Antares Microreactor Reaches Criticality At Idaho National Lab
Antares Nuclear's Mark-0 microreactor achieved initial criticality at Idaho National Laboratory on Thursday, June 4, 2026, under Department of Energy authorization.[1]
Energy Secretary Chris Wright and the Department of Energy said the Mark-0 is the first privately developed non-light-water reactor to reach criticality in the United States in more than four decades.[2] Antares CEO Jordan Bramble said the company set internal milestones of criticality in 2026, electricity production in 2027, and "power to the warfighter" in 2028.[1] He said the June 4 criticality was the first of those milestones delivered.[1]
President Donald Trump's 2025 Executive Order 14301 directed the Energy Department to create a Reactor Pilot Program and set a goal of achieving criticality for advanced reactor concepts by July 4, 2026.[1] The Antares test at Idaho National Laboratory was carried out under that Reactor Pilot Program, and Antares named BWX Technologies as a key technical partner for the demonstration.[1] The U.S. Army is listed as a participating future end user in the project.[1]
Antares said the criticality test validated key reactor-physics parameters and generated control-system performance data that will inform further reactor development.[1]
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📌 Key Facts
- Antares Nuclear's Mark-0 microreactor achieved initial criticality at Idaho National Laboratory on Thursday, June 4, 2026, under Department of Energy authorization (Mark-0 microreactor).
- Energy Secretary Chris Wright and the DOE said the Mark-0 is the first privately developed non-light-water reactor to reach criticality in the U.S. in more than four decades (Energy Secretary Chris Wright).
- Antares CEO Jordan Bramble said the company set internal milestones of criticality in 2026, electricity production in 2027, and 'power to the warfighter' in 2028, and that the June 4 criticality is the first of those milestones delivered (Antares CEO Jordan Bramble).
- The DOE Reactor Pilot Program traces to President Donald Trump's 2025 Executive Order 14301, which ordered DOE to create the program and set a goal of achieving criticality for advanced reactor concepts by July 4, 2026 (Executive Order 14301).
- BWX Technologies was named as a key technical partner for the criticality demonstration, and the U.S. Army is participating as a future end user of the technology (BWX Technologies).
- Antares said the criticality test validated key reactor-physics parameters and generated control-system performance data that will inform further reactor development (criticality test).
📰 Source Timeline (2)
Follow how coverage of this story developed over time
- Fox News confirms that Antares Nuclear's Mark-0 microreactor achieved initial criticality at Idaho National Laboratory under Department of Energy authorization on Thursday, June 4, 2026.
- The article specifies that Mark-0 is the first privately developed non-light-water reactor to reach criticality in the U.S. in more than four decades, according to Energy Secretary Chris Wright and DOE.
- Antares CEO Jordan Bramble states that the company set internal milestones of criticality in 2026, electricity production in 2027, and 'power to the warfighter' in 2028, and that the June 4 criticality is the first of those delivered.
- The piece directly links the DOE Reactor Pilot Program to President Donald Trump's 2025 Executive Order 14301, which ordered DOE to create the program and set a goal of achieving criticality for advanced reactor concepts by July 4, 2026.
- The article names BWX Technologies as a key technical partner in the criticality demonstration and confirms the U.S. Army is participating as a future end user of the technology.
- Antares says the criticality test validated key reactor physics parameters and generated control-system performance data that will inform further reactor development.