ARIES-Pathways Project Meeting Minutes
19 May 2010
UCSD, San Diego, CA
Documented by L. Waganer
Ref: Agenda and Presentation Links: Meeting Agenda
Welcome/Agenda - Mark Tillack welcomed the team and provided instructions for local internet connections and the emergency exits and safety procedures. Les Waganer summarized the agenda and mentioned that full discussions could be accommodated in the agenda.
Next meeting and call - The next meeting will be held in the July timeframe in the Washington DC area to enable attendance of the DOE personnel. The date and meeting location will be finalized in June. Farrokh Najmabadi will advise on the date/location of the meeting and the next conference call. Les Waganer will send out a Doodle invitation for a call in June.
Status of ARIES Town Meeting Planning - "Edge Physics & Experimental Validation for Fusion Power Plants" - Mark Tillack summarized the plans for the Town Meeting to be held at UCSD on June 20-21. He has solicited a good set of participants with excellent presentations and group discussions planned. Edge physics modeling and experimental results will be discussed including the R&D needs to prepare for the next large fusion machines up to and including Demo.
Thermal (heat) Load Specifications from ITER Chuck Kessel presented ITER data on their anticipated divertor heat load specifications. ITER will produce a fusion power of 300 MW to 700 MW, whereas ARIES designs are in the range of 1700-2700 MW. The plasma power for ITER is 120-200 MW and the ARIES designs would be in the range of 450-750 MW. ITER has three areas of first wall surfaces that might see up to 5 MW/m2. The ITER (single null) divertor would experience 45-90 MW (nuclear) whereas ARIES (double null) would be 155-200 MW (nuclear). Chuck also presented the first wall powers and discussed MARFE and ELMs conditions. He affirmed the need for ELM controls to eliminate or mitigate their effects. He also showed an energy density and heat flux factor for both CFC and W first wall materials. Disruption thermal loads are also a major design consideration. Chuck felt the need to develop scaling relationships and design margins for static, transients and off-normal events. The first wall must be protected from fast particle losses, ions and runaway electrons.
Plans and General Scope
Status and Update on Pathways Project - Farrokh Najmabadi said that the original scope of the ARIES project for the next few years remains as planned with no anticipated changes. We need to have some worthwhile results in the next 2-3 months to report at the July meeting, notably results from the systems code involving the 2 x 2 physics and technology parameter space, i.e., strawman physics and engineering definition.
ARIES-Pathways Task Results
Development of a Visualization Tool for the ARIES Systems Code - Lane Carlson noted that the systems code has evolved into a design space scanning tool encompassing a wide range of possible favorable power core design conditions. It also has the capability to display slopes of key parameter sets (currently code considers 80 parameters). Rapid processing is possible with the PPPL computer cluster. Being able to meaningfully display the information is the key to being a useful tool. The graphical user interface is called Visual ARIES Systems Scanning Tool (VASST), which is being designed to modify the displayed parameters and parameter spaces. COE is the most popular ordinate parameter. Lane showed many example 3-D plots for illustration.
Action: Chuck Kessel to develop benchmark low and high temperature S/C design cases. Also need to select or highlight benchmark cases at each of the corners of the design space.
Activation Assessments of 316 SS Vacuum Vessel and W-Based Divertor - Laila El-Guebaly clarified the definition of an activation assessment (post operation) and radiation damage (during operation). For the vacuum vessel, she reported on the neutron-induced swelling and activation assessment (specific activities and radwaste management schemes). All power plant materials should be recyclable and qualify as LLW. She explained the recommended VV design rationale. Austenitic steels and ferritic/martensitic steels were compared. 316 SS should be avoided as it generates high level waste. She will continue using the 1 He appm as a projected re-weldability limit for ferritic steel.
Laila explained the tungsten and tungsten alloys being considered for the divertor, especially the activation and radiation damage considerations. X. Wang and S. Malang have proposed a combined plate and finger divertor design concept with W-armor and W in the cooling channels. She investigated the activation of the newly developed W-alloys as well as the commercial W-26Re alloy. The results indicate that both W-La2O3 and W-1.1TiC alloys are recyclable and qualify for shallow-land burial, controlling the Nb and Mo impurities offers advantages, and Re-based alloys should be avoided for generating high-level waste.
