EDF Energy said that two nuclear stations, Heysham 1 and Hartlepool, which played a crucial role in providing power to the UK, could remain closed until the end of this year.
The two nuclear power stations were shut in August to allow detailed boiler inspections.
Although EDF Energy said that it expects the two stations to become operational between the end of October and the end of December, it depends on various factors.
Following the discovery of a crack on the boiler spine at Heysham 1, EDF shut down the two plants as both the stations share the same design.
Due to the ongoing problems at Heysham 1 and Hartlepool stations, Centrica, which owns a 20% stake, issued a profit warning.
In order to bring these reactors back into service, EDF Energy claimed that the programme must complete the inspections to verify there are no further defects which could develop into cracks; understand in detail the cause of the crack found on the boiler spine at Heysham 1; develop techniques for modifications to reduce the impact of any defects; and then implement modifications if necessary.
In the coming weeks, the programme team will complete the inspections and work towards the safe operation of the boilers.
EDF claimed that the "safety case" will require approval from Office for Nuclear Regulation.
The shut down of the reactors, which together have an installed capacity of around 2.4GW, comes at a time when part of the 2GW Ferrybridge coal-fired station has been temporarily closed following a fire, reports The Guardian.
Although EDF Energy operates 15 nuclear reactors in the UK, only these two reactors share the same boiler design.
Image: A crack on boiler spine was discovered at Heysham 1 plant, which led to its temporary closure. Photo: courtesy of EDF Energy.