
Residents were alarmed by a loud boom and billowing 'smoke' after a reactor unit tripped at Heysham 2 power station.
The loud noise and plume of steam came from the power station site on Wednesday at around 5pm.
EDF, owners of Heysham 1 and 2, said there was "no reason for concern".
Three fire trucks were sent to the site after a call from a member of the public, but no action was needed.
"This evening one of the units at Heysham 2 power station came offline," said an EDF spokesperson.
"This was not planned and noise caused by steam venting may have been heard by local residents.
“This steam venting is normal when a reactor comes offline and is no reason for concern. Work is under way to establish the cause of the trip and bring the unit back online.”