The nuclear power project was originally supposed to be completed in 2009, but has been marked by seemingly endless delays and cost overruns.
Last autumn, test operation finally began late. But even it has been fraught with technical problems.
Last week announced the operator TVO that they had control over what went wrong, and that the reactor can run at full power. So now the third reactor on the island of Olkiluoto on the west coast of Finland contributes upwards of 1,600 megawatts to the electricity grid.
Some final tests need to be done before the reactor is finally approved, so the new date for regular operation is now April 17.
Olkiluoto 3 has cost about four times as much as planned. Finland previously had plans to continue nuclear power expansion with more reactors after that, but they are now on hold.