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MIT News
Researchers uncover hidden pore network within nuclear fuel
Researchers uncover hidden pore network within nuclear fuel
New understanding of how nuclear fuel breaks down and changes in an operating nuclear reactor could help keep some reactors running longer, will inform the next generation of nuclear reactor fuel systems.
Zach Winn<br>MIT News
Publication Date:
August 13, 2026
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Caption:
The new findings could help keep some nuclear reactors running for longer, while informing the next generation of nuclear reactor fuel systems. Pictured is the fuel assembly type from the EBR-II reactor used in the experiment.
Credits:
Courtesy of the Idaho National Laboratory
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The moment a nuclear reactor begins operation, a complex chain of events is initiated within the fuel: Heavy atoms split into fission products, knocking other atoms out of place and creating defects that can change how the fuel swells, transfers heat, and reacts chemically over time.<br>Understanding those processes is key to understanding how safe and efficient a nuclear reactor will be. But even for some of the most-studied fuel types, the mechanisms controlling those processes are unclear.<br>Such is the case with a particular kind of metallic fuel, uranium alloyed with 10 percent zirconium by weight, also known as U-10Zr. This fuel was extensively tested in historic sodium-cooled fast reactors such as the Experimental Breeder Reactor-II (EBR-II) in Idaho and the Fast Flux Testing Facility (FFTF) in Washington state, helping establish the foundation for metallic fuel development in the U.S. Today, U-10Zr is again attracting attention for use in next-generation advanced reactors.<br>But most studies of U-10Zr took place decades ago, leaving unanswered questions about exactly how the fuel changes when it undergoes nuclear fission in a reactor and how it interacts with the protective fuel cladding surrounding it.<br>Now, together with Idaho National Laboratory (INL), MIT researchers have led one of the most detailed three-dimensional studies of irradiated U-10Zr to date. The researchers used a technique known as high energy synchrotron X-ray computed tomography at Brookhaven National Laboratory (BNL) in New York to analyze the pore networks and chemical changes that formed under irradiation during use inside the FFTF reactor, providing new insights into how the material swells, transfers heat, and interacts with the fuel cladding.<br>The findings could help keep some nuclear reactors running for longer, while also informing the next generation of nuclear reactor fuel systems.<br>“This study helps us model the pore distribution in the fuel more accurately,” says senior author Ericmoore Jossou, MIT’s John Clark Hardwick (1986) Professor of Nuclear Science and Engineering. “It also helps us design for the safe operation of metallic fuels in reactors by giving us a better understanding of the role of pores and their importance.”<br>Joining Jossou on the paper are first author and MIT postdoc Anthony Harrup; Riley Moeykens ’25, SM ’25; BNL researchers Michael Drakopoulos and Nghia Vo; and INL researchers Jana Howard, Colby Jensen, and Tiankai Yao.<br>Understanding nuclear fuel<br>A class of nuclear reactors known as sodium-cooled fast reactors generate energy from rods of metallic fuels that are sealed inside metal tubes called cladding. In each rod, heat generally moves outward from the center to the edge and then to the cladding, where liquid sodium carries heat away to be harvested into power.<br>“As you operate the reactor, the contact between the fuel and the cladding material creates chemical interactions that can be problematic,” explains Jossou. “There is a migration of materials from the fuel to the cladding, like fission gases and rare earth elements...