Stellaria
Stellaria is a French nuclear startup developing the Stellarium, a fourth-generation fast neutron molten salt reactor with 20-year fuel autonomy. It licenses reactor designs and provides operational support to data center operators and industrial customers, targeting 2035 commercial launch.
- Company typePrivate
- Founded2023
- HeadquartersSarreguemines, France
- Headcount11–50
- GTM typeB2B
- OfferingHardware or Manufacturing
What Stellaria does
Stellaria is a French nuclear technology startup founded in June 2023 as a spin-off from the Commissariat à l'énergie atomique (CEA) and Schneider Electric. The company is developing the Stellarium, a fourth-generation advanced molten salt reactor (AMR-MSR) using a fast neutron spectrum and chloride salt (NaCl) liquid fuel core. Stellaria's primary customers are large industrial electricity consumers, including data center operators, petrochemical plants, steel mills, mining operations, and healthcare facilities, with each 250 MWe (or 540 MWth) Stellarium unit capable of supplying approximately 400,000 inhabitants. The company targets first commercial deployment by 2035.
The Stellarium's defining feature is its liquid-core architecture, which enables 100% in-core fuel renewal during operation. The reactor isogenerates fissile material at a 1:1 ratio, eliminating periodic refueling and external reprocessing, and supports a 20-year fuel cycle. The design operates via natural convection without pumps, incorporates four containment barriers instead of the conventional three, and is installed underground to remove exclusion zones. It is multi-fuel capable (uranium, plutonium, thorium), features autostable operation without control rods, and is immune to xenon poisoning due to its fast neutron spectrum. Stellaria has five patents filed (one shared with CEA), an exclusive license on three CEA patents, and holds the registered STELLARIUM® trademark.
Stellaria's business model centers on licensing and selling validated, certified molten salt reactor systems to operators, supplemented by long-term power purchase agreements and ongoing operational support services. The company is pre-revenue, with its first commercial reservation being a 500 MWe pre-order from Equinix (November 2025) for AI-ready data centers. Funding totals over €36 million across a €1.75M seed round (2023), a €10M non-dilutive France 2030 grant (March 2024), and a €23M Series A (July 2025: €14M equity plus €9M non-dilutive). The 22+ person team is led by founders Nicolas Breyton (CEO, ex-Schneider Electric), Guillaume Campioni (CTO, ex-CEA), Antoine Gerschenfeld (Managing Director, ex-CEA), Bruno Desbrière (Safety Expert, ex-Institut Laue-Langevin), and Lucas Tardieu (Deputy CTO, ex-CEA), with offices in Grenoble (headquarters), Orsay (chemistry lab at IJCLab/CNRS), and a planned installation at CEA Cadarache.
Stellaria firmographics
Firmographics- Name
- Stellaria
- Legal name
- Stellaria Design
- Website
- https://stellaria.fr
- Company type
- Private
- Founded year
- 2023
- Operating status
- Operating
- Headcount range
- 11–50 employees
- Short description
- Stellaria is a French nuclear startup developing the Stellarium, a fourth-generation fast neutron molten salt reactor with 20-year fuel autonomy. It licenses reactor designs and provides operational support to data center operators and industrial customers, targeting 2035 commercial launch.
- Ownership category
- akta.pro rank
Stellaria industry classification
Industry- Product category
- Advanced Nuclear Reactors
- NAICS
- Nuclear Electric Power Generation (221113)
- SIC
- Cogeneration Services & Small Power Producers (4991)
- akta.pro primary industry
- Reactor Vessel, Internals & Primary Circuit Components (RPV, piping, pumps, valves) (EUAKADAE)
- akta.pro secondary industries
- Instrumentation & Control (I&C) Integration & Commissioning Support (EUAKAAAH), Quality Assurance / Quality Control (QA/QC) & Nuclear Codes Compliance (ASME, RCC-M, etc.) (EUAKAAAI)
Keywords
Where Stellaria is headquartered
LocationHeadquarters
- HQ city
- Sarreguemines
- HQ country
- France
- HQ region
- Europe
Offices4 records
Markets served
Stellaria business model
Business model- GTM type
- B2B
- Offering type
- Hardware or Manufacturing
- Cost components
- Personnel, Technology or R&D, Operations, Marketing or Sales, Infrastructure
Revenue model
- Reactor Licensing: Licensing and sale of tested, certified, and validated nuclear systems. The company focuses on the core of innovation - providing the reactor design and licensing it to operators.
