Stellarium, a next-generation molten salt fast reactor built to eliminate more nuclear waste than it creates, has taken a major step toward deployment.French startup Stellaria has secured its first power reservation from Equinix, marking a world first: a fast-neutron nuclear reactor intended to supply clean, continuous power to AI data centers in Europe.

Designed as a fourth-generation fast-neutron molten-salt system, Stellarium runs on liquid chloride fuel and operates in a closed fuel cycle. In July, Stellaria—spun out of the French Atomic Energy Commission (CEA) and Schneider Electric—raised €23 million to advance development. The company’s goal is ambitious: build the first commercial reactor capable of destroying more long-lived radioactive waste than it produces.

Figure 1. AI Data Centers.

Ultra-Compact, High-Efficiency Nuclear Power

Founded in 2023, Stellaria aims to support industrial growth and electrification with resilient, scalable nuclear power. The Stellarium reactor occupies just four cubic meters yet can operate for over 20 years without refueling, thanks to its closed fuel cycle and flexible fuel options—including uranium, plutonium, MOX, thorium, and minor actinides. Figure 1 shows AI Data Centers.

Stellaria says its core technology builds on proven reactor concepts while focusing only on essential innovations to accelerate development. Key features include:

• Passive safety through natural convection
• Four containment layers (one more than traditional reactors)
• Isogeneration to maintain the fuel cycle
• Atmospheric-pressure operation with no required exclusion zone

The company claims a single Stellarium unit—thanks to energy density 70 million times that of lithium-ion batteries—could power a city of 400,000 people, making it a realistic alternative to coal or gas for heavy power users.

Powering the Future of AI Sustainably

Electricity demand is rising faster than in previous years—approximately 4% annually through 2027, according to the IEA—driven by electrification, industrial rebound, and rapid expansion of AI-enabled data centers.

To address this, Equinix has pre-ordered 500 MW of Stellarium power as part of a broader shift toward alternative, carbon-free energy solutions. The reactor is expected to begin deployment in 2035, supplying stable baseload power to future AI operations.

Stellarium’s underground design, liquid-core flexibility, and ability to instantly follow load changes make it particularly suited to AI workloads, which demand highly responsive power [1]. The system also recycles and regenerates fuel—including waste from existing nuclear sites—supporting a circular nuclear economy.

“This contract sets the stage for lifetime energy-autonomous data centers,” said Stellaria CEO Nicolas Breyton. “We’re proud to support Equinix as the digital sector advances toward sustainability.”

References:

1. https://interestingengineering.com/energy/worlds-first-fast-neutron-reactor

Cite this article:

Keerthana S (2025), Europe’s First Fast-Neutron Reactor Will Soon Power AI Data Centers, AnaTechMaz, pp.174