A nuclear power station which been shut down for three days is unlikely to run again until Friday because of an "instrumentation fault", its owners said.
The Sizewell B nuclear reactor in Suffolk went offline and two turbines stopped working just after 5pm on Monday afternoon.
Engineers from EDF Energy, which owns the site, said they expect the station to be generating power again within 24 hours.
An EDF spokesperson said: "We are presently restarting the turbines and expect to be back to full generating power by this time Friday, approximately 2pm."
Residents living near the power station have been reassured that "at no time was there any risk to the public, personnel or the plant".
The last unplanned reactor shut down of this kind at Sizewell B was in August 2020.
“Like any large industrial plant, the station has a range of instruments which monitor operations to ensure it operates within safe parameters," said an EDF spokesperson.
"If a fault occurs in these instruments they will fail safe and in some cases will cause the plant to shut down."
Earlier this month, the company behind Sizewell B power station revealed it was looking to extend its operating life for 20 more years. Sizewell B is one of seven nuclear power stations in the UK and it provides 3% of the country's electricity.
Under current plans the Suffolk nuclear station would wind up by 2035, but EDF Energy has now said it will make a decision by 2024 whether that should be extended to 2055.
According to EDF, the power station is worth £40m annually to the local economy and employs about 800 local people.
The announcement coincided with the publishing of the government’s new energy strategy earlier in April, which put the focus on wind, solar, hydrogen and new nuclear.