Russia's Defense Ministry said it might have to shut down the Zaporizhzhia nuclear power plant after accusing Ukraine of shelling the facility.
Kyiv has denied attacking the nuclear plant, which is the largest in Europe and has been occupied by Russian troops since March.
"I haven't seen any confirmed evidence whatsoever of any shelling by the Ukraine military on the plant itself," said Shaun Burnie, nuclear specialist at Greenpeace East Asia, who was in Ukraine last month to monitor the Chernobyl nuclear site.
But Igor Kirillov, head of Russia's radioactive, chemical and biological defense forces, said in a briefing that the plant's backup support systems had been damaged as a result of shelling. He added that radioactive material could spread across Germany, Poland and Slovakia in the event of an accident.
Three of the plant's four transmission lines were reportedly "down" as of last weekend, most likely because of attacks, Burnie said. If the remaining transmission line were to fail, it would leave the plant vulnerable to losing grid power, which significantly increases the risk of a meltdown.
The plant's backup diesel generators and batteries remain insufficient to cool not only the six reactors, but large pools of highly radioactive spent fuel, Burnie said.
"It's an incredibly serious situation," Burnie said.
Russia has been widely accused of using the plant as a shield from which to launch attacks. Ukrainian President Volodymyr Zelenskyy called Russia's actions a kind of "unconcealed nuclear blackmail."
Using the plant in this way violates the Geneva Convention, which states that particular care must be taken if "installations containing dangerous forces" are located near fighting. About 500 Russian troops are reported to be currently at the site.
"The facility must not be used as part of any military operation," UN Secretary-General Antonio Guterres said in a statement after a meeting of the Security Council last week. "Instead, urgent agreement is needed at a technical level on a safe perimeter of demilitarization to ensure the safety of the area."
So far, no serious damage or radiation release has been detected and there is "no immediate threat" to the safety of the plant as a result of fighting. But "this could change at any moment," International Atomic Energy Agency head Rafael Grossi told the UN Security Council on August 12.
Russia to disconnect plant from Ukrainian grid?
Ukrainian state electricity provider Energoatom has accused Russian occupying forces of attacking the Zaporizhzhia nuclear plant with the goal of disconnecting it from the Ukrainian power grid.
"Artillery shelling of the Zaporizhzhia NPP is a terrorist act intended to destroy the plant's infrastructure, disrupt all of its power lines that feed electricity into Ukraine's power grid and cut off power in the south of the country," Energoatom wrote in a Telegram post on August 6.
Thursday's threat to shut down the plant aligns with the view that Russia might try to connect the plant to the grid in Crimea, which it occupied in 2014, and potentially to the Russian Federation, Burnie said.
At its peak, the Zaporizhzhia plant alone supplied 10% of energy to Ukraine. "It's a strategic asset for the Russian military," Burnie said.
Nuclear safety 'violated' by Russian occupiers
Concern has been mounting that the plant is not being sufficiently maintained.
"[It is a] violation of every possible nuclear safety measure that you can imagine," Grossi told DW on July 29.
"Is it true that there is explosives and other material stocked near the reactors?" he asked of reports that missiles and other weapons could be launched from the site, with counterattack impossible because of the extreme threat of an accident.
Grossi is also concerned that the Ukrainian staff who are under the command of the Russian occupiers at Zaporizhzhia are unable to properly carry out their duties and have faced threats of violence.
He said necessary equipment, including spare parts for maintenance of the reactors, was not being delivered because of interrupted supply chains.
"We are not sure the plant is getting all it needs," he told the AP news agency, adding that the situation is "completely out of control."
Local staff needed
Burnie said it was vital that trained local staff maintain their positions and can work safely at the nuclear site. While Russia has more than twice as many reactors as Ukraine, most are older models, meaning that their engineers don't have the expertise to run the newer technology in Zaporizhzhia, he said.
Local staff will also be needed in the event of the regular flooding from the Dnieper River, which flows through the vicinity of the Zaporizhzhia plant and could damage the dams and reservoirs that provide the cooling water for the reactors.
His team discovered a contaminated exclusion zone riddled with landmines — which stopped effective monitoring of the area. In addition, vital monitoring equipment in the Chernobyl plant had been destroyed, damaged or stolen during the Russian military occupation.
Ukrainian Foreign Minister Dmytro Kuleba renewed calls for the IAEA to send a mission to the plant to as soon as possible to monitor the situation. Russian UN Ambassador Vassily Nebenzia said IAEA officials could visit the site as soon as this month.
"I have been trying to put together a technical mission led by myself to go there to address a number of issues," Grossi told DW at the end of July. This will be difficult if fighting continues.
Edited by: Jennifer Collins
This article from August 3 last updated on August 18 to include the latest news about reported shelling at the nuclear power plant and potential Russian plans to shut down the plant.