Four US microreactors reach criticality under federal pilot program
Four prototype microreactors — from Antares Nuclear, Valar Atomics, Deployable Energy and Aalo Atomics — have reached zero-power criticality, meaning each sustained a nuclear chain reaction without generating meaningful electricity. The units were selected for the Department of Energy’s Reactor Pilot Program, which gave 11 projects land and national-lab support, and the four clearances exceed the Trump administration’s target of three by July 4.
The milestone is real but narrow. Zero-power criticality proves the physics of a design works; it does not demonstrate the cooling systems, fuel supply and engineering needed to deliver power to a grid, and analysts note it can be reached without much progress on those harder problems. Regulatory approval remains a substantial hurdle, and startup timelines in the sector have a long record of slipping.
Still, the pace signals momentum for advanced nuclear at a moment when data centers and electrification are driving up demand for firm, emissions-free electricity — the gap that microreactor developers are pitching themselves to fill.