A power station at Heysham has been closed as a precaution after a fault was found.
EDF Energy has closed both reactors at Heysham 1, as well as at its sister station in Hartlepool.
An inspection of reactor 1 at Heysham 1, in June this year, showed a defect in one of its boilers.
As a precaution the company has shut all reactors they operate which are of the same design.
A spokesman for EDF said: “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.”
The company said it was estimated that the investigations would take about eight weeks.