Revealed: Russian plan to disconnect Zaporizhzhia nuclear plant from grid

World leaders have called for the Zaporizhzhia site to be demilitarised after footage emerged of Russian army vehicles inside the plant, and have previously warned Russia against cutting it off from the Ukrainian grid and connecting it up to the Russian power network.

Other threats to nuclear security at the plant include vehicles packed so tightly into turbine halls that firefighters would struggle to access them if a fire broke out, and a campaign of terror against workers who have chosen to stay at the frontline plant.

One was beaten to death, and another so severely injured that he needed three months to recover. More than 200 have been detained, Kotin said.

During a shift between grid systems, the plant would be reliant only on a back-up diesel-powered generator, with no further options should that fail. After only 90 minutes without power the reactors would reach a dangerous temperature.

Russia seized control of the Zaporizhzhia plant in March but it is still run by Ukrainian workers. There has been increasing alarm about Russian management of the site in recent weeks, and pressure on Moscow to allow UN inspectors to visit.

Kotin is also concerned about the fire risk from vehicles packed into the turbine halls, which sit next to the two reactors still in operation. There are 14 trucks in one hall, and at least six in another, sources at the plant have told him.

Any blaze could then potentially spread towards the reactor buildings, where a fire would have disastrous implications far beyond the immediate region.

Many other military vehicles are lined up under overpasses, built to house pipes and walkways between reactor and turbine complexes, Kotin said, perhaps to provide protection from drones.

He praised about 9,000 workers who are still on duty at the plant, from a prewar workforce of about 11,000. Many evacuated their families but stayed at their posts because of the need for a skilled team to operate it.

Rockets have also landed within two dozen metres of 174 spent fuel containers housed at the plant, which would be more vulnerable to weapons than the reactors, which are built to withstand the impact of a passenger jet.

He said he also had confidence that Ukrainian workers who have sacrificed so much for the plant would be able to keep it safe.