Questions are being raised about the future of Hinkley Point B nuclear power station in Somerset.
The plant normally provides 3% of the UK's electricity
Both its advanced gas-cooled reactors are currently shut down and a campaign group has said it may never open again.
Problems at the plant include cracks in a reactor's graphite core, and cracks in boiler pipes, which are currently being repaired by engineers.
British Energy said the cracks are within its safety plan and the decommissioning date is 2011.
The company brought forward a safety inspection after the cracked pipes were revealed.
Documents seen by the BBC state it cannot make a safety case for the graphite core to cover the next 10 years of the plant's life, as it will not last that long.
A statement from British Energy said: "All British Energy nuclear power stations operate under safety cases agreed and signed off by the Nuclear Installations Inspectorate. Without this safety case approval, our stations would not operate.
"The documents [seen by the BBC] reflect only a fragment of the on-going dialogue that British Energy has with its regulator.
"The graphite cores are made up of a number of graphite bricks arranged in layers. It is accepted... that cracks will occur in some of the bricks as part of the normal ageing process within the graphite reactor core."
John Large, an independent nuclear consultant, said: "We've known there are problems with the graphite cores and now we have the cracking of the boiler tubes.
"It's the occurrence of two faults in parallel that is causing a dilemma for Hinkley."
Jim Duffy, of the Stop Hinkley group, added: "The boiler tube cracks are a fundamental problem.
"Given we've got graphite problems... I can't see it opening again."
Hinkley B's two reactors normally provide 3% of the UK's electricity.