French start-up Stellaria just made a major move in the world of nuclear energy. On December 19, 2025, the company officially filed its Application for Authorization to Create for a new facility called Alpha. While that sounds like a lot of paperwork, it is actually a huge deal because it makes Stellaria the first French company working on fast-neutron reactors to reach this stage.
Stellaria started as a spin-off from Schneider Electric and the CEA. Now, they are moving from just having a good idea to actually becoming a nuclear operator. This application is for their Alvin prototype, which they hope to turn on by 2030. The goal of this prototype is to run a series of tests that will prove their reactor design really works in the real world.
Moving past the concept stage
To get this application ready, the team had to put together about fifteen different documents that add up to over a thousand pages. It covers everything from how they will handle earthquakes and floods to how they plan to protect workers and the environment. They even had to explain how they will eventually take the building apart at the end of its life.
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“2025 marked a turning point for Stellaria. After a structuring fundraising round, followed by the signing of a first power pre-order agreement for our reactors with Equinix, the global leader in data centers, the submission of the DAC (Application for Authorization to Create) allows us to reach a new milestone,” said Nicolas Breyton, the President of Stellaria. “This step is decisive for Stellaria, as it validates the work carried out so far by its teams and partners, and fully commits the company to its responsibilities as a nuclear operator.”
“By filing this application, Stellaria moves beyond the concept stage and enters a structuring regulatory phase, in which its fundamental choices are now set,” Breyton explained.
What happens now?
Now that the papers are in, the French government has to review them. This is a long process, but Stellaria is ahead of the pack. Out of the eleven French start-ups currently working on small or advanced modular reactors, only one other company has made it this far. By getting their plans for the Alvin prototype in front of regulators now, Stellaria is positioning itself as a leader in the next generation of French nuclear power.
