Valar Atomics project achieves early criticality milestone

Valar said it is collaborating with Los Alamos National Laboratory's (LANL) National Criticality Experiments Research Center in Project NOVA (Nuclear Observations of Valar Atomics). The project is a series of criticality experiments on Valar's graphite-moderated core using high-assay low-enriched uranium (HALEU) TRISO fuel, carried out under the oversight of the Department of Energy National Nuclear Security Administration. The NOVA Core builds on LANL's 2024 Deimos experiment, which was the first criticality experiment using HALEU fuel to be carried out in the USA in more than 20 years.

Valar, a startup launched in 2023, plans to build nuclear "gigasites" with "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". It says its TRISO (tri-structural isotropic) fuelled, helium-cooled cooled and graphite-moderated reactors are "inherently safe and capable of operating at much higher temperatures than conventional plants".

The company was announced earlier this year as one of the initial selectees under the US Department of Energy's Nuclear Reactor Pilot Program, which aims to see at least three of them achieve criticality before 4 July 2026. In September, the company broke ground at Utah San Rafael Energy Lab (USREL), a unit within the Utah Office of Energy Development, for its first test reactor, called Ward250, and has completed a non-nuclear prototype called Ward Zero. It has also been selected by the department alongside Terrestrial Energy, TRISO-X and Oklo for a pilot programme to build advanced nuclear fuel lines.

Zero-power - or "cold" - criticality 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, Valar explained. 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.

NOVA Core's configuration models the Ward250 core, which the company says is scheduled to begin power operations next year. 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.

Valar Atomics Founder and CEO Isaiah Taylor described the cold criticality milestone as the dawn of a new era in US nuclear engineering. "Zero power criticality is a reactor’s first heartbeat, proof the physics holds,” he said. "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."