The European Pressurised Reactor (EPR) reactor, built by the French-led Areva-Siemens consortium on Finland's southwest coast, was started up in December for testing, 12 years behind schedule.

"Today on Saturday, March 12, 2022, at 12:01 pm (1001 GMT), the plant unit has been connected to the national grid at a power output of 103 MW," TVO wrote in a statement.

Once regular energy production begins, now expected in July 2022, it will supply about 14 percent of Finland's energy at 1,650 megawatts, it said.

The plant is to become Europe's most powerful reactor. Olkiluoto 3 will run alongside two existing reactors at Eurajoki on Finland's west coast.

The French-developed EPR reactor model was the first nuclear power station to be procured in Europe after the 1986 Chernobyl disaster, designed to relaunch nuclear power.

It was meant to be a showcase of French-German know-how, touted as offering higher power and better safety.

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

In Olkiluoto's case, the project turned into a bitter debacle and a financial disaster.

The cost ballooned from an initial estimate of three billion euros ($3.27 billion) to around 11 billion euros, according to the 2019 World Nuclear Industry Report.

The project was beset from the start by a string of technical and safety setbacks due to poor project management and workmanship, according to several reports by the Finnish economy ministry and the country's Radiation and Nuclear Safety Authority.

The repeated delays led to bitter compensation disputes between TVO and Areva, with the latter ultimately agreeing in March 2018 to pay TVO financial compensation of 450 million euros.

In the UK, Hinkley Point in southwest England has pushed back its planned electricity production by half a year to mid-2026.

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AREVA