ARIES-Pathways Project Meeting Minutes
15-16 December 2009
General Atomics, San Diego, CA
Documented by L. Waganer
Ref: Agenda and Presentation Links: Meeting Agenda
Welcome/Agenda -Ken Schultz began the meeting with the instructions for local internet connections and the emergency exits and safety procedures. Mickey Wade warmly welcomed the ARIES team to the GA facilities with a brief summary the GA fusion involvement and the ARIES contributions to fusion power. Les Waganer summarized the agenda, noting that the meeting might conclude early enabling one-on-one technical discussions.
Next meeting and call - To provide an interaction with Al Opdenaker and the OFES staff, the next meeting may be held on the East Coast, perhaps at Germantown or PPPL. Farrokh Najmabadi will discuss favorable times and locations with Al in the next few weeks and establish a time and location for the meeting. There also may be an upcoming planning meeting with Al Opdenaker and a few of the ARIES staff on the 2010-2012 ARIES program plan. The next project conference call will be scheduled sometime in January 2010. Farrokh Najmabadi will advise on the date of the meetings and the next conference call.
Plans and General Scope
Pilot Plant: The Fastest Path to Net Electricity from Fusion - Rob Goldston summarized the present situation that the US (and the world) needs to timely demonstrate the practicality of fusion. However, the ITER project schedule continues to lengthen, now with meaningful plasmas in 2028 or later. A near-term NIF success could stimulate both IFE and MFE needed technology developments. Rob believes the current plan to build a CTF followed by building a Demo might not be the fastest pathway to demonstrate practical fusion energy.
Rob thought building a pilot plant with Qeng> 1 could quickly be built immediately after ITER demonstrates some key results, at least on confinement and disruption effects, to demonstrate production of electricity while accomplishing the component test mission (e.g., tests of alternate blanket options). He thought the key areas of plasma performance, integrated plasma materials interface and neutron material interactions could be developed with new, strong programs in existing and near-term experiments to achieve sufficient competence to commence design and construction of the pilot plant in the near future. He indicated that the proposed pilot plant is only in the early planning stages and no definitive parameters have been investigated. The audience agreed on the need to hasten fusion energy production, but some were concerned that the pilot plant could not achieve the requisite long duration operation with high reliability without a CTF or a similar facility to mature and validate the components. Rob’s response is that this would be part of the mission of the pilot plant. Others thought the addition of an additional large facility step prior to DEMO would delay the commercial utilization of fusion by 20 years relative to the present plan. Rob commented that since this was on the same timeline as a CTF, but did much more, this would certainly accelerate fusion.
Status and Update on Pathways Project Farrokh Najmabadi said that the intent of the next phase of the ARIES project is to investigate the plasma materials interface (PMI) issues in the context of medium to aggressive plasma physics and technology assumptions, namely a parameter surface bounded by upgraded ARIES-I and -AT plasma physics and technology data sets. The upgraded ARIES Systems Code will facilitate this evaluation. We need to obtain concurrence of our project goals with Al Opdenaker and OFES as soon as possible. Tom Rognlien, LLNL, questioned the ARIES heat load on the divertor and suggested integrating the ITER heat loads into our predictive models. [Mark Tillack later noted that ARIES now has the ITER heat and nuclear load specifications for examination upon request.]
Planning for the Upcoming ARIES Town Meeting on Edge Physics Modeling and Experimental Verification for Fusion Power Plants Mark Tillack outlined the motivation and intended goals for the proposed town meeting, mainly to improve the understanding, modeling and experimental verification of plasma edge physics as applied to demo and power plants. The town meeting organizing committee is being expanded to include foreign modelers and researchers. During and after the meeting, the tentative town meeting agenda was revised to ensure consensus and documented conclusions would be forthcoming. It was recommended that a high level of integration occur with the PSI (Plasma Surface Interaction) Conference to be held in San Diego, May 24-28, 2010. Further, the ARIES Town Meeting should precede the PSI meeting.
