Untra nuclear reactor park targets 440 MW through eight lead-cooled reactors planned for Tierp, Sweden. The proposed project could add a major source of dispatchable nuclear power to Sweden’s electricity system.
Blykalla submitted its application to the Swedish government on August 25, 2026. The company plans to deploy up to eight SEALER advanced modular reactors at Untra. However, Blykalla has not disclosed the project’s construction cost or total investment value.
Untra Nuclear Reactor Park plans eight lead-cooled reactors
The park would use Blykalla’s Swedish Advanced Lead Reactor technology. Each SEALER unit would generate approximately 55 MW of electrical capacity. Eight units would therefore provide up to 440 MW of combined generating capacity.
The reactor design uses liquid lead as its primary coolant. Blykalla says the technology supports passive cooling during a complete loss of electrical power. Natural circulation can remove residual heat without pumps, external electricity, or operator intervention.
Furthermore, Blykalla designed the SEALER for factory serial production and transport. The company says this approach could reduce construction complexity compared with conventional large nuclear plants. The design also targets locations that traditional nuclear plants have not historically served.
Blykalla developed specialized aluminium-alloyed steel to address corrosion challenges from liquid lead. The company considers this material development central to commercializing its lead-cooled reactor technology.
Untra Nuclear Reactor Park strengthens Sweden’s power infrastructure
The proposed construction project would sit within Sweden’s SE3 electricity bidding zone. SE3 has high electricity consumption and faces a need for additional generation capacity. Untra also sits near the existing Untra and Söderfors hydropower facilities.
Consequently, the project could combine dispatchable nuclear generation with regulated hydropower.
The arrangement could create an integrated regional electricity cluster. The site also benefits from planned 400 kV transmission infrastructure through Tierp. Svenska kraftnät is developing that infrastructure under the Uppsalapaketet programme.
The location also provides access to nuclear expertise from Uppsala, Gävle, and Forsmark. Meanwhile, additional electricity could support industrial development and energy-intensive businesses. The project could also generate longer-term tax revenues for the surrounding region.
Sweden aims to produce 300 TWh of electricity annually by 2045. The government also targets 2,500 MW of new nuclear capacity by 2035. It aims to reach 10,000 MW of new nuclear capacity by 2045. At 440 MW, Untra could represent approximately 18% of the 2035 target.
Untra Nuclear Reactor Park enters multi-year approval process
The government application represents the beginning of a multi-stage development process. Swedish authorities must assess the proposed facility before construction can proceed. The Swedish Radiation Safety Authority will conduct further regulatory reviews. The Land and Environmental Court and Tierp municipality will also participate.
Blykalla targets first operations during the first half of the 2030s. However, the schedule depends on government approval and subsequent regulatory processes.
The Untra application also expands Blykalla’s Swedish nuclear development pipeline. The company submitted an earlier application for a six-reactor facility at Norrsundet. That project would provide up to 330 MW of capacity.
Meanwhile, Blykalla continues development of its first US nuclear demonstration reactor. The demonstration project could provide operational data before commercial Swedish deployment. Blykalla also works with Oklo on technical analyses for an authorized US reactor pilot.
The park adds a modular dimension to Sweden’s expanding nuclear construction ambitions, with eight lead-cooled reactors planned to deliver up to 440 MW. The project also forms part of a broader global push toward advanced nuclear technologies, alongside the $23.6 billion ITER nuclear fusion project in France, which is pursuing fusion power through one of the world’s most complex energy construction programs.
Project Fact Sheet
Name: Untra Advanced Nuclear Reactor Park.
Type: Advanced nuclear power plant.
Location: Untra, Tierp municipality, Uppsala County, Sweden.
Developer: Blykalla.
Status: Proposed advanced nuclear development.
Application status: Government approval application submitted.
Application date: August 25, 2026.
Reactor technology: Swedish Advanced Lead Reactor (SEALER).
Reactor classification: Fourth-generation advanced modular reactor.
Number of reactors: Up to eight.
Individual reactor capacity: Approximately 55 MWe.
Total planned capacity: Up to 440 MWe.
Primary coolant: Liquid lead.
Safety approach: Passive cooling and natural circulation.
Electricity zone: SE3.
Grid infrastructure: Planned 400 kV transmission connection.
Grid program: Uppsalapaketet.
Nearby power assets: Untra and Söderfors hydropower facilities.
Target operations: First half of the 2030s.
Regulatory process: Government, SSM, court, and municipal approvals required.
National target contribution: Approximately 18% of Sweden’s 2,500 MW target for 2035.
Project Team
Developer: Blykalla.
Reactor technology developer: Blykalla.
Grid operator: Svenska kraftnät.
Regulatory authority: Swedish Radiation Safety Authority.
Environmental authority: Land and Environmental Court.
Local authority: Tierp municipality.
Technology partner:
Materials partner:
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