But the Russian nuclear experts seemed to hold little sway over the army commanders, he said. The military men seemed more preoccupied with planning the assault on Kyiv and, after that failed, using Chernobyl as an escape route to Belarus for their badly mauled troops.
“They came and did whatever they wanted” in the zone around the station, Mr. Simyonov said. Despite efforts by him and other Ukrainian nuclear engineers and technicians who remained at the site through the occupation, working round-the-clock and unable to leave except for one shift change in late March, the entrenching continued.
The earthworks were not the only instance of recklessness in the treatment of a site so toxic it still holds the potential to spread radiation well beyond Ukraine’s borders.
In a particularly ill-advised action, a Russian soldier from a chemical, biological and nuclear protection unit picked up a source of cobalt-60 at one waste storage site with his bare hands, exposing himself to so much radiation in a few seconds that it went off the scales of a Geiger counter, Mr. Simyonov said. It was not clear what happened to the man, he said.
The most concerning moment, Mr. Simyonov said, came in mid-March, when electrical power was cut to a cooling pool that stores spent nuclear fuel rods that contain many times more radioactive material than was dispersed in the 1986 catastrophe. That raised the concern among Ukrainians of a fire if the water cooling the fuel rods boiled away, exposing them to the air, though that prospect was quickly dismissed by experts. “They’re emphasizing the worst-case scenarios, which are possible but not necessarily plausible,” said Edwin Lyman, a reactor expert at the Union of Concerned Scientists.
The greater risk in a prolonged electricity shut off, experts say, was that hydrogen generated by the spent fuel could accumulate and explode. Bruno Chareyron, laboratory director at CRIIRAD, a French group that monitors radiation risks, cited a 2008 study of the Chernobyl site suggesting this could happen within about 15 days.