Los Alamos National Laboratory

Los Alamos National Laboratory

Delivering science and technology to protect our nation and promote world stability

Fuel Fabrication Development (CONVERT)

The nation looks to our uranium-processing capabilities to optimize fabrication of a fuel, which will enable certain research reactors to eliminate material terrorists could steal for “dirty bombs."

  • New nuclear fuel fabrication

    New nuclear fuel fabrication, from pilot to prototype, at the Los Alamos Sigma Complex.

  • processing capabilities

    Combining process modeling and processing capabilities to scale up the fuel fabrication process.

  • material utilization

    Processing alternatives that maximize material utilization and minimize cost.

Get Expertise  

  • Fuel Fabrication Program Manager
  • David Dombrowski
  • Email

Fuel fabrication for next-generation reactors

To minimize the use of highly enriched uranium at research and test reactors around the world, Los Alamos is bringing its expertise to the crucial task of converting reactors to use low enriched uranium (LEU), which has no proliferation appeal. The work is part of a global effort led by the U.S. Department of Energy/NNSA Office of Materials Management and Minimization.

The Los Alamos Fuel Fabrication Program is working on all aspects of developing a high-density fuel: LEU alloyed with 10 weight percent molybdenum (LEU U-10Mo). Once successful, the United States can convert the last of its research reactors.

Fuel Fabrication

The Los Alamos Sigma complex has pilot-scale to full-scale capabilities for processing depleted uranium alloys and low enriched uranium alloys. Left: A metal deformation scientist and technicians perform hot rolling of low enriched uranium material destined for the AFIP-7 irradiation test assembly (far right image). Center: Thermal modeling of the low enriched uranium casting process, providing the basic shape needed as feedstock for hot rolling.

To optimize and scale-up the fuel fabrication process—from molten metal casting through final fuel plate forming—Los Alamos relies on a combination of

  • Modeling
  • Experiment
  • Advanced characterization methods
  • In-process sensors
  • Nondestructive testing
  • Systems modeling

With capabilities and safety authorization basis for pilot- and laboratory-scale processing, Los Alamos offers a viable alternative process that decreases cost and streamlines production through the following:

  • Optimizing casting of a monolithic alloy of uranium and 10 wt% molybdenum (U-10Mo) into a billet mold and a triple plate mold
  • Optimizing rolling parameters for bonding a zirconium diffusion barrier to the LEU U-10 wt% Mo fuel foil
  • Developing zirconium plasma spraying to replace the baseline roll bonding process with one that allows easy material recycling later in the process flow sheet
  • Developing cost-savings technologies for encapsulating (cladding) of the LEU U-10 wt% Mo fuel foil with aluminum by solid-state bonding
  • Developing controlled bulge testing and microcantilever measurements for determining bond strength between all materials in the laminated fuel plate structure
  • Developing nondestructive techniques (x-ray fluorescence, ultrasonic testing) for measuring thickness of the aluminum cladding and zirconium diffusion barrier in process 

Our value: from pilot to prototype

The Los Alamos Sigma Complex is the only government or industrial site in the United States with the expertise and existing equipment to make this monolithic LEU U-10Mo fuel plate at pilot scale.

The Sigma facility focuses on prototype fabrication and materials research for the nuclear weapons program as well as for threat reduction and homeland security activities. 

Los Alamos has a strong track record in

  • Performing process scale-up
  • Developing alternative process steps
  • Using advanced characterization methods to optimize processing steps

Our advanced methods include measuring the crystallographic texture using electron back scatter diffraction (EBSD), and measuring bond strength of thin laminate structures using either controlled buldge testing or microcantilever testing. We use neutron diffraction, x-ray diffraction, the hole drilling method, or the slit method to measure the residual stress.

