Microreactors are the smallest category of nuclear reactors, typically defined as producing less than approximately 20 MWe of electrical output and designed for factory fabrication, truck or air transportability, and rapid deployment with minimal on-site construction. Unlike larger SMRs that target utility-scale grid connection, microreactors are engineered for distributed applications including military forward operating bases, remote communities (mining operations, Arctic settlements, island nations), behind-the-meter industrial power, data center backup and primary power, and space applications. The key design principles are simplicity, autonomy (minimal operator staffing), and transportability, with many concepts targeting sealed core lives of 5-20 years before factory return for refueling.
The microreactor sector has attracted significant investment and multiple competing designs. Radiant Industries' Kaleidos (1 MWe) is a helium-cooled, graphite-moderated microreactor using HALEU TRISO fuel, targeting first criticality at INL's DOME facility on July 4, 2026, with plans for commercial production of 50 units per year at its R-50 facility in Oak Ridge, Tennessee. Radiant raised over $300 million in its Series D in December 2025 and has commercial agreements including 20 reactors for Equinix and a FOAK delivery to the U.S. Air Force/Defense Innovation Unit in 2028. Westinghouse's eVinci (5 MWe) is a solid-core heat pipe design targeting a DOME test in 2026. Nano Nuclear Energy (NASDAQ: NNE) is advancing multiple microreactor concepts including KRONOS (HTGR) and ZEUS (solid core battery), with a $577.5 million cash position and an MoU with EHC Investment for Gulf region deployment signed in February 2026.
Last Energy occupies a unique position with its PWR-20 (20 MWe) microreactor, using established pressurized water reactor technology in a mass-manufactured, containerized form factor. Last Energy has secured over 80 commercial agreements in Europe (half for data centers), including 4 units in South Wales, and 30 microreactors planned in Haskell County, Texas for data centers, with ERCOT grid connection filed. The company raised over $100 million in an oversubscribed Series C in December 2025 and joined the DOE Reactor Pilot Program in August 2025. BWXT is developing the BWXT Advanced Nuclear Reactor (BANR) for military applications under DOD contracts. The microreactor market is expected to grow rapidly as manufacturing-driven cost reduction, simplified licensing under the forthcoming NRC Part 53 framework, and demand from data center operators and defense applications converge to create commercially viable deployment opportunities within the next five years.