Saltfoss Energy

Saltfoss Energy ApS is a private Danish nuclear-technology startup developing small molten salt reactors. The company was founded in 2015 and is based in Copenhagen. Its technical origins are associated with a multidisciplinary group of physicists, chemists, and engineers whose educational and research backgrounds include the Niels Bohr Institute, CERN, the European Spallation Source, and the Technical University of Denmark. The company’s stated objective is to develop nuclear power that is safer, more sustainable, and less expensive to deploy than conventional large-scale nuclear generation and fossil-fuel-based electricity. The business formerly operated under the name Seaborg Technologies. In April 2025, it changed its name to Saltfoss Energy. The new identity refers to the company’s use of flowing molten salt as the medium for both fuel and heat transport, while “foss” is an Old Norse term associated with a powerful waterfall. The rebranding marked a continuation of the company’s reactor-development program rather than a shift into an unrelated business. Saltfoss Energy’s principal technology is the Compact Molten Salt Reactor, or CMSR. In contrast with conventional water-cooled reactors, which use solid fuel assemblies and water maintained under high pressure, the CMSR is designed to use fuel dissolved in liquid salt. The salt has a much higher boiling point than the temperatures expected from the reactor’s fission products, allowing the reactor to operate at approximately atmospheric pressure. This is intended to reduce the consequences of pressure-related failures and simplify aspects of the reactor system, although it does not eliminate all nuclear or engineering risks. The proposed safety system relies on a passive drain arrangement. If the reactor overheats, a frozen salt plug at the bottom of the core is designed to melt, allowing the liquid fuel to drain into cooled tanks. Once separated from the moderator and core geometry, the chain reaction is expected to stop, while the fuel cools and solidifies in the tanks rather than dispersing into the surrounding environment. The design’s main technical challenges include managing corrosion caused by hot fuel salt and ensuring the long-term reliability of the reactor, salt, structural materials, and passive safety systems. Saltfoss Energy has proposed manufacturing compact reactors in a centralized facility and deploying them on barges. The company describes the units as approximately shipping-container-sized and estimates an electrical output of about 100 MWe per reactor. Several units could potentially be installed on one barge, creating a mobile power platform that could be located near industrial or other electricity-demand centers. The proposed fueling interval is twelve years. The company has also stated that the design is intended for civilian energy use and does not have military applications or a proliferation pathway. The reactor concept has changed during development. The original thermal-spectrum design was planned to avoid graphite as a moderator by using molten sodium hydroxide in channels adjacent to and interlaced with the fuel-salt channels. In early 2023, the company decided that at least its first reactor generation would use low-enriched uranium rather than high-assay low-enriched uranium. The change was attributed to concerns that HALEU supply would not become available on the timeline required for the CMSR program. The fuel decision also led to a change from the proposed liquid sodium-hydroxide moderator to graphite. Saltfoss Energy has stated an ambition to deliver its first power barge in the first half of 2030, subject to the technical, regulatory, industrial, and financing requirements associated with commercial nuclear deployment.

Saltfoss Energy was established in Denmark in 2015 as a nuclear-technology startup focused on compact molten salt reactors. Its founding team drew on expertise associated with several major scientific and engineering institutions, including the Niels Bohr Institute, CERN, the European Spallation Source, and the Technical University of Denmark. From the beginning, the company’s work centered on adapting molten salt reactor principles into a compact commercial system intended for scalable manufacturing and practical deployment. The company’s reactor is known as the Compact Molten Salt Reactor, or CMSR. Unlike conventional reactors that use solid fuel rods and pressurized water, the CMSR concept dissolves nuclear fuel in a liquid salt. This arrangement is designed to operate at roughly one atmosphere because the salt’s boiling point is substantially higher than the temperatures expected in normal operation. The design objective is to reduce dependence on high-pressure cooling systems and to provide a more forgiving response to certain accident conditions. An important feature of the proposed system is its passive drain safety mechanism. A frozen salt plug is intended to melt if the reactor becomes excessively hot. The liquid fuel would then drain from the core into separate cooled tanks, where the chain reaction would be quenched and the fuel would cool and solidify. The concept is intended to reduce the likelihood of a severe release, but the company’s approach still depends on the performance of materials, freeze-plug systems, drain tanks, cooling equipment, and regulatory safeguards. Corrosion from the fuel salt and moderator remains a central engineering challenge. The early CMSR design was planned as a thermal-spectrum reactor without a conventional graphite moderator. Instead, it proposed molten sodium hydroxide in channels next to and interlaced with the fuel-salt channels. The liquid moderator was intended to support a compact configuration and could potentially be removed quickly as a means of controlling the fission reaction. In early 2023, however, Saltfoss Energy changed the planned fuel for at least its first reactor generation from HALEU to LEU. The company cited concerns that HALEU supply would not meet the schedule needed for the CMSR program. The change also led to the adoption of graphite rather than sodium hydroxide as the moderator for that generation. Saltfoss Energy has proposed a manufacturing and deployment model based on centralized production. Its reactors are described as being roughly the size of shipping containers, with an estimated electrical output of about 100 MWe per unit. The company intends to place reactors on barges, potentially combining several units on one platform. A barge-based architecture could provide location flexibility and allow factory manufacturing to substitute for extensive on-site construction. The proposed fueling cycle is twelve years, and the company presents the system as a civilian design without military applications or a proliferation risk. In April 2025, the company changed its name from Seaborg Technologies to Saltfoss Energy. The new name was chosen to evoke flowing salt and large-scale energy production, with “foss” derived from Old Norse terminology for a powerful waterfall. The rebrand preserved the company’s focus on molten salt nuclear technology. Saltfoss Energy has stated an ambition to deliver its first power barge in the first half of 2030. Achieving that objective will require successful completion of engineering development, fuel and materials qualification, regulatory approval, manufacturing scale-up, financing, and site or maritime deployment arrangements.