Solving fuel fabrication challenges

Innovating

  • Vacuum arc re-melting for manufacture of a DU–Mo master alloy
  • Automated macroscopic x-ray fluorescence to nondestructively measure variation of molybdenum content in U-Mo castings
  • Electric discharge machining of U-10 wt% Mo castings
  • Fuel foil annealing parameters for minimization of residual stress and fuel foil curvature
  • Laser ablation for high-precision sizing of fuel foils to final dimensions
  • Plasma spraying as an alternative process to coat bare LEU U-10Mo fuel foils with zirconium or molybdenum diffusion barriers
  • Cladding fuel foil with 6061 aluminum using hot isostatic pressing (HIP) with cost-saving novel HIP can designs and a can-less HIP approach
  • Survey and down select of parting agents suitable for use in HIP cans to allow separation of bonded fuel plates from mandrels (strongbacks) in the HIP can
  • Uranium microstructure characterization by a wide variety of techniques identifying grain size, grain orientation, chemical composition, phase structure, and interface compositions

Optimizing

  • Vacuum induction melting and casting in a variety of molds using modeling and experiment
  • Homogenization annealing parameters to more uniformly distribute molybdenum throughout a U-Mo casting prior to rolling
  • Rolling parameters for converting cast U-10Mo to a zirconium covered fuel foil
  • Plate forming process for a wide variety of fuel plate geometries
  • Systems modeling of all process logistics, material flow, and costs, enabling high-fidelity cost assessments of process variations and alternatives

Measuring

  • In situ zirconium layer thickness using handheld, nondestructive x-ray fluorescence equipment
  • In situ aluminum cladding thickness during machining by either ultrasonic squirter technology or handheld x-ray fluorescence equipment to avoid minimum cladding thickness (minclad) violations
  • Bond strength (using controlled bulge testing and microcantilever measurements) at different material interfaces in the fuel to optimize solid-state bonding of aluminum cladding to itself, zirconium to the LEU U-10 wt% Mo, and aluminum cladding to the zirconium diffusion barrier
  • Bonding surface cleanliness that leads to optimized cleaning processes for the primary materials used in fuel fabrication (aluminum 6061alloy, zirconium, U-10 wt% Mo, stainless steel, carbon steel)
  • Crystallographic grain orientation next to and across bonding interfaces
  • Number, cystallographic structure, and chemical composition of chemical reaction zones between initial bonding material interfaces
Capabilities and expertise

Melting and casting

  • Vacuum induction melting (VIM) furnaces
  • Vacuum arc re-melting (VAR) furnace
  • Arc melting for alloying
  • Plasma melting furnace
  • Microwave melting furnace
  • Molten metal filtration

Forming

  • Rolling mills (hot and cold)
  • Extrusion dies
  • Hydroforming dies and equipment
  • Swaging
  • Wire drawing
  • Hot isostatic pressing (HIP)
  • Uniaxial pressing, cold and hot
  • Cold isostatic pressing (CIP)
  • Heat treatment furnaces

Machining

  • Computerized numerical control (CNC) machining
  • Electric discharge machining (EDM)
  • Water jet machining
  • Shearing
  • Laser ablation

Coating

  • Physical vapor deposition
  • Chemical vapor deposition
  • Electroplating
  • Plasma and thermal spraying

Joining

  • Electron-beam welding
  • Laser welding
  • Tungsten/inert gas (TIG) welding
  • Friction stir welding
  • Brazing

Modeling

  • Casting
  • Forming
  • Thermomechanical stresses during hot isostatic pressing (HIP) which promote solid state bonding
  • Residual stress
Technologies and applications: emerging, developed, or potential
  • First successful production and in-reactor testing of a 32-inch-long zirconium-coated LEU foil
  • First successful production of a zirconium-coated LEU U-10Mo fuel foil over 50 inches long
  • First successful plasma spraying of zirconium on uranium alloy fuel foil
  • First successful nondestructive measurement of zirconium diffusion barrier thickness as a function of position on foil
  • Only successful measurements in the national program of aluminum-to-aluminum bond strength in laminate structures
  • First measurement of aluminum-to-zirconium bond strength and zirconium to uranium alloy bond strength in laminate structures
  • First residual stress measurements of fuel foils and fuel plates by x-ray diffraction, neutron diffraction, and slitting method
  • First residual stress measurements of fuel foils and fuel plates as a function of processing by x-ray diffraction, neutron diffraction, and slitting method
  • First successful electron beam welding of aluminum 6061 cladding plates
  • First successful solid state bonding by the can-less HIP process
  • Improved hot top geometry and decreased porosity in DU-10Mo castings made using a triple plate mold
Sponsors, funding sources, or agencies
  • DOE/NNSA Office of Material Management and Minimization

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