Sizewell B is generating electricity again after a successful outage during which one of its two turbine rotors was replaced.
The works - which also included replacing one of the four reactor coolant pumps inside the building's dome and routine servicing of valves and motors - cost £80m.
Owner EDF is investing £300m in the Leiston nuclear plant over a three-year period to improve the station's performance and reliability - and strengthen the case to expand its lifespan by 20 years to 2055.
During the outage - or shutdown - inspectors were able to examine main pipes to check for any signs of stress corrosion cracking - an issue that can sometimes occur due to mechanical stress and corrosion.
The primary circuit was given a clean bill of health by engineering experts.
Station director Robert Gunn said: “The whole team at Sizewell B is proud to bring the power station back into service again to deliver low carbon electricity for Suffolk and beyond.
"This was a particularly important outage for us as we deliver the 10 year plan for the station.
"We know the importance of energy security and the role nuclear power plays in limiting carbon emissions.
"Since we switched the station off in February we have systematically worked through a checklist of thousands of tasks to ensure the station has a clean bill of health and is set up for a successful future.”
Preparation work for the outage begins at least two years in advance of refuelling the reactor as part of a 10-year plan.
Sizewell B was switched off on Friday, February 17, and brought back online on Monday, May 22.
The power station was connected to the grid on February 14, 1995, and employs 800 people. EDF says the plant is worth £40m to the local economy and has so far saved 85m tonnes of CO2 emissions.
By 2028 Sizewell B is due to be the only generating nuclear power station from the existing fleet.
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