Starlite Project Meeting Minutes
5-7 March, 1997
UC San Diego


Attendees: L. Bromberg, F. Dahlgren, B. Dove, L. El-Guebaly, S. Jardin, 
H. Khater, T. K. Mau, R. Miller, F. Najmabadi, W. Reiersen, R. Stambaugh, D. K. 
Sze, 
M. Tillack, L. Waganer, X. Wang, C. Wong

Guests: C. Baker, I. Cook, P. Karditsas, S. Malang, S. Nishio, A. Sagara, Y. Seki, S. Ueda

Attachments: Action Item Summary, Meeting agenda

Summary

This meeting for the ARIES Advanced Concept Studies Program was held at UCSD in conjunction with the US/Japan Power Plant Studies Workshop. The workshop was held 3-5 March and the ARIES meeting followed on 6-7 March. On 5 March, several engineering papers were presented that represented the current status of some elements of the ARIES-ST assessment (see agenda for presentation material). In addition, a few members of the workshop elected to stay and attend the ARIES project meeting.

General

The meeting opened with a discussion of three letters published in the March 1997 issue of Physics Today that were highly negative of fusion. ARIES and JET were highlighted in the letters as being superficial and overly optimistic concerning their assessment of a future electric application for fusion. C. Baker described the current efforts to respond by individuals and institutions. M. Tillack and F. Najmabadi cooperated on an ARIES response. Draft comments were incorporated and the letter was submitted quickly so that it could be published in the next issue. [post-production note: Physics Today responded, saying that too many rebuttals were received to allow publication in the April issue. The rebuttals will be collected in some form and the original letter authors will be provided an opportunity to respond.]

Review of Japan/US/(EU) Reactor Workshop

Ron Miller and M. Tillack briefly summarized the workshop presentations. The presentations emphasized high power density systems, recirculating power requirements, and maintenance approaches. On 4-5 March, the concluding ARIES- RS engineering results were presented. On the afternoon of 5 March, the ARIES-ST blanket and economics work in progress were presented.

Engineering Analysis Results

Copper Centerpost Analysis Results - Fred Dahlgren outlined the general center post (CP) design requirements and significant issues. He then described his finite-difference thermal hydraulic code that modeled the water-cooled, copper CP. He assumed hexagonal, closely-packed, hollow conductors that were cooled through the central hole in each conductor. With this design, he achieved an 85% packing fraction. His present analysis only considered nuclear heating with no radial thermal conductance between conductors. Also the voltage was held constant, but the current was variable. [Dahlgren - Add ohmic heating source and hold total current constant.] The CP once-through flow rate was very sizeable at 80,000 gpm, with room-temperature and reasonable inlet pressure conditions. It was recommended that the water be a closed loop system rather than open loop so siting would not be a problem.

No insulator was used between the conductors. It was recommended that an insulator be added between the center post conductors to reduce EM forces and deflections. [Dahlgren/El-Guebaly - Select insulator material and modify the design to incorporate insulators.] The analysis results illustrated several thicknesses of shield but when the shield thickness was reduced, the CP was not correspondingly increased. [Dahlgren - Update code to increase CP radius when shield is thinned.]

F. Dahlgren showed an alternate CP design approach using copper wedges with varying size coolant passages. This design would likely have an open center hole. The wedges were tapered on the upper and lower ends to match the plasma inboard contour. [Dahlgren - Develop and analyze the proposed wedge design.]

IBC Center Post Design Results - Wayne Reiersen reported his and Don Steiner's results on a comparison of an IBC and a H2O-Cu CP design at varying aspect ratios. The results indicated that the IBC must have a larger aspect ratio to be feasible. It was also noted that the H2O-Cu CP improved at the larger aspect ratio. Wayne felt the basic IBC CP design would not be competitive with the Cu design, but he and Don intend to develop a hybrid CP design using Cu as the current conductor with a lithium coolant.

