CNN takes a look at the destruction in Chernihiv, Ukraine 3:46
Chernobyl, Ukraine (CNN) --
The sudden deafening tone of a radiation meter fills the room as a Ukrainian soldier enters.
This is where the Russian soldiers lived at the Chernobyl nuclear power plant, and the radiation levels are now higher than normal.
There is no visible source of the radioactive material in the room, but Ukrainian authorities say it came from small particles and dust brought into the building by soldiers.
"They went to the Red Forest and brought radioactive material in their shoes," explains soldier Ihor Ugolkov.
"Other places are fine, but the radiation increased here, because they lived here."
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CNN gained exclusive access to the power plant for the first time since it returned to Ukrainian control.
Plant officials explain that levels inside the room used by Russian soldiers are only slightly above what the World Nuclear Association describes as natural radiation.
One-time contact would not be dangerous, but continued exposure would pose a health hazard.
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"They went everywhere, and they also took some radioactive dust with them [when they left]," adds Ugolkov.
It is an example of what Ukrainian officials say was the negligent and careless behavior of Russian soldiers while they controlled the site of the 1986 nuclear disaster. The area around Chernobyl, namely the Red Forest, remains the area with the highest nuclear contamination of the planet, with most of the radioactive particles present in the ground.
Ukrainian officials have released drone footage of what they say were trenches dug by Russian soldiers in that area, which is particularly radioactive.
In a safe spot on the edge of that area, CNN saw a box of Russian military rations exhibiting radiation levels 50 times higher than natural values.
A Ukrainian soldier holds up a radiation meter against a package of Russian military rations.
Russian soldiers held Chernobyl for a month and are believed to have been operating in contaminated areas most of the time.
"It's crazy, really," Ukraine's Energy Minister German Galushchenko told CNN at the plant.
"I really have no idea why they did it (go to the Red Forest).
"But we can see that they went in there, the soldiers who went there, came back here, and the radiation level increased."
Although Chernobyl is not an active power plant, the sarcophagus over the reactor that exploded nearly 36 years ago needs maintenance to prevent further radiation leaks.
There is also a considerable amount of spent nuclear fuel that must be taken care of.
"That enclosure is supposed to have electricity, it's supposed to have the ventilation system and so on," explains Galushchenko.
"When the country cannot control this, and we are responsible, Ukraine is responsible for security, of course, that is a threat."
Ukraine's Energy Minister German Galushchenko says Russian soldiers have behaved irresponsibly in and around Ukraine's nuclear power plants.
Part of that threat also came from how Russian soldiers handled those responsible for maintaining nuclear facilities.
[Our staff] were here from the first day of the occupation, and they only had a chance to be replaced a month later," he says. "When people are physically and morally exhausted, when you are under the threat of weapons and you have this daily pressure from the soldiers, it is really a very difficult job.
Volodymyr Falshovnyk, 64, is a shift leader at Chernobyl.
He returned to the power plant on March 20 when the Russian military allowed fatigued personnel to rotate with their colleagues from the nearby town of Slavutych, where many of the plant's workers live.
Volodymyr Falshovnyk, 64, shift chief at Chernobyl.
He says that the staff were working under tremendous pressure, not only because of what was happening at Chernobyl, but also because of the news they were receiving from the outside world.
"Our relatives began to call and say that the city was being taken over, that there were injuries and deaths," he says.
"We asked the Russians what was going on and they said there were no regular Russian troops there, but we kept hearing there was shelling."
Falshovnyk also accused Russian soldiers of looting the power plant.
“They gave us personnel from Rosatom (Russian Nuclear Agency) to escort us, and in their escort we toured the discovered warehouses.
They robbed these warehouses all the time,” he adds.
Russian soldiers ransacked the room where the plant staff slept and looted some of their belongings, says Falshovnyk.
Operating in those conditions was intense, but nothing compared to what the security personnel endured.
The 169 Ukrainian National Guard soldiers guarding the facility were locked in the Cold War-era underground nuclear bunker, crammed into cramped quarters with no access to natural light, fresh air or communication with the outside world, according to the Minister of Internal Affairs of Ukraine.
"They were here for 30 days without sufficient lighting and food. They were not allowed to leave. On the last day they were taken from here to an unknown address," says Denys Monastyrskyy, standing inside the bunker.
The minister says he believes the men were taken to Russia, via Belarus, as prisoners of war, but he does not know for sure.
"Today we know nothing about his fate, unfortunately," he says.
Members of the Ukrainian National Guard were detained by Russian soldiers in the Chernobyl underground nuclear bunker.
CNN showed the interior of the bunker and other places usually occupied by plant personnel, Ukrainian officials claimed that Russian soldiers had looted the place.
Clothing, hygiene items, and other personal belongings were scattered all over the floor.
"The Russian military searched all Ukrainian clothing, personal belongings such as dogs, looking for probably money, valuables, laptops," Monastyrskyy continues.
"There was looting here. The Russian military stole computers and equipment."
Moscow has said very little about what its soldiers did at Chernobyl.
The Russian Defense Ministry last mentioned the nuclear site on February 26, confirming its capture and saying it had made arrangements to ensure the security of power units, the sarcophagus and a spent nuclear fuel storage facility.
Chernobyl is not an isolated case.
Russia takes control of the largest nuclear plant in Ukraine: what does it imply?
8:17
Ukrainian officials say the Russian military's behavior and treatment of Ukrainian personnel at the Chernobyl power plant highlights the danger posed by Moscow's invasion as it gains control of plants in other areas.
In addition to the decommissioned reactors at Chernobyl, Ukraine has four active nuclear power plants, including Europe's largest at Zaporizhia.
The Russian military occupied that facility in early March, when it took control of the area, bombing some of the buildings on the site in the process.
"The situation there is also horrible, especially considering how they captured Zaporizhia because they fired on the station with heavy weapons," says Energy Minister Galushchenko.
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"It's really an act of nuclear terrorism," he adds.
"I'm not even talking about bombing stations as well as a situation at the Zaporizhia nuclear power plant, but when we don't have the possibility to be responsible for nuclear safety, there is a threat."
And even though Ukraine has regained control of Chernobyl, Ukrainian officials fear Russian soldiers may try to return.
“We understand that today we must be prepared for a new attack on a nuclear power plant at any time.
We will use the best world experience to ensure that the station is protected as the border is only a few tens of kilometers away,” the interior minister said.
Monastyrskyy says.
"What we see [in Chernobyl] is a vivid example of outrage at a nuclear facility. It is the responsibility not only of Ukraine, but of the whole world, to keep the stations safe," he says.
"The whole world saw live how tanks fired at nuclear power units [in Zaporizhia]. This history should never be repeated."
Monastyrskyy says that to do that, his country needs continued international support.
"We are ready to invest in the future of Ukraine and in the future security of the world," he continues, repeating his government's call for additional weapons to be sent to Ukraine.
"Today the border between totalitarianism and democracy, the border between freedom and oppression, passes behind our backs," he says.
"We are ready to fight for it."
Daria Markina and Byron Blunt contributed to this report.
Chernobyl Russian invasion of Ukraine
