Jimmy
🇫🇷 Paris, FR · Founded 2020 · Active
Jimmy is a French start-up based in Paris that designs small nuclear heat generators for factories and plans to install, operate and later dismantle them itself. Each unit is a high-temperature gas-cooled reactor of 10 to 20 MW of heat, fuelled with TRISO particles (uranium kernels sealed in ceramic layers), and supplies process heat only, with no electricity. Customers would buy the heat at a price fixed for 20 years. In April 2024 Jimmy filed an application with the French authorities for permission to build a first generator, and in March 2026 it announced €80 million of new financing. Its website also describes an industrial platform in Saône-et-Loire.
- Sector
- Fission
- Technology
- High-temperature gas-cooled reactor
- Fuel
- TRISO particle fuel
- Role
- Reactor developer
Terms
- High-temperature gas-cooled reactor
- Helium-cooled and graphite-moderated, running far hotter than a water reactor. Fuel is TRISO particles, typically formed into pebbles or prismatic blocks, at LEU or HALEU enrichment depending on the design. The high outlet temperature suits industrial process heat as well as electricity.
- TRISO particle fuel
- Fuel kernels about the size of a poppy seed, each wrapped in layers of carbon and silicon carbide, so every particle acts as a tiny containment for its own fission products. The US Department of Energy reports that irradiated particles came through more than 300 hours of testing at temperatures up to 1,800 °C with no to minimal damage. That record covers the particle designs, temperatures and burnups actually tested; a claim outside that envelope is not covered by it.
Designs
| Design | Developer | Approach | Electrical output per unit | Size class | Licensing stage |
|---|---|---|---|---|---|
| Jimmy | Jimmy | High-temperature gas-cooled reactor | Output not stated | Not classed | No milestone recorded |