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ARIES Conference Call, 24 July 2012

Documented by L. Waganer

(Boeing) Waganer, Weaver
(FIRE) Meade
(FNTC) -
(FPA) -
(GA) Turnbull
(GT) Abdel-Khalik
(INL) Humrickhouse
(LLNL) Rensink, Rognlien
(ORNL) Rowcliffe
(PPPL) Kessel
(RPI) -
(UCSD) Tillack, Wang
(UTK) -
(UW) Blanchard, El-Guebaly


Les Waganer noted that the next meeting is scheduled for a full day on 26 September and a half a day on 27 September 2012 at Gaithersburg, probably at the Gaithersburg Hilton, pending meeting and hotel arrangements. Al Opdenaker is awaiting funding approval before making the arrangements.

The timing for the next call was not discussed, but it should be scheduled in about 3 weeks.

Les also reminded people that a draft of the May 31-June 1 meeting minutes is finished except for two remaining comments. The 3 July conference call minutes have been distributed for review, so any comments are welcome.

ARIES Technical Efforts

Preparation for the Upcoming TOFE Conference - Mark Tillack mentioned the upcoming TOFE Conference, August 27-31, 2012 in Nashville, TN. The ARIES project will have several technical papers in a special session as well as papers in other oral sessions and posters.

ARIES Session (#13):

  • Farrokh Najmabadi - Re-Examination of Visions for Tokamak Power Plants: ARIES-ACT Study
  • Mark Tillack - ARIES-ACT1 Power Core Engineering
  • James Blanchard - Fracture in All-Tungsten Divertors for ARIES
  • Charles Kessel - The Evaluation of the Heat Loading from Steady, Transient and Off-Normal Conditions in ARIES Power Plants
  • Laila El-Guebaly - Design Challenges and Activation Concerns for ARIES Vacuum Vessel
  • Xueren Wang - Overall Power Core Configuration and System Integration for the ARIES-ACT Fusion Power Plant

Other Sessions:

  • Paul Humrickhouse - MELCOR accident analysis for ARIES-ACT
  • Laila El-Guebaly - State-of-the-Art 3-D Assessment of Elements Degrading TBR of ARIES ACT-SiC Blanket
  • Hamed Hosseini Toudeshki - Vacuum Vessel Analysis and Design for the ARIES-ACT Fusion Power Plant
  • Brantley Mills - An Experimental Study of the Effects of Thermal Conductivity Ratio in Helium-Cooled Divertor Modules
  • Jordan Rader - Verification of Thermal Performance Predictions of Prototypical Multi-Jet Impingement Helium-Cooled Divertor Modules
  • Jordan Rader - Optimization of Pin-Fin arrays for Helium-cooled Finger Divertors

Systems Code Results - Mark Tillack said that the systems code, with several important changes, is running and the ACT-1d baseline is posted on the ARIES web site. Mark highlighted the major changes to the code to prepare the new ACT-1d baseline:

  1. Incorporated a new radial build
  2. Changed the calculation of energy e-folding distance in the scrape-off layer, which leads to higher heat fluxes in the divertor.
  3. Corrected the calculation of the bucking cylinder thickness
  4. Modified current drive efficiencies that impacted the recirculating power balance
  5. Changed from plate divertor to finger divertor because the high divertor heat flux for some of the scanned cases caused inordinately high pumping power. [Mark and Chuck suggested a future improvement to allow the code to select the divertor type based on the heat flux range.]

As a result of all the changes, the final design point has a major radius of 6.25 m, which is significantly higher than ARIES-AT. This will require new CAD definitions as well as new physics analyses to support the new design.

Mark noted that Farrokh Najmabadi had mentioned to him that perhaps the flux lines could be adjusted to provide more space for the outer divertor slots. Chuck Kessel said he would re-run TSC soon and look for an opportunity to angle the flux lines on the outermost flux surface more outward (toward larger major radius).

Alan Turnbull asked Chuck if the GA codes should be rerun for the larger major radius (6.25 m) case or would a complete set of physics code results be necessary to support other analyses? Chuck thought the divertor analyses would be minimally impacted, but the heating and CD analyses might need the complete set of revised physics results based on the larger radius - perhaps these analyses could be run after the TOFE conference in time for the detailed analyses by the end of the year.

Physics Code Results and Database Scans - Chuck re-affirmed that he and Mark have been working to implement new changes and validate the code results. Chuck has been analyzing the use of ICRF, ECRF and LH as the heating and current drive systems. The exact combination is yet to be determined. He also intends to assess the use of a neutral beam heating and current drive system although this would not be implemented in the ACT designs - mostly done for comparative purposes. Laila El-Guebaly asked if the penetration areas and locations Chuck had previously provided were still valid. He responded that he thought they were still reasonable. She asked Chuck to provide the penetrations to Xueren so he could include these in the CAD drawings. Les Waganer asked if all the RF launchers and antennas could be located in a single power core segment and Chuck thought for the moment they could be concentrated in a single segment, but some system openings would be elevated above the midplane.

Plasma Steady-State Solutions - Alan Turnbull did not have an update on his work, but noted that Holger St. John is implementing the CD analyses in the physics code. Alan suggested that the I mode ELM-free scenario might ultimately offer a solution to the ELM mitigation problem. The I-mode was first seen in the C-mod experiment and is characterized essentially by L-mode particle transport with H-mode energy confinement and no or very infrequent small ELMs. The DIII-D experiment is planning on investigating the I-mode operation in experiments this week.

