The two reactors have been offline for scheduled outages since late summer last year. [POWER/GB]

Dungeness B-21 was scheduled to come back online on Feb. 24 but this has been extended to April 14. Dungeness B-22 was due to come back online on Feb. 28 but this has been extended to April 6.

"Engineers at the plant are making good progress on the inspection and maintenance of conventional steam line pipes that carry steam from the boilers to the turbine," an EDF Energy spokesman said.

The pipes carry steam from the boiler to the turbine and are not within the nuclear reactor.

"Work is also continuing to complete repair work on corrosion identified during inspections on safety back-up systems," the spokesman added.

EDF Energy added it had informed Britain's nuclear regulator of the extensions to the outages.

EDF Energy, part of French utility EDF, operates 15 nuclear reactors in Britain which provide around 20 percent of the country's electricity.

In total, four of its reactors in Britain are currently offline, with a combined capacity of more than 2 gigawatts.

The other two, Hunterston B-7 and B-8, have been offline for extended outages for inspections to cracks in some of the graphite bricks which make up the reactor core.

(Reporting by Nina Chestney; editing by David Evans)