nuclear reactor  Finland
© REUTERS/Lefteris KaragiannopoulosA general view of the unfinished Olkiluoto-3 nuclear reactor in Eurajoki, Finland August 17, 2017.
Damage has been detected in the feedwater pumps of Finland's Olkiluoto 3 (OL3) nuclear reactor during maintenance work, which will likely delay the commissioning of the plant and the startup of regular production, operator TVO said on Tuesday.

The damage to Europe's largest nuclear reactor is a setback for Finland, where the national grid operator has warned of potential power blackouts in the coming winter if OL3 could not reliably supply electricity.

Imports of power to Finland from Russia stopped in May after Russian utility Inter RAO said it had not been paid for the power it sold, increasing Finland's need for OL3's output.

Under construction since 2005, OL3 was originally meant to start operation in 2009, but has faced several technical mishaps, which sparked costly delays and a lengthy legal battle.

TVO said the latest problem had occurred in pumps located in the so-called turbine island at the heart of the nuclear reactor's power production, where water from its feedwater tank is pumped into steam generators.

While the damage would "most likely" impact the reactor's scheduled startup, it was not yet clear how long any delay would be, TVO said.

Test production at OL3 began this year, and regular electricity output at the reactor had been set to start on Dec. 14, TVO has said.

"The damage detected at the pumps has no impact on nuclear safety," the company said on its website.