The race between a handful of nuclear fission startups to switch on their microreactor and small modular reactors before Independence Day is heating up.
Yesterday, Los Angeles-based space and defense-focused nuclear startup Antares moved into the “final innings” of turning on its Mark-0 microreactor after the Department of Energy approved its Documented Safety Analysis (DSA), green-lighting the final design and safety review before the DOE’s Reactor Pilot Program’s July 4 deadline.
Going nuclear: Antares—which has raised ~$134M to date—is one of 10 startups in the mix for the DOE’s Reactor Pilot Program, launched after a May 2025 executive order that called for at least three test reactors to hit criticality (when a nuclear fission chain reaction becomes self-sustaining) by Independence Day.
- The program aims to speed up the regulatory timeline for nuclear firms building small modular reactors, which the Pentagon is eyeing for off-grid power supply on military installations.
- Antares had its Preliminary Documented Safety Analysis (PDSA), the safety basis document companies need to design and construct new or modified nuclear facilities, approved back in January, which CEO Jordan Bramble told Tectonic was “the most significant milestone of the entire process” to reaching criticality.
- Other startups in the mix include some well-funded, familiar names like Aalo Atomics, Oklo, Valar Atomics, Radiant Energy, along with Atomic Alchemy, Deep Fission, Last Energy, Natura Resources, and Terrestrial Energy.
Final countdown: The DSA approval now means the company is ready to kick off the Readiness Review, the final phase before the DOE gives Antares the go-ahead to switch on its Mark-0 reactor.
- Mark-0, Antares’ first demonstration reactor, will be tested at the DOE’s Idaho National Laboratory using a full-scale core and the same facility and fuel as their electricity-producing one that’s scheduled to come online in 2027.
- It’s built to be modular and compact enough to operate off the grid in remote locations, such as military installations, and is expected to provide between 100 kW and 1 MW of power over a 4 to 6-year period.
- It’s designed to run on TRISO fuel, a new type of ceramic pellet fuel that’s safer than traditional nuclear fuels.
Pole position: Along with being on track to reach criticality before July 4, Antares is pretty fired up.
Bramble told Tectonic that they have the “first DSA to get approved in the program” and are the first company to enter the fourth and final stage of the DOE’s authorization plan, about a week ahead of schedule. “I don’t think we’ve ever once been the first company to submit any of these documents, but we’ve always been the first to get them approved. We’ve actually been able to accelerate our schedule.”
“At the end of the day, the DOE has a bar for safety and engineering rigor, and you have to meet that before they’re going to approve anything,” Bramble added. “We’ve gone from a clean sheet design of a control system— basically zero—to now for putting [it] in a reactor in about nine months’ time, which is an incredibly awesome feat for the team.”
Energy boost: Antares and their nuclear frenemies in the program moving pretty fast is good news for the Pentagon, especially the Army, which launched the Janus Program—a next-generation nuclear power program aiming to deliver energy to domestic military installations (at least to start) by September 2028—last October.
“You hear people say it’s a marathon, not a sprint, but it’s been a marathon where you’re sprinting,” he said. “There’s a lot of work that’s gone into this, but I think we’re really showing everyone what the country is capable of.”