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

2.  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.

3.  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

4. 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.

5. 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)

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 ?