British Energy said the fire had posed no risk to the public
The cause of a fire which shut down Dungeness B nuclear power station is being investigated by engineers.
The active reactor at the plant in Kent was taken offline after the fire broke out in a boiler annexe just before midnight on Monday.
Operator British Energy said there was no risk to the public and there was no release of radioactive material as a result of the fire.
All 52 staff on site were accounted for and no-one was injured.
Experts have been on site trying to find out what happened.
A British Energy spokeswoman said: "They are looking at the cause of the fire and will be bringing the reactor back online as soon as possible."
The plant has two reactors - one was already out of action for maintenance, but the fire meant the other one also had to be shut down.
Currently the plant is not producing power for the National Grid, but when both reactors are working they can produce enough power for 1.5 million customers.