DTE Energy subsidiary Detroit Edison said the 1,140MW Fermi 2 Nuclear Power Plant located in Michigan, US, has returned to service.
The owner has completed refueling and maintenance works at the plant, following an outage that began last month.
Detroit Edison has synchronized the plant, to the company's electrical system, which is currently operating at 25% capacity.
DTE Energy senior vice president and chief nuclear officer Jack Davis said, "This maintenance work will help us to continue sending clean, safe energy to our customers in southeast Michigan."
Fermi 2 site vice president Joseph Plona said, "These are long-term reliability improvements for our facility that will help us continue to operate the plant safely and efficiently for years to come."
The team of workers replaced 1/3 of the fuel in the reactor and performed over 15,000 separate activities which included inspection and equipment maintenance upgrade of cables, piping and transmission switchyard.
The plant is expected to operate at its full capacity eventually