Engineering Group Conference Call

17 April 1996

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


An ENG group conference call was held at 9:30 pacific time (11:30 central) at the call-in number (314) 234-2875.

Mark Tillack summarized that the phone call would be organized by topics of general interest and high leverage. The key topics covered were

Strawman Engineering Input Parameters

Laila El-Guebaly reviewed the data revisions supplied to C. Bathke for the next strawman. The vanadium lifetime was increased from 11 MWy/m2 to 15 MWy/m2 (200 dpa). This corresponds to 2.5 FPY (full power years) for the first wall and blanket and 15 FPY for the next level of replaceable components. Some minor modifications were made to the shielding; for example, the outboard shield thickness was reduced due to the presence of the VV door. Some discussion ensued over the adequacy of the shielding at the location where the port wall is thinned to allow the TF coils to be located as close-in as possible. Laila will look into this, but felt it would not be a problem. Although the local wall thickness of the VV ports in the area of the TF coil is only 5 cm, the effective shielding thickness is much larger due to the predominant direction of the neutron streaming.

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.

Magnet System Definition

Leslie Bromberg noted that he intended to use multilayer insulation (MLI) rather than superinsulation for thermal protection of the coils. Mylar would not be used. The total thickness of MLI may be applied either to the coil, to the vacuum vessel (or cryostat) or divided between them. Mark suggested that we should place it all on the coil if there is no objection.

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.

Divertor Physics and Engineering Parameters

Clement Wong explained the concern that the temperature and density in the radiating mantle may be insufficient to radiate the necessary amount of power to the first wall to keep the divertor within its design limits. Tom Petrie will do the new edge calculation within 1 week. Dave Ehst will work with Tom to confirm the plasma edge conditions and its ability to achieve the necessary power balance.

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.

RF Heating and Current Drive Engineering Parameters

T.K. Mau noted that he has recommended a first wall surface area of 2.9 m2 be devoted to RF heating and current drive. This is equivalent to slightly more than 1% of the outboard wall area. During the recent project meeting, it was recommended that he try to modify the waveguide opening aspect ratio to reduce the toroidal width. He found that this would adversely affect the directivity. Thus, he felt the ICRF waveguide dimensions given in the meeting should be retained.

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.

Vanadium Lifetime Design Properties

Mike Billone reviewed his recommended design parameter curves and data properties for the V-4Cr-4Ti material. When asked to rationalize the differences between this lifetime prediction and those associated with BCSS, this one resulted from the use of a new material, new data, new analysis, and more limited operating conditions. M. Billone felt confident with his interpretation of the data up to 100 dpa; but from 100 dpa to 200 dpa, he felt the predicted performance carried a higher level of risk (hence, use a dashed line). Radiation creep should increase linearly with neutron damage, so there is confidence in the extrapolation of this parameter to high fluence.

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.

LOCA Analyses Results

Igor Sviatoslavsky mentioned that Elsayed Mogahed is continuing to analyze the loss of coolant results for the inboard blanket and shield. The temperatures are remaining high, and options are being investigated to bring the temperatures within acceptable limits.

Preliminary Safety Analyses Status

Clement Wong noted that Bob Thayer needs some advice regarding the use of the MACCS code that calculates the atmospheric dispersion terms. Clement Wong and Don Steiner are trying to confer with GA and INEL people to help him with this code.


The next full project conference call will be 24 April. An engineering group call is scheduled for 8 May. There may be an Engineering Group meeting sometime in May in the Midwest if needed. The decision should be made on or before May 8.