Advanced micro reactor achieves criticality in only two years

5 hours ago

Antares Nuclear Inc.'s Mark-0 microreactor achieved zero-power criticality at Idaho National Laboratory, the first advanced reactor to do so under the DOE's Reactor Pilot Program.
The milestone, reached on June 4, marks the 53rd reactor built at INL since 1951 and the first novel design to achieve criticality there in over 50 years.
Zero-power criticality verifies the reactor's self-sustaining chain reaction at negligible energy output, serving as a key scientific and engineering validation for future steps.
Antares, founded in 2023 and with over $140 million in funding, plans to deploy electricity-producing reactors for defense and space customers by 2028.
The Mark-0 uses HALEU TRISO fuel, with supply agreements including Urenco, and builds on fuel specifications from BWX Technologies developed under Project Pele.
Antares's roadmap includes the Mark-1 full-power reactor in 2027 and the commercial R1 microreactor (100 kWe to 1 MWe) for military and grid-independent applications.
Other companies like Valar Atomics, Aalo Atomics, Radiant Nuclear, and Oklo are also advancing under the Reactor Pilot Program, targeting criticality milestones by July 4, 2026.
The DOE's Nuclear Energy Launch Pad was established in March 2026 to extend the authorization pathway to additional projects beyond the initial program cohort.
U.S. Energy Secretary Chris Wright highlighted this as the first privately developed non-light-water reactor to reach criticality in the U.S. in over 40 years.

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