LANL’s ZiaCore microreactor reaches criticality

[Marlin]

LANL's ZiaCore microreactor reaches criticality

https://www.ans.org/news/2026-08-03/article-8265/lanls-ziacore-microreactor-reaches-criticality/

[Core Content]

Los Alamos National Laboratory achieved zero-power criticality with its ZiaCore microreactor design during a four-week testing period at the National Criticality Experiments Research Center. The experiments, conducted at temperatures exceeding 800 degrees Celsius, utilized zirconium hydride moderation and heat pipe cooling to validate the performance of the system's core components.

This milestone provides data on temperature coefficients of reactivity for microreactors using low-enriched uranium fuel. By utilizing off-the-shelf materials and internal fabrication, the project aims to demonstrate a scalable power source capable of eight years of operation without refueling. These results contribute to the broader development of small-scale nuclear technologies and inform future regulatory and commercial deployment strategies.

Last week, Los Alamos National Laboratory announced that its ZiaCore microreactor was brought to zero-power criticality at high temperatures in April through May of this year during four weeks of experiments on the Deimos test bed at the National Criticality Experiments Research Center (NCERC).

The design: According to a LANL press release from May 2025, a key question driving ZiaCore's design at its inception in 2021 was, "What would happen if we developed a reactor with real-world, off-the-shelf materials?"

The team came up with a system that uses a zirconium hydride moderator and heat pipe cooling and won $5.5 million in funding over three years from LANL's Laboratory Directed Research and Development (LDRD) program with an October 2023 start date.

Read the full article at ans.org:
https://www.ans.org/news/2026-08-03/article-8265/lanls-ziacore-microreactor-reaches-criticality/