33. ADVANCED TECHNOLOGIES AND MATERIALS FOR FUSION ENERGY SYSTEMS
An attractive fusion energy source will require the development of superconducting magnets and materials as well as technologies that can withstand the high levels of surface heat flux and neutron wall loads expected for the in-vessel components of future fusion energy systems. These technologies and materials will need to be substantially advanced relative to today's capabilities in order to achieve safe, reliable, economic, and environmentally-benign operation of fusion energy systems. A list of items under the heading “Goods and Services that are needed by the Fusion laboratories” can be found in the Office of Fusion Energy Sciences Website (URL: http://www.ofes.fusion.doe.gov/). Grant applications are sought only in the following subtopics:
a. Plasma Facing Components—The plasma facing components (PFCs) in energy producing fusion devices will experience 5-15 MW/m2 under normal operation (steady-state) and off-normal energy deposition up to 1 MJ/m2 within 0.1 to 1.0 ms. Refractory solid surfaces represent one PFC option. These PFCs are envisioned to have a refractory metal heat sink cooled by helium gas and a plasma facing surface, consisting of an engineered refractory metal surface or a thin coating of refractory material, that minimizes thermal stresses. The materials being considered include tungsten and molybdenum. Grant applications are sought to develop: (1) innovative refractory alloys having good thermal conductivity (similar to Mo, at a minimum), resistance to recrystallization and grain growth, good mechanical properties (e.g., strength and ductility), and resistance to thermal fatigue; (2) innovative refractory metal heat sink designs for helium gas cooling; (3) efficient fabrication methods for engineered surfaces that mitigate the stresses due to high heat flux; and (4) joining or coating methods, for attaching the plasma facing material to the heat sink, that are reliable, efficient to manufacture, and capable of high heat transfer.
Another option for plasma facing components is a flowing liquid surface; therefore, in the near term, plasma interactions with thin flowing films are of critical interest. This will require the production and control of thin, fast flowing, renewable films of liquid lithium (less than 1 mm in thickness) for particle control at divertors. Grant applications are sought to develop: (1) techniques for the production, control, and removal of flowing (velocity 0.01 to 10 m/s) liquid lithium films (0.5-5 mm thick) over a temperature controlled substrate or free surface liquid jets (velocity 1.0 to 10 m/s); (2) advances in materials that are wet by lithium at temperatures near the lithium melting point and that produce uniform, well-adhered films; (3) techniques for active control of lithium flow and stabilization in the presence of plasma instabilities (time and space varying magnetic field); (4) computational tools that model flow and magnetohydrodynamic response of flowing liquid metals; and (5) cost-effective experimental techniques that integrate items (1) to (4) above to allow advanced plasma-material interaction testing and simulation.
b. Blanket Materials—The pebble-bed solid breeder configuration introduces several operational limits: thermo-mechanical uncertainties caused by pebble bed wall interaction, potential sintering and subsequent macro-cracking, and a low pebble bed thermal conductivity – all of which result in small characteristic bed dimensions and limit windows of operation. A new form of solid breeder morphology is required that holds the promise for increased breeding ratios, dictated by increased breeder material density; long term structural reliability; and enhanced operational control, compared to packed beds. Grant applications are sought for new solid breeder material concepts that include: (1) increased breeder material densities (>80%); (2) higher thermal conductivities (provided by a fully interconnected structure as opposed to point contacts between pebbles); (3) bonded contacts to cooling structures (instead of point contacts between pebbles and wall); (4) the absence of major geometry changes between beginning-of-life and end-of life (such as sintering in pebble beds) in the presence of high neutron fluence; and (5) structural integrity in freestanding and self-supporting structures with significant thermo-mechanical flexibility.
Flow channel inserts (FCIs) act as magnetohydrodynamic and thermal insulators in ferritic steel channels containing, for example, a slowly flowing tritium breeder such as molten Pb-17Li alloy. The insert geometry is approximately C-shaped in straight channels, with more complex shapes possible for insertion in manifolds and other complex-geometry elements in the flow path. Although SiC/SiC composite is a candidate FCI, its use would differ from its application as a structural material, in that high thermal and electrical conductivity is not desirable; in particular, electrical conductivity should be as low as possible, with a target range from 1 to 10 W-1m-1. In addition, strength requirements are reduced compared to its application as a structural material because the primary stresses and pressure loads will be very low; however, the insert must be able to withstand thermal stresses from temperature gradients in the range of 10-20 C/mm. Grant applications are sought to develop manufacturing techniques for radiation resistant, low thermal/electrical conductivity SiC/SiC composites that would not allow the Pb-17Li alloy to penetrate any porosity in the matrix. For instance, a final “sealing” layer of SiC matrix material is envisioned that would be near theoretical density and cover any porosity or exposed fibers in the main body of the insert. Two-dimensional weaves are generally thought to be satisfactory, and an effective way to reduce electrical conductivity normal to the insert interface with the Pb-17Li (the more important of the directions). In addition, grant applications are sought to experimentally determine the compatibility between the SiC/SiC composite and such breeder materials as Pb-17Li alloy, as well as the insert integrity under cyclic thermal loading.
