"The Olkiluoto 3 unit was in normal production when a fault in the turbine plant automatically stopped the facility's electricity production. The facility operated as intended during the fault," TVO said in a statement on Monday.

"The cause of the fault was revealed to be a malfunctioning temperature measurement in the generator's cooling system," it said, adding that "the incident had no impact on nuclear safety."

TVO said the reactor was expected to return to production on Tuesday at noon (1000 GMT) following repairs.

The next-generation European pressurised water reactor (EPR), built by the French-led Areva-Siemens consortium, produces around 14 percent of Finland's electricity.

It was put into regular service in April 2023, some 18 years after construction began and 14 years after it was originally scheduled to go into commercial production.

Like several other EPR projects, it was plagued by repeated construction delays and billions of dollars in cost overruns.

With a capacity of generating 1,600 megawatts, Olkiluoto 3 is the single largest nuclear reactor in Europe, while Ukraine's Zaporizhzhia plant, with its six reactors, is the largest nuclear plant.

Nuclear technology has seen renewed popularity in recent years as a way to reduce carbon emissions.