Memo: Starlite -8
Date: 9 November 1995
Subject: 25-27 October 1995 Starlite Project Meeting Minutes @ UCSD
To : Starlite Project Team
From: L. Waganer
Participants: C. Bathke, L. Bromberg, B. Dove, D. Ehst, L. El-Guebaly, S. Jardin, B.J. Lee, V.D. Lee, T.K. Mau, R. Miller, F. Najmabadi, D. Steiner, I. Sviatoslavsky, D-K. Sze, M. Tillack, L. Waganer, X. Wang, C. Wong + brief visits from C. Baker, B. Conn, and E. Reis
(Note: Action Item List and Agenda are at the bottom.
Special Topic - Modeling of Disruptions and Related Effects
S. Jardin reviewed PPPL tools and codes to assess electromagnetic perturbations of tokamak plasmas and the resultant effects. There are several classes of current transfer:
* Toroidal current in vessel due to decreased plasma
* Toroidal current in vessel due to plasma movement (Vertical Displacement Event)
* Poloidal current in vessel due to plasma diamagnetism
* Poloidal current flows from an open field line into structure such as divertor
To analyze such events, the time-varying plasma is modeled and these data are coupled into a FEM model of the structure to determine the currents in the structure. The 3-D currents and the magnetic fields produce local forces, stresses, and deformations on the structure.
S. Jardin presented three levels of sophistication in modeling these effects. The least complex is a simple wire representation of the plasma interacting with an axisymmetric structure. The next level of complexity is the TSC code to model inductive transfer of current into the structure that is modeled with the SPARK code. The most complex model (TSC + Halo) includes the effects of conductive halo currents. These data may be fed into the IVBRAN structure modeling code. Some inter-mixing of the plasma current and structural models are permissible.
When current is induced in the structure in the toroidal direction, the effect is minimal because the poloidal fields are relatively weak. If the structure has a toroidal break, the toroidal current is forced to form an eddy current. The poloidal components of the currents strongly interact with the large TF magnetic fields.
The project team felt they needed the capability to run codes such as these at some future time after the general structural approach is chosen. The ability to run the most sophisticated code is desirable, but this may not be practicable with the existing budget. It may be possible to substitute the ITER or the TPX plasma model for the Starlite plasma.
D-K Sze discussed the thermal effects of disruption. (Data was provided by M. Hassanein.) Disruption events may transfer to a surface a large amount of energy (1-20 MJ/m2) with high energy ions and particles (20 eV to 1 keV). Vapor shielding from initial ablation may slow the damage rate. Thus a beryllium-coated surface may exhibit less overall damage than a tungsten-coated surface. [Action: Hassanein is to evaluate erosion of a bare vanadium wall and add to the existing set of data for Be and W.] The Engineering Group also would like information on the erosion rate as a function of surface inclination to the local vertical.
E. Reis, from GA, discussed the structural analysis of the TPX disruption events on the TPX divertor. GA initially used a relatively complete magnetic manual with hand analysis of the structure which produced results that benchmarked well with subsequent, more sophisticated models (divertor halo events modeled with SPARK and IVBRAN). Iterations between electromagnetic and structural analyses led to design improvements. A complete model including the entire vacuum vessel was in work when the project was canceled.
General Project Topics
During the meeting, the results of the House/Senate conference bill on the fusion budget were announced. The FY96 fusion funding will be $244M with specific language to align the fusion program more toward research on product enhancements and alternate concepts. In response to that change in emphasis, Starlite has re-oriented its efforts to define and assess Reverse Shear tokamak physics in a commercial power plant in lieu of a Demo plant. The ARIES Team also can provide an independent assessment of alternate concepts, if desired.
