Overview
- Antares completed a zero‑power fueled criticality demonstration at Idaho National Laboratory on June 4, 2026, proving a self‑sustaining chain reaction at negligible power but not producing electricity.
- The Mark‑0 uses a sodium heat‑pipe cooling system and HALEU TRISO fuel compacts processed by BWX from DOE/NNSA feedstock, a configuration tested to confirm reactor physics for this novel design.
- The result is the first novel privately developed reactor to reach criticality at INL in more than 50 years and the first milestone under the DOE Reactor Pilot Program aimed at multiple criticalities by July 4.
- Next steps for Antares include reactor‑physics experiments at INL, a program of sustained electricity testing targeted for 2027, and planned deployments to U.S. military sites in 2028, subject to further tests and NRC licensing.
- Fuel supply and regulation remain bottlenecks: the demonstration relied on government‑provided HALEU and longer‑term commercial HALEU production and Nuclear Regulatory Commission approvals are required for commercial operation.