Los Alamos conducts first critical experiment using high assay low enriched uranium in decades

A research team at Los Alamos National Laboratory recently performed the first critical experiment with high assay low enriched uranium (HALEU) TRi-structural ISOtropic (TRISO) fuel in four decades at the National Criticality Experiments Research Center (NCERC) in Nevada. It achieved its objective of establishing an advanced reactor testbed. 

“With companies such as Amazon, and Google investing in nuclear energy to power their data centers, this experiment is extremely important to provide validation data for HALEU,” said Holly Trellue, Los Alamos’ Engineering Institute leader. “It will help us contribute to the next generation of nuclear reactors in the United States.” 

As new advanced nuclear reactors are designed and built to use uranium with higher enrichments up to 20%, experiments to understand performance of the material are paramount to designing and licensing new reactor types. Traditional Light Water Reactors use uranium with enrichment up to 5%. 

Through a project called Next Generation Small Nuclear Reactors, the team conducted an experiment that could improve emerging nuclear technology called advanced and small modular reactors (SMRs) such as microreactors.  Microreactors can easily be transported and provide small, mobile power sources. These reactors have numerous applications, including data centers, defense, microgrids, ground operations, oil exploration, providing power to remote villages and for disaster relief. 

The experiment used a combination of existing components that have long been in the NCERC inventory, such as the fuel and beryllium reflector, and new components such as large graphite monoliths containing the fuel. After years of extensive engineering design, components for the experiment were developed and assembled.

The resulting experiment, named Deimos after the moon of Mars, required meeting numerous engineering design challenges. Deimos also provides a test bed in which the center portion can be replaced with new materials and geometries relevant to advanced reactor designs driven by HALEU TRISO and several follow-on projects using Deimos have already been funded.

“We are excited and proud to make use of unique Los Alamos’ capabilities to advance the nation’s advanced reactor goals, and we look forward to future experiments that Deimos enables,” said Chris Stanek, Los Alamos Nuclear Energy director.

Resurrecting a capability 

HALEU TRISO is not a new fuel type. TRISO has been proposed in graphite-based reactor designs for decades and is known to be accident tolerant.  A critical experiment called the Compact Nuclear Power Source designed to validate nuclear data and criticality in a graphite-based HALEU TRISO matrix was performed in the 1980s at Los Alamos on a critical assembly machine called Mars, which was decommissioned in 1992. 

Resurrecting this capability to perform measurements with TRISO fuel and other materials important to advanced reactors at normal and elevated temperatures is important to supporting validation and verification of simulations before new reactor designs are built. 

“Deimos will become a vital platform to further the development of microreactors,” said Erik Luther, of Los Alamos’ Finishing Manufacturing Science Group and co lead on the project. “These will be crucial to fulfilling our nation’s energy needs.” 

Funding: This work was funded by the Laboratory Directed Research and Development Program and the Department of Energy’s Office of Nuclear Energy.

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