Leslie Bromberg stressed the need to have a CP structure which reacts the out-of- plane loads. Incorporating insulators would help reduce such loads. He also said he had tested a short sample of a 30K conductor which could be used as the center post conductor. Laila El-Guebaly recommended a 1-meter-thick shield for this high- temperature superconductor. Another possibility was the Neil Taylor approach of a liquid-helium cooled, high purity aluminum CP at 30K. [Reiersen, Bromberg, Dahlgren, Wang, El-Guebaly, Sze - Develop CP designs for four approaches; (1) H2O-Cu, (2) Li-Cu, (3) LHe-Al, and (4) LHe-S/C. Design should include CP, shield, and outer TF legs plus electrical and coolant routing scheme through CP, TF coils, divertor, and blankets.]

Center Post Shielding and Blanket Neutronics - Laila El-Guebaly reviewed the key parameters and design limits principally for the CP conductor and shielding. She presented the results for a range of shield thicknesses. [El-Guebaly - Recommend shield composition and thickness for each CP configuration noted above to meet waste disposal, resistivity, and lifetime requirements. Fixed values are desired, but economic considerations may require parametric solutions.]

Experimental data showed that copper alloys rapidly embrittle at only 0.1 dpa; hence, the design team needs guidance for all copper alloy structural designs (DP, divertor, coolant passages). [Blanchard - Provide design guidelines for brittle materials, especially Cu, SiC, and ceramic materials such as insulators]. If copper operates above 180 C, it may prevent swelling.

The proposed lithium titanate solid breeder is similar to lithium zirconate but has a lower level of activation. Like other solid breeders, it needs a neutron multiplier such as beryllium to achieve tritium self-sufficiency. Use of beryllium results in an expensive blanket. As a preliminary analysis assumption, Laila chose a 1-cm-thick steel kink shell. [Jardin - Determine if the 1-cm-thick kink shell is adequate.]

Design and Analysis of Helium-Cooled High Heat Flux (HHF) Components - Xueren Wang proposed use of a helium-cooled divertor in the ARIES-ST reactor. A water-cooled system would pose a safety hazard in proximity to a lithium-cooled blanket. But he had difficulty reaching the necessary level of 5-6 MW/m2 surface heat load requirement with a 8 MPa helium coolant and high coolant outlet temerature. [Wang - Check the stress level at the 8 MPa level and increase the pressure if possible.]

TF Coil Bus Bar Design Implications - Leslie Bromberg noted the size of the copper bus bars necessary to handle the 30 MA of current. Not only was the size and capital cost excessive, the power losses in the leads contributed to a sizable operating cost. He suggested the use of the 30K superconductor for TF coil bus bars. [Bromberg - Develop a conceptual design and sketches of a 30K S/C bus bar and power supply system. Compare to a normal Cu design.]

Safety Analysis Results for LAR Tokamaks - Hesham Khater used a composition of F82H ferritic steel which contained 20 wppm of silver. The high content of silver does not allow the FW and shield to qualify as LLW according to Fetter limits. The Fetter limits can be met if the new composition of F82H ferritic steel which contains less than 1 wppm of silver is used. However, the new composition needs to be isotopically tailored to significantly reduce the Nb trace element. The silver content of CP copper needs to be reduced by an order of magnitude to allow for its disposal as LLW according to Fetter limits. The CP has about 6 FPY lifetime to meet the 10CFR61 NCR limits.

H. Khater presented a simple LOCA analysis performed by El-Sayed Mogahed. The simple model did not include conduction along and out of the end of the CP. He had used a shield, but it was suggested that he run a case without a shield to determine if an unshielded Cu CP was a safety hazard. [Mogahed - Rerun LOCA analysis of the Cu CP without a shield.] Khater used the temperature profiles obtained from the simple LOCA analysis to calculate off-site doses caused by radioactive material mobilization. The off-site doses are less than the 10 mSv required to avoid evacuation in case of an accident. The large amount of Be used in the current design present a serious safety hazard. The issue of hydrogen combustion and over pressurization poses a serious threat to obtaining the desired level of radioactivity confinement.

