Chernobyl cooling systems have lost power but meltdown risk is low

A power outage at Ukraine’s Chernobyl nuclear power plant has knocked out spent fuel cooling systems, leading to a potential risk of overheating and releasing dangerous levels of radiation. But due to the age of the fuel, it should be safe until power is restored.

The International Atomic Energy Agency (IAEA) reports that several Ukrainian electricity substations were hit by Russian military strikes, causing power outages in Chernobyl. “The IAEA is actively monitoring developments to assess the impact on nuclear safety,” IAEA Director General Rafael Grossi wrote in an article on X.

Spent nuclear fuel from reactors continues to emit radiation for years, creating heat that must be vented or the fuel can melt and emit a dangerous spike of radiation. Fuel from the old Chernobyl reactors is stored in a large cooling basin that is constantly replenished with fresh, cold water to keep its temperature low.

But without electrical power – which the IAEA says the site now lacks – this cooling has stopped, which will allow the water temperature to rise and increase the rate of evaporation.

“When fuel comes out of a reactor, it will be hot for a while, because there will be fission products and there will be radioactive substances that will give off gammas, betas and alphas – just emitting energy, which has to be removed, otherwise it will eventually melt,” says Paul Cosgrove of the University of Cambridge.

But what works in Chernobyl’s favor is that its stored fuel is older and has therefore already had time to emit much of its radioactive energy and cool down. The risk is now lower than it was in 2022, for example, when New scientist reported similar power outages at Chernobyl.

“It’s always a worry when a nuclear site loses power, but the worry about nuclear risks is often orders of magnitude greater than the risks associated with other events with similar consequences,” says Ian Farnan, also at Cambridge.

Chernobyl Reactor 4 exploded in 1986, but Reactor 2 was shut down in 1991, Reactor 1 stopped producing electricity in 1996, and Reactor 3 – the last at the site – was decommissioned in 2000.

The exact specifications of the storage pools that hold the remaining fuel from Chernobyl’s reactors remain confidential, Cosgrove says. But he is aware of an inspection by regulators in 2022, which found the risk of spent fuel overheating in a power outage was low. “This fuel has been sitting in there for 20 years, so it’s decomposed. More and more of that energy will be gone,” he says.

Electricity supplies to Chernobyl – and indeed much of Ukraine – have been up and down since Russia’s full-scale invasion. But in recent months, Russia has increased its attacks against Ukrainian infrastructure.

The Chernobyl blackout is the latest in a series of Russian actions that have compromised nuclear security, including occupying Chernobyl for several weeks and preventing staff from properly maintaining it, taking control of the Zaporizhzhia nuclear power plant in a similar but long-standing manner, and striking the New Safe Containment building, which covers the ruins of Chernobyl Reactor 4, with a drone in February last year.