Plant owner Entergy Nuclear said Tuesday that Indian Point 3 went back online Monday. The transformer that was destroyed in the May 9 fire has been replaced.
The cause of the fire is under investigation. And a cleanup continues of oil from the transformer that leaked into the nearby Hudson River.
In addition, federal regulators are looking into the accumulation of water near electrical safety equipment after the fire.
The other reactor on the site was unaffected. Together the reactors generate about a quarter of the power used in New York City and Westchester County.
The facility is about 30 miles north of midtown Manhattan.