One of the two nuclear reactors at the Torness power station in East Lothian has stopped generating electricity.
The plant's operator, EDF Energy, said the decision to halt the energy production was unplanned but insisted there was no cause for concern.
Routine maintenance work was due to begin on reactor two this weekend.
The company said that the work could now begin earlier than planned. It has yet to release information about why the reactor came offline on Sunday.