• 2025

  Seaborg Technologies renamed Saltfoss Energy

  [1]Saltfoss Energyen.wikipedia.org

  The company adopted the Saltfoss Energy name in April, linking its identity to flowing molten salt and large-scale energy production.

• 2023

  First-generation reactor fuel strategy revised

  [1]Saltfoss Energyen.wikipedia.org

  Saltfoss Energy chose low-enriched uranium instead of the originally planned HALEU for at least its first reactor generation, citing HALEU supply timing. The associated moderator concept changed from molten sodium hydroxide to graphite.

• 2015

  Company founded in Denmark

  [1]Saltfoss Energyen.wikipedia.org

  The startup was established in Denmark to develop compact molten salt reactor technology for civilian power generation.

• Target for first power barge

  [1]Saltfoss Energyen.wikipedia.org

  The company has stated a target of delivering its first power barge in the first half of 2030.

Saltfoss Energy positions itself as a developer of compact, inherently safer and potentially lower-cost nuclear power based on molten salt technology, centralized manufacturing, and mobile barge deployment.

• Molten salt nuclear reactor

  Compact Molten Salt Reactor (CMSR)

  Saltfoss Energy’s principal reactor design uses nuclear fuel dissolved in molten salt rather than solid fuel rods. The concept is intended to operate at approximately atmospheric pressure and to use a passive drain system in which a melting freeze plug allows fuel to leave the core during an overheating event. The design is being developed in compact form, with an estimated output of about 100 MWe per reactor and a proposed twelve-year fueling cycle. The first generation is planned around low-enriched uranium and graphite moderation.

• Nuclear power platform

  Barge-mounted power system

  The proposed deployment platform would place one or more compact reactors on a barge. Saltfoss Energy’s model combines centralized reactor manufacturing with mobile or relocatable marine deployment. Multiple approximately container-sized reactor units could potentially be installed on one barge, creating a power platform for electricity supply near suitable demand centers. The concept remains subject to engineering, maritime, nuclear-safety, licensing, and infrastructure requirements.

• 2025

  Rename the company Saltfoss EnergyStrategy

  Background

  The company formerly known as Seaborg Technologies sought a name that reflected its molten-salt technology and its intended scale of energy production.

  Action taken

  In April 2025, the business changed its name to Saltfoss Energy.

  Aftermath

  The rebranding retained the company’s focus on compact molten salt reactors and its proposed barge-based deployment model.

  Source

• 2023

  Adopt LEU and graphite for at least the first reactor generationStrategy

  Background

  The original CMSR concept was associated with HALEU fuel and a molten sodium-hydroxide moderator. The company assessed that HALEU supply might not become available on the timetable required for its development program.

  Action taken

  Saltfoss Energy switched at least its first planned reactor generation to low-enriched uranium and changed the moderator concept to graphite.

  Aftermath

  The change aligned the initial design with the company’s stated fuel-supply timetable while altering important aspects of the reactor’s physics and engineering configuration.

  Source

1. 1Saltfoss Energyen.wikipedia.org