Microreactors Achieve Criticality Milestone

By July 4, 2026, four American companies—Antares Nuclear, Valar Atomics, Deployable Energy, and Aalo Atomics—successfully achieved zero-power fuelled criticality. This critical milestone meets a deadline established in May 2025 under President Trump's Reactor Pilot Program.

Antares Nuclear was the first to reach this point on June 4 at Idaho National Laboratory, proving the safety of its Mark-0 microreactor. This achievement marks the first criticality for a new, privately developed non-light-water reactor in the U.S. in over four decades. Antares' R1 microreactor is anticipated to begin producing electricity in 2027, with military deployments expected in 2028.

Valar Atomics' Ward 250 reactor achieved criticality on June 19 in Utah and subsequently generated 10 kW of electricity, powering an AI chip. Deployable Energy's Unity microreactor also reached criticality on July 1, validating its supply chain and regulatory pathway. Aalo Atomics completed the set of four on July 4, progressing towards a commercial-scale system slated for 2027.

The government's Reactor Pilot Program provided essential support, including access to facilities, expertise, and regulatory guidance, accelerating these developers' progress. This initiative is crucial for boosting nuclear output and advancing advanced reactor technologies towards commercialization.