France-based Blue Capsule Technology has begun construction of the ELISE test rig for sodium at high temperatures. Construction began this week at Peyrolles-en-Provence, in collaboration with France’s CSTI GROUPE.
“ELISE will replicate the conditions of the Blue Capsule high-temperature reactor (HTR), with temperatures reaching 750°C,” said the company’s Technical Director, Domnin Erard. “This full-size installation will stand at nine metres high when completed, and provide valuable data on thermo-hydraulics and the natural circulation of liquid sodium at high temperatures.”
Blue Capsule is planning to build a proof-of-concept sodium loop and a non-nuclear prototype by 2030. ELISE is the first installation on Blue Capsule Technology’s development roadmap and is set to run for several years. This new milestone is funded by fresh investment by the company’s historical investors, as well as CSTI Groupe, Robatel and Helionix.
President of Blue Capsule Technology, Edouard Hourcade, said the ELISE installation will be the “first of its kind” in France, and will be opened to other players in the field, “either institutional or commercial”. He added: “It is important that the broader nuclear energy sector can benefit from ELISE. But it’s also a milestone for our company and a sign of steady progress.”
Blue Capsule Technology is developing a sodium-cooled HTR for energy-intensive industries such as cement and metal refining, hydrogen production, and chemical sites (for fertiliser and soda ash production). These industries increasingly need a reliable source of fossil-free heat, steam and electricity. The Blue Capsule HTR will provide all three: heat to 700°C, steam/vapour to 650°C, and 50 MWe as needed by the customer, with subterranean capsules co-located onsite, close to demand. The reactor is designed to operate for 60 years. Blue Capsule is aiming for a cost to the end user of €50 ($60) per MWh for industrial heat.
The reactor will use low-enriched (less than 5% uranium 235) TRi-structural ISOtropic (TRISO) fuel for optimal safety. Blue Capsule said the design is optimised for more favourable economics due to the lower volume of building materials compared with traditional high temperature gas-cooled reactors. The company chose low-enriched TRISO “given the wide use of low-enriched uranium (LEU) in the industry, and the export potential of reactors that use LEU”.
In November 2025, Blue Capsule Technology announced an agreement to advance its cooperation on fuel with French company Framatome. The term sheet agreement covers qualification of TRISO fuel particles for Blue Capsule. It also includes manufacturing of fuel elements for the Blue Capsule HTR. In parallel, Framatome announced the launch of dedicated pilot line for TRISO fuel at its Romans-sur-Isère site in France.
As to regulation, in May 2025, Blue Capsule advanced to Phase 2 (the Preparatory Review) of its technical discussions with French Nuclear Safety & Radiation Protection Authority (ASNR – L’Autorité de Sûreté Nucléaire et de Radioprotection). Construction of the non-nuclear prototype is scheduled to begin in 2027-28 followed by construction of the reactor in 2029-30 for deployment in the early 2030s.
CSTI Groupe President Nicolas Corselle noted: “The construction of ELISE in Peyrolles-en-Provence marks a major technological step forward and reflects the strength and quality of the work accomplished together. Our commitment today as an investor is a natural continuation of this operational partnership. Investing in Blue Capsule is, for us, a way to affirm our conviction: the decarbonisation of energy-intensive industries will rely on innovative, safe, and economically competitive nuclear solutions.”
To date, Blue Capsule Technology has announced partnerships with the CEA, Framatome, Egis, CSTI GROUPE, DigIntel, ROBATEL and Veolia | Nuclear Solutions, as well as key suppliers such as Laborelec and Mersen. The company’s “historical investors” include Eren Groupe SA, Exergon, AUDACIA Coinvest, and CEA Investissement.
Aix-en-Provence-based start-up Blue Capsule was founded in 2022 as a spin-off from France’s Alternative Energies & Atomic Energy Commission (CEA – Commissariat à l’énergie Atomique et aux énergies Alternatives). Its project was a winner of the “Innovative Nuclear Reactors” call under the France 2030 investment plan, receiving a €10m grant and completing private funding rounds to support its prototype development.