- Operations Support: Support services for reactor operators once reactors are in exploitation. Ongoing technical support, maintenance, fuel management, and operational assistance.
- Power Purchase Agreements: Long-term electricity supply contracts with industrial clients such as data centers. Pre-order agreements securing future power capacity (e.g., Equinix 500 MWe agreement).
Go-to-market motion2 records
Distribution channels2 records
Marketing channels12 records
Stellaria product offering
Product offeringCore offering
Stellaria develops, licenses, and sells the Stellarium — a fourth-generation fast neutron molten salt reactor (AMR-MSR) with a liquid chloride-salt core capable of renewing 100% of its fuel during operation. The company provides licensed nuclear systems, ongoing operational support, and long-term power supply to large industrial clients (data centers, petrochemical plants, steel mills, mining operations, hospitals).
Product overview
Stellaria offers a portfolio of fourth-generation molten salt nuclear reactor products centered on the Stellarium platform. The product line progresses from the Alvin critical fission experiment (100 kW, planned 2029), through the MegAlvin prototype (10 MW, planned 2030), to the commercial Stellarium reactor available in 110 MWe and 170 MWe configurations (planned 2035). The Stellarium is a fast neutron, liquid-core molten salt reactor (AMR-MSR) capable of regenerating 100% of its fuel during operation, operating via natural convection, and designed for underground installation. Stellaria also provides reactor licensing and operational support services for deployed units.
Differentiator
Problem solved
Functional benefit
Products and services
- Stellarium (Commercial Reactor) Fourth-generation fast neutron molten salt nuclear reactor (AMR-MSR) with a liquid chloride-salt core capable of renewing 100% of its fuel during operation. Multi-fuel capable (uranium, plutonium, thorium), operates via natural convection without pumps, produces 250 MWe or 540 MWth per unit, with a 20-year fuel cycle and underground installation design. Targets large industrial clients including data centers, petrochemical plants, steel mills, mining operations, and hospitals.
- Stellarium 110 MWe Configuration 110 MWe modular configuration option for the Stellarium reactor, suitable for industrial sites requiring moderate power output with flexibility for scaling. Part of the Stellarium product family.
- Stellarium 170 MWe Configuration 170 MWe modular configuration option for the Stellarium reactor, providing higher power output for larger industrial facilities and energy-intensive operations. Part of the Stellarium product family.
- Alvin (Critical Fission Experiment) Critical fission experiment (mini-reactor) with 50cm core diameter and 100 kW power capacity. Validates neutronic-thermal-hydraulic coupling calculations and demonstrates safety features for the commercial Stellarium reactor. Planned to be hosted at the INB ALPHA installation at CEA Cadarache.
- MegAlvin (Prototype Reactor) Prototype reactor with 10 MW power capacity, planned for 2030 at the CEA Cadarache facility within INB Alpha. Enables endurance testing and fuel qualification, material structure testing, and specific molten salt reactor system testing. Precursor to commercial Stellarium deployment.
- Reactor Licensing and Operational Support Services Licensing and sale of tested, certified, and validated molten salt nuclear systems to operators, complemented by ongoing operational support, maintenance, fuel management, and technical assistance for reactor operators once units are in exploitation.
Quantifiable outcome
- 99% less CO2 per MWh compared to gas and coal-fired power stations
- +6 more outcomes
Companies that use Stellaria
Customer profileNamed customers1 record
Segments4 records
Ideal customer profiles3 records
Stellaria technology and API
TechnologyTechnology focussed Yes
API detail
- Has API
- No
- API docs
- API detail
Core technology
AI maturity
App detail
Feature8 records
Stellaria partnerships and signals
Strategic signalPartnerships
16 partnerships are on record, tiered core and supporting.
- CEA (Commissariat à l'énergie atomique)coreCEA is a major public research organization supporting Stellaria's technical development. Signed Letter of Intent (LOI) in April 2026 for INB ALPHA feasibility study at Cadarache. CEA provides technical support for the project and shares expertise in fast neutron reactors. Stellaria is a spin-off from CEA. Collaboration on codes and simulation adapted for molten salt reactors.
