ARIES-Pathways Project Meeting Minutes
26-27 August 2009
Georgia Technology, Atlanta, GA
Documented by L. Waganer
Ref: Agenda and Presentation Links: Meeting Agenda
Welcome/Agenda -Minami Yoda welcomed the group and told the ARIES Team about the facilities, the refreshments and the evening dinner plans. Les Waganer reviewed the agenda for the meeting.
Next meeting and call - The next meeting will be held in San Diego, either at UCSD or GA, on December 15th and 16th (all day Tuesday and half day on Wednesday). The next project conference call will be scheduled sometime in September 2009, depending on the scheduling of the DOE project review meeting schedule. Farrokh Najmabadi will advise on the date of the review meeting and the next conference call.
ARIES Project Status
Farrokh Najmabadi summarized the ARIES-Pathways project results to date that included updating the physics and technical solutions for several key issues especially the DCLL blanket and off-normal events, introducing the Technology Readiness Level concept and implementing this process into several ReNeW Thrusts and providing in-depth support to the DOE ReNeW pre-planning workshops. Other activities included upgrading/documenting significant aspects of the systems code and the cost database and algorithms, and implementing new processes for surveying and integrating the physics and the engineering data landscape. It is hoped that ARIES can provide specific support and critique of the laboratory proposals in response to ReNeW initiatives. Hopefully, ARIES can provide a longer term and unbiased view of the near term fusion R&D objectives.
A new ARIES proposal approach for DOE was adopted to better integrate and consolidate the efforts of the ARIES team organizations to provide a more unified project solution while allowing the submission of individual proposals to DOE. In the near future, it is anticipated that some members of the ARIES team will be invited to DOE to discuss the integrated ARIES proposal.
ARIES-Pathways Task Results
DCLL Blanket Analysis and Power Core Layout (on the ARIES-DP Design) - Xueren Wang acknowledged contributions from his co-authors in support of this design analysis and power core layout. He presented three distinct cases for assembly gap shielding the vacuum vessel and underlying components, namely 1) a large block of W or WC with large steps as proposed by Laila El-Guebaly in March 09, 2) a thinner block with smaller steps and 3) a still thinner block and even smaller steps. It appeared the analysis did not consider closure of the gaps due to thermal or neutronic-induced swelling. Mechanical properties for the shielding blocks were provided for the thermal analysis of the three cases with an overestimated average inboard neutron wall loading (NWL). However, there are no detailed nuclear heating rates currently available for the three cases A, B, C. With the initial geometry and heating calculation from Tim Bohm's 3-D neutronic analysis based on the original ARIES-AT DCLL radial build, Cases A and B would experience excessive temperatures with overestimated NWL levels. On the other hand, Case C would have acceptable temperatures. Case B could be acceptable if the heating input were reduced by 25% as suggested by Laila, taking into account the ratio between average to peak NWL at the IB region. Laila El-Guebaly said that only Case A is acceptable from the neutronics standpoint as the 5-cm step size is critical to attenuate the streaming neutrons. It should be noted that all design and nuclear parameters are preliminary. The new ARIES-DB design may call for lower NWL which may make the Case A acceptable.
Xueren has also been working on the preliminary layout of the ARIES-DB Power Core for two trial plasma cases. A common layout was prepared for both cases, largely derived from ARIES-RS and ARIES-AT. Xueren also sketched in the plumbing layout for the removable module, but the ARIES team noted that the inlet and outlet pipes should not be directed upward into the vacuum vessel access port but be directed downward below the access port so there is adequate remote maintenance equipment access. The maintenance approach again reflects the ARIES-RS and ARIES-AT maintenance approaches.
