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June 4, 2026
Department of Energy Celebrates First Advanced Reactor Criticality<br>Today, as part of the U.S. Department of Energy Reactor Pilot Program, Antares… Read more
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Department of Energy Celebrates First Advanced Reactor Criticality
Today, as part of the U.S. Department of Energy Reactor Pilot Program, Antares Nuclear’s advanced reactor design, the Mark-0, successfully completed a zero-power fueled criticality demonstration at DOE's Idaho National Laboratory.
Energy.gov
June 4, 2026
Estimated Read Time min
WASHINGTON —The rebirth of America’s nuclear industry has officially arrived. Today, as part of the U.S. Department of Energy (DOE) Reactor Pilot Program, Antares Nuclear’s advanced reactor design, the Mark-0, successfully completed a zero-power fueled criticality demonstration at DOE's Idaho National Laboratory. This test confirms that the reactor can operate safely and establishes a basis that would allow subsequent reactors to produce electricity in 2027 and beyond. The Mark-0 is the first of multiple advanced reactors anticipated to go critical by the July 4th deadline set by President Trump in his May 2025 executive order.<br>“It is fitting that on the eve of our nation’s 250th anniversary, we are witnessing a historic moment for American energy,” U.S. Energy Secretary Chris Wright said. “For the first time in more than four decades, a new privately developed non-light-water reactor has reached criticality in the United States. Thank you to President Trump for his bold leadership and thank you to the bold scientists and entrepreneurs at Antares and Idaho National Laboratory who helped make this moment possible. I look forward to seeing continued progress in the American nuclear renaissance."<br>Criticality is the culmination of carefully planned and executed steps that result in a reactor going operational. The Mark-0 criticality test is a tremendous accomplishment that validates the safety and operational performance of Antares Nuclear’s fission reactor. One of the most significant technological achievements in nuclear energy in over 40 years, this test will go on to inform the design and licensing of future commercial reactor deployments. When commercialized after further tests and licensure by the Nuclear Regulatory Commission, microreactors like those that Antares makes are anticipated to be used in a variety of terrestrial and space applications and to ensure readiness at military installations requiring reliable energy.<br>As the 53rd reactor to be built at Idaho National Laboratory site since 1951, Mark-0 joins the storied ranks of test reactors that served as the blueprint for our nation’s current reactor fleet.<br>“The skeptics didn’t believe President Trump's Reactor Pilot Program could achieve criticality in less than a year. Today, we celebrate the first of the pilot projects to reach criticality and the people who rolled up their sleeves to...