Finland's much-delayed Olkiluoto 3 nuclear reactor started test production on Saturday, operator TVO said, delivering power to the national grid which over time is expected to reduce the need for electricity imports and lead to lower prices.

Plagued by technological problems that became the subject of lawsuits, the 1.6 gigawatt (GW) reactor had originally been due to open in 2009. It is Finland's first new nuclear plant in over four decades and Europe's first in almost 15 years.

Olkiluoto 3 started test production at just over 0.1 gigawatt, a small fraction of its capacity, with a ramp-up to full, regular electricity output planned by the end of July.

"OL3 significantly improves Finland's electricity self-sufficiency and helps in achieving carbon neutrality goals," operator Teollisuuden Voima (TVO) said in a statement.

Once fully operational, it is expected to meet 14% of Finland's electricity demand, reducing the need for imports from Russia, Sweden and Norway.

"Olkiluoto 3 will decrease Finland's import dependency and it will become a cheaper price zone," Aurora Energy Research economist Alexander Esser told Reuters.

Finland's net imports of power averaged 13 terawatt hours (TWh) over the last few years, which should drop to 5-8 TWh by 2025 with Olkiluoto 3 in operation, Esser said.

Nuclear power remains controversial in Europe, with some countries such as Germany phasing out reactors amid safety concerns, while others including France and Britain discussing new developments.

TVO is owned by Finnish utility Fortum and smaller energy and forestry firms.

Finland is the only Nordic country with a large power deficit, said Marius Holm Rennesund, a partner at Oslo-based consultancy Thema.

Thema predicts that Finnish wholesale power prices will drop to 60 euro per megawatt hour (MWh) in 2023 from a predicted average of 70 euro/MWh in 2022, although the expected reduction will also come from lower gas prices.

In 2024, Finnish wholesale power prices will likely fall further to 45 euros/MWh, Rennesund said.