Russia cut power to defunct Chernobyl nuclear plant, Ukraine says

Radiation protection engineers walk in front of the New Safe Confinement (NSC), a metal dome encasing the sarcophagus covering the destroyed fourth reactor at the Chernobyl Nuclear Power Plant. (AFP)

The site of Ukraine's defunct Chernobyl nuclear plant -- partially destroyed in a 1986 meltdown -- lost power on Wednesday after Russia shelled a nearby substation, Kyiv said.

The UN's atomic energy watchdog said the blackout affected the confinement structure housing the plant's damaged reactor core, and that two emergency diesel generators were now supplying it with electricity.

The incident comes eight days after the Russian-occupied Zaporizhzhia nuclear plant in southern Ukraine also lost power -- an ongoing situation that Ukraine calls "critical" but that Russia says is "under control".

Both incidents have heightened concerns about the safety of Ukraine's nuclear sites, which have suffered repeated attacks since Russia's 2022 invasion.

"Today, a Russian strike on one of our energy substations in Slavutych caused a blackout lasting more than three hours at the former (Chernobyl) Nuclear Power Plant facilities," Ukrainian President Volodymyr Zelensky said on Facebook.

"This included the New Safe Confinement, which protects the environment from remnants of reactor four after the 1986 explosion, as well as from radioactive debris and dust," he added.

He accused Russia of posing a threat to global security and called for a "strong response".

The International Atomic Energy Agency said the plant had lost connection to a substation in the town of Slavutych, without elaborating.

"The site swiftly switched to alternate lines and power was restored, except for the New Safe Confinement (NSC), which covers the old sarcophagus built after the 1986 Chernobyl accident," the United Nations agency said.

"Two emergency diesel generators are now supplying the NSC with electricity."

The New Safe Confinement, completed in 2016, is a large shield-like structure that surrounds the unit four reactor and prevents the release of radioactive material.

A Russian drone attack damaged the confinement structure in February, but did not result in increased radiation in the surrounding area, Ukrainian authorities said.

- Zaporizhzhia off the grid -

The Russian-occupied Zaporizhzhia nuclear plant has meanwhile been disconnected from the power grid since last Tuesday.

Both Russia and Ukraine have traded blame for causing that blackout.

The plant's six reactors, which before the war produced around a fifth of Ukraine's electricity, were shut down after Moscow took over.

But the site needs power to maintain the cooling and other safety systems that prevent the reactors from melting down and releasing radiation into the atmosphere.

Zelensky said Tuesday the situation there was "critical" and that one of the backup diesel generators had "malfunctioned".

The Moscow-installed operator said Wednesday that the situation there was "under control".

Since the start of the war, Zaporizhzhia has seen multiple safety threats, including frequent nearby shelling, repeated power cuts and staff shortages.

The site sits near the city of Energodar on the Dnieper river, the de facto front line in southern Ukraine.