"Today, the Government has granted the power plant a licence to produce electricity until 2050," economy minister Mika Lintila told a press conference.

The plant in Loviisa, comprising two units of the Soviet designed VVER-440 type pressurised water reactors, accounted for around 10 percent of Finland's electricity production in 2022, plant operator Fortum said.

The operating licenses for the two units -- built in 1977 and 1980 -- were due to expire in 2027 and 2030.

Over the past five years, state-owned energy company Fortum has invested around 300 million euros ($320 million) in refurbishing the plant, estimating that the lifetime extension will require another billion euros by 2050.

The Finnish coalition government, which includes the Greens, expressed support for extending licences for existing nuclear power plants in a policy statement from 2019.

Finland has also finished the construction a new reactor -- Olkiluoto 3 -- on the country's west coast, but it has yet to go into regular production and is already more than 12 years behind schedule.

Operator TVO said Thursday that the start of the plant's regular production had been further delayed due to a defect in the pressuriser safety valve, pushing back the date from March to April 4.

Finland had been counting on the new reactor for its electricity needs this winter, with fears of energy shortfalls after Russia -- formerly a major energy supplier to Europe -- invaded Ukraine.

Fortum added that the spent fuel from Loviisa will be disposed in the nuclear waste repository Onkalo, currently under construction.

The network of tunnels more than 400 metres (1,312 feet) deep in the bedrock, scheduled to be operational by 2025, is Finland's solution for storing nuclear waste for 100,000 years below the Earth's surface.