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.”


Appeal launched to help save Morecambe sports and social club
Reopening date announced after Morecambe Jobcentre closes for repairs
Lancaster charity urges residents to know how they’re affected by Renters' Rights Act
Lancaster district residents urged to check their details as annual electoral canvass begins
E-bikes and e-scooters seized during police crackdown on Lancaster cycle track
Four vehicles involved in road collision in Carnforth
LISTEN: Popular vlog tells story of couple's second-hand bookshop dream in Morecambe
Emergency team in Silverdale receives donation of life-saving kits
MP offers support to staff after Morecambe FC reported to The Pensions Regulator
Track night at Lancaster sports club to launch police safety scheme for women and girls
PHOTOS: Live music day to raise funds for homeless people in Lancaster hailed as huge success
Former bank turned live music venue in Morecambe to reopen under new management
New parking system set to launch at Royal Lancaster Infirmary
Museum in Lancaster up for award launched by TV historian David Olusoga
MP fights for refunds after Heysham medical centre patients get parking fines in error
Two teenagers arrested after car stolen during Hest Bank burglary
Parents demand further action after health watchdog probe into asbestos complaints at Lancaster school
LISTEN: Lancaster medical students praised for helping man who collapsed
Man arrested on Morecambe beach after report of assault
Police probe burglaries in villages near Carnforth

