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Radioisotope Power Systems

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Radioisotope Thermoelectric Generators are still functioning on Voyagers I and II launched in 1977 - Voyager 1 is now beyond the heliopause of our Solar System - Courtesy NASA/JPL-Caltech
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Mars Rover Curiosity with the Multi-Mission Radioisotope Thermoelectric Generator (in back with white fins), launched in 2011, is still operating. - Courtesy NASA/JPL-Caltech

The Radioisotope Power Systems Program at ORNL has a nearly 50-year history of materials development (refractory metal alloys and carbon bonded carbon fiber) and the fabrication of unique components for the Department of Energy, NASA and other government agencies. In addition to production activities, the Program provides a wide range of capabilities that span the entire sphere of alloy design, production, mechanical property testing, component testing and qualification. Manufacturing equipment and expertise exist to cast metal alloy ingots and process them into finished metal shapes by extrusion, rolling, forming, machining, assembly, and welding. Nondestructive examination and quality systems are employed throughout the process to ensure customer requirements are maintained. Areas of expertise can be grouped into the four following areas: 

  • Alloy Design, Production and Processing
  • Component Manufacture
  • Testing and Evaluation
  • Quality Systems, Dimensional Inspection, NDE, and Material Characterization Techniques

An entire array of nondestructive testing capabilities is available for the evaluation of alloys and structures including radiography, liquid penetrant, visual, ultrasonic, and thermal imaging.

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Iridium Vent Clad Assembly

Alloy Design, Production and Processing

Specialty alloys are produced in development or small production size lots using powder processing, electron beam melting, inert gas arc melting, and vacuum arc remelting. Extensive experience exists for the production of reactive, refractory, and precious metal alloys. An example of a high performance alloy developed and produced at ORNL is the iridium DOP-26 alloy. This platinum group alloy is used to encapsulate radioactive materials for NASA deep space missions. The alloy was designed for high-temperature strength and ductility to survive impact damage from potential accident scenarios. Other examples of developmental alloys are refractory alloys for the friction stir welding tool for welding heat resistant alloys. Further processing of ingots is accomplished by extruding, rolling, and heat treating to produce finished sheet and/or foils.

  • Vacuum Arc Remelting
  • Vacuum Electron Beam Melting
  • Extruding
  • Heat treating
  • Rolling
  • Sintering
  • Zone melting
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Carbon Bonded Carbon Fiber Insulators Used in General Purpose Heat Source Modules for Radioisotope Power Systems.

Component Manufacturing

A wide array of room temperature and high temperature manufacturing equipment is employed to produce final shapes or components. A unique carbon bonded carbon fiber (CBCF) insulating material is produced at ORNL to provide reentry protection for nuclear fuel clads in radioisotope thermoelectric generators. Facilities are maintained for vacuum molding, high temperature carbonization and machining of insulating components. ORNL has experience in forming and machining many alloys including steels, superalloys, refractory and precious metals. Other processing technologies employed are air, vacuum, hydrogen, and inert atmosphere heat treating, diffusion bonding and powder sintering. One component made using these processes is a high temperature precious metal filter. ORNL has vast experience in welding and brazing technology including arc processes, laser, electron beam, and friction stir welding. Surface modification of alloys and components is performed by laser and plasma arc lamps.

  • Forming
  • Heat treating and sintering
  • Machining
  • Arc, electron beam, friction stir and laser welding
  • Inert-gas glove box welding
  • High temperature carbonization
  • Surface modification

Testing and Evaluation

Testing and evaluation of materials, components, and small structures can be performed with a wide variety of testing techniques. Capabilities include tensile, compression, torsion, bend, creep, fatigue, stress relaxation, Charpy impact, fracture toughness, and corrosion testing. Pressure burst or biaxial creep-rupture testing of pressurized capsules is used for more complex stress loadings or for validation of designs. Environmental chambers are used to test in a wide range of temperatures, gas atmospheres, or in vacuum including ultrahigh vacuum. Numerous machines are available for different load levels and speeds. Thermal property testing capabilities include diffusivity/conductivity, thermal expansion, and emissivity. Weldability testing and simulation can be performed on specialty alloys including Sigmajig, Varestraint, and Gleeble test methods. These tests can be used for determining the effect of minor element content on the weldability of an alloy or to simulate the effects of welding on the microstructure. Mathematical modeling and life prediction analysis is also performed to predict long-term behavior of materials and components based on experimentally determined data.

  • Weldability
  • Mechanical Properties
  • Impact and Burst
  • Creep and Stress Rupture
  • Physical Properties
  • Thermal Properties 
  • Modeling and Life Prediction

Quality Systems, Dimensional Inspection, NDE, and Material Characterization Techniques

Quality systems encompass activities to ensure that work is performed as specified and within design intent so that results are defensible and transferable to other agencies or contractors. All activities are conducted to DOE orders and national consensus standards, e.g. DOE Order 414.1D, 10CFR 830, Subpart A, ANSI/ISO/ABQ Q9001, ANSI Z1.13, NQA-1, and Space and Defense Power Systems/PQAR-1.

Extensive dimensional/visual inspection, nondestructive examination (radiography, dye penetrant, visual, ultrasonic, and thermal imaging), and material characterization (metallography, SEM/EDS, EPMA, AES, TEM) capabilities are available for the evaluation of materials and components.

  • Quality systems to DOE orders and consensus standards
  • Radiography
  • Ultrasonic
  • Dye Penetrant
  • Dimensional/Visual
  • Thermal Imaging
Program Manager E-mail Phone
Miller, Roger 865.241.7338
Administrative Assistant
STUART, Lindsay 865.574.2698
Quality Engineer
VEACH, Rex 865.574.1692
Welding Engineer
FARAONE, Kevin 865.341.0257
Task Managers
COX, Greg 865.576.1417
GALLEGO, Nidia 865.241.9459
MURALIDHARAN, Govindarajan 865.574.4281
MILLER, Roger 865.241.7338
ROMANOSKI, Glenn 865.574.4838
Metallurgical Manufacturing Engineer
Materials Specialists
PIERCE, Dean 865.574.7797