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Stellarium is a 4th-gen molten salt reactor designed to destroy more nuclear waste than it produces.
ByJijo Malayil
Nov 28, 2025 09:38 AM EST
French startup Stellaria secures its first power reservation from Equinix for Stellarium, the world’s first fast-neutron reactor that reduces nuclear waste.
The agreement will allow Equinix data centres to leverage the reactor’s energy autonomy, supporting sustainable, decarbonized operations and powering AI capabilities with clean nuclear energy.
The Stellarium reactor, proposed by Stellaria, is a fourth-generation fast-neutron molten-salt design that uses liquid chloride salt fuel and is engineered to operate on a closed fuel cycle.
In July, the startup spun out of the French Alternative Energies and Atomic Energy Commission (CEA) and Schneider Electric, raised €23 million (about $26.88 million USD) to develop the type of nuclear reactor capable of eliminating more waste than it produces.
Compact clean power
Founded in 2023, Stellaria aims to drive reindustrialization by providing a clean, resilient, and scalable nuclear energy source for the modern era.
Stellarium is aimed at meeting rising electricity demand, which uses liquid chloride salt fuel in a closed fuel cycle. It could become the world’s first reactor to destroy more long-lived nuclear waste than it produces, a feat no commercial reactor has yet achieved.
The reactor will be highly compact, occupying just four cubic metres, and capable of using a wide range of nuclear fuels, including uranium, plutonium, MOX, minor actinides, and thorium.
Despite its ambitious goals, the Stellarium builds on proven reactor principles, deliberately limiting innovations to what is essential for faster development. Key design features include passive cooling via natural convection, isogeneration to sustain the fuel cycle, and four physical containment barriers—one more than most current reactors. It is designed to operate for over 20 years without refueling.
According to Stellaria, with an energy density 70 million times higher than lithium-ion batteries, a single Stellarium reactor could power a city of 400,000 people. This makes it a compelling, practical alternative to coal and gas for energy-intensive industries.
Sustainable AI energy
Global electricity consumption is projected to rise by 4 percent per year through 2027, the fastest growth in recent years, according to the International Energy Agency.
According to Stellaria, this surge is driven by unprecedented electrification, expanding data centres supporting AI, and a rebound in industrial production. The rising demand is straining ageing grids and challenging energy suppliers, highlighting the need for new power sources to sustain growth.
Now, Stellaria and Equinix have signed a pre-order agreement for 500 MW of power, part of Equinix’s broader push into alternative energy. In August, Equinix announced collaborations with five energy providers, including Stellaria in France, to support the expansion of its AI-Ready data centres. Through this agreement, Equinix has secured the first power capacity reservation on Stellaria’s Stellarium reactor, which the company plans to deploy starting in 2035.
Under the agreement, Stellarium will supply Equinix’s data centres with a carbon-free, controllable energy solution, enabling fully autonomous operations. The reactor’s underground design, liquid core, and atmospheric-pressure operation enhance safety, requiring no exclusion zone. Its liquid core enables rapid adaptation to load variations, providing flexible, responsive power as needed.
“The digital sector is fully engaged in sustainability to reduce environmental impact: this contract lays the foundation for lifetime energy autonomous data centres, and we are proud to support a major player like Equinix in this project,” said Nicolas Breyton, CEO of Stellaria, in a statement.
According to Stellarium, it also supports fuel regeneration through infinite reuse, partly using waste from existing nuclear plants, and promotes sustainability through its multi-fuel capability. The collaboration represents a significant step toward clean, resilient, and flexible energy for AI-driven infrastructure.
Original:
https://interestingengineering.com/energy/worlds-first-fast-neutron-reactor
