Sizewell nuclear plant operating at half power following steam leak
Planned maintenance means that Sizewell B power station at Sizewell, near Southwold is temporarily operating at half power.
Engineers took one of the nuclear station's two turbines offline at 5am on Wednesday to carry out the work.
It is not known how long Turbine One will be out of service, but station owner EDF Energy said Turbine Two would continue to generate power safely for about one million homes.
The shutdown follows a steam leak in pipework that saw Turbine Two taken offline for just under a fortnight in November.
EDF Energy said the unit had been shut down to allow inspection and maintenance work to be carried out to the turbine exhaust pipework, well away from the nuclear area of the site.
The company may also take the opportunity to carry out additional maintenance while the unit is offline.
EDF Energy said the decision to take the turbine down was 'a precautionary measure' following the repairs to the other turbine last year.
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Sizewell B station director, Jim Crawford, said: 'Safety is our overriding priority at Sizewell B power station.
'Excellent teamwork between our staff, EDF Energy headquarters and contactors allowed us to deal with last year's steam leak, quickly and safely.'
'Although we have not suffered any similar problems with pipework relating to Turbine One, we decided to take the unit offline as a precautionary measure to allow us to carry out detailed inspection and maintenance work to ensure we don't encounter any similar problems in the future.'
An EDF Energy spokesman added: 'We will confirm when the unit has returned to service.'
Sizewell B's turbines each have rows of blades on a long shaft.
Steam is used to spin the turbines by blowing over the blades.
Each shaft has a large electrical generator on the end, which, when spinning, sends electrical power out on to the grid.