Finland's much-delayed Olkiluoto 3 (OL3) nuclear reactor resumed test production of electricity on Wednesday after an outage of more than two months, facility operator TVO said.

In a blow to Finland's energy security, the operator in October said damage was found after test production, further delaying a startup that was originally scheduled to take place as long ago as 2009.

The reactor was briefly back in test mode in late December and early January before being closed for maintenance.

TVO said it expected OL3 to ramp up to full capacity on Wednesday followed by tests in the coming weeks, adding regular production was planned to begin on April 17.

During testing in September, OL3's output for the first time hit full capacity of 1,600 megawatts, making it the most powerful electricity production facility in Europe and the third-most powerful globally, according to TVO. (Reporting by Terje Solsvik; Editing by Jacqueline Wong and Rashmi Aich)