Antares Nuclear and Valar Atomics say their experimental reactors have achieved “zero-power” criticality under a Department of Energy pilot program created after President Trump signed an executive order in 2025. The initiative aims to see at least three test reactors reach criticality by July 4, 2026, a deadline that has drawn scrutiny from safety advocates over accelerated oversight.
Valar Atomics said its Ward 250 reactor achieved “zero-power fueled criticality” on June 18 at the Utah San Rafael Energy Lab in Emery County, Utah. The Department of Energy (DOE), which is overseeing the project under its Reactor Pilot Program, also announced the June 18 criticality milestone.
Antares Nuclear reached a similar benchmark earlier in the month. DOE and multiple industry and news reports said Antares’ Mark-0 microreactor achieved zero-power criticality on June 4 during testing at Idaho National Laboratory.
The Reactor Pilot Program was launched by DOE in 2025 following President Trump’s executive order directing the agency to streamline reactor-testing processes. DOE has said the program’s goal is to “construct, operate, and achieve criticality” of at least three test reactors using DOE’s authorization process by July 4, 2026—the date of the United States’ 250th anniversary of the Declaration of Independence.
The administration’s speed-focused approach has prompted warnings from some nuclear-safety and environmental advocates, who argue that accelerated timelines and streamlined reviews risk weakening long-established safeguards. DOE, for its part, has said the program uses a DOE authorization framework and that safety requirements remain in place as the projects move through testing.
Other companies involved in advanced-reactor development have also signaled they are working toward the July 4, 2026 target, though schedules and technical milestones vary by project and are subject to change.
