Company planning commercial advanced molten salt nuclear plant by 2035
French advanced nuclear reactor developer Stellaria and the French Alternative Energies and Atomic Energy Commission (CEA) have signed a letter of intent (LOI) for a feasibility study into the construction of key facilities at CEA’s Cadarache site.
Th LOI is for an Alpha basic nuclear installation (installation nucléaire de base, or INB) housing a test model, a fast-spectrum molten salt demonstration reactor and a salt fabrication facility to supply the prototype and demonstration reactor.
Stellaria said the signing of the LOI lays the foundations for critical experiments known as Alvin, scheduled for 2030 at the Alpha INB facility. The Alvin experiments will allow Stellaria to validate its modelling and calculations.
Once the Alvin experimental programme is complete the Alpha INB will also house the MegAlvin prototype reactor. Modification of the facility so it can house MegAlvin will begin around 2032.
The main objective of the MegAlvin project are to conduct endurance and qualification tests on fuel, testing structural materials and systems specific to molten salt reactors, and obtain operational feedback for the commissioning of Stellaria’s first commercial reactor, the Stellarium, in 2035.
Stellarium is a Generation IV molten salt design. Molten salt reactors are said to have advantages over more traditional water-cooled plants, including improved safety and higher efficiency. Inherent safety features include low-pressure operation, reduced waste and the use of standard low-enriched uranium fuel.
The startup raised €23m ($26.8m) in 2025 to support technical and regulatory studies and has previously signed a power pre-order agreement with data centre operator Equinix.
Stellaria also received €10m in public funding under the federal France 2030 programme in 2024, supporting technical studies and regulatory preparation for its prototype reactor.
In February Stellaria submitted an application to the French authorities for the potential construction the Alvin prototype.