Scrape-off Layer Modeling in the Divertor Region - Tom Rognlien said he has been continuing to model the effects of using argon in place of neon as the impurity control gas. Using argon results in approximately 25% more radiative power and the private-flux region has a lower helium concentration, thus the efficiency of helium pumping will suffer. Tom is recommending retaining neon as the impurity control gas.

Marv Rensink has been analyzing partially-detached plasmas (which are applicable to the ITER divertor) as opposed to the baseline ARIES-ACT detached plasma condition. Marv explained that the detached plasma has a temperature of 1-2 eV across the entire divertor target surface, whereas the partially-detached plasma has the 1-2 eV temperature only in a local area near the strike point while the remainder of the divertor (in the far SOL) is at a higher temperature. Tom Rognlien thought that the fully detached plasma condition could be maintained with feedback control and it might be possible without any feedback control. He also thought that simulations by the ITER modelers indicate that the detached plasma condition may be unstable in the ITER divertor geometry.

CAD Updates in the ACT Designs - Xueren Wang has started making CAD design changes to reflect the new larger major radius power core and new radial builds.

Safety Analysis - Paul Humrickhouse was initially on the conference call, but he had to leave early. Mark Tillack noted that they had been in communication and Mark has to supply Paul with the new power core component temperatures and volumes so Paul can update his safety analysis (for his TOFE paper).

Neutronic Analyses and Radial Build- - Laila El-Guebaly asked Mark Tillack if any decision has been made regarding the placement of the vacuum door on the maintenance port enclosures. She believes this door is needed to provide shielding for the sides of the TF magnets. At present, the baseline design reflects a vacuum door and boundary at the extreme outer end of the port enclosure, with He-cooled shielding behind the replacement sectors. For this design option, he advocated a multi-part structure: one piece at the bottom to include the access pipe penetrations (removed with the sectors) and one larger piece above that, which can be removed before the sectors. Mark mentioned an alternative concept of using a thin, helium-cooled vacuum door (providing minimal shielding) at the inner portion of the port enclosure. The door could be fitted with rupture disks to mitigate accident overpressures in the power core, which is one down-side of sealing vacuum at the back of the sectors. A water-cooled shield could be located directly behind this vacuum door without violating the "no water inside the vessel" rule. This door concept significantly reduces the vacuum volume, lessens the surface area for tritium retention, and allows adequate shielding of the TF coils. Laila will assess this option for neutronic shielding. Resolution of this design is pending Farrokh's assessment.

Chuck had suggested adding vacuum ducts behind the structural ring from the lower divertor region up to the upper ducts to enhance the vacuum conductance, but Mark Tillack said it would be easier to have vacuum ducts penetrate between the lower TF and PF coils and plumbing than install vacuum ducts behind the outer structural ring. Until Mark can talk to Farrokh about the vacuum vessel and pumping arrangement, no baseline can be established.

Laila El-Guebaly has been assessing the waste disposal ratings of the vacuum vessel and structural ring using the candidate materials and the new radial build dimensions. She reaffirmed the vacuum vessel, with bainitic FS should have a 40 FPY lifetime and the structural ring with ODS steel a 10 FPY lifetime. With the considered materials, the inboard vacuum vessel and structural ring have HLW (high level waste) rating with the "Nominal" impurities present in the steel. "Nominal" impurity levels are those that are usually supplied in commercial steel making processes. On the other hand, last year, Arthur Rowcliffe suggested the use of "Present" impurities designation that represents the lowest impurity values presently achieved with modest effort (and cost) for the activation analyses. These "Present" impurity levels allow the vacuum vessel to barely achieve the desired LLW rating while the structural ring easily qualifies as LLW. Arthur asked Laila if the strengthening agent, yttrium oxide, would be an activation concern. She replied the Nb impurity is the main contributor to the WDR and Y does not seem to be problematic. Les Waganer asked if other strengthening oxides, could be used that would avoid the activation concern. Arthur said there were other oxides that could be used.

The preferred material for the structural ring is ODS steel as it has higher strength and temperature ratings than F82H ferritic steel. Mark Tillack noted that the rule of thumb is that ODS steel can operate at 100°C higher temperatures than F82H steel.

Experimental Modeling of Prototypical Divertor - Said Abdel-Khalik said that Georgia Tech has completed the experimental setup of the helium cooling loop of the divertor plate and finger models and they are starting the testing phase. He mentioned the test setup would be ultimately capable of operating at prototypical pressures, but at temperatures less than prototypical temperatures. Results are expected in 4-6 weeks.

Reliability Modeling and Power Core Structures - Tom Weaver mentioned that he has been working to get Dan Driemeyer on board to help in the design and analysis of high temperature structures for the power core.

FESAC News - Dale Meade noted that the FESAC panel that is to assess the U.S. fusion (non-ITER) program priorities is now soliciting public comments to sample the fusion community's opinions. Dale thought it more important for the ARIES Team to continue with the present analysis and design efforts rather than try to respond to the panel.

Mark mentioned that he had heard about an IAEA Demo workshop at UCLA and wondered about more details and if anybody on the ARIES Team was invited or attending. [Chuck is invited and he later inquired to Hutch Neilson who responded that it was an IAEA DEMO Program Workshop at UCLA on Oct 15-18. This is by invitation-only IAEA workshop after nomination by each person's government. An IAEA form is necessary along with an abstract for a poster presentation. Contact Al Opdenaker for more information.]