In the near term, all completed project assessments and documents will be readied for publication in early December. The Physics Group identified some effort to prepare a status report of the tokamak physics assessment. The ferritic steel assessment is nearly ready for publication but needs some final cost numbers and a materials appendix from M. Billone. The vanadium alloy assessment report is in final review for content and format by M. Tillack. The mission statement for the Demo exists but it needs to be reviewed in terms of a commercial mission statement. [Action: Waganer to realign the Mission Statement.] R. Miller has prepared a document outlining the groundrules, procedures, and database for assessing fusion economics. [F. Najmabadi, M. Tillack, and R. Miller will oversee the format, editing, and publication of the Annual Report. Critical schedule milestones should be identified for authors, if required. Tentative publication date is 1 December 1995.]
The next Engineering Group conference call is scheduled for Wednesday, 15 November and the next project conference call will be Wednesday, 29 November. [The Physics Group has scheduled their next conference call on Tuesday, 21 November, at 12:30-1:55 EST. Their number is 314-234-0973.] Tentatively, the next project meeting will be 31 January - 2 February with confirmation of the date on the 29 November conference call.
[Action: F. Najmabadi to define the schedule and the near-term milestones envisioned for the restructured Starlite program.]
R. Miller discussed the Economic and Costing Issues and how/when these will be addressed in the project. Key issues involved economic requirements, energy modeling and forecasting, EPRI models and guidelines/requirements, unit costs, O&M costs, changes for independent power producer (IPP) financing, and disuse of LSA credits. More international collaboration is anticipated with Japan and the EU.
Mark Tillack summarized the need to discuss and adopt a basic machine configuration to enable the design to progress to the next level of system definition and analysis. Present activity is to define envelopes and general configuration approaches. Ultimately the project would like to define in more detail the area outside the magnets ( e.g., the cryostat, biological shield, and beyond).
D. Lee presented a preliminary design approach incorporating the A=4.5, 7/18/95 strawman, C. Wong's divertor, and L. El-Guebaly's modified radial build. After examining the blanket volume near the divertor, L. El-Guebaly suggesed the first wall near the divertor to more closely approach the separatrix field lines. [Action: C. Wong to define the SOL e-folding distance and forward that data to C. Bathke to define a new first wall flux line to be 4 e-folding distances from the separatrix.] [Action: D. Lee to provide IB & OB surface areas and divertor volume on the new configuration.] The IB divertor slot to remain at 0.8 m but the OB should be increased to 1.0 m. [Action: C. Wong to determine pressure requirement in the divertor slots.]
The logic for the location of the TF and PF coils and vacuum vessel was discussed by the Engineering Group. The outermost PF coils can be raised and lowered to accommodate the necessary maintenance clearances. The pros and cons of single- versus double-walled vacuum vessels were discussed. It was decided to adopt a double-walled design with bolted doors and welded seals on planar extensions between TF coils. The size of the TF coils will likely be determined by manifolds and plumbing considerations. [Action: D. Lee, after receipt of the optimal aspect ratio and other design inputs, shall revise the configuration to include FWBS, divertor, vacuum vessel, coils, and plumbing. Penetrations and segmentation of the FWBS and divertor are to be included.] [Action: C. Wong to recommend the vacuum duct sizes to be employed in the divertor region]. [Action: D-K Sze and C. Wong to define the header and manifold sizes and locations for the FWBS and divertor regions and forward to D. Lee.] [Action: Sze to recommend OB coolant flow direction to accommodate drainage and passive convective flow.]
L. Bromberg presented his magnet analysis results for the TF coil cap configurations. The only configuration with acceptable results had a 30 cm cryogenic steel cap extending from the inboard bucking cylinder over the top of the TF coils and down to the maintenance port opening. The structure toroidally necked down in the area of the maintenance port to a reinforcement just on the outside shadow of the TF coils (still 30 cm thick.) L. Bromberg said that if the caps were reduced in overall diameter and the upper/lower cap thickness reduced, the stresses in the caps would remain acceptable and the stresses in the outer TF coil legs would be reduced. [Action: L. Bromberg to revise cap structure and re-analyze stresses. If acceptable, forward configuration to D. Lee. Provide guidance to C. Bathke regarding the necessary clearance between the TF and the PF coils for the cap structure.] [Action: C. Bathke to relocate and/or reshape the PF coils. The innermost PF coils may also be reshaped to reduce the overall major radius.] [Action: X. Wang to transfer ProEngineer output to ANSYS code.]
