Blue Capsule Starts Construction of ELISE High-Temperature Sodium Test Loop

Blue Capsule Technology has started construction of ELISE, a full-size, full-scale high-temperature sodium test loop at Peyrolles-en-Provence that the company says will reach temperatures up to 750°C and stand nine metres high when complete. The installation is intended to replicate the operating conditions Blue Capsule expects for its sodium-cooled high-temperature reactor and to run experimental campaigns that will inform its reactor development roadmap.

Domnin Erard, Technical Director at Blue Capsule, described the facility’s technical aims: “ELISE will replicate the conditions of the Blue Capsule high‑temperature reactor (HTR), with temperatures reaching 750°C. 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.”

Edouard Hourcade, President of Blue Capsule, framed ELISE as both a company milestone and a shared sector resource, saying the facility would be the “first of its kind” in France and “will be opened to other players in the field, either institutional or commercial ... 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’s public material describes the reactor concept as a sodium-cooled HTR aimed at industrial heat and steam delivery, stating in LinkedIn copy: “Because our reactor is a sodium-cooled high temperature reactor (HTR), that aims to produce industrial heat to 700°C, and steam to 650°C. … ELISE will let us examine in detail the merits of sodium coolant at high [...]” The company also posted in French that “… ELISE nous permettra d’étudier en détail les avantages du sodium comme fluide caloporteur à haute température, en circulation naturelle et à pression atmosphérique,” indicating tests of natural circulation at atmospheric pressure.

Blue Capsule named CSTI Groupe as a construction collaborator for ELISE and described the facility as the “first installation on the company’s development roadmap” that is “set to run for several years.” The company plans to follow ELISE with a proof-of-concept sodium loop and a non-nuclear prototype by 2030. Blue Capsule’s marketing positions the reactor as “Europe's only tri-vector energy solution at high temperatures” and lists target industrial users including ammonia, soda ash, steelmakers, cement, alumina production and hydrogen producers using high-temperature electrolysis (SOEC).

Key technical and program questions remain. The quoted 750°C test temperature differs from the company’s stated reactor aims of 700°C heat and 650°C steam; Blue Capsule has not yet clarified whether 750°C is a test-envelope maximum or applies to specific loop locations. The company has not published a construction completion or commissioning schedule, the contractual scope of CSTI Groupe’s work, project funding or budget figures, regulatory and permitting arrangements for sodium handling at Peyrolles-en-Provence, or detailed sodium safety and containment measures.

Blue Capsule announced the start of ELISE construction on 18 February 2026; the company’s statements and linked training activity at CEA Cadarache and INSTN signal a coordinated technical and personnel readiness effort as the program moves into multi-year test campaigns.