ARIES-Pathways Task Results
Highlights of the ISFNT-9 Meeting, Oct 11-16 Dalian, China - Laila El-Guebaly and Farrokh attended and presented papers at the ISFNT-9 meeting in China. Laila said there were representatives from most fusion-literate countries, but China had the most attendees. There were no session titles, so it was difficult to find talks of interest. Farrokh thought many oral talks were repeats, but the posters were good. Many talks discussed the implications of the slowed ITER construction and late operational phase. The EU representatives thought their countries would design and construct their Demos immediately after ITER as they felt the CTF was not needed. Some TBM testing might occur in fusion facilities other than ITER. IFMIF is felt to be needed, but a site has not been determined. With IFMIF, EU can qualify Eurofer ferritic steel and Japan plans to qualify SiC/SiC composites for fusion applications in ~10 years. The next ISFNT meeting will be held in Portland, OR, and hosted by INL.
Technical Approach for Improved First Wall Protection - Siegfried Malang noted that the usual power plant study assumption for steady-state FW heat flux is nominally 1 MW/m2. In the case of He-cooled RAFS blankets, the current design capability, based on elastic behavior of the structural material, is very close to this nominal value. These designs should be able to accommodate short peak heat pulses significantly above this 1 MW/m2 using the mass of the blanket as a heat sink. The concern is that over a fraction of the first wall surface, the local heat load may go to significantly higher levels than 1 MW/m2 for longer periods, perhaps a minute or more, which exceeds the short transient case and cannot be accommodated with the heat sink capability of the blanket. The magnitude of this higher level heat flux is unknown, but for scoping analyses, Siegfried set the goal at 2 MW/m2. In this case, some additional tungsten (W) armor is required. The design criteria is that the FW in this region should have the same lifetime as the remainder of the FW and the steady-state cooling should accommodate the higher heat flux - no short term increased coolant flow isrequired.
The proposed solution is that in the special TBD locations, additional tungsten (W) armor will be added as pins embedded in the RAFS FW structure. These pins could be from 1 to 4 mm in diameter. Siegfried has been postulating design and fabrication methods for the wall armor. Xueren Wang will begin to conduct FE analyses to determine the thermal and stress capabilities of this configuration. Some reduction in TBR and an increase in FW temperature during LOCA/LOFA are anticipated and certain RAFS temperature and stress limits will be considered. Siegfried discussed the implications of the ASME code for calculating stresses and strains.
Analysis Results for New First wall Protection Schemes - Xueren Wang reviewed the ARIES-CS DCLL blanket design and analysis results, namely 0.76 MW/m2 with a maximum ODS temperature of 642°C and a RAFS temperature of 546°C. The new first wall proposed by Siegfried Malang uses W pins embedded in a ODS with a lower structure of RAFS. The goal is to accommodate a heat flux of 1 MW/m2 for steady state conditions and 2 MW/m2 for longer transient events. Xueren showed some component design concepts and representative fabrication approaches. Xueren discussed the calculated temperature distribution and stresses in the elastic region. The stresses in the 2-mm RAFS layer under the W pins was too high and the thickness was reduced to 1 mm, which brought the temperatures and the stresses within the design limits for the 1 MW/m2 case. A higher heat transfer coefficient may be required for the 2 MW/m2 case with higher pumping losses and power required. At present, the RAFS design temperature is slightly exceeded for the 3 Sm stress allowable. More sophisticated thermal and structural analyses, including non-elastic behavior, plastic strain, and creep, are needed to confirm the design approach or a modified design is needed.
Update on the High Performance Divertor Target - Xueren Wang showed the previous helium-cooled divertor with the combination of plate and finger elements to address both nominal and high heat zones. Previous thermal analysis focused on the high temperature components. This analysis concentrated on the body of the fingers and the coolant passages. The analyses confirmed that both finger and the back elements can meet the design requirements for 10 MW/m2 heat loads. The next investigation is the non-linear behaviors of these divertor concepts.
