The plant, more than 12 years behind schedule, had been expected to finally come fully online in December.

But TVO reported in October that damage had been detected in the feedwater pumps located in Olkiluoto 3's turbine island.

A detailed investigation into the cracks is ongoing and once it is finished "a decision will be made on the startup of the plant unit."

If all goes well, regular electricity production "would start in February 2023", TVO said, but "there are still uncertainties related to the schedule".

Before the damage was detected, the plant unit had been conducting full power tests during which it periodically stopped producing electricity for several days or even weeks.

Finland had been expecting to rely on Olkiluoto's new EPR reactor for its electricity needs this winter, with fears of energy shortages after Russia, a major energy supplier to Europe, invaded Ukraine.

But the regular production date has been pushed back multiple times in 2022 alone.

The most powerful nuclear plant unit in Europe, Olkiluoto 3 reached full power in September for the first time since construction began in 2005.

The French-developed European Pressurised Reactor model was designed to relaunch nuclear power in Europe after the Chernobyl catastrophe of 1986, and was touted as offering higher power and better safety.

But EPR projects in Finland, France and the UK have been plagued by delays and cost overruns.