Antares Mark-0 Advanced Microreactor Achieves Zero-Power Criticality at Idaho National Laboratory (powermag.com)

• Zero-power criticality achieved June 4, 2026, at INL RACE facility.
• First reactor under DOE Reactor Pilot Program (Executive Order 14301).
• HALEU TRISO fuel fabricated by BWXT using Project Pele specification.
• Power generation planned for 2027 (Mark-1); military deployment by 2028.
• HALEU supply secured via Urenco contract for Advanced Fuels Facility (2031).

"Antares Nuclear Inc.'s Mark-0 — a sodium heat-pipe-cooled microreactor fueled by HALEU TRISO fuel compacts — achieved zero-power criticality on June 4, 2026, at Idaho National Laboratory's RACE facility. It is the first advanced reactor to reach criticality under the DOE's Reactor Pilot Program, established by Executive Order in May 2025. The milestone validates reactor physics and control systems; no electricity is generated. Antares plans to produce power with Mark-1 in 2027 and deploy for military customers by 2028. Fuel was fabricated by BWXT using a TRISO specification developed for Project Pele."