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FAQ for Everyone
What is Stellaria?
Originating from CEA and Schneider Electric, Stellaria is a French startup specializing in molten-salt nuclear reactors, with the goal of reinventing sustainable fast-neutron nuclear energy.
What is a Stellarium?
A Stellarium is a revolutionary nuclear reactor conceived, developed, and designed by Stellaria and its partners. It is the world’s first reactor to operate with a liquid fuel capable of destroying more waste than it produces. As an ideal tool for supporting reindustrialization, it brings autonomy, resilience, safety, and sustainability to industrial sites lacking a complete and competitive solution for process electrification.
What does Stellaria promise?
To deliver a large-scale decarbonization solution with unparalleled safety, capable of competing with gas- and coal-fired power plants. For example, the Stellarium will be able to power a city of 400,000 inhabitants thanks to an energy density 70 million times greater than that of a lithium-ion battery.
What innovations is this reactor built around?
Although revolutionary, the Stellarium is based on many well-established concepts and incorporates only a few key innovations—allowing for rapid progress in its design.
Its use of natural convection, isogeneration, and a liquid fuel composed of chloride salts are major innovations. Additionally, including four containment barriers—rather than the three found in most current reactors—and integrating safety considerations from the beginning can also be regarded as significant advancements.
How does the Stellarium reactor work?
The Stellarium is fueled by a mixture of fissile nuclear materials—such as uranium, plutonium, or thorium—and sodium chloride, a compound similar to table salt. When the salt is heated to a very high temperature, the atoms of the fissile materials vibrate and collide, releasing and absorbing neutrons in the process. This stage is crucial, as the reactor’s ability to produce energy depends on sustaining the chain reaction and maintaining its stability over years of operation.
Where will it be installed?
The location for the first Stellariums has not yet been determined. Our first priority is to identify a site suitable for hosting our critical experiment, where we can perform all the necessary tests to validate the project before full deployment. While several options are currently being explored, the final site selection has not yet been made.
Advanced FAQ
What's the difference between isogeneration and isoreactivity?
The Stellarium is an isogenerator, meaning it recreates its fuel as it consumes it, maintaining a 1:1 ratio. This core isogeneration results in isoreactivity—a term describing the Stellarium's ability to sustain a constant neutron count over several years. Isogeneration influences the fuel cycle, while isoreactivity enhances safety by minimizing neutron loss, thereby reducing the need to deploy compensation rods.
How does Stellaria position itself within the fuel cycle?
Stellaria is one of the few startups on the market aiming to close the fuel cycle within the core itself. By reusing spent fuel from existing nuclear power plants, we offer a path toward ending uranium mining—strengthening France’s energy sovereignty and independence. After 20 years in storage, the salt is reprocessed, and its materials can either be returned to a Stellarium or sent back to today’s nuclear reactors. It’s a continuous, virtuous cycle. Moreover, because the Stellarium is isogenerative, it requires neither frequent recharging, like the RNR-Na, nor proximity to a fuel reprocessing facility.
How much nuclear material does the Stellarium consume?
Since the Stellarium is an isogenerator and recreates its own fuel, it can be considered as consuming no material.
However, according to our calculations, to produce 250 MWe over a 20-year cycle, it will contain 9.4 tonnes of plutonium in its core. Over three cycles (i.e., 60 years), a total of 18.8 tonnes of plutonium will be mobilized since the initial fuel charge, reprocessed after 20 years, will return to the reactor at the end of the cycle.
What kind of waste does the reactor produce?
Our reactor vessel is the primary waste product we generate. After 20 years of operation, it will have accumulated enough fission products to require replacement in order to keep the Stellarium running optimally. Moreover, the fission products it contains have a significantly shorter lifespan than those from conventional power plants—around 300 years of radioactivity in our case, compared to tens or even hundreds of thousands of years for others.
What is the advantage of natural convection?
Natural convection is a simple, passive physical phenomenon that we use to facilitate fuel circulation within the vessel. This eliminates the need for active components such as pumps, which would otherwise need to be specially engineered to withstand the highly corrosive environment of a molten-salt nuclear reactor.
What is the advantage of operating without a pump?
The main advantage of not using a pump is reduced exposure, as it limits intervention and handling in a hazardous environment. It also avoids issues such as imbalance, vibrations, and cavitation (the collapse of vapor bubbles that generate high-pressure shock waves, making the system more dangerous). Unlike other molten-salt reactors that use pumps to circulate fuel salt, we rely instead on natural physical laws combined with a heat exchanger designed for minimal pressure loss.
Is there a risk of the reactor exploding?