One of the missions of the International Thermonuclear Experimental Reactor (ITER) project is the integrated testing of fusion blanket materials and components in a true integrated fusion environment. This ITER fusion environment includes radiation and magnetic fields, along with surface and volumetric heating, under pulsed and/or steady-state plasma operation. The “test blanket modules” (TBMs) will be complicated systems of different functional materials (breeder, multiplier, coolant, structure, insulator, etc.) in various configurations with many responses and interacting phenomena (e.g., thermomechanical, thermofluid, nuclear). As part of the design and validation process for these various experiments [5], the overall simulation of a “virtual” TBM is required to integrate all of the individual simulations at the system level. Such a project would be inherently multi-scale and multi-physics and will require careful code and algorithm design. Therefore, grant applications are sought to develop a TBM simulation code that can provide visual animations of: (1) fluid flow and thermal hydraulic characteristics; (2) the thermal response of all materials (structure, breeder, multiplier, coolant, insulator, etc); (3) structural responses such as stress and deformation magnitudes with respect to different loadings, including both steady-state surface heat flux and dynamic loadings; and (4) other important performance characteristics of the TBM. The overall code framework/structure must effectively link all of the simulation components of the virtual TBM and serve as an efficient, useful, and user-friendly tool.
c. Superconducting Magnets and Materials—New or advanced superconducting magnet concepts are needed for plasma fusion confinement systems; i.e., high field magnets (12 to 20 T) and low loss pulsed magnets. Grant applications are sought for: (1) innovative and advanced materials and manufacturing processes that have a high potential for improved conductor performance and low fabrication costs; (2) cryogenic superconductor materials with high critical current density, low sensitivity to strain degradation effects, and radiation resistance; (3) novel, low-cost cable designs and fabrication techniques, which minimize conductor strain; (4) superconducting joints for high field and pulsed applications; (5) novel, advanced sensors and instrumentation for non-invasively monitoring magnet and helium parameters (e.g., pressure, temperature, voltage, mass flow, quench, etc.); (6) thick (15-30 cm), weldable, structural case materials with high strength and toughness at 4 K; (7) welding techniques for such thick cryogenic structural materials; and (8) radiation-resistant electrical insulators (e.g., wrapable inorganic insulators and low viscosity organic insulators, which exhibit low out gassing under irradiation).
Subtopic a: Plasma Facing Components
5. Bastasz, R. and Eckstein, W., “Plasma-Surface Interactions on Liquids,” Journal of Nuclear Materials, 290-293: 19-24, 2001. (ISSN: 0022-3115)
6. Mattas, R. F., et al., “ALPS – Advanced Limiter-divertor-Plasma-facing Systems,” Fusion Engineering and Design, 49-50: 127-134, 2000 (ISSN: 0920-3796)
7. Sharafat, S., et al., “Ceramic Foams: Inspiring New Solid Breeder Materials,” to be presented at the International Breeder Blanket Interactions Workshop, Karlsruhe Germany, September 16-17, 2004. (Available at http://www.fusion.ucla.edu/pub.html)
8. Sharafat, S., et al.,, “An Innovative Solid Breeder Material for Fusion Applications,” to be presented at the 16th ANS Topical Meeting on Fusion Energy and Technology, Madison, WI., September 14-16, 2004. (Available at: http://www.fusion.ucla.edu/pub.html)
9. Tillack, M. S., et al., “Fusion power core engineering for the ARIES-ST power plant,” Fusion Engineering and Design, 65: 215-261, 2003. (ISSN: 0920-3796)
10. Norajitra, P., et al., “The EU advanced dual coolant blanket concept,” Fusion Engineering and Design, 61-62: 449-453, 2002. (ISSN: 0920-3796)
11. Abdou, M., et al., “US Plans and Strategy for ITER Blanket Testing,” to be presented at the 16th ANS Topical Meeting on Fusion Energy and Technology, Madison, WI., Sept. 14-16, 2004. (Available at: http://www.fusion.ucla.edu/pub.html)
Subtopic c: Superconducting Magnets and Materials
12. Seeber, B., ed., Handbook of Applied Superconductivity, 2 Vols., Bristol, England: Institute of Physics Publishing, January 1998. (ISBN: 0750303778)
13. Lee, P., ed., Engineering Superconductivity, New York: Wiley Interscience, 2001. (ISBN: 0-471-41116-7)
14. Asner, F. M., High Field Superconducting Magnets, Oxford, England: Oxford Science Publications, 1999. (ISBN: 0-19-851764-5) (Product description, including TOC, plus ordering information available at: http://www.oup-usa.org/toc/tc_0198517645.html)
15. Poole, C. P., Jr., et al., eds., Handbook of Superconductivity, Academic Press, 2000. (ISBN: 0125614608) (Ordering information and full index available at: http://www.amazon.com/exec/obidos/tg/detail/-/0125614608/104-6888958-8643120?vi=glance
16. Iwasa, Y., Case Studies in Superconducting Magnets: Design and Operational Issues, New York: Plenum Press, 1994. (ISBN: 0-306-44881-5)
17. Wilson, M. N., Superconducting Magnets, Chilton, England: Clarendon Press, Oxford, 1983. (Monographs on Cryogenics) (ISBN: 0-19-854805-2)
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