A planned outage at Britain's Hinkley Point B-8 nuclear reactor has been extended by three months, data from EDF Energy shows.

The 480 megawatt reactor went offline on Friday night and was originally due to return to service on March 17. The restart date has now been extended to June 5.

An upcoming outage from April at Hinkley Point B-7 reactor has been extended to June 20 from May 19.

"We have decided to take more time to complete the forthcoming inspection outages at Hinkley Point B to allow for additional analysis and review of the core inspection findings which as always we will share with our regulator, ONR," a company spokesman said, referring to the Office for Nuclear Regulation.

The reactors have to undergo such inspections after cracks developed faster than expected in graphite bricks in the reactor core at another of the company's nuclear fleet in Britain.

(Reporting by Nina Chestney; Editing by Edmund Blair and Jane Merriman)