A nuclear core designed by California-based startup Valar Atomics achieved zero-power criticality at the National Criticality Experiments Research Center (NCERC) at Los Alamos National Laboratory (LANL) on November 17, 2025, the Department of Energy (DOE) announced.
The NOVA Core, a graphite-moderated core fueled by High Assay Low Enriched Uranium (HALEU) TRISO fuel and utilizing boron-carbide control elements in stainless steel, reached the milestone at 11:45 AM PT. The experiment was operated by LANL on the Comet critical assembly at NCERC. Zero-power criticality signifies a self-sustaining chain reaction of uranium-235 within a nuclear core, but without generating heat or operating temperatures.
Valar Atomics, founded in 2023, is developing a high-temperature gas-cooled reactor (HTGR) design, known as Ward250. The NOVA Core’s configuration was specifically selected to model a subsection of the Ward250 core, according to Valar. The Ward250 aims to produce industrial power and carbon-based fuels, and is slated to begin power operations next year under the DOE’s Advanced Reactor Pilot Program, established by Executive Order 14301.
The project, dubbed “Project NOVA” (Nuclear Observations of Valar Atomics), builds upon previous work at NCERC, including the Deimos critical assembly in 2024, which established the core test geometry and instrumentation approach. The central portion of the NOVA core was constructed by Valar Atomics.
According to the DOE, zero-power criticality allows Valar to verify assumptions about fuel, moderators, active reactivity control, and burnable poisons, and to gain a greater understanding of the core’s neutronic characteristics. Experiments will continue in the coming weeks to evaluate the neutronic behavior and key performance characteristics of the HTGR design.
The NCERC is the only general-purpose critical-experiments facility in the United States, operating under the oversight of the National Nuclear Security Administration (NNSA). Valar Atomics secured $19 million in seed funding to develop its first test reactor, and has an initial contract with the Philippines Nuclear Research Institute to pilot a test-scale reactor and build two full-scale reactors.
In September, Valar began ground-breaking for a test reactor at the Utah San Rafael Energy Lab (USREL), part of the Utah Office of Energy Development (OED). Valar founder & CEO Isaiah Taylor has indicated the Ward 250 will be a 100-kWt reactor.
The DOE Pilot Program aims for at least three test reactors to reach criticality by July 4, 2026.
