A nuclear reactor was shut down at Heysham Power Station after smoke was seen coming from the plant.
The Heysham 1 reactor was shut down at 6pm on Thursday as a precaution after smoke within some lagging on a turbine was spotted.
EDF, who run the station, said a dry powder extinguisher was used to deal with the smoke.
Lancaster Fire and Rescue attended but were not needed. No-one was injured in the incident.
Station director Ian Stewart said: “The site’s own fire teams handled this small incident professionally and calmly within a few minutes, my thanks go to Lancashire Fire and Rescue for its support.
“Although this is a very minor incident we will be looking into the cause and ensuring that we learn any lessons from it which will help us avoid any repeat event in the future.”