A nuclear reactor at EDF-owned Hartlepool power station has been taken out of service for a planned £30 million maintenance programme.
The County Durham station provides 1185 MW to the grid.
The “extensive” work will take place over a nine-week period and will see inspections inside the reactor, as well as the installation of new equipment.
One of the biggest projects will be replacing a generator transformer which increases the voltage in the site’s electricity before it is sent to the grid.
Maintenance periods, known as statutory outages, take place every three years and are planned in advance with National Grid to ensure there is no impact on national supplies.
The big six supplier says around 500 extra workers will join the site’s 700-strong team during the work.
Craig Dohring, station director at Hartlepool, said: “We produce enough low carbon electricity for around two million homes each and every day.
“We only deliver that by continually investing in our people and the power station and this shutdown is part of that programme.”
Hartlepool’s other reactor will continue working as normal throughout the work.