I. Sviatoslavsky presented a modified power core configuration with a curved structural access door and a tighter fitting TF coil. He presented a FWBS segmentation scheme with unequal segment sizes. The group felt the compact TF coil configuration did not allow enough room for the internal plumbing and vacuum pumping ducts. However several of the ideas for toroidal translation of blanket modules were recommended for further study. To incorporate a stabilizing shell, it is necessary to have a continuous mechanical and electrical shell. [Action: Sviatoslavsky to develop an attachment scheme to provide a structural conducting shell nominally at the reflector location.] [Action: Kessel is to define the physical properties of the conducting shell (material, thickness, area coverage, conductivity, and continuity in poloidal and toroidal directions). El-Guebaly will determine effect on breeding and shielding.]
M. Tillack presented Thanh Hua's heat transfer modeling and results for liquid metal systems. These analyses incorporated volumetric heating terms. Both laminar and eddy (2D- turbulent) flow could be analyzed but laminar flow will be used for conservative results. Results will be presented parametrically to bracket the final solution. [Action: L. El-Guebaly to provide FWBS heat loads for thermal-hydraulic analysis.]
M. Tillack also presented his assessment of heat transfer enhancement possibilities. Given the existing capabilities of the team, the heat transfer of the undeveloped, entry-region flow will be modeled directly (rather than assuming fully-developed temperature profiles, which is too pessimistic). Fully-developed velocity profiles will be used unless better definition of the fluid entry region can be obtained. Eddy diffusivity is easy to model parametrically, however, it appears that the FW will be able to remove the surface heat even without enhanced eddy diffusivity.
C. Wong presented the design approach for the divertor based upon the magnetic field topology of the strawman design. The intent is to assume a divertor lifetime consistent with the first wall. However backup approaches for more frequent replacement are being conducted. The energy split assumed is 40% for the inboard divertor channels and 60% on the outboard channels. Bong Ju Lee predicted an electron temperature in the slot that seems too high when the radiative power at the SOL was calculated. [Action: B.J. Lee to validate the temperature analyses approach with particles and energy conservation]. Based on pessimistic assumptions, Wong showed that the present divertor will have maximum surface loading around 5 MW/m2, even without the radiative power dissipation from the SOL and divertor region. Ali Mahdavi will begin to initiate the next level of detailed analysis to find the best approach for the radiative divertor design.
C. Wong presented results of a waste disposal rating (WDR) analysis performed by H. Khater for a tungsten coated divertor. The results for 50 cm thick divertor cassettes with 2 mm of tungsten on the divertor surface and 0.5 wppm of Nb impurities indicated that such divertor components can satisfy the Class-C waste disposal rating according to both NRC and Fetter guidelines. It could also qualify as Class A waste according to NRC assuming that all neutron-induced tritium generated in the V structure will diffuse out to the Li coolant.The effect of the W coating on the dose at the site boundary needs to be addressed.
D-K Sze described the first wall and blanket system. The coolant flow is a once-through design. In regard to the assumed vanadium lifetime of 150 dpa, Sze said the actual lifetime is design dependent. Hydrogen embrittlement will not be considered as a life-determining criteria. Radiation-creep is thought to be the life-limiting mechanism. For the thermal energy conversion system, a sodium intermediate loop will be used with double walled heat exchangers. Vanadium faces the lithium coolant while stainless steel faces the sodium. When asked if there is sufficient energy deposited portions of the outer shield to warrant energy recovery, D-K Sze noted that 1-5% of the energy is deposited in the secondary (low temperature) shield. The hot, primary shield receives around 25% of the energy. L. El-Guebaly is to calculate final energy distribution values. [Action: D-K Sze to review the Prometheus final report to determine if any figures can be modified - if so, he should contact L. Waganer.] [Action: Blanchard to finish assessment of EM load modeling.] [ Action: Wang to develop CAD model of FWBS design.] [Action: Wang and Lee to confirm ability to transfer CAD files between ProEngineer and Unigraphics.]
