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Note on FCI R&D for DEMO for informal discussion DCLL Design Meeting, April 23-24, 2007, UCLA Y. Katoh (ORNL)
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T allowance for SiC-based FCI What influences T limit? –Mechanical constraint is the primary factor (elastic strain would be less severe when deformation is allowed) –Stress/strain concentration could be mitigated by design When constrained, T limit is determined primarily not by stress but by elastic strain –Strain to fracture (or matrix cracking for composites) is ~0.1% for crystalline SiC. CVD SiC: f = ~400 MPa, E = 450 GPa CVI SiC/SiC: PL = ~150 MPa, E = ~250 GPa SiC foam (22%) : f = ~10 MPa, E = ~14 GPa (Sharafat presentation) –Strain due to T is not tunable th = T th, / 2 (1- 2 ) ; T = ~400K when th = ~0.1. –Some SiC composites (eg, PIP) exhibit f >> 0.1%, but are not radiation- resistant. –SiC fibers, even of high cyrstallinity, exhibit f ~ 0.5%, due to small diameters and smooth surface. High f material development may be possible. –Presently foam’s f is small in spite of small ligament diameter, perhaps due to stress concentration at nodes.
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T allowance for SiC-based FCI (continued) Thermal expansion and swelling are two sources of secondary stress – swelling > th for most T range of interest th gives the most optimistic case in terms of thermal stress –Swelling is monotonic with dose and tends to saturate at a low dose, whereas thermal stress loading will be repeated Understanding irradiation creep is critical to assess T allowance. –Worst case scenario is that thermal stress relaxes quickly by transient creep, and swelling stress does not much relax. dose/time stress and/or deformation Creep adds complexity thermal swelling
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Thermal conductivity Bulk thermal conductivity of SiC –1/K b = 1/K unirr + 1/K rad-defect –1/K rad-defect dominates to 1/K b when irradiated for high purity SiC. –1/K rad-defect is a function of operating temperature (almost) alone once saturated at low doses. –Some impurities may reduce K b effectively, however. Further lowering thermal conductivity requires porous structures. –K p /K b = (1-p) , = 3/2 for spherical pores, -> ∞ for lamella. –Small K p /K b usually means low interlaminar strength.
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Thermal conductivity, continued Irradiated bulk thermal conductivity of high purity SiC and composites is mostly known –~1 W/m-K will be a realistic goal that may be achieved by architectural and matrix modification to 2D composites. Katoh, FED (2006)
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Questions regarding Pb-Li compatibility Effect of impurities in Pb-Li on corrosion is always an issue. FS dissolution may impact Pb-Li / FCI compatibility. Experiment needed? Applied electronic field is known to promote wetting and reactivity on some interface systems. Could it happen to systems of interest such as Pb-Li / SiC and Pb-Li / FS? –Wetting / non-wetting may be a minor issue for overall heat loss, but may be an important issue in corrosion standpoint. –Electrical insulation by FCI may be more important than has been assumed.
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FCI materials for DEMO: still an open question SiC-based –Fibrous composites 2D Complex architectures –Non-fibrous porous CVI foam Polymer-derived Etc. –Hybrid, etc. Other materials –Nitride ceramics –Oxide ceramics –Aluminum-containing alloys + insulating interior –Etc. Example of ideal FCI structures: Closed-porous insulator with fibrous composite faces
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For DEMO, solid transmutation will be a critical issue Electrical insulation Corrosion resistance
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Cost consideration Is cost consideration for FCI important now? –Do we know how much is too much for FCI? Cost of SiC/SiC –Presently dominated by high fiber cost –SA3 fiber cost can approach to that of generic SiC fiber when production scale is increased (i.e. if market exists) –Type S fiber cost can approach to the present cost of SA3 fiber when scaled up Cost comparison –Nicalon Type S SiC fiber: $14k / kg –SA3 SiC fiber: $5k / kg –Generic SiC fiber: $300 / kg –R&H CVD SiC: $5k / kg –F82H: several hundred $ / kg ?
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