French nuclear start-up Stellaria has raised €23 million in a major new funding round to accelerate the development of its fast neutron molten-salt nuclear reactor, Stellarium, with the goal of reaching commercial deployment by 2035. The announcement was made on July 24, 2025, in Grenoble, marking a significant step forward for the company’s fourth-generation clean energy technology. The financing was co-led by US impact investor At One Ventures and France’s Supernova Invest, with participation from earlier backers including CEA Investissements, Schneider Electric, Exergon, and Technip Energies.
This latest capital infusion follows Stellaria’s successful 2023 seed round and includes €10 million in non-dilutive support through France 2030’s “Innovative Reactors” initiative. The funding will enable Stellaria to conduct regulatory and technical studies required for its planned prototype installation in 2029.
What is Stellaria building in France?
Stellaria is focused on building the Stellarium, a fast neutron molten-salt reactor designed to regenerate its own fuel continuously during operation. This self-regenerating capability, central to the company’s design, is aimed at ensuring 20 years of operation without the need for fresh nuclear fuel, significantly reducing long-lived radioactive waste, especially minor actinides.
The Stellarium falls under the fourth-generation nuclear reactor category and is engineered for high efficiency, long-term sustainability, and a dramatically reduced carbon footprint. According to Stellaria, replacing fossil-fuel-based heat sources with their reactor could slash CO2 and particulate emissions at industrial facilities by as much as 99%. The company’s long-term vision is to support decarbonization across industrial sectors and electrical grids, offering a flexible energy solution for high-demand users.
How will Stellaria use the €23 million funding?
Stellaria stated that the €23 million will be directed toward several critical development activities in the lead-up to the Stellarium prototype. These include advancing R&D, finalizing the reactor’s core technical design, and preparing for licensing and safety documentation ahead of construction.
The investment will also support the doubling of Stellaria’s workforce to strengthen its in-house technical and regulatory teams. A significant portion of the funding will be used to expand Stellaria’s research laboratory in Grenoble, the company’s headquarters and main development site.
Key deliverables from this funding phase include the submission of an Application for Authorisation to Create (DAC) a Basic Nuclear Installation (INB) to France’s nuclear safety authorities. This filing will be a milestone in Stellaria’s journey toward building one of the world’s first fast-neutron liquid-core reactor demonstrators.
According to Stellaria CEO Nicolas Breyton, the funding reflects investor confidence in the reactor’s technical maturity and its potential to reshape the nuclear fuel cycle into a circular, low-waste model. Breyton emphasized that Stellaria’s technology aims to enable electro-intensive industries to achieve full energy autonomy for the operational lifetime of their infrastructure.
What sets Stellarium apart in the next-gen nuclear field?
Molten-salt reactors (MSRs) are considered a promising avenue for safe and efficient nuclear energy. Unlike conventional water-cooled reactors, MSRs use liquid fuel, typically a mixture of salts containing fissile materials, which allows them to operate at higher temperatures and lower pressures. This design improves efficiency while reducing the risk of catastrophic failure.
Stellaria’s Stellarium goes a step further by incorporating fast neutron technology into its molten-salt architecture. Fast neutrons enable more effective fuel use and allow the reactor to burn and transmute actinides that would otherwise become long-term waste. This results in reduced need for high-level waste repositories and enhances fuel sustainability.
Moreover, Stellarium’s closed-cycle fuel regeneration feature aims to minimize reliance on external uranium enrichment or reprocessing infrastructure, offering the potential for decentralized and self-sufficient energy systems, especially in industrial settings with heavy power and heat demands.
How does Stellaria fit into France’s nuclear innovation roadmap?
France has long maintained a strong nuclear energy portfolio and is actively investing in next-generation technologies through its France 2030 initiative, which seeks to reindustrialize the economy while decarbonizing its energy sector. The initiative has earmarked substantial funding for small modular reactors (SMRs), advanced fission, and fusion research.
Stellaria’s success in securing €10 million in non-dilutive financing from France 2030’s “Innovative Reactors” program signals the French government’s endorsement of molten-salt reactor innovation as a viable path forward in its broader clean energy transformation. By fostering partnerships with public and private stakeholders, Stellaria aligns with national strategies targeting energy sovereignty and deep industrial decarbonization.
Stellaria also benefits from its dual heritage—spun out of the French Alternative Energies and Atomic Energy Commission (CEA) and supported by Schneider Electric. This positions the company at the intersection of government research, industrial technology, and venture innovation.
What are the industry implications of Stellaria’s reactor breakthrough?
The Stellarium, if successfully deployed by its 2035 target, could serve as a benchmark for compact, scalable, and self-sustaining nuclear reactors tailored for industrial zones, chemical plants, and even off-grid applications. This could represent a departure from centralized gigawatt-scale nuclear plants, allowing for modular deployments closer to the point of energy use.
Its impact on the fuel cycle is also noteworthy. By regenerating its own fuel and consuming waste-like elements such as minor actinides, the reactor could significantly ease the burden on long-term storage infrastructure—a persistent challenge in the global nuclear landscape.
From an investment perspective, Stellaria’s funding round indicates growing investor appetite for advanced nuclear technologies that combine clean energy goals with economic viability. Impact investors like At One Ventures are increasingly prioritizing hard tech solutions capable of scaling net-zero outcomes, while strategic industrial partners like Technip Energies bring deep engineering expertise to accelerate time-to-market.
As more countries look to diversify their clean energy portfolios beyond renewables, scalable nuclear systems like the Stellarium are gaining renewed attention. The success of Stellaria’s reactor could also encourage international regulators and funding bodies to expand support for liquid-core and fast-neutron reactor designs, which remain underrepresented compared to conventional pressurized water reactor (PWR) systems.
What’s next for Stellaria?
Stellaria’s immediate priority is to complete the technical and licensing groundwork required to build its first demonstrator facility. If regulatory approval progresses on schedule, construction could begin before the end of the decade, with the prototype targeting operational readiness by 2029.
Concurrently, Stellaria aims to expand its industrial collaborations and strengthen its role in European and global nuclear R&D networks. The company may also begin exploring international export markets in the early 2030s, particularly in regions with high industrial demand and limited grid access to renewables.
CEO Nicolas Breyton has described this phase as “foundational,” positioning Stellaria not just as a reactor developer but as a catalyst for a new generation of clean, resilient, and autonomous energy systems. As the company continues to scale its team and infrastructure, the success of the Stellarium program may prove pivotal in reshaping how advanced nuclear energy is delivered, governed, and commercialized.
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