Westinghouse eVinci reaches zero-power criticality at 663°C

Westinghouse Electric Company said on September 15, 2026 that its eVinci microreactor test reached zero-power criticality at 663°C on September 3, 2026 at the National Criticality Experiments Research Center (NCERC), which the company describes as a National Nuclear Security Administration capability in Nevada, and that its researchers then made a subcritical reactivity measurement at a peak core temperature of 1,011°C. The release calls that 1,011°C peak core temperature a record high temperature for a reactivity measurement at NCERC and credits Los Alamos National Laboratory and the Nevada National Security Site as partners.

The run continues the zero-power criticality campaign Westinghouse reported on August 25, 2026 for a test on August 24, one of the five microreactor criticalities The Duck Curve counted in its survey of the summer's zero-power tests. What is new is temperature. Per the September 15 release, the September 3 results generated "high-quality, temperature-dependent data" to further strengthen analytical models and accelerate prototype design, and the work advances the understanding of how the design behaves as representative materials are heated toward operating conditions. The release gives no duration for the September 3 run.

Dan Sumner, Westinghouse president and chief executive officer, described the program's approach in the release as "turning uncertainty into validated evidence." The company's boilerplate describes eVinci as a heat-pipe, TRISO-fueled, graphite-core design meant to provide electricity around the clock for eight years without refueling.

The Department of Energy's Office of Nuclear Energy posted its own account, dated September 16, 2026 on the page. It credits Los Alamos "in collaboration with Idaho National Laboratory, the Nevada National Security Site, and the DOE/NRC Collaboration for Criticality Safety Support for Commercial-Scale HALEU Fuel Cycles and Transportation," a list that adds Idaho National Laboratory and the DOE/NRC collaboration, neither of which the September 15 Westinghouse release names. DOE describes the design as sized for 5 megawatts of electricity on sites as small as two acres, with a commercial version Westinghouse expects to run eight or more years before refueling. Under a "What's Next?" heading, DOE's page points to the Army: in August 2026, it says, eVinci was selected for the next phase of the Janus Program, the Army's initiative to power military installations with microreactors, an award The Duck Curve covered when the Army named five vendors on August 26.