en.Wedoany.com Reported - Founded in 2023, the Grenoble-based nuclear startup Stellaria has selected the CEA Cadarache site in the Provence-Alpes-Côte d'Azur region to build its first experimental nuclear reactor.
Company founder and CEO Nicolas Breton stated that Cadarache, as a historic and well-known nuclear test reactor site, is an ideal location for installing the prototype device. In early May 2026, Stellaria signed a letter of intent with CEA to build two experimental facilities named "Stellarium" on the site. The company submitted a construction permit application to the French Nuclear Safety Authority in December 2025 and expects to receive an acknowledgment of receipt within the next few days.
Stellaria's two Stellarium experimental reactors will test fission reactions based on liquid regenerative fuel. Breton explained that through fuel regeneration, the same batch of fuel can support reactor operation for decades, achieving an unprecedented level of renewability globally; in terms of safety, due to the extremely rapid expansion rate of the liquid core, there will be no loss of control under any circumstances. The first small Stellarium (50×50 cm), named Alvin (in honor of Alvin Weinberg, the father of molten salt reactors from the 1960s), is planned to start construction in 2029 and achieve first fission in 2031. The second larger facility, Megalvin, will begin experiments in 2032. Neither prototype will be connected to the grid for power generation; instead, they will be used to verify the feasibility of fast neutron molten salt reactors.
Stellaria plans to conduct two rounds of financing in 2027 and 2029 respectively to support project development. The company is also building a new 1,000-square-meter laboratory in Fontaine, Isère department, for fluid dynamics and mechanical experiments. Following successful experiments, Stellaria aims to build an operational 230 MWh commercial molten salt fast reactor power station by 2035, with the specific site yet to be determined. Breton stated that Stellaria's project offers an excellent opportunity for France and Europe to reclaim leadership in nuclear innovation—"Nuclear power has somewhat tended to make new things with old technology in the past, while we are proposing a completely new perspective around fast neutron reactors, which will be more economically competitive."
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