Discussion of LAR Blanket Issues - Dai-Kai Sze reviewed the blanket materials and coolant choices along with significant issues and performance limits. One common assupmtion is that the thermal conversion must be high efficiency (implying high temperature) to compensate for the large recirculating power fraction inherent with the LAR device. With this high temperature requirement and the use of Be, the solid breeder cannot handle more than 1-2 MW/m2 due to the limiting capability of heat transfer in the solid breeder. The lithium-vanadium system is limited to a surface heat flux of 1 MW/m2 due to the long coolant path on the ST first wall. [Sze - Examine a helium-cooled first wall with the lithium-cooled blanket.]

Siegfried Malang suggested we push the assumption that lithium and water should not be used together in the power core. Instead, we can offer several barriers that would offer in-depth protection against a single accident scenario. [Sze - Work with Malang to develop a water-cooled CP and Li-cooled blanket design approach with several layers of protective barriers.]

More General

ARIES-ST Systems Issues and LAR Comparisons - Ron Miller noted he is now responsible for the ARIES Systems Code. One of his first efforts was to verify the joule losses in the CP. After a comparison, he felt it was reasonably correct. He will run the systems code to develop a new strawman when sufficient information is available. [Miller - Run two cases for A=1.4 and 1.6 with data supplied by S. Jardin.]

Highlights of the Innovative Concept Workshop - Steve Jardin attended the Innovative Concepts Workshop in Los Angeles earlier this week. He noted that new grant money ($3M) is available to help develop some of these concepts. Some of the concepts were old, others were new and innovative. Others are just curiosities.

Highlights of the US/Japan High Power Density Components and Devices Workshop - Clement Wong presented the key results from the workshop held two weeks ago, by showing the impact of high average plasma power density on the blanket and divertor designs. The GA-LAR design was shown with the following parameters; He/stagnant-Li/V-alloy blanket design with R = 1.45 m, A = 1.75 m, A=1.4, k = 2.5, and an average NWL of 8 MW/m2. This 1490 MWe machine was estimated to have a COE of 57.65 mill/kWh with a thermal efficiency of 46%.

Specific observations from the workshop were: for experimental devices like ITER, LHD, NSTX, and LAR-VNS with no power conversion, a very high divertor surface loading (such as 30 MW/m2) may be handled by sub-cooled,boiling water flow. For power plant designs, like ARIES-RS and GA-LAR, is is desirable to minimize the volume of the fusion power core by raising the average neutron wall loading to the range of 4 to 8 MW/m2. But due to the need for efficient power conversion and reasonably high coolant outlet temperature, the acceptable divertor surface loading may be limited to 5-6 MW/m2.

Scope and Preliminary Results of Alternate Applications Study - Les Waganer explained that the name “Alternate Applications” may have to be changed to “Non-Electric Applications” to eliminate confusion with Alternate (confinement) Concepts”. He presented the study purpose and the general study plan. The positive and negative attributes of fusion were shown. These will be generalized to apply to all applications considered. He then showed a list of products that can be obtained from fusion reactions. A few detailed examples of classes of applications were presented to illustrate the depth of the product descriptions planned. The study group’s next action is to compile the product descriptions and develop an attribute list that encompasses all products such that the attributes for each application may be quantified. It was recommended that breeding fissile fuels be cataloged and described, but not developed.

Physics Analysis Results

Results of High-Elongation, Low-Aspect Ratio Stability Studies - Steve Jardin presented stability results over the aspect ratio range of 1.2 to 2.0. The regime of 1.4 to 1.6 looked most attractive. All cases investigated had a bootstrap fraction of <99%. He had two cases which had near identical equilibria at A = 1.4 and A = 1.6. These two cases were recommended to be analyzed by the systems code. [Jardin - Verify vertical stability of the data sets.] His general conclusions for all cases presented are:

GA Physics Results - Ron Stambaugh reported higher elongation is possible at lower aspect ratios and broader current profiles. He feels high bN is the key to high bT (fusion power) and high bP (bootstrap fraction). He does not see a motivation to reduce the aspect ratio below 1.4. He still shows the relationship of bN = 12/A but the postulated the general plasma performance over a range of scaling of the general form, bN = 12/Ax for x = 0 to 2.0. He proposed that the best equilibrium case was at A = 1.4 which had very similar data to those of Jardin.

