It’s Tuesday, and today we’re looking at Stellaria, a French company in the nuclear energy space. Founded by Nicolas Breyton, Guillaume Campioni, Lucas Tardieu, Bruno Desbriere, and Antoine Gerschenfeld, the company recently raised €23 million in a round led by At One Ventures and Supernova Invest, with participation from CEA Investissements, Schneider Electric, Exergon, and Technip Energies.
The Context
France has been Europe’s nuclear energy leader for decades. After the 1973 oil shock, Prime Minister Pierre Messmer launched a sweeping program to expand the country’s nuclear capacity, setting off a build-out that continued for many years.
Today, nuclear accounts for 68% of France’s electricity production — the highest share worldwide. The country also ranks third globally in both total electricity generated from nuclear power and number of reactors.
For our purposes, there are three essentials to understand about France’s nuclear sector: it’s supported by a long-standing and mature ecosystem; it enjoys consistent public backing; and there are active plans for further expansion.
1. Developed ecosystem. The French nuclear industry is highly integrated, built around a closed fuel cycle (reprocessing used fuel to recover uranium and plutonium) and dominated by state-backed players — EDF for power generation, Orano for the fuel cycle, and CEA for research. It supports around 220,000 jobs across 3,000 companies engaged in power generation, fuel cycle operations, research, manufacturing, waste management, and training.
Through the decades the industry spawned throughout several formal and informal clusters:
Nuclear Valley — spanning Bourgogne-Franche-Comté and Auvergne-Rhône-Alpes, Nuclear Valley is an industry association with 440 members, from major firms to SMEs, research labs, and training bodies. Its role is to strengthen the supply chain by helping members find partners, secure funding, and train talent.
Normandy — with just 4% of the national population, the region hosts 20% of nuclear facilities and 12% of the workforce. It is home to Orano’s La Hague recycling site and a cask manufacturing plant for used fuel storage in Cherbourg. Normandie Energies also plays a role in training nuclear professionals.
Auvergne-Rhône-Alpes — prominent for fuel cycle front-end operations. The Tricastin site handles uranium conversion and enrichment, while Framatome runs a fuel fabrication plant in Romans-sur-Isère. Finally, Grenoble hosts several major research institutions, including the ILL, a leading neutron science center.
Provence-Alpes-Côte d'Azur — a research-heavy region, home to Cadarache, one of Europe’s largest nuclear R&D centers, the ITER project, the world’s largest fusion experiment, and INSTN, a leading nuclear training institute.
2. Public support. The French public strongly backs nuclear power. About 75% support using it to generate electricity, and 60% favorfurther development — the second-highest level in Europe, compared with 47% in Germany, 43% in Italy, and 38% in Spain. Confidence in safety oversight is relatively strong too: 56% of the population consider nuclear plant controls to be effective, rising to 69% among those living within 10 km of a plant.
However, it’s important to note that even the French think that nuclear has the most disaster potential. 24% believe that nuclear plants are most likely to cause a serious accident, slightly ahead of radioactive waste storage (17%). And 69% believe that the safety of nuclear installations should come before energy production.
3. The 2030 plan. France 2030 is a €54 billion investment plan launched in 2021, aimed at accelerating the country’s transition to a sustainable and innovative economy by 2030. It sets out ten objectives, the first being the development of small modular reactors to address France’s lag in reactor construction. €1 billion has been allocated to innovative reactor programs, including support for selected startups. The plan also includes building six EPR2 reactors, a new generation designed to be simpler, more standardized, and more reliable than previous models.
The Product
Stellaria is an unusual company for me to write about because it doesn’t actually have a product yet.
That said, the concept it’s working on is compelling and fits squarely within the themes we cover at Geography & Tech.
Backed by France’s ambitions to expand nuclear power, and supported by the France 2030 initiative, Stellaria is developing small modular reactors (SMRs), specifically molten salt reactors (MSRs).
