By Jessie Yeung, Adam Renton, Jack Guy, Laura Smith-Spark, Adrienne Vogt, Melissa Macaya and Maureen Chowdhury, CNN
Ukraine's nuclear regulator told the International Atomic Energy Agency (IAEA) there is "no change reported in radiation levels at the Zaporizhzhia Nuclear Power Plant site," the IAEA tweeted on Friday.
Ukrainian officials said early Friday a fire had broken out at the nuclear plant as Russian forces attacked "from all sides," with firefighters unable to reach the site.
Though reports of a fire at Ukraine's Zaporizhzhia nuclear power plant are alarming, there's still a lot we don't know, nuclear weapons expert Jeffrey Lewis said Friday.
So far, radiation monitoring conditions — which were updated just a few minutes ago — look "normal," according to Lewis, director of the East Asia Nonproliferation Program at the James Martin Center for Nonproliferation Studies.
There are radiation detectors "all over the place," that would be able to pick up on any spikes in radiation, he said. "Reactors are big, sealed and concrete structures. They should not catch on fire. We don’t know what caused the fire."
Biggest fear: If a potential fire breaches the containment structure of the reactor, that's when it could get dangerous, Lewis said.
But there should be workers at the site 24/7, who could stop the reactor before the fire reached it, he added.
"The biggest fear would be if the containment zone would be damaged, let’s say, by a missile," he said.
James Acton, co-director of the Nuclear Policy Program at the Carnegie Endowment for International Peace, said the biggest concern was if the fire disrupted the reactors' cooling systems. If they can't cool themselves, the fuel inside could overheat and melt down.
"I’m sure the reactor has been shut off, but the fuel inside is still radioactive and still requires cooling. You have to keep the reactor cool for as long as the fuel is in. The reactor has to be kept continuously cool," he said.
If the cooling stopped, a meltdown could range from taking place in a few hours or days, depending on how radioactive the reactor is.
From CNN's Kaitlan Collins
US President Joe Biden has just spoken with Ukrainian President Volodymyr Zelensky as the White House continues to monitor the reported fire at the Zaporizhzia nuclear power plant.
The Director General of the International Atomic Energy Agency (IAEA), Rafael Mariano Grossi, has spoken with Ukraine's Prime Minister and the country's nuclear regulator about the reported fire at the Zaporizhzhia nuclear plant, the IAEA said on Twitter early Friday.
Grossi "appeals for halt of use of force and warns of severe danger if reactors hit," the tweet added.
IAEA's warning: Earlier on Friday — before the fire broke out — the IAEA released a statement warning that Russian troops were approaching the area and any fighting near the plant could be disastrous.
Ukraine told the IAEA "a large number of Russian tanks and infantry 'broke through the block-post' to the town of Enerhodar, a few kilometres from the Zaporizhzhia Nuclear Power Plant (NPP)," the IAEA said in a statement.
It added that Ukraine's regulatory authority had sent them an "urgent letter," warning that Russian troops were moving directly toward the nuclear plant and the situation was "critical."
In the statement, Grossi had "appealed for an immediate halt to the use of force at Enerhodar and called on the military forces operating there to refrain from violence near the nuclear power plant."
The International Atomic Energy Agency (IAEA) said in a tweet it is "aware of reports of shelling at Zaporizhzhia Nuclear Power Plant," and that it was in contact with Ukrainian authorities about the situation.
Some context: Earlier, the mayor of a nearby town said the nuclear plant was on fire amid intense fighting in the area, with firefighters unable to reach the site. Ukraine's foreign minister said Russian troops were "firing from all sides" at the plant.
From CNN's Kaitlan Collins
A White House official says they are monitoring the Zaporizhzhia nuclear power plant, where Ukrainian officials say a fire has broken out as Russian troops attack "from all sides."
The Russian army is "firing from all sides upon Zaporizhzhia nuclear power plant, the largest nuclear power plant in Europe," Ukraine's Foreign Minister Dmytro Kuleba tweeted on Friday.
"Russians must IMMEDIATELY cease the fire, allow firefighters, establish a security zone!" Kuleba said.
The mayor of the town of Enerhodar said earlier that firefighters are unable to reach the fire, which is ongoing.
From CNN's Jonny Hallam
Firefighters are unable to reach the fire at the Zaporizhzhia nuclear power plant, according to the mayor of the nearby town of Enerhodar, Dmytro Orlov, in a Facebook post.
“The Zaporizhzhia Power Plant is notifying of a threat at the first block of the power plant! The fire at the plant is continuing. The firefighters cannot reach the location of the fire,” he posted.
Earlier, the mayor posted to Facebook saying: "Intense fighting is ongoing on approach routes to the Zaporizhzhia nuclear power plant. Our National Guard fighters are defending. There are victims, but the exact number and condition so far cannot be determined under the circumstances."
From CNN's Hira Humayun
The Zaporizhzhia nuclear power plant in Ukraine is on fire, according to Dmytro Orlov, the mayor of the nearby town of Enerhodar.
“A threat to world security!!! As a result of relentless shelling by the enemy of the buildings and blocks of the largest nuclear power plant in Europe, the Zaporizhzhia nuclear power plant is on fire!!!” Orlov posted to Facebook.
“I demand, stop! Immediately stop shelling the Zaporizhzhya nuclear power plant point blank,” the mayor said in a video message.
In an earlier post he wrote, “stop shelling the Zaporizhzhia power plant".