He proposed the group investigate a pilot plant option, but this suggestion was rejected as the charter is for a commercial power plant. He also suggested overdriving the bootstrap current to establish the plasma current. [Mau - Evaluate a bootstrap overdrive option for startup.]

Startup and Current Drive Systems for ST Power Plants - T.K. Mau reported new analysis results that would suggest a factor of 5 to 10 improvement in edge drive current drive system efficiency. Hence, off axis CD is now possible. He would like to use High Harmonic Fast Wave (HHFW) as the current profile control technique. He would suggest some off-axis and edge SOL CD to optimize the beta limit. He would also use the core auxiliary heating system for low beta startup.

Physics Plans for the Near Future - Steve Jardin summarized the following general investigation areas:

PPPL, Free Boundary Equilibrium Analyses (divertor, SOL thickness)
Vertical Stability
Rotation Requirements
Beta Enhancement with Edge CD and Finite Edge Density

UCSD, CD Options
Startup Scenarios (HHFW and Bootstrap Overdrive)
Beta Enhancement with Edge CD

GA, Stability Studies with Non-Zero Plasma Pressure at the Plasma Edge
Transport Analyses
Startup Scenarios

Engineering Plans for the Near Future - M. Tillack reviewed the ARIES-ST schedule to highlight development of design options during the next few months, with concept selection for the baseline design at the next meeting. L. Waganer stressed that we must have enough definition (including design sketches) so that informed decisions can be made at that time. Mark summarized the blanket, centerpost, and divertor material and coolant options to be evaluated (see action items). Mark also suggested that the helium-cooled divertor include Cu, V, and SS structural options as well as a liquid metal variant with both closed-channel and free-surface flow. [Wang - Assess expanded He-cooled and liquid metal-cooled divertor options.]

Administrative


Action Item Summary

Dahlgren
Add ohmic heating source and hold total current constant.
Dahlgren/El-Guebaly
Select insulator material and modify the design to incorporate insulators.
Dahlgren
Update code to increase CP radius when shield is thinned.
Dahlgren
Develop and analyze the proposed wedge design.
Reiersen, Bromberg, Dahlgren, Wang, El-Guebaly, Sze
Develop CP designs for four approaches; (1) H2O-Cu, (2) Li-Cu, (3) LHe-Al, and (4) LHe-S/C. Design should include CP, shield, and outer TF legs plus electrical and coolant routing scheme through CP, TF coils, divertor, and blankets.
El-Guebaly
Recommend shield composition and thickness for each CP configuration noted above to meet waste disposal, resistivity, and lifetime requirements. Fixed values are desired, but economic considerations may require parametric solutions.
Jardin
Determine if the 1-cm-thick kink shell is adequate.
Blanchard
Provide design guidelines for brittle materials especially Cu, SiC, and ceramic materials such as insulators.
Wang
Check the stress level at the 8 MPa level and increase the pressure if possible.
Bromberg
Develop a conceptual design and sketches of a 30K S/C bus bar and power supply system. Compare to a normal Cu design.
Khater
Redo the LOCA analysis with axial conductance.
Khater
Rerun LOCA analysis of the Cu CP without a shield.
Sze
Examine a helium-cooled first wall with the lithium-cooled blanket.
Sze
Work with Malang to develop a water-cooled CP and Li-cooled blanket design approach with several layers of protective barriers.
Miller
Run two cases for A=1.4 and 1.6 with data supplied by S. Jardin.
Jardin
Verify vertical stability of the data sets.
Mau
Evaluate a bootstrap overdrive option for startup.
Wang
Assess expanded He- and liquid metal-cooled divertor options.


