Overview
- Antares’ Mark-0 reached initial criticality on June 4, 2026, achieving a self-sustaining nuclear chain reaction at Idaho National Laboratory under Department of Energy authorization.
- The demonstration confirmed key reactor physics and control-system performance and produced test data the company and DOE say will support development and licensing.
- Antares ran the test with partners including INL and BWXT, used TRISO-style fuel tied to Project Pele technology, and counted the U.S. Army as a prospective end user.
- The milestone advances a Reactor Pilot Program created by Executive Order 14301 to speed advanced reactor testing and meets the program’s aggressive timetable while leaving electricity trials and deployments for later dates.
- Commercial rollout and overseas sales could follow if regulators approve designs and a larger commercial supply of HALEU becomes available, but NRC licensing and fuel availability remain the key near-term constraints.