Design and Analysis of an Innovative First Wall Concept - At the last meeting, Xueren Wang proposed a W and ODS FS first wall armor concept using micro pins that might be capable of sustaining a steady state heat flux 1 MW/m2 and a fast transient surface heat flux up to 2 MW/m2. Stress analysis should use the "design by analysis" instead of "design by rule" approach. The fabrication approach recommended is to braze together the FS wall, an ODS-sieve plate, and the W-pins in a one step furnace operation. A finite element model helped analyze the module. Creep is not considered at this stage. He showed many analyses results for different parameters and conditions, primarily the elastic-plastic analysis. Thickening the FS wall from 1 mm to 2 mm might help reduce the plastic strain. 3-D analyses may be needed to confirm actual behavior. Laila suggested considering the degradation of the thermal conductivity of W due to neutron irradiation. Based on the limited data available, Xueren could parameterize the impact of the drop in thermal conductivity on the ARIES divertor design.
Extrapolating Experimental Results for Model Divertor Studies to Prototypical Conditions - Minami Yoda presented the Georgia Tech results on the model divertor studies. The objective is to experimentally evaluate and model advanced gas-cooled divertor design concepts to validate designs and predict/enhance their performance. The goal is to exceed 10 MW/m2 for both steady state and transient conditions. The plate-type divertor has been modeled analytically and experimentally. The pin-fin array is being analyzed to see if it can improve the thermal performance. Minami explained the experimental test setup and fluid conditions. The pin-covered surfaces improved the heat transfer coefficient by as much as 90 to 180% with a corresponding maximum pressure drop of 40% increase. This higher HTC of the assembly is primarily due to the added surface area.
In summary, a 2-mm rectangular slot jet of He impinging on a pin-covered surface can accommodate heat fluxes up to 18 MW/m2 with a pumping pressure increase of 40%. The results do not include the degradation of W thermal conductivity due to irradiation.
Action item: GT or UCSE - Do an elastic stress analysis on the 2-mm slot case.
Action Item: Laila El-Guebaly- Investigate thermal conductivity of W after irradiation.
Modified Design of the ARIES T-Tube Divertor Concept - Jeremy Burke reviewed the original T-tube design approach, design details and thermo-fluid analysis results. The original design had a uniform inlet tube chamber, whereas the new design has a tapered tube with the cross-sectional area decreasing away from the inlet. This design improvement yielded almost uniform temperature distributions on the armor. In the future, transient thermal loading will be considered. Plastic deformation analysis could be performed to determine if the design will accommodate heat loads as high at 10 MW/m2. Joining the tungsten to the FS is a concern along with the subsystem reliability with the very large number of joints.
Action Item: UCSD to model the stresses in this design concept.
Pilot Plant Discussions
Pilot Plant Study (PPPL) - Hutch Neilson provided the motivation and goals for the next step fusion nuclear facility, including burning plasmas, component testing and electric power production demonstration. Hutch's team is defining an integrated pilot plant that produces greater than net electricity, is flexible to accommodate component testing, incorporates new technologies and is affordable. Risk is very important for the design of the pilot plant. Also the pilot plant must measurably reduce the risk for the future power plants. The time horizon for the maturation of the pilot plant physics and technology bases is assumed to be in the 2025 timeframe (beginning of final design phase). The confinement concepts being considered are the advanced tokamak, compact stellarator and the spherical torus - each concept has its distinct advantages and disadvantages with the tokamak being the most advanced at the present time. Key issues are magnet current density (power core size), blanket and shield thickness (power core size), divertor /FW heat flux limits (power density and life), and maintainable configuration (viability as a power plant).
The current study plan focuses on assessing current physics and technology readiness with postulation of these physics and technology issues to the 2025 time horizon. This establishes the necessary R&D program and the risk to the pilot plant if the R&D programs are not successful. There are a series of reports and papers with the final report due in December 2010. Several ARIES team members are contributing to this effort.