Westinghouse’s eVinci microreactor reached zero-power criticality at 10:39 a.m. Pacific time on August 24, 2026, and the company announced it the next day. This was a physics test. The reactor made no usable heat or power.
What actually happened in Nevada?
The test took place at the National Criticality Experiments Research Center (NCERC), a National Nuclear Security Administration facility at the Nevada National Security Site that is used for criticality experiments. Los Alamos and Idaho National Laboratories took part.
Zero-power criticality means the core sustained a chain reaction at a power level too low to produce heat. Westinghouse used it to validate its models and core design assumptions. POWER Magazine describes it as a physics-validation experiment, not a fueled power demonstration. Westinghouse CTO Lou Martinez Sancho said the milestone reflects the company’s heritage of innovation.
Did it produce electricity?
No. Zero-power criticality does not generate heat or power, and electricity generation is expected only in later fueled testing. The test validates neutron physics. It does not test heat removal, power conversion or fuel performance at power.
What is the eVinci?
It is a heat-pipe-cooled microreactor with a solid steel-monolith core and TRISO fuel using HALEU. POWER reports the commercial configuration at 5 MWe and 13 MWth. World Nuclear News cites a 15 MWt core design, so the thermal figure differs by source. Westinghouse claims about eight years of full-power operation between refuelings. That is a design target, and like the 5 MWe figure it is a company claim that no fueled test has confirmed. Heat pipes move heat without pumps, a feature the company also stresses. For a similar approach, see our post on the NuCube heat-pipe reactor.
Who gets to use it, and when?
Not ordinary customers yet. If it works as planned, the first users would be defense, space and government customers, which is where the near-term pipeline points. The Saskatchewan Research Council contract was canceled in fall 2025. Nothing here is a product you can order, and the sources give no price, construction schedule or permit status.
Why It Matters to You
- Directly, not much today. This is a lab milestone.
- Indirectly, a small reactor that runs for years without refuelling could one day supply remote bases or sites that now depend on shipped-in fuel, if later fueled tests and regulators allow it.
- The 2028 date is only a program target for first on-base deployments.
Is eVinci approved for Malmstrom or Fort Drum?
Not yet for Malmstrom. An April 23, 2026 Westinghouse release says the Air Force, with DIU, proposed eVinci for Malmstrom Air Force Base in Montana. Westinghouse and its partners will evaluate siting and construction under the Advanced Nuclear Power for Installations (ANPI) program. The release reports no final deployment decision, construction contract or cost, and although its headline says “selected,” its text says the reactor is proposed and siting is to be evaluated. POWER notes a 2028 target for first on-base microreactor deployments under ANPI.
Westinghouse Government Services also won a Fort Drum, New York, slot in the Army’s Janus Program, with no output or schedule disclosed.
What comes next, and what is the NRC’s role?
The next major step is fueled operation at INL’s DOME test bed, where a scaled 3 MWth eVinci test reactor is planned, according to POWER. POWER also reports an agreement in principle with Urenco to secure HALEU supply.
On regulation, POWER reports the NRC accepted the eVinci Principal Design Criteria Topical Report in March 2025. That is a design review step, not a license.
Sources
- World Nuclear News: Criticality testing milestone for Westinghouse’s eVinci microreactor (Aug 25, 2026)
- POWER Magazine: Westinghouse eVinci Reaches Criticality Milestone at Nevada Test Site (Aug 26, 2026)
- Westinghouse: eVinci Microreactor Selected for Malmstrom Air Force Base (Apr 23, 2026)