Agenda

Japan/US Workshop/ARIES Project Meeting
Room 5101, Engineering Bldg., Unit 1
University of California, San Diego

Wednesday, 5 March 1997


8:30    Coffee and Socializing
ENGINEERING SESSION (Chair: Prof. Kiyoshi Yoshikawa)

9:00    Overview of ARIES-RS Neutronics and Radiation Shielding 
        Dr. Laila El-Guebaly (UW)

9:45    Comparison of Radioactive Waste Disposal of a Fission and Fusion Reactors 
        Dr. Yasushi Seki (JAERI)

10:30   Break

10:45   The Configuration and Maintenance of the ARIES-RS Power Plant 
        Mr. Les Waganer (MDA)

11:30   Engineering Design and Materials Consideration of the DREAM Reactor
        Dr. Shuzo Ueda (JAERI)

12:15   Lunch

LOW-ASPECT-RATIO SPHERICAL TOKAMAK (Chair: Dr. Mark Tillack)

2:00    New Ideas for Spherical Tokamak Power Station Design 
        Dr. Neill Taylor (UKAEA)

2:45    Present Status of Structural Material Development at Japanese
        Univertities and NIFS  - Prof. Yiutai Katoh (Khoto University)

3:30    Break

3:45    ARIES-ST Blanket Design 
        Dr. Dai Kai Sze (ANL)

4:30    ARIES-ST Systems
        Dr. Ronald Miller (UCSD)

5:15    Close-out of Japan/US Workshop

        [Dinner: by arrangement]


ARIES Project Meeting
Room 479, Engineering Bldg., Unit 2
University of California, San Diego

Thursday, 6 March 1997


8:00    Coffee and Socializing                                UCSD Hosts
Administrative
8:30    Discussion of Agenda                                  Waganer
8:35    Programmatic Overview                                 Dove/Najmabadi
Spherical Tokamak Engineering Session
8:50    Short Summary of Engr Talks in Joint Session          Tillack
9:10    Centerpost Design and Analysis                        Dahlgren
9:40    Centerpost Discussion                                 Team
9:50    IBC Centerpost Study Results                          Reiersen
10:20   Break
10:30   Centerpost Shielding and Blanket Neutronics           El-Guebaly
11:00   Design and Analysis of Helium Cooling of HHF Components     Wang
11:30   Tritium Issues in Liquid Metal Divertor Designs (not presented)  Sze
        Buss Bar Design Assessment (added)                    Bromberg
12:00   Safety Analysis Results for LAR Tokamaks              Khater
12:30   Lunch to 1:30
1:30    Engr Summary/Direction for Next Six Months (delayed to Fri. am)  Tillack
General
2:00    ARIES-ST Systems Issues & LAR Comparison Study Results   Miller
2:30    Highlights of the Innovative Concept Workshop            Jardin
3:00    Break
Alternate Applications Session
3:15    Alternate Applications - Scope and Preliminary Results   Waganer
General
4:00    Summary of the US/Japan High Power Workshop              Wong
4:30    Discussion of LAR Blanket Engineering Issues             Sze, et al
5:30    Adjourn for Dinner


ARIES Project Meeting
Room 479, Engineering Bldg., Unit 2
University of California, San Diego

Friday, 7 March 1997


8:00    Coffee and Socializing                                    UCSD Hosts
Spherical Tokamak Physics Session
8:30    Results of High-Elongation, Low-Aspect Ratio Stability Studies  Jardin
9:00    GA Physics Study Results                                  Stambaugh
9:30   Startup and Current Drive for ST Power Plants              T.K.Mau
10:00   Discussion Period
10:15   Break
10:30   Physics Summary and Direction for Next Six Months         Jardin
11:00   Action Items, Plans, Report Status                        Najmabadi
11:30   ADJOURN