Valar Atomics’ Ward 250 nuclear reactor achieved criticality on June 18, 2026, in Orangeville, Utah, marking a historic milestone for advanced nuclear energy development in the United States. The achievement represents the first criticality for a Department of Energy-authorized advanced reactor outside a national laboratory, according to the Salt Lake Tribune and multiple DOE announcements.
Criticality occurs when a nuclear reactor achieves a self-sustaining chain reaction capable of producing a steady release of energy. According to the Nuclear Regulatory Commission, this happens when “each fission event releases a sufficient number of neutrons to sustain an ongoing series of reactions.” For Valar, the Ward 250 completed a zero-power fueled criticality demonstration, validating the reactor’s core physics and operational design before power ascension begins.
The Ward 250 project was launched under President Trump’s Executive Order 14301, signed in May 2025, which established the DOE Reactor Pilot Program and set an ambitious goal: at least three advanced reactors must achieve criticality by July 4, 2026, the nation’s 250th birthday. Valar CEO Isiah Taylor called the moment “historic” and “the culmination of two years of work,” noting that the team would begin power ascension in the coming days.
The Utah milestone follows an earlier breakthrough by Antares Nuclear, whose Mark-0 microreactor achieved criticality on June 4, 2026, at Idaho National Laboratory. Antares became the first private company to bring an advanced reactor to criticality under the DOE pilot program, according to the Department of Energy. For Idaho National Laboratory, the Mark-0 represented the first novel reactor design to achieve criticality at the site in more than 50 years.
Advanced nuclear reactors like the Ward 250 and Mark-0 are smaller and more flexible than conventional light-water reactors. They can be factory-produced, transported, and deployed in diverse locations to power industrial processes, remote facilities, or provide grid electricity. The Ward 250 uses TRISO fuel—a robust, next-generation nuclear fuel that enhances safety margins. Small modular reactors (SMRs) and advanced designs are expected to produce between 50 and 500 megawatts, roughly one-third the capacity of traditional nuclear plants, but with improved operational flexibility and lower capital costs.
The criticality demonstrations validate the safety and operational performance of these designs and bring the nation closer to a new era of nuclear energy. With two reactors now critical and others in the pipeline under the DOE Reactor Pilot Program, the U.S. nuclear industry is advancing toward the July 4 deadline. The success of these projects signals a broader shift toward deploying advanced nuclear technology to meet future energy demands and climate goals.
Sources
- The Salt Lake Tribune — confirmed Ward 250 criticality on June 18, 2026, in Orangeville, Utah; noted it was the first DOE-authorized reactor outside a national lab to achieve criticality nationwide
- U.S. Department of Energy — announced Antares Mark-0 criticality on June 4, 2026, at Idaho National Laboratory; provided details on the Reactor Pilot Program and Executive Order 14301
- Deseret News — reported Valar Atomics’ Ward 250 reaching criticality
- FOX 13 News Utah — covered the small modular reactor achieving criticality in eastern Utah
- PBS NewsHour — explained the definition and significance of criticality in nuclear reactors
- World Nuclear Association — described small modular reactor flexibility and deployment opportunities
