C. Bathke, M. Billone, L. Bromberg, L. El-Guebaly, D. Lee, T.K. Mau, S. Malang, R. Miller, F. Najmabadi, I. Sviatoslavsky, D-K Sze, M. Tillack, L. Waganer, C. Wong
Guest: D. Ehst
Mark Tillack summarized that the phone call would be organized by topics of general interest and high leverage. The key topics covered were
The divertor support structure was reduced to 20 cm. If a few cm of shielding are placed inside the divertor behind the plates, then these 20- cm structures can last until the 15-yr replacement interval.
Laila reiterated that we require 73 cm absolute minimum shield thickness between the inner strike point and the back of the shield . For more information on the latest design detail, visit the Engineering Design Book on the Starlite Web site.
Mark suggested that a picture of the radial build at the top/bottom, i/b and o/b would be useful to visualize the radial segmentation, and agreed to create one.
The permanent components were designed for 30 FPY, which has been used as the life of plant. This sparked discussion regarding the plant lifetime and the technique of dividing the blanket/shield to meet the damage limits. Agreement was reached that the plant lifetime would be extended to 35 FPY at the next strawman round (not the one being developed currently). [A subsequent agreement between R. Miller and L. El-Guebaly determined that 40 FPY should be used by the project.] This provides some design margin and variability in the availability and plasma performance values as well as extending the plant lifetime. Laila should scale existing analysis results, which will take approximately one week. The existing limit of 30 FPY will be retained for the current strawman. It would be better for the systems code to define the limits using a criteria of Mwy/m2 as opposed to the current use of FPY.
Laila wanted Leslie to explicitly define the materials in the winding pack, stabilizer, structure, insulation, etc. - Leslie said he would have it by tonight.
Leslie investigated the effect of reducing the height of the coils by 1m (above midplane) and found it was acceptable from the standpoint of bending stresses. This configuration will be the assumption for the next strawman. C. Bathke will need the definition of the centerline of the current around the coil. Leslie will continue his stress analysis to examine further height reductions.
Leslie also affirmed that modification of the coil cross-sections was technically feasible and ITER magnet experts confirmed his approach. The magnitude of the change would be an outboard leg width reduction of ~10% (8-10 cm). Leslie will also define the technique to transition the aspect ratio from the inboard leg to the outboard leg.
C. Bathke reported the results of a trade study on the effects of reducing the size of the TF coils and modifying the coil aspect ratio. Reducing the TF coils by 1 m in height (above midplane) and 1 m in radius reduced COE by 4 mils/kWh (D-shape was retained in this analysis), and reducing the TF coil total outboard width by 10 cm reduced the COE by 1 mils/kWh. Note that in the upcoming strawman, the coil would not be constrained to be a true D-shape; hence the geometry would be somewhat different. Also, the cost of the coil would have to change due to the changing coil composition, which may decrease the potential savings.
In any case, F. Najmabadi noted that the fraction of power to the first wall will exceed the 0.5 MW/m2 level (from the mantle, SOL, or whatever), requiring some design modification. To assure the first wall and blanket will have a robust design, Dai-Kai adopted a design heat flux limit of 1.0 MW/m2. The primary drawback is in design complexity. The nominal Zeff to be used in the systems code will be assumed to be 1.7, pending a new recommendation by T. Petrie.
The remaining RF systems were defined and located in the same sector, below the midplane. There was some discussion about sufficient room for piping on the side of the ICRH waveguides, and D. Lee will examine the available space.
It was noted that LOCA conditions may cause the copper surface layer to exceed melting temperatures (1083 deg-C). Tungsten was discussed as an alternate material, but the lower electrical conductivity will require thicker coatings for equivalent conductivity. At present, the lifetime of the non-structural copper is not expected to limit the component lifetime.
Chuck suggested that the maintenance time for the rf sector may be longer than the others. General consensus was that this is probably not a concern.
The trend indicated by the swelling data is an increase to a peak value at an intermediate neutron damage level followed by a decrease. However, the swelling database beyond 100 dpa is too limited to validate the extrapolation of the recommended swelling correlation. The principal reservation at ORNL is over the swelling extrapolation. They prefer a straight line extrapolation.
Les inquired what is the interpretation of the reduction of swelling vs. fluence. Mike indicated that swelling is not from He bubbles - it's from solid-state compounds which may break up at higher fluence.
Given the recommended design correlations, lifetime is limited by irradiation creep. Extrapolations of lifetime beyond 100 dpa carry uncertainties associated with the uncertainties in the swelling behavior. For the purpose of Starlite, 200 dpa will be used as the prevailing engineering judgment.