Antares Nuclear Achieves Criticality with TRISO HALEU Fuel in DOE Pilot Program

A Historic Milestone in Fuel Testing

The development of advanced nuclear fuel is a critical bottleneck for next-generation reactors, but recent breakthroughs are paving the way forward. Antares Nuclear has successfully achieved initial criticality with its Antares 0 reactor, a monumental achievement that validates its core design and fuel integration strategies. This milestone was reached on June 4, 2026, at the Idaho National Lab under authorization from the Department of Energy.

TRISO HALEU Fuel Integration

At the heart of this success is the use of TRISO (Tristructural Isotropic) HALEU fuel. Antares is developing modular, transportable reactors specifically fueled by this advanced material. The fuel for the Antares 0 demonstration was provided by BWX Technologies, a leading name in nuclear fabrication. The successful utilization of TRISO HALEU fuel proves that the complex manufacturing and certification processes required for advanced fuels are yielding tangible results.

Antares 0 became the first reactor under the DOE's Reactor Pilot Program to meet the July 4, 2025 deadline, showcasing rapid progress in advanced fuel deployment.

This achievement is particularly notable because Antares 0 is the first reactor under the DOE's Reactor Pilot Program to meet the strict July 4, 2025 deadline. By becoming the first private company to achieve criticality under this program, Antares has demonstrated not only the viability of its reactor design but also the readiness of its fuel supply chain partners.

Scaling Up Fuel Fabrication

The success of the Antares 0 criticality test sets the stage for commercial deployment. To support its future microreactor projects for defense and space missions, Antares has secured multi-year HALEU supply contracts with both Centrus Energy and Urenco. While Centrus will provide unobligated U.S.-origin fuel, Urenco will produce fuel at its Capenhurst facility in the UK, scheduled to come online in 2031. This dual-source strategy ensures that Antares' ambitious TRISO HALEU fuel requirements will be met as it scales from successful testing to full commercial operation.

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