Researchers in the U.S. have secured three million two hundred thousand dollars in federal funding to design a compact, economical linear accelerator (linac) that can transmute long-lived nuclear waste into safer material.
The U.S. Department of Energy’s (DoE) Argonne National Laboratory (ANL) and Fermi National Accelerator Laboratory (Fermilab) were given the funding as part of ARPA-E’s Nuclear Energy Waste Transmutation Optimized Now (NEWTON), program.
The program, part of a nearly one hundred- and twenty-five-million-dollar investment to manage and reduce the nation’s high-level nuclear waste, aims to make the reprocessing of U.S. spent nuclear fuel economically viable within the next thirty years.
This aligns with Argonne and Fermilab’s joint effort to modernize superconducting linear accelerators by developing a smaller, more affordable, and more reliable system designed to power nuclear waste transmutation which is a process that converts long-lived radioactive isotopes into shorter-lived ones.
With more than ninety thousand metric tons of spent nuclear fuel stored across U.S. power plants, particle accelerators are considered the most promising existing technology to address the problem.
Specialized components known as superconducting cavities are stacked within linear particle accelerators. These systems efficiently generate proton beams that create an intense flux of neutrons from heavy-element targets usually made of lead or bismuth. The neutrons are released through a process called spallation.
Michael Kelly is an Argonne physicist and team leader. He said that when directed at radioactive waste inside a reactor, the neutrons multiply and essentially ‘burn’ the spent nuclear fuel, transforming it into a material that decays much faster.
Most current accelerator cavities are typically made of pure niobium. They are bulky and can cost several hundred thousand dollars apiece. They also require cooling by expensive centralized cryogenic systems that consume large quantities of liquid helium at temperatures between minus four hundred-and fifty-four degrees Fahrenheit and minus four hundred- and fifty-two-degrees Fahrenheit. When grouped into units of six to eight, called cryomodules, they can be as big as a railroad freight car.
The researchers have now turned to niobium-three-tin (Nb₃Sn), an emerging material in accelerator science. This coating is only a few microns thick. It can be vapor-deposited inside accelerator cavities to improve efficiency and reduce the consumption of helium.
Instead of relying on large central cooling systems, the researchers plan to use compact cryocoolers distributed along the linac, minimizing the risk of single-point failures.
Kelly said, “We think it’s a big deal,” adding that the team won’t know exactly how much the size and cost can be reduced until they’ve accomplished a lot more research and development. “That’s a major part of what this R&D intends to address.”
According to the team, the new niobium-three-tin cavities will require less helium for cooling and could even replace today’s large, water heater-sized cavities with much smaller ones, potentially a fifth the size, roughly comparable to a coffee can.
Fermilab’s expertise in cryogenic systems and cavity coatings is expected to play a huge part in advancing the technology. Scientists Grigory Eremeev and Sam Posen are leading efforts to improve the vapor diffusion process. Eremeev points out that the challenge of adapting coatings to complex geometries is a problem that the team is actively working to solve.
The new technology also deals with the risk of total shutdown if a central cryogenic plant fails. Current designs rely on large liquid helium refrigerators that, if malfunctioning, can bring the entire system offline. The researchers now plan to replace this arrangement with a distributed network of compact, fault-tolerant ten-watt cryocoolers.
By decentralizing the cooling system, the researchers aim to reduce the chances of system-wide failure and ensure smoother operation. The linac must achieve an uptime of at least ninety five percent to keep the transmutation process stable. Repeated stops and restarts can place stress on the spallation target. This increases the risk of mechanical and thermal damage over time.
Posen concluded in a press statement, “Support from DoE made it possible to develop highly capable niobium-three-tin coating facilities at Fermilab and to develop techniques to achieve high performance in cavities with complex geometries. Now we are building on that foundation, advancing coating techniques and applying them to these exciting applications.”
The linac project is among eleven chosen in 2025 to share forty million dollars in ARPA-E NEWTON funding aimed at advancing technologies for recycling spent nuclear fuel.