The sixth reactor had been operating in “island mode” for the past three days, it said, feeding only its own needs after power lines were severed by Russian shelling.
The restoration of one of these lines on Saturday enabled the operator to make the decision to place the site in “the safest state – cold shutdown”.
If lines continue to be damaged, the plant will rely on back-up diesel generators, “the duration of which is limited by the technological resource and the amount of available diesel fuel”, Energoatom said.
In a statement posted on Telegram, Energoatom said the sixth and last functioning reactor was disconnected from the national grid at 3.41am and that “preparations are underway for its cooling and transfer to a cold state”.
Operations at the Russian-held Zaporizhzhia nuclear power plant in Ukraine have fully halted, Energoatom, the state agency in charge of the plant, said on Sunday.
The agency said the restoration of power to the plant had allowed it to do the safest thing and power down its sixth and last working reactor.
Kyiv on Wednesday called for residents of Russian-occupied areas around the plant, Europe’s largest, to evacuate for their own safety. Russia and Ukraine accuse each other of shelling the nuclear plant, risking a nuclear disaster.