"The electricity production of OL3 was interrupted on Sunday evening November 19 due to a fault detected in the turbine island," TVO wrote on social media platform X.

"The cause is currently being investigated," it said, adding that it did not know when production would resume.

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, 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.