New Fuel Design Boosts Efficiency in Nuclear Reactors

ORNL's ULIMES fuel concept aims to improve overall reactor performance.

Published on Feb. 21, 2026

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A new approach to nuclear fuel developed at Oak Ridge National Laboratory could enhance the performance of new light water nuclear reactors. The Uranium Dioxide Liquid Metal Suspension (ULIMES) fuel concept uses uranium dioxide fuel particles suspended in liquid metal to form a flowing fuel system that circulates fuel through a reactor core, improving a reactor's ability to cool itself and offering significant safety and cost benefits.

Why it matters

Light water reactors make up most of the U.S. operating nuclear reactors, so innovations in nuclear fuel design like ULIMES have the potential to meaningfully improve the efficiency and safety of a significant portion of the country's nuclear power generation.

The details

The ULIMES design uses uranium dioxide fuel particles suspended in liquid metal to form a flowing fuel system that circulates fuel through a reactor core. This design improves a reactor's ability to cool itself, offering a major gain in efficiency, in addition to driving significant safety gains and lowered maintenance costs. The concept is also compatible with materials already used to construct light water reactors.

  • ORNL has signed a research license agreement with Australian investment firm Out The Back ventures in 2026 to fund additional ULIMES research.

The players

Keong Chan

The managing director of OTB Ventures who signed the ULIMES licensing agreement with ORNL.

Ian Greenquist

An ORNL researcher who signed the ULIMES licensing agreement with OTB Ventures.

OTB Ventures

An Australian investment firm that signed a research license agreement with ORNL to fund additional ULIMES research.

Oak Ridge National Laboratory (ORNL)

A U.S. Department of Energy science and energy laboratory that developed the ULIMES fuel concept.

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What they’re saying

“ULIMES bridges today's reactors with tomorrow's technologies, using proven materials to provide next-generation performance without next-generation construction costs.”

— Ian Greenquist, ORNL researcher (Mirage News)

What’s next

ORNL and OTB Ventures will continue to collaborate on further research and development of the ULIMES fuel concept.

The takeaway

The ULIMES fuel design represents an innovative approach to improving the efficiency and safety of light water nuclear reactors, which make up the majority of the U.S. nuclear power fleet. By leveraging existing materials and reactor designs, ULIMES has the potential to provide significant performance gains without requiring costly infrastructure overhauls.