The 1986 meltdown at the site was the world's worst ever nuclear incident. Since Russia invaded in 2022, Kyiv fears another disaster could be just a matter of time.

In February, a Russian drone hit and left a large hole in the New Safe Confinement (NSC), the outer of two radiation shells covering the remnants of the nuclear power plant.

It functions as a modern high-tech replacement for an inner steel-and-concrete structure -- known as the Sarcophagus, a defensive layer built hastily after the 1986 incident.

Ten months later, repair work is still ongoing, and it could take another three to four years before the outer dome regains its primary safety functions, plant director Sergiy Tarakanov told AFP in an interview from Kyiv.

"It does not perform the function of retaining radioactive substances inside," Tarakanov said, echoing concerns raised by the International Atomic Energy Agency.

The strike had also left it unclear if the shell would last the 100 years it was designed to.

The gaping crater in the structure, which AFP journalists saw this summer, has been covered over with a protective screen, but 300 smaller holes made by firefighters when battling the blaze still need to be filled in.

Scaffolding engulfs the inside of the giant multi-billion-dollar structure, rising all the way up to the 100-metre-high ceiling.

Charred debris from the drone strike that hit the NSC still lay on the floor of the plant, AFP journalists saw on a visit to the site in December.

- 'Main threat' -

Russia's army captured the plant on the first day of its 2022 invasion, before withdrawing a few weeks later.

Ukraine has repeatedly accused Moscow of targeting Chernobyl and its other nuclear power plants, saying Moscow's strikes risk triggering a potentially catastrophic disaster.

Ukraine regularly reduces power at its nuclear plants following Russian strikes on its energy grid.

In October, a Russian strike on a substation near Chernobyl cut power flowing to the confinement structure.

Tarakanov told AFP that radiation levels at the site had remained "stable and within normal limits".

Inside a modern control room, engineer Ivan Tykhonenko was keeping track of 19 sensors and detection units, constantly monitoring the state of the site.

Part of the 190 tonnes of uranium that were on site in 1986 "melted, sank down into the reactor unit, the sub-reactor room, and still exists," he told AFP.

Worries over the fate of the site -- and what could happen -- run high.

Another Russian hit -- or even a powerful nearby strike -- could see the inner radiation shell collapse, director Tarakanov told AFP.

"If a missile or drone hits it directly, or even falls somewhere nearby ... it will cause a mini-earthquake in the area," he said.

"No one can guarantee that the shelter facility will remain standing after that. That is the main threat," he added.