Small Modular Nuclear Reactor Achieves Criticality in Test

<p>On June 5, 2026, Antares, a startup, announced that its test reactor at the Idaho National Laboratory reached criticality, marking it as the first new reactor design to achieve this milestone. Criticality indicates that the nuclear reactions within the reactor have become self-sustaining, though it does not imply that the reactor is generating power.</p><p>This development follows an executive order issued by the Trump Administration over a year ago, which aimed to expedite nuclear power development in the United States. The order directed the Department of Energy to have three different reactor designs reach criticality within a year. While various startups have emerged focusing on smaller reactor designs, only one has been fully licensed to date.</p><p>Antares's reactor design utilizes a new fuel system known as TRISO, which simplifies reactor complexity and enhances safety by integrating these aspects into the fuel design. The TRISO fuel consists of small pellets with a uranium oxide core, surrounded by multiple layers of carbon to moderate energy from fission reactions, all encased in a durable ceramic shell designed to withstand high temperatures.</p>