Westinghouse just cleared a major hurdle on the road to small, factory-built nuclear power. On August 25, 2026, the company achieved eVinci microreactor criticality in a zero-power test. Engineers ran the experiment at the National Criticality Experiments Research Center in Nevada. The test proved the reactor’s physics work exactly as designed, before a single watt of real power ever flows.
What Happened at the Nevada Test Site
Westinghouse ran the test with help from Los Alamos National Laboratory and Idaho National Laboratory. The US Department of Energy backed the effort too. The team loaded a mockup of the eVinci core into the test reactor and brought it to “zero-power criticality.” That means the core sustained a controlled chain reaction on its own, without generating any usable heat.
Zero power sounds like a modest goal, but it catches design flaws early. Engineers use it to confirm neutrons behave the way their computer models predicted. They do this before committing to a fueled reactor that actually makes heat.
What eVinci Microreactor Criticality Testing Actually Proves
The test validated three things. The reactivity control elements work. The fuel-to-moderator ratio matches the design. The core configuration behaves as engineers expected. Get any of those wrong, and a reactor either won’t start or won’t shut down cleanly. Getting them right the first time saves years of redesign work.
Westinghouse Chief Technology Officer Dr. Lou Martinez Sancho called it proof of the company’s drive to push nuclear technology forward. The bigger story is the method behind it: Westinghouse blends rapid modeling, simulation, and physical testing to mature designs faster while cutting technical risk.
Built to Run Nearly a Decade Without Refueling
The commercial eVinci produces 5 megawatts of electricity and up to 13 megawatts of heat. It uses heat pipes instead of pumped coolant loops, the same passive-safety approach behind the NuCube heat-pipe reactor’s recent safety validation. Heat pipes remove moving parts and simplify the safety systems engineers must certify.
The reactor runs on TRISO fuel and needs no refueling for eight years or more. It delivers heat up to 600°C, hot enough for industrial customers, not just the power grid. The entire unit fits in a footprint about half the size of a hockey rink.
Where eVinci Goes From Here
Westinghouse now moves to fueled testing at Idaho National Laboratory’s DOME facility, using a scaled 3-megawatt demonstration reactor. That puts eVinci alongside the Kaleidos microreactor testing already underway at the same lab. The US Air Force is evaluating eVinci for Malmstrom Air Force Base, and Westinghouse is targeting deployment there by 2028. The company also locked in a fuel supply deal with Urenco for the enriched uranium the reactor needs.
That defense focus is deliberate. Westinghouse shelved a planned commercial project in Saskatchewan last fall to concentrate on military, space, and government customers first. Those markets value reliability and can absorb higher early costs while manufacturing scales up.
Read the original coverage at World Nuclear News.
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