Nuclear reactors at Heysham 1 power station which were shut down as a precautionary measure could remain offline until the end of December, EDF Energy said.
Meanwhile National Grid has announced plans to provide an electricity reserve due to the decreased output from Heysham 1 and Hartlepool.
This will enable them to take account of major developments in the market, including possible changes in generation availability.
Cordi O’Hara, National Grid’s Director of UK Market Operation, said: “This is a sensible precaution to take while the picture for this winter remains uncertain.
“At this stage we don’t know if these reserve services will be needed, but they could provide an additional safeguard.”
On August 11, EDF Energy reported that the four nuclear reactors at its Heysham 1 and Hartlepool power stations would be shut down to allow a detailed programme of boiler inspections to take place.
This precautionary measure was taken after the discovery of a crack on a component known as a boiler spine at Heysham 1.
Hartlepool power station was also shut down because both stations share the same unique design with each of its 16 boilers supported by this boiler spine component.
Since then, EDF Energy has put in place a detailed and fully resourced boiler inspection programme at both sites and further boiler inspections are now underway.
Dates for returning the stations to service depend on the findings and completion of the inspections.
EDF Energy will give further updates on the progress of the programme when it is able.