Participants: Sze, Billone, Dove, Wong, Bathke, Waganer, D. Lee, Bromberg, Jardin, Hofer, Steiner, Miller, Najmabadi, Malang, Mau, Tillack, El-Guebaly, Sviatoslavsky
New Reverse Shear Analyses Results
Steve Jardin summarized C. KesselÕs recent results on the vertical stability and control analyses for a reversed shear plasma with an aspect ratio of 4. The plasma elongation was reduced from 2.0 to 1.9 to allow the vertical control shell to be moved to the area of the reflector/shield gap. Specifics:
Two coil locations were investigated: (1) in the reflector shield gap, and (2) behind the shield:
Location Reflector shield gap Behind the shield Coordinates, m R = 5.75, Z = ± 2.35 R = 7.00, Z = ± 2.50 Coil Peak Power, MVA 15 40 Peak Current, kA-t 75 100 Peak Voltage, kV/t 0.1 0.2 RMS Random Disturbance, cm 1.0 1.0
Even though the power was considerably higher in the second case, F. Najmabadi recommended the active coils be placed behind the shield to: (1) reduce the cooling requirements, (2) ease the coil connections between adjacent modules, and (3) reduce the neutron damage to the coil insulators. It was recommended that this rationale be documented. There was also discussion as to the coil configuration: (1) discrete coils for each module with leads in and out, or (2) a continuous coil with jumpers between modules. The physicists recommended a continuous coil as the fields from the return elements tended to counteract the fields of the main coil elements. Igor Sviatoslavsky is investigating the coil design approach and will work closely with C. Kessel on effectiveness of proposed design approaches. Power consumption in the coil elements was discussed and F.ŹNajmabadi determined the resistive power consumption was small, on the order of 1 MW/m3, for a typical 100 cm2 coil cross-section.
The second set of KesselÕs results, discussed by Jardin, involved the MHD Stability and Kink Shell Analyses. With the plasma elongation reduced to 1.9, it was assumed the second vanadium structural layer (2 cm thick) in the blanket could be used as a kink stability shell. The close proximity of the shell (0.094Źm from the plasma boundary) makes the kink stability very high so the plasma beta is strictly limited by the ballooning modes and the bootstrap current. The shell is only needed on the outboard blanket modules with coverage ± 85” from the midplane. Also the coverage need not be toroidally continuous, hence each 1/16 blanket sector would be adequate. Analysis results indicate that the maximum betaN is 5.35 and beta is 5.54. With a 10% beta reduction to 4.98, betaN is 4.82 and the plasma-driven current is 89%.
The new equilibrium results were forwarded to C. Bathke for EQDISK calculations and on to T.K.ŹMau for current drive analyses. For the systems code, C. Bathke needs the Z-effective, the impurity species, and the edge temperature and density from C. Wong. It was decided that when Clement Wong gets his preliminary results, he should send them to the Physics group for assessment prior to release (on 2/21) to C. Bathke for use in the systems code.
Divertor Physics and Design Definition Update
Tom Petrie and Phil West of GA are helping to scope the mid-plane and divertor SOL parameters. Tom assumed that the ratio of ne,sep/< ne > ~1/3. The goal is to limit the maximum heat flux to the divertor plate to be ² 5 MW/m2. The electron pressure is conserved between the mid-plane and the divertor. Te,div will be an independent variable evaluated between 10 eV and 100 eV. Based on the injection of TBD impurities, the equations for ne,mid, Te,mid and ne,div will be solved. The Zeff of the core will also be determined. A flat impurities profile will be assumed in the calculations. These data will form the first round inputs to the core physics-equilibrium, current drive, bootstrap, and system code calculations. These assumptions will have some impact on power plant performance, but it is a necessary first step of the iterative process. Jardin and Wong agreed on an exchange of data and a conference call early next week to discuss next actions.
Status of Engineering Design Inputs for Systems Code
All engineering inputs should be forwarded to Laila El-Guebaly early next week so she can distribute the data to the engineering group for review prior to release to C. Bathke on 2/21.
It was stressed we should confirm the thickness of the vacuum vessel as many calculations are dependent upon the inboard thickness. Waganer noted that an analyst has the vacuum vessel modeled. Dennis Lee explained that the model contains a 10 cm solid shell to estimate the loading conditions and the areas of concern, perhaps around the ports. Modeling of the sheet and stringer (bulkhead) approach for a double-walled design would be too involved at this point. For purposes of the engineering data inputs, it should be assumed the 20 cm inboard and 30 cm outboard should be considered reasonable at this point.
Leslie Bromberg said he would have the coil case dimension by COB on 2/14. He is working on the cap segmentation scheme and hopes to have something to D. Lee soon.
Xueren Wang is working with C. Wong on the divertor piping configuration to bring the divertor coolant temperature up to 650”C. He hopes to have the configuration completed this week. Composition of the divertor is approximately 30% lithium and 70% vanadium.
One of the meeting action items was to determine the distance the outer TF coil legs should be radially increased to enable withdrawal of a complete OB blanket sector. (Some portion of the OB shield may remain inplace.) Dennis Lee determined that the distance should be 1.7 meters. The critical dimension was determined to be on the midplane, thus the systems code should be capable to determine the dimension. D. Lee will supply C. Bathke the local VV thicknesses and clearances to add to the TF coil sizing algorithm. L. Bromberg noted that the size of the coil cross-section will vary because the coil is defined to be a constant tension coil. Sze will provide this week the piping quantity and size for each blanket and shield sector.
C. Wong went over some of the analyses being conducted on the divertor. One of the key decisions is to recommend the impurity species Š argon is the leading candidate at this point. He is working with C. Bathke to determine the SOL field expansion in the divertor. The determination of the heat flux profile, thermal-hydraulics, and plumbing routing is an iterative process to be worked with D-K Sze. Igor Sviatoslavsky agreed to help define the internal divertor structure.
The definition of the divertor vacuum ducts and the vacuum system was briefly discussed. A 5-cm slot will be used, one in each inboard divertor slot and one in each outboard slot. This results in four slots total. These slots are pumped through 25-35 cm diameter vacuum ducts through the divertor structure and shield, 32 ducts total. To provide neutron shielding, the ducts should have at least one and preferably two 90” bends. Igor S. thought there was sufficient conductance in the area outside the shield to enable the use of large pump ducts through the vacuum vessel only on top or bottom of the vacuum vessel/cryostat. Location at the top or bottom is TBD. Sze will be responsible for the selection and specification of the vacuum pumps.
Laila El-Guebaly noted that she will use the standard FENDL library on all future neutronic calculations. This would result in a 10% lower neutron multiplication. Reoptimizing the shield for the 20-30 cm VV design has resulted in a 5-cm thinner shield. Jake Blanchard and his students can do the stress calculations on the blanket and shield.
Safety and Licensing Status
Don Steiner noted he is just about to complete the review and write-ups for the Interim Report. Bob Thayer is working on the preliminary safety analysis of ARIES-II, concentrating on the probability versus risk. He is integrating the accident scenarios obtained from Clement Wong and Steve Herring.