No. None of the components in our reactor operate under pressure, so there is no risk of energy build-up or sudden rupture.
Is the reactor a fire hazard?
No. We use argon in the reactor’s cells and barriers—such as the interstitial space and the vessel head. This inert gas contains no oxygen, eliminating any risk of fire inside the reactor.
How safe is the reactor?
We have designed the reactor to be as safe as possible: it cannot explode or catch fire, and all of its nuclear structures are buried to provide added protection against external hazards such as earthquakes or floods. It also features no fewer than four containment barriers to keep radioactivity as close to the core as possible.
What are the risks for the surrounding areas?
In addition to being buried, the Stellarium vessel is surrounded by three steel safety barriers and a concrete structure, providing a total of four containment layers. Thanks to these barriers, only a few millisieverts are measured at the perimeter—an amount equivalent to natural background radiation.
Is there water in the reactor?
Unlike pressurized water or boiling-water reactors (such as the one used at Chernobyl), the Stellarium is not cooled by water but by a heat-transfer salt. This eliminates the risk of water dissociating into hydrogen and oxygen, thereby avoiding the possibility of explosions like those at Fukushima.
What would happen if the reactor's cooling circuit was cut?
If the cooling circuit is interrupted, the salt will naturally begin to heat up. As it heats, it expands, which reduces the likelihood of collisions between neutrons and fissile atoms. This slows the chain reaction until it eventually comes to a complete stop.
What happens if the salt leaks?
If the vessel were to be punctured, its contents would not escape but would be contained between multiple steel barriers. Additionally, a reservoir located beneath the vessel is designed to capture any leaking fuel salt. Any chain reaction is rendered impossible thanks to its original and purpose-built geometry.
What are the control rods for?
The Stellarium's control mechanism relies on the thermal properties of the heat transfer fluid and the turbine, making traditional control rods unnecessary. In fact, due to the expansion of molten salt during load variations, the system is naturally self-regulating. When the load decreases, the reactor heats up, which slows down the nuclear reaction. This quickly leads to a new equilibrium point. Conversely, the reactor cools when the load increases, causing the salt to contract and the neutron activity to rise. The reaction is, therefore, intrinsically self-stabilizing.
Can the reactor be poisoned by xenon?
Xenon (the element behind the Chernobyl accident) acts as a neutron poison due to its strong ability to absorb neutrons. In a thermal neutron reactor, xenon's neutron absorption cross-section is about a million times greater than that of U-235 (2.65 × 10⁶6 barns for xenon compared to 1.5 barns for U-235). In fast neutron spectra, however, xenon’s capture cross-section drops to 8 × 10⁻⁴,-4 while that of U-235 is 0.09. Since the Stellarium reactor operates with the fastest neutron spectrum on the market, xenon has no poisoning effect on it.
How long does the Stellarium last?
Unlike pressurized water reactors, where the reactor vessel cannot be replaced, all Stellarium components are designed to be replaceable. The fuel has a reactivity lifespan of 20 years, which is longer than the reactor hardware's, and it can be renewed and reused over multiple cycles. The only non-replaceable element is the civil engineering—the building itself—which ultimately determines the reactor’s operational lifespan.
We estimate the Stellarium’s lifespan to be 26 years: 20 years of operation plus 6 years required to remanufacture the salt. This is significantly longer than, for example, a sodium-cooled fast reactor (RNR-Na), which typically has a lifespan of around 15 years.
Investors
Worldwide deployment
Our alliance with major global partners provides the industrial framework necessary to sell turnkey complete reactors to our customers worldwide. We place great importance on integrating our projects into the industrial fabric of the countries where they are developed (local content).
A business model based on 2 pillars
We focus on the core of innovation: licensing and selling tested, certified and validated molten salt nuclear systems and supporting operations once the reactor is up and running.
Our deliverables
We have assembled a team of multidisciplinary senior experts, enabling us to produce our preliminary design in record time. It has already been submitted to the ASN for review.
A global market
Our industrial alliance enables us to provide a complete service, from construction to fuel reprocessing, to add value to the assets of the major energy companies in each country.
Our IP strategy
We have filed 5 patents, 1 of which is shared with the CEA. We also have an exclusive licence to 3 CEA patents developed during the incubation phase.
Our roadmap
We are developing our thermal-hydraulics and chemistry-corrosion laboratories and are aiming for our first fission by the end of 2027. This roadmap is synchronised with R&D and the production of fuel salts through our consortium with Orano. The first Stellarium is scheduled for 2032, with a connection to the grid by the end of 2034.
Écosystème local
Press
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Contact us :
06 29 80 89 51
manon.colonna@stellaria.fr