L. El-Guebaly presented the design margin factors to be applied to the magnet shielding. She presented the modified radial build and will optimize the shield for the new vacuum vessel design. She also addressed the need to minimize duct size and use bends to reduce effects of neutron streaming. [Action: Lee to modify penetrations to eliminate direct line of sight and include right angle turns.] After the divertor coolant/structure fraction and configuration are determined, additional replaceable shielding may be required.
T.K. Mau described the new approach to RF heating and current drive using a folded waveguide as opposed to a loop antenna. The waveguide is preferred because of high power handling (<= 40 MW/m2) and a more compact size. Both 1/2 and 1/4 waveguides may be used but the 1/4 waveguide is preferred because of the smaller depth (1.37 m for ICRF and 0.37 m for HFFW). Since this waveguide uses direct line of sight to the plasma, the shielding behind the launcher may need to be increased.
C. Bathke presented the cost comparison charts for the physics operating regimes. These data were used to select the Reverse Shear and the Second Stability regimes as the final contenders for the Starlite plasma. From economic consideration, these two regimes display similar results. For physics reasons, the Reverse Shear was chosen as the design of choice. C. Bathke incorporated several changes in the current analysis; reduced FW/B/R end-of-life fluence values, lower neutron multiplication, different radial build, and the revised costing base of ARIES-II-IV. Then using new data from C. Kessel's equilibria scaling and T.K. Mau's current drive scaling, C. Bathke analyzed a set of cost data for a range of aspect ratios from A=3 to 4.5. At aspect ratios of 4 and greater, the TF coils are at the limiting condition of 16 T. The variation of COE for a range of COE from 3 to 4 is small with A=3.5 being marginally the lowest cost system. It was thought that increasing the aspect ratio to A=4 would provide a radial build margin for a modest cost increase. However, C. Bathke presented trade study results that showed adding a gap and increasing the plasma major radius resulted in only modest cost penalties. [Action: C. Bathke to verify that A=3.5 is optimal and increasing the radial build may be implemented at a modest cost.]
[Action: Waganer and Tillack to establish an engineering parameter list to define the technical baseline. ]
Engineering Group Results
For the general session, M. Tillack summarized the Engineering Group's progress on defining the configuration and the major action items assigned.
Physics Group Meeting
The Starlite Physics Group held a separate meeting to report on recent analyses, discuss the findings, and plan future work to meet the project needs. The areas of special emphasis during this meeting included current drive, equilibrium and safety, and divertor and edge physics.
T.K. Mau presented RF current drive analysis results for the reverse shear physics case. Equilibra cases were found for aspect ratios of 3.0, 3.5, 4.0, and 4.5 with trade-offs between high beta and high bootstrap current fraction. Currents were driven in plasma regions where bootstrap currents were less than required. The power requirements over a range of plasma temperatures for each aspect ratio were computed for input to the systems code.
Dave Ehst identified physics and engineering parameters that may be used to determine relative economic attractiveness of alternative plasma operating modes. These parameters are: effective safety factor (q*), normalized beta ([[beta]]N), physics current drive efficiency ([[gamma]]B), electric-to-absorbed current drive efficiency (hd), and normalized capital cost of current drive hardware (cd). These parameters may be combined to describe the performance of the system hardware for the plasma operating modes. Data was presented comparing pulsed operation with a steady-state, current driven operation which indicated necessary levels of performance for comparable economics.
B.J. Lee presented results showing the slot lengths for the inner and outer legs of the divertor. Trades studies were conducted over a range of slot lengths from 30-50 cm for the inner divertor slot and 75-100 cm for the outer slot. Criteria were puffing requirement for impurity entrainment, low average heat flux at plate, peaking of radiation power density (PRPD) by impurities, and position of ionization front on which PRPD is peaked. The inner 30-cm slot was not chosen due to high PRPD and a close ionization front. Results for the 40 and 50 cm slots were similar, so the 40-cm inner slot was chosen. For similar reasons, the 75-cm slot was chosen for the outer divertor region. The total pumping requirement for both slots is 390 + 550 (helium and fuel) Pa-m3/s.
