Engineering Group Conference Call

8 May 1996

Chuck Bathke, Mike Billone, Leslie Bromberg, Dick Cole (MDAC), Laila El-Guebaly, Dennis Lee, Siegfried Malang, Ron Miller, Elsayed Mogahed, Igor Sviatoslavsky, Dai Kai Sze, Mark Tillack, Clement Wong.

General Notices:

Dennis Lee is leaving the fusion program, including both Starlite and ITER. Dick Cole and/or others will replace him, TBD.

Chuck will be out for 2 weeks for paternity leave. Use e-mail rather than telephone to contact him.

Three principal topics discussed on this call were:

A. The new strawman
B. Action items and immediate design issues
C. Administrative items

A. New Strawman

Chuck Bathke released the latest strawman this morning.

The magnitudes of the changes are settling down. Some of the most recent design changes were deferred to the next round. Engineering input from Laila, coil input from Leslie, and Physics input from Dave Ehst were obtained and incorporated. The major conclusions are summarized below.

1. Adjustments to the blanket and shield thicknesses were made (dependent upon first-wall neutron wall loading). The effect is minor.

2. The first-wall fluence lifetime was extended to 15 MW- yr/m2.

3. Replacement of the FW/B/S has been refined to allow different lifetimes. The back of the blanket is replaced at1/4 the rate of the FW (the dividing line is currently at 40 cm - this will be optimized later). More detail on the cost savings obtained by segmentation will be presented at the next meeting. Plant factor effects will be added by Miller.

4. The height of the TF coil has been reduced by 1 m. This results in a 4 mill/kWh savings, mainly from PF coil cost reduction. (The height change reduced the PF coil system weight from 3000 tonnes down to 1700 tonnes.) Leslie will examine the stresses for this case. Obviously, bending stresses will be worse. However, other changes in the coils serve to moderate the overall stress level, so that our current expectation is that the design will be acceptable.

The outer leg of the TF coil at equatorial plane is the same as before, but the top of the port is slightly closer-in. Miller asked if anyone has checked for clearance. Bathke suggested that if the shield slope changes faster than the coil (as a function of poloidal angle) then it's probably OK. This needs to be confirmed.

Laila inquired whether we could save more by bringing in the outboard leg of the TF coil. The real driver is the height of the TF coil, such that only minor improvements are available now. Shaping of the TF coil cross section will be considered only if sector removal becomes a problem again.

5. The overall cost of the plant has gone down approximately 5 mill/kWh. Previously we had 80 mill/kWhr for LSA=2, which has moved to 74 mill/kWhr. This will drop to ~74.5 mill/kWhr with the Physics changes.

6. The cryostat appears fairly expensive ($90M) using $68/kg. The amount of steel is 2 x 4cm. (ITER used 2 x 2cm, but with more webbing in a 20-cm interspace.) Clement will contact Bob Bourque (GA/ITER) to find the ITER costs. We need to reduce this, preferably by a factor of at least 3-4. Additional structure in the head and around the ports is not included yet.

7. The VV has been moved closer (50 cm gap now). The build in the TF coil plane has been used in ASC. The inter-coil build will be examined later.

8. (added following the call) More information on the PF coils (e.g., weights, forces) was added in the ASC output. Looking at this information highlights some of the PF-coil problems:

1) some of the PF coils experience forces of the order of ~1 GN, and
2) the inboard stack is so tall that the top coil is actually a divertor
coil that has a current and force of opposite sign of the other coils in the stack.

B. Action Item Status and Immediate Design Issues

The status of the action item list has been updated on the Web server. Some of the key inputs are summarized below.

1. Leslie has not provided input to the design book. Mark will contact Leslie to be clear on what is expected.

2. Dennis will redo the drawings now, based on the latest strawman. These will be distributed as soon as they are available.

3. The FW/B/S will be redrawn also.

4. Leslie is working on a design memo which will include a description of the coil cross section and composition of the coils. Unit costs also will be included (probably using 316 SS instead of inconel because the crown structure and other effects helped reduce the stresses enough to use steel).

5. Work on the divertor power balance is ongoing in the Physics group. The reference power balance for our purposes has not changed yet, and probably will not change a lot.

