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Note on FCI R&D for DEMO for informal discussion

Note on FCI R&D for DEMO for informal discussion. DCLL Design Meeting, April 23-24, 2007, UCLA Y. Katoh (ORNL). D T allowance for SiC-based FCI. What influences D T limit? Mechanical constraint is the primary factor (elastic strain would be less severe when deformation is allowed )

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Note on FCI R&D for DEMO for informal discussion

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  1. Note on FCI R&D for DEMOfor informal discussion DCLL Design Meeting, April 23-24, 2007, UCLA Y. Katoh (ORNL)

  2. DT allowance for SiC-based FCI • What influences DT 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, DT 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: sf = ~400 MPa, E = 450 GPa • CVI SiC/SiC: sPL = ~150 MPa, E = ~250 GPa • SiC foam (22%) : sf = ~10 MPa, E = ~14 GPa (Sharafat presentation) • Strain due to DT is not tunable • eth = DT ath, / 2 (1-n2) ; DT = ~400K when eth = ~0.1. • Some SiC composites (eg, PIP) exhibit ef>> 0.1%, but are not radiation-resistant. • SiC fibers, even of high cyrstallinity, exhibit ef ~ 0.5%, due to small diameters and smooth surface. High efmaterial development may be possible. • Presently foam’s ef is small in spite of small ligament diameter, perhaps due to stress concentration at nodes.

  3. DT allowance for SiC-based FCI (continued) • Thermal expansion and swelling are two sources of secondary stress • aswelling > ath for most T range of interest • a= ath 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 DT allowance. • Worst case scenario is that thermal stress relaxes quickly by transient creep, and swelling stress does not much relax. stress and/or deformation thermal dose/time • Creep adds complexity swelling

  4. Thermal conductivity • Bulk thermal conductivity of SiC • 1/Kb = 1/Kunirr + 1/Krad-defect • 1/Krad-defect dominates to 1/Kb when irradiated for high purity SiC. • 1/Krad-defect is a function of operating temperature (almost) alone once saturated at low doses. • Some impurities may reduce Kb effectively, however. • Further lowering thermal conductivity requires porous structures. • Kp/Kb = (1-p)b, b = 3/2 for spherical pores, b -> ∞ for lamella. • Small Kp/Kb usually means low interlaminar strength.

  5. Thermal conductivity, continued Katoh, FED (2006) • 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.

  6. 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.

  7. 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

  8. For DEMO, solid transmutation will be a critical issue • Electrical insulation • Corrosion resistance

  9. 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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