Antares Achieves Criticality for First Privately Developed Advanced Reactor in 40 Years

On June 4th at Idaho National Laboratory, the privately developed Antares Mark-0 microreactor achieved initial zero-power fueled criticality. This milestone marks a significant breakthrough for American nuclear energy, as it is the first non-light-water reactor to reach this stage of development since the early 1980s. The event occurred ahead of schedule under the Department of Energy’s Reactor Pilot Program.

When a reactor goes critical, it signifies that a self-sustaining chain reaction has been initiated within its core at an extremely low power level to ensure safety and facilitate data collection without generating significant heat or radiation. This achievement is not just another licensing milestone but represents actual fission taking place in the reactor.

Antares's success follows a series of regulatory approvals and strategic partnerships, including securing the first-ever Documented Safety Analysis approval under DOE-STD-1271 and signing a groundbreaking multi-year commercial HALEU supply deal with Urenco. These steps have paved the way for Antares to validate key reactor physics and overall system performance for their R1 transportable microreactor design.

The Mark-0 demonstration utilizes TRISO fuel fabricated by BWX Technologies, leveraging advancements from the Department of Defense’s Project Pele military microreactor program. This collaboration with the U.S. Army positions Antares as a frontrunner in the development of advanced nuclear technologies for both civilian and military applications.

Energy Secretary Chris Wright highlighted the significance of this achievement on the eve of America's 250th anniversary, noting it as a testament to the resurgence of American innovation in nuclear energy. Assistant Secretary Ted Garrish acknowledged initial skepticism about achieving criticality within such a short timeframe but emphasized that today’s milestone is just the beginning.