The Olkiluoto 4 nuclear reactor unit is scheduled to achieve initial criticality and begin low-power testing on April 4, 2026. Owned by the German energy company Uniper, this 1,600 MW EPR reactor is the first new nuclear unit to start up in Finland since the 1980s. It is located on the existing Olkiluoto island site in the municipality of Eurajoki. This major industrial milestone is intended to bolster Finland's electricity self-sufficiency and provide stable baseload power for the national grid. Uniper's project director, Lena Schütt, confirmed the schedule for the reactor's start-up. According to the announcement, Schütt stated, "All systems are ready for the controlled nuclear reaction to begin." The focus on energy security is expected to amplify interest in this project.
The unit is expected to enter full commercial operation in the latter part of 2026, following the completion of low-power testing and regulatory approvals. This operational start date marks a key moment for Finland's energy infrastructure. The project represents a substantial addition to the country's power generation capacity, and its development has been closely monitored by industry observers and policymakers alike. Its completion will add a major source of carbon-free electricity to Finland's energy mix.
This new reactor unit joins the existing nuclear facilities at the Olkiluoto site, underscoring a continued commitment to nuclear energy as part of the national strategy. The scheduled start of operations follows years of planning and construction work. Its successful launch will be a landmark event for both Uniper and Finland's energy sector.