28 April 18 Jan 2012 Author: Lester M. Waganer, email@example.com-->
ARIES Documents -- Meetings ArchiveARIES Conference Call, 3 April 2012
Documented by L. Waganer
Farrokh Najmabadi mentioned the next ARIES meeting might be held in the Washington, DC area as this could coincide with a planning meeting with FES personnel, but details are yet to be determined.
The next phone call should be held in late April before the possible May meeting. Les Waganer will set up a Doodle query on possible dates.
Lane Carlson has or will be leaving UCSD for a new position in General Atomics. In the meantime, project personnel will be running the Systems Code until a replacement person can be found.
ARIES Technical Efforts
Radial Build with Emphasis on Vacuum Vessel - Farrokh Najmabadi mentioned that Laila El-Guebaly has been defining radial builds for the ACT power cores. Farrokh has been working with her to keep the radial build and configuration somewhat similar to the AT configuration, but with the new thin VV design. There may be some relocation of the components and functions, but the overall build should be comparable. The ACT vacuum vessel (VV) coolant is helium, but the VV will be hotter than room temperature, implying a higher pressure vessel or cooling passages. The primary shielding component may be outside the VV (that is, further away from the plasma). However the VV will provide some shielding function. The radial build is still evolving, trying to best satisfy many criteria. Chuck Kessel thought running the VV and some shielding elements at higher temperatures would help control dust and tritium accumulation. Per Arthur Rowcliffe, the likely temperature range was thought to be between 400°C and 550°C based on material considerations. Also, the 3Cr-3VW steel is a possible structural material. Siegfried Malang and Arthur Rowcliffe provided input on temperature constraints on FS and other materials.
Laila said her Option 5 in her recent E-mail dated 2/6/2012 is very similar to the one now being considered, placing the primary low-temperature shield outside the VV. The shield will likely use WC filler and water coolant. She is also concerned about eliminating the inner door at the outboard maintenance port as it was an important shielding element for the protection of the TF coils and other externals. The inner door also provides an additional confinement element.
Farrokh and Siegfried discussed the rationale for keeping the skeleton (support) ring as either 1) a lifetime element or 2) a long-lived element that is replaced as needed during regular maintenance periods. There was also a discussion if the VV needs to be re-weldable or not - the example used was the (unlikely) replacement of a TF coil, which might entail removing a quarter or more of the VV.
Farrokh strongly suggested we return to using a super-insulation thermal shield in place of the ITER approach of the 2-cm thick helium-cooled thermal shield. Les Waganer noted that the super-insulation is extensively used in spacecraft design and is known as multi-layer insulation (MLI). Paul Humrickhouse noted that ITER is using the thermal shield to help dissipate the decay heat in an accident case and also by injecting air into the torus. He will research this topic and report at the next meeting. Laila asked Paul to report the maximum inboard temperature in the absence of air injection.
Paul Humrickhouse wanted the inboard and outboard VV coolant circuits connected so the heat from the inner region could circulate via natural convection to the outer region in the case of a LOCA.
There was some discussion of the thickness of the radial assembly gaps, considering thermal and neutron swelling. Several approaches have previously been proposed to shield against neutron streaming
Bottom Divertor Design and Plumbing - Mark Tillack reported that he and others have been concentrating on the design of the divertor surface to be compatible with the latest physics results. It was concluded that the driving factor is the design (space) constraints to provide tritium breeding and shielding in the area while having sufficient space at the bottom divertor region for the coolant plumbing for all the inboard components. Marv Rensink and Tom Rognlien felt that the physics solutions would be flexible enough to be compatible with the divertor design being considered. However the next design iteration would be evaluated for compatibility. Mark and Xueren Wang have been defining some conceptual approaches for the bottom divertor, links are provided from ARIES home page under "What's New". The most favorable approach is the Jogged Sector Bottom. Mark noted that additional changes are needed to sufficiently define this approach.
Tilt of Divertor Plates - Chuck Kessel said that the detail is still lacking on the exact tilt of the divertor plates with respect to the local field lines. The tilt of the inner divertor plates is not too critical as the particle and heat loading is less severe on the inner plates. He suggested shaping the inner blanket closer to the plasma to maximize the inner divertor region breeding capability.
Divertor Physics Results - Marv Rensink and Tom Rognlien said that the length of the inner divertor plates may grow from 15 cm to 25 cm. They also felt that their results would be compatible with the design approach suggested by Mark Tillack.
Water-Cooled Low Temperature Shield - Arthur Rowcliffe discussed the material aspects of the low-temperature shield. He asked Laila to forward to him the details she has developed so he can better define the materials and their properties throughout their lifetimes.
Plasma Core Physics - Chuck Kessel said that his time-dependent solutions for the aggressive physics scenario are close to the ARIES System Code results, indicating that the systems code is finding viable operating points. The changes that would make the relationship more accurate are using the 95% shape parameters, rather than those at the separatrix, and slightly more peaked temperature profiles.
Power Core Design and Mechanical Analysis - Xueren Wang has been refining the design of the two conceptual approaches. He has been employing Laila's new radial builds for the definition of the inboard and outboard components. He has been working with Mark on the divertor region designs. After the CAD is better defined, Christina Koehly (FZK, now KIT) will analyze the MHD losses in the pipes he has been defining. He has also been working on the thermal stress analyses of the inboard blanket.
Divertor Fatigue Analyses - Jake Blanchard is trying to assess the impact of ELMs on the divertor plates. As a starting point, he assessed the heat fluxes as the nominal value + 20% and he found this level not to be a problem.
Farrokh asked Jake if he had addressed his January meeting action item to analyze the use of localized webs to lower the VV stresses below the design limit. Jake said he would address this issue.
3-D Neutronic Analyses - Laila said she is working to define and analyze the SiC blanket option with their 3-D neutronics code now that the design is better defined. She will be concentrating on the inboard and outboard regions. She will also work with Mark on the divertor areas. She is optimistic that the design may be able to use a lower lithium enrichment than 70%. She would also like to begin to add some penetrations on the outboard region to improve the fidelity of her analysis.