernobyl, the structures or soil could explode or catch fire. Lyman said there are still "hotspots" in the area that contain relatively high levels of cesium-137, a radioactive isotope.
"There's cesium in soil and you don't want to disturb it," he said, adding, "The less you disturb it, the better."
Higley said lingering isotopes wouldn't release as much radiation as the ones present at the time of the 1986 disaster. The most contaminated area of the site, reactor No. 4, is also encased in a metal dome meant to confine its radioactive material for a century. That radioactive material is mostly solidified inside the reactor core, Lyman added.
"With nuclear material, you have to be in a form that is dispersible if it's going to cause this serious, wide-scale radiation release," he said. A modern-day explosion would likely break the radioactive material into chunks instead of airborne particles, he added, meaning it wouldn't travel very far.
A fire could cause the radioactive material to degrade and potentially spread through the air, but even then, scientists don't expect a repeat of the Chernobyl disaster.
"If you're talking about the kind of contamination that was seen when the reactor originally exploded, where it was cemented into the atmosphere and it traveled all over Europe and really around the Northern Hemisphere, that's not likely to occur just from a single explosion," Lyman said.
During the 1986 disaster, the reactor core skyrocketed to 2,912 degrees Fahrenheit, causing the uranium fuel rods inside to melt, along with their zirconium cladding, parts of the reactor such as steel and concrete, and sand that was dumped into the core to extinguish the flames. This created around 100 tons of radioactive "lava" that oozed into rooms below the reactor and hardened over time.
Higley said a conventional weapon isn't capable of creating those same conditions — and the site's metal dome should mitigate some of the fallout.
"When Chernobyl happened, they had a massive steam explosion brought about by the actions in the core and that dispersed material over quite a wide range," Higley said. "If you put a shell [on] something, it just doesn't have quite that same energy."