Nevada National Security site 17th November 2025 – Los Alamos national Laboratory (LANL) and Valar Atomics announced today that Valar Atomics’ NOVA Core has achieved zero-power criticality at LANL’s National Criticality experiments research Center (NCERC) at the Nevada National Security Site (NNSS). approach-to-criticality operations began on November 12, and zero-power criticality was achieved at 11:45 AM PT on November 17th, 2025.
zero-power criticality, or “cold criticality”, is the foundational milestone wich precedes nuclear operation with power. It is a self-sustaining chain reaction of uranium-235 within a nuclear core, but without reaching full operating temperatures or actively removing heat with a working fluid. Zero-power criticality allows Valar to gain a greater understanding of the neutronic characteristics of the core and verify assumptions about fuel, moderators, active reactivity control, and burnable poisons.
Project NOVA (Nuclear Observations of Valar Atomics), a collaboration between LANL NCERC and Valar Atomics, is a series of criticality experiments on a HALEU TRISO (High Assay Low Enriched Uranium Tristructural-isotropic)-fueled core.The campaign builds on earlier work at NCERC, including the Deimos critical assembly in 2024, which established the core test geometry and instrumentation approach used as the foundation for NOVA. The central portion of the NOVA core was built by Valar Atomics. Experiments will continue over the coming weeks to evaluate the neutronic behavior and key performance characteristics of Valar’s High-Temperature Gas Reactor (HTGR) design.
The experiments are being conducted at the NCERC, the United States’ only general-purpose critical-experiments facility, under National Nuclear Security Administration (NNSA). Located within the NNSS and operated by Los Alamos National Laboratory, NCERC provides the test assemblies, instrumentation, and expertise to conduct safe, controlled reactor physics experiments under DOE/NNSA oversight.
The NOVA core,built by Valar Atomics and operated by LANL on the Comet critical assembly at NCERC,is a graphite-moderated,HALEU TRISO-fueled nuclear core with boron-carbide control elements in stainless steel. The design builds on the Deimos assembly, incorporating proven structural and measurement components.
NOVA’s configuration was selected to closely model Valar Atomics’ Ward250 core, which is scheduled to begin power operations next year under the DOE’s Advanced Reactor Pilot Program, created in response to Executive Order 14301. NOVA uses the same fuel,moderator,and reactivity-control scheme as Ward250,enabling LANL researchers to collect high-fidelity neutronics data and validate Valar Atomics’ physics models ahead of Ward250 power operations.
This test provides key performance data on Valar graphite-core design and validates the physics models and simulations that underpin Ward250 design.
“Project NOVA provides us with real-world data which will help us answer key questions about TRISO fuel performance in our core and validate our proprietary software stack, which we use to design our power reactors.” saeid Sonat sen, Valar Atomics’ Lead Core Designer.
Project NOVA’s success confirms the physics underpinning Valar’s HTGR design, and clears the way for power operations in the next phase of testing. it marks a decisive step toward commercial-scale, factory-built nuclear reactors capable of powering heavy industry, hydrogen production, and AI-era data infrastructure with carbon-free energy.
“This milestone underscores collaborative efforts propelling nuclear innovation responsibly,” said
Valar Atomics Achieves Cold Criticality Milestone in Advanced Reactor Program
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Nevada National Security Site, NV – November 17, 2024 – Valar Atomics, a venture-backed startup, has announced the triumphant achievement of cold criticality in its advanced reactor core at the National Criticality Experiments Research Center (NCERC) at the Nevada National Security Site (NNSS). this marks the first time a venture-backed startup has reached this milestone, a crucial step towards the company’s goal of deploying advanced nuclear reactors.
The achievement is part of “project NOVA,” a campaign encompassing a series of criticality experiments in six different configurations. These experiments are being conducted in collaboration with Los Alamos National Laboratory (LANL) and will provide critical data for future high-temperature operations. LANL is responsible for analysis and validation of the results. Experiments are expected to continue for several weeks at NNSS.
Data gathered from Project NOVA will be used to refine system conditioning, helium-loop operations, and temperature ramp-up protocols within Valar’s advanced-reactor program. This work directly supports the U.S.Department of Energy’s (DOE) Nuclear Reactor Pilot Program, which aims to achieve full reactor criticality by July 4, 2026.
Roles and Responsibilities:
* valar Atomics: Provided the reactor core, TRISO fuel, and system configuration.
* LANL/NCERC: Provided the critical assembly, facility safety envelope, experimentalists, test instrumentation, experiment platform and reflectors, data analysis, and validation oversight.
* NNSA Nevada Field Office: Provided oversight of the experiment, which was conducted without power production, grid connection, or full-temperature operation.
“cold proves the physics. Hot proves the power,” emphasizes the importance of this initial step. Cold criticality demonstrates the fundamental physics of the reactor design, paving the way for subsequent testing at higher temperatures to validate power generation capabilities.
About NCERC
The National criticality Experiments Research Center (NCERC), operated by Los Alamos National Laboratory at the Nevada National Security Site, is the only general-purpose critical experiments facility in the United States. NCERC supports nuclear science experiments,training,and instrumentation growth to ensure the safety and advancement of nuclear technology. Funding and management are provided by the DOE Nuclear Criticality Safety Program through the national Nuclear Security Administration (NNSA). https://www.nnss.gov/about-us/facilities/ncerc/
About the U.S. Department of Energy
The U.S. Department of Energy (DOE) advances America’s national, economic, and energy security through scientific and technological innovation in the nuclear, energy, and environmental sectors.https://www.energy.gov/
About valar Atomics
Valar Atomics is developing nuclear gigasites – clusters of thousands of high-temperature reactors designed to meet the growing demand for energy, industrial heat, and carbon-neutral fuels, especially for modern industry and artificial intelligence infrastructure.Utilizing TRISO fuel, helium coolant, and graphite moderators, Valar’s reactors are designed for inherent safety and high-temperature operation, exceeding the capabilities of conventional nuclear plants.
Valar Atomics has already broken ground on Ward 250, its first nuclear test reactor in Utah, completed Ward Zero, a non-nuclear prototype, and established a partnership with the philippines Nuclear Research Institute. The company has been selected by the DOE for both the nuclear Reactor Pilot Program and the Advanced Nuclear Fuel Line Pilot Program. https://valaratomics.com/
Sources:
* Valar Atomics Press Release: https://valaratomics.com/news/2024/11/17/valar-atomics-achieves-cold-criticality-milestone-in-advanced-reactor-program/
* NNSS NCERC Website: https://www.nnss.gov/about-us/facilities/ncerc/
* U.S. Department of Energy Website: https://www.energy.gov/
* DOE Nuclear Reactor Pilot Program: https://www.energy.gov/ne/us-department-energy-reactor-pilot-program