Fighting at the Zaporizhzhia nuclear power plant in Ukraine: what should we be worried about?

The past week has seen shelling around the Zaporizhzhia nuclear power plant in Ukraine, which has been occupied by Russian forces for nearly six months. Ukrainian President Volodymyr Zelenskyy has recently agreed to a mission from the International Atomic Energy Agency to the site (the Russians haven’t yet), while the Turkish President Recep Tayyip Erdogan is voicing fears of “another Chernobyl.”

How risky is the situation, really? Things are certainly very dangerous, but the prospects of something on the scale of “another Chernobyl” are unlikely. Cosmos investigates.

What’s happening at Zaporizhzhia?

“It’s very much in the middle of an active war zone,” says Tony Irwin, technical director of SMR Nuclear Technology and chair of Engineers Australia’s Sydney division nuclear engineering panel.

Prior to March no civilian nuclear power plant had ever been attacked by a foreign army. Since Zaporizhzhia’s capture on 4^th March, the plant has been administered by Russia, but still operated by local Ukrainian staff.

“The staff really are under extreme pressure,” says Irwin.

“I feel very sorry for the operators, as an ex-operator myself – it’s a very difficult situation. And they’ve got to get on and off site through an area that’s a war zone.”

Zaporizhzhia (pronounced za-poh-ree-shia) is the biggest nuclear power plant in Europe. The site has six reactors, two of which are still operating. The other four have been put into “cold shutdown,” described by Irwin as “the safest state to be in”.

“It means you’ve stopped the nuclear reaction. The fission reaction’s stopped, and you’ve cooled down the reactor to less than 100 degrees, so not so much heat is being produced in the reactor.

“You still have to supply water to keep the reactor cool, because there’s still this decay produced, but you don’t have to supply so much water.”

Prior to early August, conditions around the plant had been relatively stable. But in recent weeks, the facility has come under fire again with both Ukrainian and Russian forces saying the other side has escalated hostilities.

The IAEA has been monitoring the plant remotely, but has received conflicting information from both sides and wants to send a mission to the site to investigate in person. It hasn’t been able to do this since the invasion started.

Ukraine has three other active nuclear power plants, all of which remain under its control.

What are the safety risks?

Nuclear power plants are designed with extensive fireproofing and multiple redundancies in their systems in case any equipment fails or is destroyed. But the situation at Zaporizhzhia is novel.

One of the biggest concerns is electricity. Should electrical supply to the plant fail, it could trigger a meltdown of the reactors.

“They’ve only got one of the four external transmission lines now in service, plus they’ve got a backup line from a local plant,” says Irwin.

Nuclear power plants have diesel generators on-site in case of electrical failure, but these are also vulnerable to fire – and they need a fuel supply to work.

“I don’t know how they’re getting on with the logistics – to get essential materials in and out of the plant, like diesel fuel supplies and spare parts.. That could be a problem,” points out Irwin.

Damage to the reactors themselves is unlikely to cause trouble – but again, not impossible.

“These are pressurized water reactors with substantial concrete containment, so that they are pretty good at being able to withstand those sorts of attacks, ” says Irwin.

The Chernobyl reactor which exploded in 1986 was an RBMK reactor, which uses a very different design to the pressurised water reactors currently used in Ukraine.

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Read more on Chernobyl: Safety risks at Russian-captured nuclear power plants

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Irwin thinks the worst-case scenario is a meltdown similar to the 1979 Three Mile Island accident in Pennsylvania, US. This accident had a partial meltdown of a reactor core, but there was only slight lift in background radiation, and there has not since been any evidence of unusual health trends in the area.

“It’s definitely not a Chernobyl-type explosion. I don’t think it’s even a Fukushima-type release,” says Irwin. “But it’s not a good situation.”

In response to the Russian attack and subsequent extinguished fire on 4^th March, the IAEA outlined Seven Pillars of safety and security at nuclear power plants – including things like physical integrity, logistical supply chains, and reliable communications with the regulator. All of these seven pillars have been breached at some point during the occupation.

What is the IAEA planning to do?

Ukraine has agreed in principle to an IAEA mission to the power plant, but Russia has not.

Such a mission would have three aims.

“The first one is nuclear safety, to see that the plant is being safely operated – which obviously is a concern at the moment – to have a look at the physical state of the reactors and the equipment,” says Irwin.

The second aim is to undertake safeguards to “verify that nuclear material is used only for peaceful purposes”, according to the IAEA’s statement.

“The IAEA regularly do inspections on all nuclear power plants, to make sure that nuclear material is under safeguards and is not being diverted for other purposes,” says Irwin. Remote data suggests that the material is still under these safeguards, but “they want to do a physical inspection of nuclear material to make sure it is as they think”.

The third aim is establishing that the nuclear plant is secure.

“Is the plant secure? Is nuclear material on the plant secure?” explains Irwin.

The IAEA performed a similar mission at the decommissioned Chernobyl plant, after the Russians abandoned it.