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 which 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.” said 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 Dr Rian Bahran, Deputy Assistant Secretary for Nuclear Reactors. “Confirming core physics at zero power with oversight enables Valar’s path to elevated operations, leveraging all DOE capabilities to aid the Reactor Pilot Program’s target of criticality by July 4th and accelerating the AI race via advanced energy generation solutions.”
“Zero power criticality is a reactor’s first heartbeat, proof the physics holds,” said Isaiah Taylor, Founder & CEO, Valar Atomics. “I’m incredibly proud of the Valar team that took this from blueprint to splitting the atom, securing the first criticality ever achieved by a venture-backed company. We extend our gratitude to the phenomenally talented team at Los Alamos and especially NCERC for their close partnership on Project NOVA. The NCERC team remains one of the most crucially important teams for the future of atomic energy in America by maintaining a high standard of competence and vital capability to conduct criticality experiments. This moment marks the dawn of a new era in American nuclear engineering — one defined by speed, scale, and private-sector execution with closer federal partnership.”
“President Trump asked industry and the labs to make nuclear great again. We got together and decided to start with the basics of fission. This team delivered incredible results safely so we can keep moving up the technical ladder. America should be thrilled, but wanting more,” said Max Ukropina, Valar Atomics’ Head of Projects.
About Project NOVA
Project NOVA is a zero-power criticality (or “cold criticality”) physics-validation campaign conducted in partnership with LANL NCERC and Valar Atomics under DOE oversight at the Nevada National Security Site. The program’s goal is to confirm Valar’s reactor core design and fuel performance under low-temperature, zero-power conditions and validate Valar’s software simulation stack — providing the critical data required for subsequent high-temperature operations. The Project NOVA campaign encompasses a variety of criticality experiments in six different configurations with subsequent analysis and results by LANL. After today’s commencement, Project NOVA experiments are expected to continue over the course of several weeks at NNSS.
Data from NOVA will inform system conditioning, helium-loop operations, and temperature ramp-up protocols within Valar’s advanced-reactor program, supporting the Administration’s goal through the Nuclear Reactor Pilot Program to reach full reactor criticality by July 4, 2026.
Roles and SafeguardsValar 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
The experiment was conducted under the NNSA Nevada Field Office Oversight, without power production, grid connection, or full-temperature operation.
Cold ≠ Hot: Cold proves the physics. Hot proves the power.
About NCERC
The National Criticality Experiments Research Center (NCERC), located at the Nevada National Security Site and operated by Los Alamos National Laboratory, is the United States’ only general-purpose critical experiments facility. NCERC supports nuclear-science experiments, training, and instrumentation development to ensure the safety and advancement of nuclear technology. NCERC is supported by the DOE Nuclear Criticality Safety Program, funded and managed by the National Nuclear Security Administration for the Department of Energy.
About the U.S. Department of Energy
The U.S. Department of Energy (DOE) advances America’s national, economic, and energy security by supporting scientific and technological innovation across the nuclear, energy, and environmental sectors.
About Valar Atomics
Valar Atomics is building America’s first nuclear gigasites — clusters of thousands of high-temperature reactors designed to supply the energy, industrial heat, and carbon-neutral fuels that modern industry and AI infrastructure demand. Using TRISO fuel, helium coolant, and graphite moderators, Valar’s advanced reactors are inherently safe and capable of operating at much higher temperatures than conventional plants.
Under Project NOVA, Valar’s reactor achieved cold criticality — the first instance of such a milestone by a venture-backed startup. The company has broken ground in Utah on Ward 250, its first nuclear test reactor; completed Ward Zero, its non-nuclear prototype; partnered with the Philippines Nuclear Research Institute; and been selected by the DOE for both the Nuclear Reactor Pilot Program and Advanced Nuclear Fuel Line Pilot Program.