IN Brief:
- Blykalla has applied to develop up to eight SEALER reactors at Untra in Tierp municipality.
- The proposed site would provide up to 440MW alongside nearby hydropower and new 400kV transmission infrastructure.
- Tierp creates a second Swedish commercial development track alongside Blykalla's earlier Norrsundet proposal.
Blykalla has submitted an application to the Swedish government for a second commercial advanced nuclear reactor park, proposing up to eight lead-cooled SEALER units at Untra in Tierp municipality.
The Uppsala County development would provide up to 440MW of electrical capacity if all eight reactors are built. Each SEALER unit is designed for approximately 55MWe, allowing capacity to be added through multiple modular reactors rather than one large generating unit.
The application follows Blykalla’s earlier proposal for six reactors at Norrsundet in Gävle municipality, which would provide around 330MW. The Norrsundet project is already progressing through Sweden’s nuclear financing process, making Tierp a separate development rather than another stage of the same site.
Blykalla selected Untra partly because it is located in bidding zone SE3, where Swedish electricity consumption is concentrated. The proposed site is close to hydropower at Untra and Söderfors and to new 400kV transmission infrastructure being developed through Tierp municipality.
Modular generation meets transmission planning
The network location gives the project a different context from a reactor proposed in an isolated region with limited transmission capacity. Firm generation at Tierp would sit close to existing controllable hydropower and an expanding high-voltage network, although detailed connection studies and reinforcement requirements have not yet been published.
Government approval is only the first stage of a longer licensing process. Blykalla says the development would also require scrutiny by the Swedish Radiation Safety Authority, the Land and Environmental Court, and Tierp municipality before construction could proceed.
The company is targeting first operation during the first half of the 2030s. That timetable remains conditional on regulatory approvals, engineering development, financing, supply chain readiness, site works, and successful qualification of the reactor technology.
SEALER is a lead-cooled advanced modular reactor. Liquid lead provides the primary coolant, with the design relying on natural circulation to continue removing decay heat during a loss of power rather than depending entirely on electrically driven pumps.
Lead cooling also creates demanding materials requirements. Blykalla has developed aluminium-alloyed steels intended to resist corrosion in the liquid-lead environment, one of the technical problems that has historically limited wider commercial use of lead-cooled reactor concepts.
The company’s commercial proposition relies heavily on repeatable factory production. A 55MWe reactor is small enough for more of the nuclear system to be manufactured in controlled industrial facilities and transported to site, with generating capacity increased by installing additional modules.
That approach could reduce repeated site engineering only if the design remains sufficiently standard between projects. Significant changes to buildings, safety systems, components, manufacturing methods, or licensing evidence at every location would erode much of the serial-production advantage.
Supplier qualification will therefore be central to the programme. Nuclear-grade steels, components, instrumentation, electrical equipment, control systems, fabrication processes, inspection regimes, and quality documentation all need to be capable of repetition across a fleet.
Blykalla is building that industrial base through relationships with companies including ABB, Höganäs, Kanthal, ESAB, and Alleima. It is also constructing an electrically heated test facility at Oskarshamn with Uniper to support development before a commercial nuclear unit operates.
The Tierp proposal adds a second Swedish location on which the company can test whether its reactor architecture is genuinely transferable. Different sites bring different ground conditions, cooling arrangements, security requirements, network interfaces, planning considerations, and local approval processes.
The modular format also changes the generating profile of the completed station. Eight 55MWe units would provide roughly the same aggregate output as one 440MW plant, but individual reactors could be commissioned, maintained, and potentially taken offline separately rather than removing the entire site’s output during a single-unit outage.
That operational granularity could affect outage planning and system availability, although actual performance will depend on the final plant design and operating regime. It also allows construction to be staged if financing and licensing arrangements support sequential deployment.
Sweden has set a national target of 300TWh of annual electricity production by 2045 and has identified new nuclear capacity as part of the route towards meeting rising demand. Blykalla says a fully built Tierp facility would represent around 18% of the government’s 2,500MW new-nuclear ambition for 2035.
The number remains prospective. The application establishes a proposed site and capacity, but no reactor has yet been authorised for construction at Tierp, and the commercial performance of the SEALER design remains to be demonstrated at operating scale.
That makes the second site useful for a different reason: it tests whether the technology can progress as a repeatable fleet rather than as a single heavily customised demonstration. Blykalla now has two Swedish commercial proposals with different locations and network conditions. The next milestones will show whether the same 55MWe reactor can pass licensing and engineering review without losing the standardisation on which much of its economic case depends.
