goingcritical:radiant-kaleidosUnited States · Microreactor
Radiant Kaleidos
Status: Under construction target criticality Q3 2026 (confidence: high) Reactor status full glossary → Announced Publicly announced — a site and design are proposed, but construction has not begun. Site preparation Early site and civil works are under way; the first safety-related ("nuclear") concrete has not yet been poured. Under construction Formal construction has begun, marked by the first nuclear concrete. Fuel loaded Nuclear fuel has been loaded into the core. The reactor is fuelled but has not yet gone critical. Critical Has reached first criticality — a self-sustaining chain reaction, usually at low power — but is not yet connected to the grid. Grid connected Synchronised to the electrical grid and exporting power for the first time, but still in commissioning and power-ascension testing — not yet in commercial service. In commercial operation — the operator has formally declared the unit in regular commercial service. Shut down Permanently shut down and no longer generating; may be defuelled, undergoing decommissioning, or preserved in place. Canceled Abandoned before completion.
Site: DOME test bed (NRIC), Idaho National Laboratory, Idaho
First full-power test authorization (DARK approval, Feb 2026) under the Reactor Pilot Program; took possession of INL's DOME facility April 1, 2026; also selected for the Nuclear Energy Launch Pad
Five-phase fueled test campaign at DOME over summer 2026, from zero-power criticality up to 150+ hours at full power; first TRISO fuel tranche delivered July 1, 2026
Details
| Design | Kaleidos — helium-cooled, HALEU TRISO-fueled portable microreactor (1 MWe) |
| Capacity | 1 MW (thermal where reported) |
Milestone history
- Announced August 12, 2025
- Construction start —
- Fuel load —
- First criticality target Q3 2026