Westinghouse Electric Company successfully completed the zero-power criticality test for its eVinci microreactor on August 24, 2026, at 10:39 a.m. Pacific Time, at the National Criticality Experiments Research Center (NCERC) in Nevada. The result validated the computational models and core design assumptions of the reactor, confirming that the technology behaves exactly as predicted.
The test was conducted in collaboration with Los Alamos National Laboratory and Idaho National Laboratory, within a National Nuclear Security Administration (NNSA) facility at the Nevada National Security Site. Zero-power criticality — the reactor’s ability to sustain a stable fission chain reaction at minimal energy levels, without generating appreciable heat — is the benchmark verification for any new reactor before advancing to operational phases. No electricity was produced: the sole objective was to confirm the neutron behavior of the core against simulation models.
The eVinci design combines advanced heat pipe technology, TRISO fuel, graphite core materials, and control drums, all housed in a compact architecture tailored for remote and operationally demanding environments. The reactor is designed to deliver up to 5 MWe from a 15 MWt core, operate without refueling for eight or more years, and be transportable in standard shipping containers. Target applications range from military bases to space missions. Westinghouse assembles it in a factory setting, eliminating much of the on-site construction complexity typical of conventional plants.
This milestone fits within the broader context of the DOE Reactor Pilot Program, established by Executive Order 14301 in June 2025, which set a goal of achieving criticality for at least three private reactors by July 4, 2026. The eVinci test follows those of Antares Nuclear and Valar Atomics by several weeks. The Department of Energy had already conditionally selected eVinci in July 2025 for fueled testing at Idaho National Laboratory’s DOME facility — housed within the historic Experimental Breeder Reactor-II structure — alongside Radiant’s Kaleidos microreactor. The version destined for DOME is a 3 MWt variant, a scaled-down configuration relative to the commercial design, conceived to demonstrate key performance characteristics and support the licensing pathway.
Data gathered during this test campaign will feed into upcoming design improvements, prototyping, and manufacturing process development. This is the approach Westinghouse calls “rapid product development”: integrated cycles of testing, modeling, and design refinement to reduce technical risk and compress the technology maturation timeline. The next milestone — fueled operation at DOME — will be the most demanding proving ground before commercialization. If the tests confirm expected performance, eVinci is positioned to become one of the most versatile tools in the emerging distributed nuclear energy landscape.