Physics Group Results
Steve Jardin summarized the Physics Group meeting results in the general meeting session. He reported near agreement on the Figure of Merit approach and the assigned values for each parameter. More experimental data would be beneficial to help narrow the error band. A consistent set of physics parameters have been generated for use in the systems code from an aspect ratio of 3 to 4.5. The requirement for a stability shell has been determined parametrically over a range of radii. [Action: D. Ehst volunteered to do a thermal erosion calculation on the divertor due to "giant Elms".] Steve Jardin has been asked to present a paper on the Low Aspect Ratio Starlite Reactor Design. The paper is to be given at the International Low Aspect Ratio Tokamak Workshop to be held at PPPL on November 13-15.
Licensing and Safety Group Results
D. Steiner noted that as a consequence of budget reductions and the closing of the MHTGR program Cadwallader and Dunn were not able to complete the preliminary safety analyses. However, C. Wong reported that Silady will be available and Cadwallader and Dunn will be available as consultants, therefore safety tasks from GA can continue pending the level of budget support. Steiner also noted that one of his graduate students will be able to participate in LOFA, LOCA and safety analysis. Steve Herring will be working on providing the source of the ARIES-II accident scenario analysis.
ACTION ITEM LIST
Responsibility Action Item Due Date Hassanein Evaluate erosion of a bare vanadium wall and add to xx Dec 95 existing set of data for Be and V Waganer Realign the Mission Statement 3 Nov 95 Najmabadi, Oversee the format, editing, and publication of the 1 Dec 95 Tillack, and Annual Report. Critical schedule milestones should Miller be identified for authors if required Najmabadi Define the schedule and the near-term milestones 3 Nov 95 for the restructured Starlite program. Wong Define the SOL e-folding distance and evaluate the 15 Nov 95 impact to the divertor design. Forward data to Bathke to define a new first wall flux line to be 4 e-folding distances from the separatrix D. Lee Provide IB & OB surface areas and divertor volume 1 Dec 95 on the new configuration Wong Estimate pressure requirement in the divertor slots 15 Nov 95 D. Lee Revise the configuration to include FWBS, divertor, 1 Dec 95 vacuum vessel, coils, and plumbing. Penetrations and segmentation of the FWBS and divertor are to be included. Sze Recommend the vacuum duct sizes to be employed in 1 Dec 95 the divertor region Sze Define the header and manifold sizes and locations 15 Nov 95 for the FWBS and divertor regions and forward to D. Lee Sze Recommend OB coolant flow direction to accommodate 15 Nov 95 drainage and passive convective flow Bromberg Revise cap structure and re-analyze stresses and 15 Nov 95 send to Lee. Provide guidance to Bathke regarding the necessary clearance between the TF and the PF coils for the cap structure Bathke Relocate and/or reshape PF coils. The innermost PF 22 Nov 95 coils may also be reshaped to reduce the overall major radius Wang Transfer ProEngineer output to ANSYS code xx Nov 95 Sviatoslavsky Develop an attachment scheme to provide a 15 Nov 95 structural conducting shell nominally at the reflector location Kessel Define the physical properties of the conducting 15 Nov 95 shell (material, thickness, area coverage, conductivity, and continuity in poloidal and toroidal directions. El-Guebaly Determine effect of conducting shell on breeding 15 Dec 95 and shielding El-Guebaly Provide FWBS heat loads for thermal-hydraulic 15 Nov 95 analysis B.J. Lee Revise Te-stagnant calculation, and making sure 1 Dec 95 that energy and particles are conserved in the SOL. Include detailed momentum equations for impurities to benchmark DIII-Ds experimental results with injection of deuterium injection. Use particle and heat fluxes in place of point inputs of temperature and density. Sze Review the Prometheus final report to determine if 3 Nov 95 any figures can be modified Blanchard Finish assessment of the EM load modeling. 15 Nov 95 Wang, Lee Confirm ability to transfer CAD files between 15 Nov 95 ProEngineer and Unigraphics D. Lee Modify penetrations to eliminate direct line of 15 Nov 95 sight and include right angle turns. Bathke Verify that A=3.5 is optimal and increasing the 31 Oct 95 radial build may be implemented at a modest cost Waganer, Tillack Establish an engineering parameter list to define 10 Nov 95 the technical baseline. Ehst Conduct a thermal erosion calculation on the 30 Nov 95 divertor due to "giant Elms".
