Antares NuclearIn Development
A full-scale, zero-power demonstration of the R1 core at Idaho National Laboratory's RACE facility, built under DOE's Reactor Pilot Program. It has no power conversion or heat-removal loop; the test validated reactor physics, control-drum behavior, and the DOE authorization pathway using BWXT-fabricated HALEU TRISO.
Latest update Sep 18, 2026
01
Achieved initial (zero-power) criticality on June 4, 2026. Not an electricity-producing plant. Antares plans to reuse the same INL facility and fuel batch for the Mark-1 electricity-producing reactor in 2027.
02
03
Announced next steps from Antares Nuclear that mention Mark-0.
2027
Operate a full-power, electricity-producing advanced reactor at the same INL test facility used for Mark-0, using the same HALEU TRISO batch and a nitrogen closed Brayton cycle. Antares has said Mark-1 is scheduled to operate for more than six months in 2027. As of September 18, 2026 this remained a company target, not a started campaign.
04
Antares Nuclear's Mark-0 sodium heat-pipe microreactor achieved zero-power criticality at Idaho National Laboratory on June 4, 2026, becoming the first privately developed advanced reactor to reach that milestone under the Department of Energy's Reactor Pilot Program - a Trump executive-order initiative targeting at least three advanced reactor criticalities by July 4. The Mark-0 is fueled by HALEU TRISO compacts and uses a heat-pipe-cooled, fast-spectrum design initially targeting U.S. military bases, with commercial electricity sales targeted for late 2027 and full deployment by end of 2028 - at the same Idaho National Laboratory campus where Oklo is constructing its Aurora powerhouse under an NRC-issued combined construction and operating license. The DOE has selected eleven advanced reactor projects under the RPP, and the Antares milestone validates the regulatory testing infrastructure and fast-fission design path that underpins the broader U.S. advanced nuclear build-out.
05
Antares' commercial factory-built microreactor: a TRISO-fueled prismatic graphite core with graphite and boron carbide control drums, passive sodium heat pipes, a fin-and-tube primary heat exchanger, and a recuperated nitrogen closed Brayton cycle at under 300 psi. Packaged with integrated shielding and a transport cradle for defense-critical assets, rated at 100 kWe to 1 MWe for 6+ years without refueling and without a grid connection.
Space variant of the R1 heat-pipe microreactor. Under a $161M Space Force Strategic Breakthrough award, Antares will run a nuclear ground demonstration of the R1-S, integrate it with a spacecraft for flight certification, and use Mark-1 to power an operational ground-to-space asset during 2027 testing.
06
NuScale Power
Full-scale SMR power plant with 12 modules generating up to 924 MWe of carbon-free electricity.
NuScale Power
Self-contained 77 MWe pressurized water reactor module with integrated steam generators.
NuScale Power
Mid-size SMR plant configuration with 6 modules producing up to 462 MWe.
Oklo
Oklo's fast-fission powerhouse product line is designed for build-own-operate deployment, targeting customers that want firm clean power in a smaller footprint than traditional large reactors.