- CNRS (IJCLab)coreFrench National Center for Scientific Research. IJCLab in Orsay hosts Stellaria's chemistry team. International experts in molten salt chemistry studying corrosion phenomena and synthesis pathways. Active collaboration since 2024.
- ASNR (Autorité de sûreté nucléaire et de radioprotection)coreFrench nuclear safety and radiation protection authority. Reviewing Stellaria's DAC (Authorization to Create) application for INB ALPHA. Placed Stellaria in preliminary phase for DAC completion. Active regulatory dialogue ongoing.
- EquinixcoreGlobal data center infrastructure company (Nasdaq: EQIX). Pre-order agreement for 500 MWe of power capacity from Stellarium reactors. First reservation of energy capacity on Stellarium. Powers AI-ready data centers with 24/7 carbon-free energy. Régis Castagné: 'Their Stellariums natively generate 250 MWe of clean energy and consume their own waste, eliminating on-site storage needs.'
- Schneider ElectriccoreStrategic partner and investor providing digital energy management and automation technologies. Schneider Electric supplies power distribution and control systems for the reactor. Frédéric Godemel, DG Energy Management: 'Stellaria is on track to develop the first molten salt fast neutron reactor in the world by 2035.' Co-founder of the company.
- Technip EnergiescoreLeading engineering and technology company for energy transition. Partner for modular factory construction and industrial deployment. Supports scaling up of molten salt reactor technology. Benjamin Lechuga: 'Technip Energies is happy to continue its engagement alongside Stellaria.'
- OranocoreNuclear fuel cycle specialist covering uranium extraction through spent fuel recycling. Consortium partner for France 2030. Collaborative R&D on fuel chemistry, salt synthesis, and spent fuel reprocessing. Sharing group with Thorizon and Naarea for fast reactor fuel supply chain.
- Unitel TechnologiessupportingDigital infrastructure company that deployed a revolutionary AI/HPC cluster for Stellaria. Enabled calculation of reactor digital twin parameters in record time. Full technological sovereignty with 24/7 uninterrupted operation. Kévin Polizzi: 'This AI cluster is not just a secure infrastructure; it's a tool for energy transition and industrial sovereignty.'
- Oak Ridge National Lab (ORNL)supportingUS Department of Energy national laboratory. Stellaria participated in molten salt reactor workshop in Tennessee (November 2024) alongside US researchers and DOE officials. Technical exchange on molten salt technology, nuclear security, non-proliferation, and fission gases.
- Centrum výzkumu Řež (Czech CEA equivalent)supportingCzech nuclear research institute. Stellaria met with the team to discuss sustainable nuclear energy. Participation in ENES2024 Europe Nuclear Energy Conference in Czech Republic.
- Generation IV International Forum (GIF)supportingInternational cooperation platform for fourth-generation nuclear technology. Stellaria presented advances and concept details at GIF committee meeting at IJCLab. Participation in MSR working group alongside Canadian and US teams.
- TU DelftsupportingTechnical University in the Netherlands. Stellaria co-supervises a doctoral student with TU Delft as part of European academic network development.
- France 2030 Export Programsupporting30-month international development program through Business France. Access to 100-country network. Support for international stakeholder engagement and co-building international offerings.
- ThorizonsupportingDutch molten salt reactor developer. Part of the sharing group with Orano and Naarea for fast reactor fuel supply chain, transport, packaging, fabrication and reprocessing facilities.
- NaareasupportingFrench molten salt reactor startup. Part of the sharing group with Orano and Thorizon for fast reactor fuel supply chain development.
- SCK CEN (Belgium)supportingBelgian Nuclear Research Centre. Part of Stellaria's emerging European academic and research network for nuclear innovation.
Scale indicators20 records
Recent moves7 records
Expansion highlights6 records
Stellaria competitors and assessment
Company assessmentDirect peers
- Naarea: French molten salt reactor startup developing the XAMR (eXtrasmall Advanced Molten Salt Reactor). Most direct peer given similar technology focus, French regulatory environment, similar stage, and shared participation in the Orano/Thorizon fuel cycle sharing group.