Building 302 Conference Room (ITER Home Team Building)
University of California, San Diego
8:45 Opening Remarks, Meeting Agenda and Overview Najmabadi
Special Issues 1: Modeling of Disruptions and Their Effects
9:00 PPPL Tools for EM Analyses Jardin
9:45 Thermal Effects of Disruptions Hassanein
More Special Issues
10:30 Starlite Costing Issues Miller
Afternoon Parallel Meetings of the Physics and Engineering Groups
Physics Group: (Fusion Library, 459 EBU-II)
1:15 Determination of Slot Lengths of Divertor for Demo B.J. Lee
1:45 COE Physics Tradeoff Bathke
2:30 RF Current Drive for RS Demo Options Mau
3:00 RS Comparison with Second Stability Ehst
3:30 RS Equilibrium and Stability Update Jardin
Reverse Shear General Discussion Period All
4:15 Revised Figure of Merit for Divertor B.J. Lee
4:30 Current Drive Figure of Merit Ehst
5:00 Physics Figure of Merit Status and Direction Mau
Figure of Merit General Discussion Period All
5:45 Starlite Presentation at ST Workshop May/Bathke/Jardin
Engineering Group: (Engineering Group: Building 302 Conference Room)
12:30 Liquid Metal Heat Transfer Enhancements Tillack
1:00 Heat Transfer Results and Modeling Capabilities Hua (Tillack)
Establishing the Engineering Baseline
1:30 Engineering Group Status and Goals Tillack
(Design Status, Major Milestones, Key Issues to be Resolved)
[All following talks should include Proposed Design Approach, Details and Critical Characteristics of Specific Configuration, and List of Performance Parameters To Be Achieved. Do Not Need to Discuss or Present All Of The Material, But it Must Be Available To Support The Development of the Design Baseline.]
1:45 Power Core Configuration and Maintenance Approach Lee
2:30 Summary of ARIES/PULSAR Configuration and Maintenance Najmabadi
2:45 Vacuum Vessel and Main Support Structure Sviatoslavsky
3:15 Magnet Configuration Bromberg
3:45 Divertor Wong
4:15 First Wall and Blanket Sze
4:45 Neutronics and Shielding El-Guebaly
Starlite Demo Project Meeting
Room 584, Engr Building Unit 2, University of California, San Diego
Thursday, 26 October 1995
General Session of Engineering Meeting
8:30 Structural Analysis of TPX Disruption Events E. Reis
9:15 RF Heating and Current Drive Mau
9:45 System Code Input Summary El-Guebaly/Bathke
10:15 Engineering Wrapup Tillack
Full Project Meeting - Starlite Progress Reports
10:45 Starlite Strawman Results and Discussion Bathke
1:00 Physics Results/Chosen Plasma Operating Parameters Jardin
2:00 Summary of Engineering Design Approach/Parameters Tillack
3:00 Safety and Licensing for Starlite Design Steiner
3:30 Starlite Design Integration Process Najmabadi
4:30 Configuration working group (plumbing, ducts, ports, etc.)
Adjourn for Dinner
Friday, 27 October 1995
Room 584, Engr Building Unit 2, University of California, San Diego
8:30 Design Integration Group Meeting
9:30 Project Work Plan and Near Term Milestones, discussion Najmabadi