goingcritical:radiant-kaleidosUnited States · Microreactor

Radiant Kaleidos

Status: Under construction target criticality Q3 2026 (confidence: low) ? 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. Operating 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.

Developer: Radiant Industries

Site: DOME test bed (NRIC), Idaho National Laboratory, Idaho

OaklandPortlandSeattleDenverVancouverSalt Lake CityWichita

Company-stated target was all five phases of the fueled DOME campaign — zero-power criticality up to 150+ hours at full power — complete by Q3 2026. That window closed on 30 September 2026 with no reported criticality and no revised target from Radiant; the unit left El Segundo by road on 12 August 2026 and its arrival and emplacement at DOME have not been publicly confirmed. First TRISO fuel tranche was delivered to the DOME facility on 1 July 2026, six weeks before the reactor shipped.

Details

Design	Kaleidos — helium-cooled, HALEU TRISO-fueled portable microreactor (1 MWe)
Capacity	1 MW (thermal where reported)

Milestone history

1. Announced August 12, 2025
2. Construction start —
3. Fuel load —
4. First criticality target Q3 2026