Heysham 1 and Hartlepool reactors are still offline after being closed in August, and EDF officials say they may not be returned to power until the end of the year.
As for the effects this will have, BBC correspondent John Moylan said that the announcement means "up to a quarter of the nuclear fleet being offline as the UK enters winter".
The BBC believe the fault was a crack in the boiler in one of the reactors, leading to all four reactors (two on each site) being closed. The Guardian, on the other hand, reports that it was a fault on a "spine" which holds the pipeworks in the boiler. This then led to concerns that the same flaw could be present in the other three reactors of the same construction.
Cedrec's take
Whatever the reason for closure, it is better safe than sorry. It does mean that more is demanded of the remaining sources. Whether that will see a spike in prices and if that spike is directly related remains to be seen.
