Finland’s nuclear energy sector is small by international fleet size but unusually important to the national electricity system. Five operating reactors at two sites provide close to two-fifths of the country’s electricity, giving Finland one of the highest nuclear generation shares in Europe. The system also covers more of the nuclear lifecycle than most national programs. Finland operates both western and Soviet-designed reactors, has added one of the world’s largest generating units, is extending the life of its older plants and is preparing the first deep geological repository intended for the permanent disposal of spent nuclear fuel.
This combination makes Finland’s nuclear program more than a source of electricity. It is part of the country’s approach to energy security, industrial competitiveness and low-carbon power. The next stage will depend less on building another large reactor and more on maintaining the existing fleet, completing the spent-fuel disposal system and deciding whether smaller reactors can serve district heating and industrial demand.
Five Reactors Carry a Large Share of Finland’s Electricity Supply
Finland has two nuclear power stations. Fortum operates two reactors at Loviisa on the country’s southern coast, while Teollisuuden Voima, commonly known as TVO, operates three units at Olkiluoto in western Finland.
Together, the five reactors have approximately 4.4 gigawatts of net generating capacity. They supplied just over 31 terawatt-hours of electricity in 2024, equal to approximately 39% of national electricity consumption. This high share gives nuclear power a central role in maintaining domestic supply during Finland’s cold winters, when electricity demand can rise sharply.
The composition of the fleet is distinctive. Loviisa 1 and 2 are VVER-440 pressurized water reactors based on Soviet technology but adapted with western safety systems. Olkiluoto 1 and 2 are boiling water reactors supplied by Sweden’s Asea-Atom. Olkiluoto 3 is a much larger European Pressurized Reactor, or EPR.
Finland therefore manages three different reactor designs within a five-unit system. This requires separate technical expertise, maintenance programs and fuel arrangements, but it has also prevented the sector from depending entirely on one reactor model or supplier.
Nuclear generation supports an electricity market that also includes substantial hydropower, wind power, biomass and cross-border trade. As Finnish wind capacity has expanded, nuclear plants have continued to provide large volumes of predictable generation when weather-dependent output is lower.
Olkiluoto 3 Changed the Scale of Finnish Nuclear Power
Olkiluoto 3 began commercial operation in 2023 after a long and difficult construction process. The 1,600-megawatt unit is Finland’s largest power reactor and one of the largest electricity-generating units in Europe.
Its arrival changed Finland’s electricity balance. The three Olkiluoto reactors produced approximately 23.4 terawatt-hours in 2025, covering about 28% of the electricity used in the country. Olkiluoto 3 alone can influence national power prices, import requirements and transmission-system operations because of its size.
The reactor was originally expected to enter service much earlier. Construction began in 2005, but the project encountered design changes, quality-control problems, legal disputes and repeated schedule delays. Its eventual completion demonstrated both the potential output of a modern EPR and the financial and industrial risks attached to first-of-a-kind nuclear construction.
TVO operates under Finland’s Mankala model. Its shareholders, including industrial companies and municipal energy businesses, receive electricity at production cost in proportion to their ownership. The structure links nuclear generation directly to Finnish industrial and utility demand rather than relying only on conventional wholesale electricity sales.
Olkiluoto 1 and 2 remain important alongside the newer reactor. Both units began operating around 1980 and have since received capacity improvements and technical upgrades. Their current operating licences run until 2038. TVO has examined options for extending their operation further and potentially increasing their output, although any extension would require environmental assessment, investment and regulatory approval.
Loviisa Moves from Soviet-Era Construction to Operation Through 2050
The two Loviisa reactors entered commercial service in 1977 and 1981. Although based on the Soviet VVER-440 design, the plant incorporated containment, control and safety features developed with western suppliers. The result became an early example of combining technologies from different nuclear industries within one plant.
The Finnish government granted new operating licences for both units in 2023, allowing Fortum to continue operating them until the end of 2050. The extension will require extensive modernization. Fortum expects the total investment associated with long-term operation to reach approximately €1 billion, with work covering turbines, automation, cooling systems and other major plant equipment.
Loviisa normally provides roughly one-tenth of Finland’s electricity. Keeping it in operation limits the amount of replacement capacity that Finland would otherwise need to build during the 2030s and 2040s.
Fuel supply has also become a strategic issue. The reactors were historically designed for Russian-origin fuel. Fortum signed an agreement with Westinghouse to develop and supply an alternative fuel type, creating a western supply option for the plant. This diversification became more important after Finland and other European countries reassessed their energy relationships with Russia.
The operating extension means Loviisa will remain part of Finland’s nuclear system for almost seven decades. Its future performance will depend on whether modernization projects can control ageing, preserve reliability and maintain regulatory confidence over the extended period.
Onkalo Places Spent-Fuel Disposal at the Centre of the Program
Finland’s most internationally significant nuclear project is not a reactor. It is Onkalo, the deep geological repository being developed at Olkiluoto for spent fuel from both Finnish nuclear power stations.
Spent fuel will first cool in storage before being sealed inside cast-iron inserts surrounded by copper canisters. The canisters will be placed in deposition holes approximately 430 metres underground and surrounded by bentonite clay. The surrounding bedrock provides an additional barrier intended to isolate the material over extremely long periods.
The planned repository has capacity for about 6,500 tonnes of spent uranium in approximately 3,250 canisters. Posiva, which is jointly owned by TVO and Fortum, submitted its operating-licence application in 2021. Full-scale trial operations have tested the encapsulation and disposal process using canisters without actual spent fuel.
Posiva has targeted 2026 for the start of disposal, subject to the completion of licensing and commissioning. If operations begin as planned, Finland will become the first country to place spent reactor fuel in a purpose-built deep geological repository for permanent disposal.
The project gives Finland an unusually complete nuclear policy. The country has not treated spent fuel as a problem to be left for a future government or stored indefinitely at reactor sites. Nuclear operators are legally responsible for waste-management costs, with funds collected through the state nuclear waste-management system.
Onkalo does not remove every technical or regulatory question surrounding spent fuel, but it gives Finland a defined route from electricity generation to final disposal. That strengthens the political and institutional basis for continued nuclear operation.
Smaller Reactors Could Define Finland’s Next Nuclear Phase
Finland has no large reactor currently under construction. The proposed Hanhikivi 1 project was terminated in 2022, ending plans for a Russian-designed reactor in northern Finland. After the delays associated with Olkiluoto 3 and the collapse of Hanhikivi, another conventional large-reactor project would require a strong commercial case and a stable financing structure.
Current activity is increasingly focused on small modular reactors. Finnish developers and municipal energy companies are examining reactors designed primarily for district heating rather than large-scale electricity generation. This is particularly relevant because Finnish cities use extensive heat networks that still require low-carbon replacement options.
A non-nuclear pilot facility for a Finnish-designed heating reactor began construction in Helsinki in 2026, while a proposed small-reactor heating project in Kuopio entered the environmental assessment process. These projects remain at an early stage and do not yet represent commercial nuclear plants.
Finland is also reforming its nuclear legislation to create a clearer licensing system for modular reactors, heat-only facilities and new construction methods. The government submitted a proposal for a new Nuclear Energy Act to Parliament in March 2026.
The established fleet will remain the foundation of Finnish nuclear generation for the foreseeable future. Olkiluoto 3 has already increased domestic supply, Loviisa is licensed through 2050 and Onkalo is approaching operation. Finland’s next major nuclear decision is therefore likely to concern how nuclear technology is used rather than simply how much reactor capacity is built. District heating, industrial heat and smaller installations may determine whether the sector expands beyond its two existing power-station sites.