- Thorizon: Dutch molten salt reactor developer focused on the Thorizon One reactor. Direct peer given similar MSR technology focus, European regulatory environment, and partnership with Orano in the fast reactor fuel supply chain sharing group alongside Stellaria.
- Terrestrial Energy: Canadian company developing the Integral Molten Salt Reactor (IMSR), a molten salt fission reactor. Direct peer given MSR technology focus and similar goal of commercial deployment of advanced nuclear technology for industrial applications.
- Kairos Power: US company developing the fluoride salt-cooled high-temperature reactor (KP-FHR). Direct peer in the molten salt reactor space, pursuing similar goal of commercial advanced reactor deployment with safety-by-design philosophy.
Emerging players
- Seaborg Technologies: Danish company developing the Compact Molten Salt Reactor (CMSR) for floating power plants. Emerging peer in the MSR space with similar technology focus but different deployment model (marine-based).
- Moltex Energy: UK/Canadian company developing the Stable Salt Reactor (SSR-W). Emerging peer in molten salt reactor space with similar focus on simplified, safer nuclear technology for industrial and grid applications.
- Copenhagen Atomics: Danish thorium-based molten salt reactor developer using modular reactor design. Emerging peer in the MSR space with similar technology focus on thorium fuel cycle and modular deployment for industrial applications.
Broad incumbents
- TerraPower: Bill Gates-backed advanced reactor company developing the Natrium sodium fast reactor. Broader incumbent in advanced nuclear space pursuing similar goal of commercial Gen IV deployment with industrial decarbonization focus.
- X-energy: US company developing the Xe-100 high-temperature gas-cooled reactor and TRISO fuel. Broader incumbent in advanced nuclear space targeting industrial applications including data centers and petrochemical facilities.
- Rolls-Royce SMR: UK consortium developing a 470 MWe small modular reactor based on conventional PWR technology. Broader incumbent in the SMR space pursuing similar goal of modular, factory-built nuclear reactors for industrial and grid applications.
Market position
Strengths5 records
Weaknesses5 records
Competitive moat5 records
Key risks6 records
Key highlights6 records
Customer concentration
Stellaria social profiles
Digital presenceStellaria financial estimates
Financial estimateRevenue estimate
Valuation estimate
Stellaria leadership team
Management profileNumber of profiles
Profiles7 records
Stellaria funding detail
Funding detailFunding overview
Funding rounds1 record
Investors6 records
Funding detail is available on the Subscription and Enterprise plan.Contact sales →
Stellaria M&A and investment
M&A and investmentM&A
Investments
M&A and investment is available on the Subscription and Enterprise plan.Contact sales →
Frequently asked questions about Stellaria
What does Stellaria do?
Stellaria develops, licenses, and sells the Stellarium — a fourth-generation fast neutron molten salt reactor (AMR-MSR) with a liquid chloride-salt core capable of renewing 100% of its fuel during operation. The company provides licensed nuclear systems, ongoing operational support, and long-term power supply to large industrial clients (data centers, petrochemical plants, steel mills, mining operations, hospitals).
Is Stellaria a public or private company?
Stellaria is a private company. It is classified as venture growth investor backed and is currently operating.
When was Stellaria founded?
Stellaria was founded in 2023. It employs 11 to 50 people.
Where is Stellaria based?
Stellaria is headquartered in Sarreguemines, France, in the Europe region.
How does Stellaria make money?
Three revenue lines are on record. Reactor Licensing is the primary driver. The others are operations Support and power Purchase Agreements.
Who are Stellaria's main competitors?
Direct peers on record are Naarea, Thorizon, Terrestrial Energy and Kairos Power. Emerging players are Seaborg Technologies, Moltex Energy and Copenhagen Atomics. Broad incumbents are TerraPower, X-energy and Rolls-Royce SMR.
Does Stellaria have an API?
No public API is recorded for Stellaria.
What industry is Stellaria in?
Stellaria's product category is Advanced Nuclear Reactors. Its primary akta.pro industry code is EUAKADAE, Reactor Vessel, Internals & Primary Circuit Components (RPV, piping, pumps, valves), with a secondary code of EUAKAAAH, Instrumentation & Control (I&C) Integration & Commissioning Support. Its NAICS code is 221113 and its SIC code is 4991.