High Performance Divertor Target Plates, a Combination of Plate and Finger Concepts - Siegfried Malang acknowledged design and analysis support from Xueren Wang. Siegfried outlined the mechanical characteristics of this design that has a tungsten (W) base plate that is fabricated by machining the deep channels and brazing the upper face plate with the connecting holes for coolant flow. Then small cooling modules with W armor are brazed onto the lower cooling-channel plate. Siegfried pointed out the improvements of the ARIES high performance diverter target plate design as compared to the EU design concept (i.e., no transition between W-alloy and steel at modules and double containment of high-pressure helium). He claimed that the fabrication of the new design would be simpler than the fabrication of the complicated fingers for the EU design. Details of the finger fabrication and the fabrication of the transition zone at both ends of the plate were explained. Also shown were thermo-mechanical results for the modified finger module. As a next analysis step, the behavior of the divertor target plate under cyclic loading conditions and fast transients will be investigated. Laila suggested examining the sensitivity of temperatures and stresses to the change in thermal conductivity with neutron irradiation.
ARIES-DB Design Issues and Activation of Divertor W-Alloys - Laila El-Guebaly is concerned about the DB recirculating power level, the new TF magnet dimensions and composition, and the activation of the divertor materials. She analyzed two preliminary cases (with and without radial manifolds). With the currently predicted power flow and assumed system efficiencies, the new ARIES systems code indicates ARIES-DB must generate 4500 MW thermal power to deliver 1000 MWe net. This situation is aggravated by the 680 MWe pumping power and 210 MWe current drive/heating estimates. Recently, it was discovered that the pumping power calculation had some errors and these are being corrected to yield 260 MWe. Said Abdel-Khalik volunteered to send L. Waganer and L. El-Guebaly typical power flows for current and new generation fission plant designs. The current drive/heating power should be checked and reduced to the ARIES-AT level (~90 MWe).
The assumed TF magnet composition in the systems code is Inconel whereas it should be JK2LB per the approach used in ARIES-CS. The helium coolant fraction seems high at 25%. The winding pack may be too thin and the outer coil case too thick.
Laila is concerned about the divertor activation, tungsten decay heat (and temperature response during off-normal events), and survivability of the tungsten armor. There are several candidate tungsten alloys that could be used for the divertor. There remain a few questions, such as: are the divertor materials able to be cleared, recycled, and disposed and is there any high level waste? She illustrated the specific activity of several of tungsten alloys. She concluded that the W-divertor would not be able to be cleared after 100 years; however, it could be recycled and may qualify for Class C Low Level Waste. The W-La2O3 exhibits the lowest activity. The impact of the brazing materials on the divertor activation has not been assessed yet.
Laila showed the DB-DCLL blanket and shield radial build with lower density Ultramet SiC insulating inserts. For this design approach and parameters, she developed the key neutronic parameters and radiation limits. She also illustrated the inboard, outboard, and divertor radial builds with and without radial manifolds. The upper and lower radial builds are challenging due to neutron streaming through the large vacuum ducts and the high tungsten decay heat.
Laila also did a comparison between the ARIES-AT and the ARIES-DB key engineering parameters. She noted several key results and highlighted that the DB COE is considerably higher with the current parameters and design assumptions (pumping and total power may decrease). She presented several observations and recommendations to improve the DB concept.
Update on Thermal Performance of Gas-Cooled Plate-Type Divertor - Minami Yoda presented the Georgia Tech experimental testing results on the gas-cooled plate-type divertor with jet impingement and heat transfer enhancement by a pin-fin array. The intent is to robustly accommodate heat fluxes up to 10 MW/m2. To simplify testing, experiments are conducted at conditions matching and spanning non-dimensional parameter regions for Reynolds number using air as the coolant. CFD codes are used to help predict expected thermal and power performance. Test setups were described that were similar to the proposed design configuration. To reduce thermal stresses, the test setup added a 2-mm stagnant He-coolant region outside the outlet manifold and an 8-mm tungsten-alloy base. Fabrication of the pin-fin array was challenging and time consuming using an EDM process. Cooling performance data was shown comparing the pin fins to the bare surface. The pin-fin improved cooling performance by ~150%-200% while the pressure drop only increased by ~40-70%.
