The U.S. Energy Department announced that Antares Nuclear Inc. achieved a critical milestone in nuclear energy development. The company's Mark-0 microreactor reached criticality on June 4, marking the first time a privately developed advanced reactor in the U.S. has achieved a self-sustaining nuclear chain reaction. The demonstration was conducted at the Idaho National Laboratory in partnership with the Energy Department and the U.S. Army.
Energy Secretary Chris Wright called the achievement a "historic day in the American nuclear renaissance," emphasizing its potential to lower energy costs and enhance national energy security. The reactor uses liquid sodium for cooling, improving efficiency and reducing risks like steam explosions. However, sodium requires strict safety measures due to its reactivity with air and water.
The milestone is part of a broader U.S. initiative to accelerate nuclear energy deployment. President Donald Trump signed executive orders in May 2025 to streamline regulatory approvals and boost domestic nuclear capacity. The Energy Department aims to have operational reactors ready by 2027, with the Mark-0 being the first of several advanced reactors expected to reach criticality by July 4, 2025.
Skeptics caution that microreactors may not be safe or economically viable, highlighting the need for further testing and cost assessments. The reactor is still years away from commercial use, but the achievement signals progress in advanced nuclear technology.