EL SEGUNDO, Calif. – Valar Atomics, a US-based nuclear startup, announced this week it has successfully achieved “cold criticality” during a test conducted in November at the Nevada National Security Site, with crucial assistance from Los Alamos National Laboratory (LANL). This achievement marks a significant step forward in advanced nuclear reactor development and positions Valar Atomics as a frontrunner in a competitive Department of Energy (DOE) pilot program.
Understanding Cold Criticality and Valar Atomics’ Breakthrough
Cold criticality, also known as zero-power criticality, signifies a self-sustaining nuclear chain reaction of fissionable material without generating significant heat or producing power. It is a foundational benchmark in reactor development, allowing engineers to validate reactor physics and core design at safe, low-power levels before proceeding to full operational temperatures.
Valar Atomics’ NOVA Core reactor assembly, developed by the El Segundo-based company, reached this state on November 17, 2025. The test utilized special uranium-235 fuel sourced through the DOE and equipment from Los Alamos National Laboratory. Valar Atomics provided the reactor core and its general configuration, which emulated a smaller-scale design of their Ward 250 reactor.
Isaiah Taylor, Founder and CEO of Valar Atomics, emphasized the importance of this milestone, stating it is “a reactor’s first heartbeat, proof the physics holds.” He highlighted the rapid progress, noting that the team took the project “from blueprint to splitting the atom.”
Los Alamos’ Critical Contribution
Los Alamos National Laboratory played a pivotal role in facilitating this achievement. The New Mexico-based lab, renowned for its historical involvement in the Manhattan Project, provided the facility at the Nevada National Security Site and key equipment necessary for the criticality test. This collaboration underscores the federal partnership driving advancements in private nuclear energy innovation.
Broader Implications for the Future of Nuclear Energy
The successful achievement of cold criticality by Valar Atomics is a significant development within the broader context of the US’s renewed push for advanced nuclear power. It comes as part of the Department of Energy’s Nuclear Reactor Pilot Program, launched in August, which selected 11 advanced nuclear projects from 10 companies. The ambitious goal of this program, spurred by the Biden-era Inflation Reduction Act and an earlier Trump administration executive order, is to construct, operate, and achieve test reactor criticality in at least three reactors by July 4, 2026.
Valar Atomics’ milestone positions them as the first company within this pilot program to publicly announce achieving criticality. The company has an aggressive timeline, aiming to power up a full reactor by the July 4, 2026, deadline. This rapid pace of development is seen by some as unprecedented since the Manhattan Project era.
Impact on Small Modular Reactors (SMRs) and Clean Energy
The advancements made by Valar Atomics are particularly relevant for the development of small modular reactors (SMRs). SMRs are designed to be more flexible, scalable, and potentially safer than traditional large-scale nuclear power plants. Criticality demonstrations like Valar’s provide crucial data and validation for these next-generation designs, which are vital for accelerating the transition to clean, carbon-free energy.
The Inflation Reduction Act’s incentives and funding for a domestic nuclear supply chain and infrastructure improvements at national laboratories are designed to foster such innovations, aiming to bolster the US’s energy independence and address climate change.
Expert Perspectives and What’s Next
While Valar Atomics celebrates this milestone, some nuclear experts offer a tempered view. Nuclear consultant Nick Touran acknowledged the impressive institutional capability to quickly conduct tests at Los Alamos but noted that Valar Atomics is “certainly not the first startup to split the atom.” However, he conceded that running cold criticality tests to ensure fuel geometry works with reactor technology is a “prudent” choice.
Valar Atomics, founded in July 2023, recently secured a significant funding round of $130 million with backing from investors such as Palmer Luckey and Palantir CTO Shyam Sankar. This capital will be crucial as the company continues its push toward achieving full-scale, power-producing criticality. The data gathered from this cold criticality test will be instrumental in informing the design and operation of their future full-scale test reactor, moving closer to their ambitious goal of delivering operational nuclear power.