Cost Model Update and Comparison (to the ARIES-AT) - Les Waganer noted that he was requested to update and document the ARIES Systems Code costing algorithms and this task has taken several years to complete. At the April 2009 ARIES meeting, he presented the final algorithm results. Since April, he has been documenting the algorithms and their basis in detail. He then wrote an Excel spreadsheet to compare and validate his results. The Main Heat Transfer and Transport account appeared to be too expensive as compared to the remainder of the Power Core subsystems and this has been adjusted accordingly. The magnet subsystem algorithms were defined by Leslie Bromberg and are embedded in the Systems Code, but they need to be documented. Several other subsystems are not defined yet (Heating and Current Drive, Vacuum System (except for the vessel), Radioactive Waste, Fuel Handling, Maintenance, and I&C) need additional engineering and cost definition.
Les presented each major subsystem cost definition as compared to ARIES-AT and explained the basis and the differences and discussed where more definition is needed. The indirect and financial cost factors represent major cost elements. These factors are trying to be brought in line with the ongoing fission Gen-IV power plant studies. Notably, using the GEN-IV financial factors alone, the fixed charge rate is lowered by 40% and the COE by 30%.
Les recommended discontinuing the use of Level of Safety Assurance (LSA) cost factors that historically have been applied to many fusion plant cost accounts to take credit for reduced cost by not using the nuclear grade materials and equipment required for previous generation fission plants (ref ESECOM report, 1987). Instead, any fusion plant should be examined for specific use of enhanced safety and nuclear materials related to fusion safety and environmental guidelines. It was decided by the ARIES team that the use of the LSA factor methodology would be discontinued and individual plant subsystems would examined and, if warranted, additional cost would be levied on that subsystem.
Update on Systems Code plus New DCLL Code Results - Zoran Dragojlovic did not attend the meeting and did not have resources to create a presentation on this subject.
IAEA Technical Meetings Report
Farrokh Najmabadi summarized the 3rd IAEA technical meeting on the on 1st Generation Fusion Power Plants. He said there were a lot of discussion over the past few years to eliminate the title of "1st Generation" fusion power plants and just call the meeting Future Fusion Power Plants. Obviously, there was a lot of diversity in the purpose and the design philosophy for the fusion power plant designs.
Laila El-Guebaly summarized the highlights 2009 IAEA TM on Power Plant Designs and Safety. There were about 6 US participants out of 80 participants from 16 countries. The panel discussion on how fast fusion can be a reality with no funding constraints (e.g., provide electricity to the grid) was quite interesting. Note, the opinions provided were personal and not that of their government. The UK (Ward) thought that a demo could be operational in 2020. Japan thought a demo was possible by 2030 and a power plant by 2050. China (Wu) wanted a demo ASAP, perhaps by 2035. The US (El-Guebaly) thought of a demo operation by 2025 and a power plant by 2035, while Goldston mentioned a pilot plant combined with CTF with electricity production to the grid by 2027. Laila noted that the ITER DT phase is now scheduled to commence in 2026.
Laila gave a presentation on "40 Years of (Magnetic) Power Plant Studies" that included a timeline and main features of major power plant design studies within the US, EU, Japan, and China. She included in this presentation international magnetic fusion roadmaps that highlighted what technologies should be developed, what facilities are required, and what is the timeline to the first power plant. Laila also had a presentation on radwaste management that discussed the recycling and clearance options.
The 9th IAEA TM on Fusion Power Plant Safety concentrated on the safety and licensing of ITER. Per Taylor, ITER now has obtained the construction permit and the licensing document was submitted last year. The French asked ITER project to prove that detritiation efficiency will be 99% and to validate the MELCORE code for use in ITER. The Cryostat is no longer necessary to be a confinement barrier.
The Joint Session had discussions that touched on which confinement concept should be used in Demo, how should international collaboration on Demo be structured, and what about a fusion hybrid? The US generally views that the fusion power plant must be economically competitive, whereas the EU and JA think that safety and environmental advantages of fusion will be the principal considerations.
ARIES 1010-2012 Work Plan
To develop a more integrated and cohesive ARIES work plan for 2010-2012, a common work plan has been developed to identify the combined and synergistic contributions of the entire team toward its common goals. The ARIES Team organizations have written and submitted their individual DOE proposals to support the unified ARIES effort.
During the meeting, each organization discussed the key elements of their proposed effort to support the 2010-2012 ARIES project. Due to confidentiality issues, these presentations and discussions will not be documented.