The U.S. Department of Energy announced that Antares Nuclear, Inc. achieved zero-power criticality at Idaho National Laboratory with its Mark-0 microreactor. This historic milestone marks the first time a privately developed, non-light-water reactor has achieved a self-sustaining chain reaction in four decades.
Here is the breakdown of the Mark-0 milestone and what it means for the nuclear energy industry:
What Does Criticality Mean?
- Not a Crisis: In nuclear physics, “criticality” means a reactor has achieved a stable, self-sustaining fission chain reaction. It simply means the nuclear fuel is balanced, and it is the necessary first step before the reactor can eventually generate commercial electricity.
Reactor Specifications & Design
- Developer: Torrance, California-based Antares Nuclear, Inc.
- Fuel Type: High-assay low-enriched uranium (HALEU) tri-structural isotropic (TRISO) fuel compacts
- Coolant: Sodium heat-pipe-cooled microreactor design
- Location: Tested at the Idaho National Laboratory’s Reactor and Critical Experiment (RACE) facility.
The Regulatory Context
- DOE Reactor Pilot Program: This test is the first major milestone completed under the U.S. Department of Energy pilot program established after President Trump’s executive order in May 2025.
- The “Nuclear Renaissance”: The DOE celebrated the milestone as a turning point, designed to spur private capital investment and accelerate the approval of next-generation, advanced nuclear infrastructure.
Next Steps & Timelines
- 2027: The successful zero-power testing establishes the foundation for subsequent operational models aiming to produce commercial electricity.
- 2028: Antares plans to supply mobile, scalable power to the U.S. military (“power to the warfighter”) as the commercial sector scales up.
If you are interested in tracking the future of this program, I can provide additional details regarding:
- How the HALEU TRISO fuel cycle operates
- The broader list of companies in the DOE Reactor Pilot Program
- Technical differences between sodium-cooled microreactors and traditional light-water reactors