I’m no nuclear physicist, and most of my readers aren’t either, so let’s focus on what makes Stellaria’s approach different from traditional reactors without getting too technical:
Fuel reuse. A long-standing challenge in nuclear is what to do with spent fuel like uranium, plutonium, or thorium. Stellaria’s design reuses this fuel. More than that, it is “isogenerative,” meaning it can continuously recreate as much fissile material as it consumes. In today’s reactors, only a small fraction of the fuel undergoes fission, leaving behind long-lived waste that must be stored for hundreds of thousands of years. Stellaria’s MSR instead burns many of these long-lived transuranics, turning them into much shorter-lived isotopes — waste that decays in about 300 years rather than 300,000 — while also cutting the total volume of waste by around four times
Easy assembly and maintenance. Instead of being a single massive installation like conventional nuclear plants, Stellaria’s reactor is built from modular, brick-like components. This should make assembly much quicker than traditional plants. It also simplifies maintenance: instead of shutting down the whole system, individual “bricks” can be swapped or repaired. The idea is to make nuclear deployment, upkeep, and scaling both faster and cheaper.
Safety. Stellaria’s MSR is claimed to be roughly ten times safer than today’s reactors. Molten salt coolant operates at low pressure and absorbs heat efficiently, avoiding the risk of steam explosions like those at Chernobyl or Fukushima. The system also uses a “freeze plug” — a chunk of solidified salt at the reactor’s base that melts if the reactor overheats, passively draining the fuel into tanks where the chain reaction stops automatically.
Efficiency. According to Stellaria, its MSR could operate for up to 20 years without refueling and deliver an energy density tens of millions of times higher than lithium-ion batteries. One unit could power a city of about 400,000 people. The design is also compact — roughly 2 meters wide and 5 meters tall — and highly flexible, with the ability to ramp power output up or down by ~30% per minute.
Unique design features unlock not only product differentiation, but a business model one.
The Business Model
There are two main ways Stellaria’s business model differs from traditional nuclear projects. First, because the plant is more compact, capital expenditure per unit is roughly half that of conventional builds. Second, since the reactor runs on reused fuel, Stellaria is less exposed to supply chain disruptions and price volatility.
In practice, that means Stellaria’s plants:
Are cheaper to build due to their size and efficiency.
Are cheaper to maintain thanks to their modular, brick-like design.
Have more predictable economics because of the fuel factor.
Are more versatile and can be deployed in more locations, again thanks to their compact footprint.
The company likens its model to Nespresso: it will provide the reactor along with the associated fuel system. The vessel containing fuel and coolant is replaced — every five years initially, but potentially extending to 25+ years as the technology matures. Stellaria expects to begin generating revenue in 2031 and to reach €1 billion in sales by 2035.
The Bear Case
I think, as with most emerging technologies — and the company acknowledges this — there are technical challenges that need to be solved. Molten salt reactors, modular refueling, and large-scale fuel recycling are not yet proven at industrial scale. Nuclear energy is controversial, so securing both governmental and public approval can be difficult. Unlike in traditional industries, a single roadblock here could slow the company down for years — and overcoming that roadblock would require many millions in additional funding.
If the technology works but turns out to be less scalable or efficient than Stellaria currently projects, raising further funding might become a challenge.
It’s a very big bet, and for it to succeed three components — technology, funding, and regulation — all have to align.
The Bull Case
But if those factors do align, the product Stellaria promises is extraordinary. If the company delivers on its vision, it will be entering a market with powerful tailwinds: European countries are seeking energy independence, and the AI boom is driving unprecedented demand for electricity. If Stellaria can provide that energy at lower cost and in a deployable, modular form, it would be a huge win for the data center industry in particular — and that market is unlikely to slow down anytime soon.
The Takeaway
While preparing this article, I came across a chart. And honestly, it’s depressing. From what I understand, today’s technology is already good enough to make another Chernobyl impossible. Yet countries around the world still pour money into oil and gas, or build absurd wind farms, while the solution to the world’s energy problems is sitting in plain sight.
