Finland’s much-delayed and costly new nuclear reactor, Europe's most powerful by production capacity, has completed a test phase lasting more than a year and started regular output, boosting the Nordic country’s electricity self-sufficiency significantly.

The Olkiluoto 3 reactor, which has 1,600-megawatt capacity, was connected into the Finnish national power grid in March 2022 and kicked off regular production on Sunday. Operator Teollisuuden Voima, or TVO, tweeted that "Olkiluoto 3 is now ready" after a delay of 14 years from the original plan.

It will help Finland to achieve its carbon neutrality targets and increase energy security at a time when European countries have cut oil, gas and other power supplies from Russia, Finland’s neighbor.

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"The production of Olkiluoto 3 stabilizes the price of electricity and plays an important role in the Finnish green transition," TVO President and CEO Jarmo Tanhua said in a statement. The company added that "the electricity production volume of Europe’s largest nuclear power plant unit is a significant addition to clean, domestic production."

Construction of Olkiluoto 3 began in 2005 and was due to be completed four years later. However, the project was plagued by several technological problems that led to lawsuits. The last time a new nuclear reactor was commissioned in Finland was more than four decades ago.

The Olkiluoto 3 is Western Europe’s first new reactor in more than 15 years. It is the first new-generation EPR, or European Pressurized Reactor, plant to have gone online in Europe. It was developed in a joint venture between France’s Areva and Germany’s Siemens.

Primarily because of safety concerns, nuclear power remains a controversial issue in Europe. The launch of the Finnish reactor coincides with Germany’s move to shut down its last remaining three nuclear plants on Saturday.

Experts have put Olkiluoto 3’s final price tag at around $12 billion — almost three times what was initially estimated. Finland now has five nuclear reactors in two power plants located on the shores of the Baltic Sea. Combined, they cover more than 40% of the nation's electricity demand.

The conservative National Coalition Party, or NCP, which won Finland’s April 2 general election, wants to increase the share of energy that the country of 5.5 million gets from nuclear power still further.

NCP leader Petteri Orpo, Finland’s likely new prime minister, said during the election campaign that the new Cabinet should make nuclear power "the cornerstone of the government’s energy policy."