HEYSHAM Nuclear Power Station has shut down two reactors after a defect was detected.
A routine test carried out in June found 'an unexplained result' in the boiler spine of reactor one.
It has been shut since June 11 but today EDF Energy announced they made a 'conservative decision' to shut down reactor two because it is of a similar design.
They have also closed both reactors at their Hartlepool site.
EDF Energy say the closure poses no risk to public health and that there should be no changes to their customers' current energy service.
A statement on EDF Energy's website states: "More detailed inspections of the affected boiler spine during an outage on Heysham 1 Reactor 1 that commenced in June 2014 have confirmed a defect in the location indicated by the initial findings.
"Heysham 1 Reactor 1 remains shut down while work continues to characterise the nature of the defect.
"Although routine inspections of other boiler spines have not previously indicated any similar defects, EDF Energy has taken the conservative decision to shut down Heysham 1 Reactor 2 and Hartlepool Reactors 1 and 2 that are of similar design over the next few days to carry out further inspections in order to satisfy itself and the Regulator that the reactors can be safely returned to service.
It is estimated that the reactors will be closed for up to eight weeks.
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