Antares, a nuclear energy startup, passed a major phase for its Mark-0 reactor. The U.S. Department of Energy (DOE) officially approved the company’s safety analysis, meaning the government has signed off on the final design and the safety plans that support it.

The recent milestone follows a preliminary safety approval back in January. Now, the company is moving into the “Readiness Review” phase. This is the last big step before they get the green light to power up their reactor pilot. If everything stays on schedule, they plan to reach criticality before July 4, 2026.

“We are entering the final innings, and that’s incredibly exciting,” said Jordan Bramble, CEO and founder of Antares. “Getting here was only possible with strong support from our partners at Idaho National Laboratory and BWXT, and leadership at DOE, along with relentless work from the Antares team.”

Proving the Reactor Works

This demonstration will test important pieces like reactor physics and the control systems.

The company has been working with BWX Technologies since late 2025 to make the fuel, using a specific type of uranium called HALEU provided by the DOE. They’ve managed to keep a tight schedule in an industry known for long delays.

“We developed this timeline in 2023 and we have hit every milestone since,” Bramble said. “This is a clear sign that we are proving our safety basis every step of the way, and I’m proud of the way this team has cleared key checkpoints, on schedule, again and again.”

The government seems to agree. Rian Bahran, Deputy Assistant Secretary of Energy for Nuclear Reactors, noted that the DOE is happy to see this progress.

Once the Mark-0 tests wrap up, the company plans to use the same facility and fuel for the Mark-1 next year, with hopes of producing electricity in 2027. From there, they are looking toward 2028 to start commercializing these reactors.