A reactor at Suffolk's Sizewell A nuclear power station has been shut down after an electrical power failure.
Emergency services were called to the site just after 1900 BST on Friday after a local resident reported smoke and hearing a bang.
The reactor was safely shut down and no injuries were reported.
A spokesman for British Nuclear Group, which owns the plant, said the incident was more of an inconvenience than a danger.
The reactor is expected to remain closed for several days.