ARIES-DB Design Issues - To highlight the urgency of obtaining the necessary TBR accuracy, Laila El-Guebaly presented the cost to procure additional tritium (T) to supplement on-site processed tritium - the cost exceeds $100,000 per gram of T per day for a 2-GW fusion power plant. Due to recent FNG test data results at ENEA Italy, Laila was able to lower the recommended TBR for all new blanket designs from 1.10 down to 1.07. As data and analyses are improved, this allowance will continue to decrease. Laila determined that the plasma burn up fraction has no major impact on TBR, but a low burn up fraction requires a large tritium inventory. There continues to be a disagreement between the ARIES and the UCLA teams on the methods to estimate the net TBR. There is a question whether the lithium fraction is 17% (past assumption) or 15.7% in LiPb eutectic. It was decided that the correct percentage is 15.7%.
Laila had some ITER data on re-welding 316SS thin plates and tubes with He-concentrations up to ~ 3 appm. She is concerned about our ARIES-AT vacuum vessel design, which uses F82H ferritic steel, both 2-cm thick plates for the center spool and port extensions and 3-cm thick plates for doors and door frames. Laila showed her idea about segmenting the outboard blanket to accommodate the stabilizing shells and alleviate the problem of neutron streaming through assembly gaps. Farrokh questioned the need for inner shielding wedges as the circumferential thermal expansion should close part or all of the gap, thus shielding wedges might not be needed. Laila is concerned about degradation of all physical properties of materials inside the power core due to neutron irradiation.
ARIES Systems Studies: ARIES-I and ARIES-AT Type Operating Points - Chuck Kessel discussed his approach to define detailed operating points with the systems code to represent the combinations of moderate and advanced physics and engineering spaces typical of ARIES-I and ARIES-AT (one case for each of the unique combinations). He then explained that the data and final design parameters from both cases need to be revisited due to more recent findings and analyses. For ARIES-I, this involves the type of superconductor and the field limitations, and updated plasma physics limits, such as (H98, fdiv,rad, qpeak,div, Btcoil, n/nGr, etc). Chuck had run the code to generate many different candidate operating points and showed a table of some of the representative points. He intends to compute the COE for these points in the next months. The COE and other critical parameters will help him select the representative ARIES-I points for the SiC/SiC and DCLL designs.
The parameters for the ARIES-AT revised operating space are similar with higher or different values. He also has generated a set of candidate operating points, from which he will select the representative points for consideration and evaluation.
A key question to be answered involves establishing the limits on technology advancement, such as in the (A) magnet materials and field limits, (B) limits in divertor radiated power and (C) plasma elongation capabilities. In essence, shall we limit the moderate to aggressive technology assessment to just the blanket type or shall all power core technologies have a moderate and aggressive solution?
Update on Systems Code Implementations- Zoran Dragojlovic was unable to attend the meeting and make a presentation.
ARIES Safety-Related Components and Nuclear Grade Requirements Laila has been investigating which power core components are critical to a plant safety function, such as the ability to confine radioactivity and provide adequate exposure limits for the workers and the general public. Presently, there are no rules, codes or regulations or future fusion power plants, although the DOE has guidelines for DOE experimental fusion facilities as does France for the ITER facility. NRC has standards for fission plants that use several ASME codes. Nuclear grade (N-stamped) components have detailed design analysis, high quality assurance, stringent testing requirements, and extensive process control - all those factors lead to much more costly components. Brad Merrill, INL, recommended considering the vacuum vessel, all piping external to the VV, cleanup/isolation/monitoring systems, and the bioshield/confinement building as safety-related structures, systems and components that are considered for greater scrutiny. Note that the components and systems inside the power core are not considered as critical safety items. These categories are quite similar to those of ITER. Fusion safety classification requirements may not be more stringent than those applied to reach required reliability for high availability and/or investment protection. Since unit costs are unknown, ARIES Systems Code should evaluate COE for range of material unit costs (1 - 4 times off-the-shelf values provided by L. Waganer).
Laila said that the US NRC is interested in regulating the design and construction of new fusion facilities. The ASME has initiated an action to develop a code that would apply to fusion power systems, but not to experimental facilities. The US fusion community needs to be involved in the process and monitor its progress.