US Private Microreactor Achieves Criticality, Eyes Export Markets Including India

The United States has marked a major milestone in its advanced nuclear programme after a privately developed microreactor achieved first “zero-power criticality” under the Department of Energy’s Reactor Pilot Program, signalling renewed momentum in next-generation nuclear technology.

The Mark-0 demonstration reactor , developed by Antares Nuclear and hosted at Idaho National Laboratory, achieved sustained nuclear chain reaction on June 4, completing a key validation step for reactor physics, control systems, and safety modelling. Officials say it is the first advanced reactor in the programme to reach criticality ahead of a federal July 4 deadline.

The test, conducted under a streamlined DOE authorization pathway, is part of a broader U.S. push to accelerate deployment of small modular reactors (SMRs) and microreactors for industrial, defence, and remote applications. The reactor itself is not power-producing and is designed for experimental validation rather than electricity generation.

Industry bodies including the Nuclear Energy Institute say the milestone strengthens U.S. ambitions to commercialise export-ready nuclear systems. Companies such as Westinghouse Electric Company and Radiant Industries are also advancing competing designs, including eVinci and Kaleidos microreactors.

The reactors use HALEU TRISO fuel and compact designs intended for rapid deployment, including potential use in remote grids and space missions. Engineers say data from the test will support licensing for full-power prototypes expected later in the decade.

The development also comes as Washington pushes regulatory reforms giving the Department of Energy greater authority over early-stage approvals, speeding up innovation cycles.

India remains a key target market. New Delhi is expanding its nuclear sector under the SHANTI Act , opening private participation and targeting 100 GW nuclear capacity by 2047 through a mix of large reactors and indigenous SMR programmes.