6. The heat flux in the divertor is determined by considering several factors: The SOL thickness at the midplane is 1 cm and expands to 3 cm at the divertor (based on experiments). Radiation from the core and divertor is added to the particle flux, and the heat flux profile is obtained based on experimental observations (not from simply projecting the 3 cm SOL onto a 15 degree slope).

7. Elmer Reis did stress analysis on segment of divertor plate at peak heat flux location. Thermal stresses in the divertor are a problem - not from the distribution, but the peak of 5 MW/m2. The boundary condition is a constraint to planar movement of the boundary faces. The peak stress with 2 mm W is 522 MPa, whereas 3Sm is 360 MPa. Cutting through W all the way to the V, gives ~400MPa. Including pressure stresses doesn't help much.

Elmer Reis is still looking further into design modifications that could improve the mechanical response. For example, he is looking at cutting into the wall supporting the channels. Reducing back plate rigidity also would help.

8. Structural design of the divertor supports is underway (by Igor) and a preliminary design concept has evolved. Further design development awaits the estimate of disruption induced forces. Documentation will be distributed later.

9. Turbo pumps were assessed for vacuum pumping, and they appear impractical (too big). So we will stay with cryopumps.

10. Igor needs more geometry definition from Dennis to complete the assessment of vacuum pumping from top to bottom. He is pessimistic at this point. Dennis will provide info, including specification of top-to-bottom channels.

Pumping at both top and bottom is feasible, but we should use one side only if possible. First we should establish if we can do it.

Igor will provide the per-sector gas conduction area needed to Dennis. It needs to be larger than the radial penetrations.

11. Clement indicated that the amount of induced radioactivities from Ar and Kr (calculated by Hesham Khater) are so small that they pose no safety concern.

12. An evaluation of erosion rates will be initiated.

13. The initial results of the disruption EM forces is expected within a week from Jake Blanchard. Clement asked for a BOTEC (back-of-the- envelope calculation) estimate as a minimum, if the analsysis results are not available.

14. Mike Billone reported on efforts to establish h levels in V. A memo was sent to the materials community regarding the embrittlement limit (current estimate is 1000 appm). Surface implantation and inventory numbers have been obtained from Hassanein. The accumulation rate (over 1 um near the surface) is about the same order as the total transmutation. Mike will look into transport (diffusivity, surface desorption) next. Laila will send H and T production rate information to Mike.

15. The 200 dpa limit on V lifetime has been adopted, subject to Blanchard's calculations. We wouldn't want to go any higher. Jake's calculations are out, so this should be easy to confirm. The limit is based on primary (coolant pressure) stress. Since the divertor primary stress also is low, we expect the lifetime to be compatible with our goal of replacement with the first wall.

16. Results of the LOCA analsyis were sent to DK Sze. The IB and OB are now solved together. The peak temperature is now 1155/1165 for IB/OB. The inboard reflector was changed to V, which lowers the temp. by 200 C. Emmissivity and segmentation are different from ANL calculation; the discrepancies appear to have been worked out now.

Dale Smith was quoted as saying that 1200 is the max allowable V temperature in a LOCA due to phase change. At this level, the structure would not collapse, but the sector would have to be removed and replaced.

17. Laila is waiting for input from Dennis on the rf sector for her shielding assessment.

C. Administrative Items

A full engineering group meeting prior to Reno was not scheduled. We will hold smaller working-group meetings, as needed. In particular, a divertor meeting is expected in San Diego, and a blanket meeting is under consideration (TBD by next week), to be held in Chicago or Madison depending on the content.

The agenda for Reno was discussed. Attendees were encouraged to plan on staying all day Friday. We will discuss the design status, which should be largely completed. It is especially important that decisions affecting other systems are settled by then. We also should plan to discuss the conclusions of the design phase and the post-design phase activities (documentation and critical issues assessments).

Final report preparations were discussed. Mark sent out an e-mail message to this effect. Clement suggested that Mark develop an additional level of detail in the outline, which will be done shortly.

Complaints about the team method for publishing were aired. Until an executive decision is made to indicate otherwise, the use of TeX as the team standard will continue to prevail. Therefore, the Engineering group should plan to present their deliverables in that format. Unlike the Assessment Phase documentation, Tillack will not extend an open invitation to translate from other formats.