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Antares Achieves Criticality, Eyes 2027 Electricity Output

6/5/2026

Summary

Antares Nuclear Achieves Criticality

Antares Nuclear achieved criticality with its Mark-0 microreactor at DOE Idaho National Laboratory on June 4, 2026, becoming first of ten companies to meet July 4, 2026 deadline for three criticalities.
CEO Jordan Bramble said it validates reactor’s control system and moves Antares toward electricity production in 2027.
Antares will use high-assay low-enriched uranium (HALEU) fuel from BWX with Urenco and plans to deploy an R1 unit at Joint Base San Antonio by 2028.

Summary

Mark-Zero Goes Critical

Mark-Zero reactor went critical at DOE’s Idaho National Laboratory.
DOE said the Mark-Zero reactor is the first privately developed non-light-water design to go critical, a blueprint backed by President Donald Trump.
U.S. Energy Secretary Jennifer Granholm called the Idaho achievement one of the most significant nuclear milestones in forty years.
Senator Jim Risch and state leaders said Idaho is leading charge toward advanced reactors and noted economic and energy-security benefits.

Summary

DOE Launches Pad

The Mark-0 test became the 53rd reactor built at Idaho National Laboratory.
Antares announced plans to adapt its microreactor for space-flight missions.
Assistant Secretary Ted Garrish said skeptics doubted the program could reach criticality within a year.
The Department of Energy launched the Nuclear Energy Launch Pad to accelerate advanced nuclear technology deployment.
CEO Jordan Bramble said the effort built camaraderie among Antares, the DOE and Idaho National Laboratory teams.

Summary

Antares Goes Critical

DOE announced June 4, 2026 that Antares Nuclear Inc. reached criticality in a pilot program with nine rivals.
The program includes competitors Oklo, Aalo Atomics, Atomic Alchemy, Deep Fission, Last Energy, and seeks fast-track approval.
The White House pursues a dual-track strategy to expand large reactors and small modular designs for energy security.
DOE aims for at least three test reactors to achieve criticality by July 4, 2026 and cites regulatory reforms that cut red tape.

History

Historical Context

In 1951 EBR-I at Argonne’s Idaho site produced 200 kW of electricity, the first usable nuclear power and the world’s first breeder reactor. Designed by Walter Zinn’s team, the achievement proved fast-neutron, sodium-cooled reactors could generate electricity. Today the Antares Mark-0 microreactor reaches criticality at the same Idaho National Laboratory location, echoing that pioneering proof-of-concept.

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Antares Nuclear Achieves Criticality

Antares Nuclear achieved criticality with its Mark-0 microreactor at DOE Idaho National Laboratory on June 4, 2026, becoming first of ten companies to meet July 4, 2026 deadline for three criticalities.
CEO Jordan Bramble said it validates reactor’s control system and moves Antares toward electricity production in 2027.
Antares will use high-assay low-enriched uranium (HALEU) fuel from BWX with Urenco and plans to deploy an R1 unit at Joint Base San Antonio by 2028.

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