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ARIES-Pathways Project Meeting Minutes

12-13 December 2007

Gerogia Institute of Technology, Atlanta, GA

Documented by L. Waganer

Organization ARIES Pathways Project
Boeing Waganer, Weaver (Phone)
General Atomics Schultz, Turnbull (phone)
Georgia Tech Abdel-Khalik, Yoda, Zack Fiis
INL Cadwallader
PPPL Meade
RPI Steiner
UCSD Dragojlovic, Malang, Mau, Najmabadi, Raffray, Tillack, Wang
UW-Mad El-Guebaly

Ref: Agenda and Presentation Links: Meeting Agenda


Welcome – Abdel-Khalik and Minami Yoda welcomed the ARIES team to Georgia Tech. They provided snacks and refreshments for the group. Les Waganer reviewed the meeting agenda.

Plans and General Scope (of ARIES Pathways Study)

Farrokh Najmabadi described the Fast Track approach to commercial fusion and the E-Demo that the EU is considering. Farrokh asked if we could divide the demonstration elements into smaller projects that could be matured on smaller facilities that would provide a faster and less expensive pathway to commercial fusion. The risk with this approach is the ability to properly integrate the development elements at a later date. The alternative would be to have a larger and more costly integrated test facility.

Don Steiner noted that the development pathway of fission involved no standardized design, yet we are envisioning a common fusion design be proposed to reduce the cost of the mature plants (several of a kind).

Farrokh would like to concentrate on the key issues that are necessary to convert the scientific R&D into industrial R&D (basic research to applied research). Any technology demonstrator facility must be able to include both scientific and industrial demonstrations to minimize the risk to the investors. The ARIES system code should help quantify the key parameters and evaluate the alternative technologies.

Dale Meade mentioned that often we devise development pathways or plans that are serial, which results in a very long development time and cost. We need to think of ways to do more in parallel.

Someone offered the opinion that we need to assess which fusion devices and components are the best to develop, rather than try to develop all concepts in parallel and then decide which is best. Maybe use smaller facilities for development and demonstration of component and subsystem capabilities. However, this approach increases the investor risk because the prototypes are not the desired size and may not perform as required when integrated. What are the quantifiable metrics to make sure the facility elements are really mature and will perform as promised? Do we need to define the requirements for the developmental steps that are needed to mature a commercial fusion capability?

Mark Tillack said we need to quantify the (technical and programmatic) issues to be resolved before we can devise a development plan or pathway. Said Abdel-Khalik further noted that we need to have some statistical measure of each issue to judge the fidelity of the need and present capability. Dale Meade seconded the need to quantify the needed issues so we can properly address how we plan to mature fusion. (Note, Les Waganer's presentation later on TRLs partially addresses these questions.)

Summary of FESAC Planning Panel Final Report - Dale Meade summarized the Greenwald Panel report of December 2007. The panel was charged by FESAC to identify and prioritize the broad scientific and technical questions to be answered prior to Demo, assess available means to resolve these questions, and identify any research gaps to be addressed. The assessment primarily focused on the tokamak with other magnetic approaches serving as support facilities.

The demo mission is considered to be an electrical producing prototype tokamak fusion plant that demonstrates high availability, reliability, and all relevant and necessary technologies in a representative fusion environment. It is the final facility before a commercial fusion power plant. The panel did not address aggressiveness of the plasma operations, technologies, or materials. Also, potential funding approaches were not addressed.

The panel identified general themes that Demo must have:

  • a predictable, high-performance, steady-state burning plasma,
  • the plasma/material interface must be predictable and robust, and
  • the fusion power handling and tritium fuel systems must be robust, reliable, (and efficient) to deliver useful electrical energy

Dale then further elaborated on each of these theme areas.

The panel outlined the prioritization criteria for the issues: importance, urgency and generality. The panel grouped the issues into three tiers relating to degree of maturity (solution not known, solution foreseen, and solution not yet achieved). (See slide 14 for more details.)

Fifteen specific gaps were assessed by the panel, either understanding the basic issue, development of a knowledge database, or demonstration of a solution. (See slides 15-19 for more details).

The panel made three recommendations that involved developing a long-term strategic (R&D) plan to recognize and address all scientific (and technical) challenges and recommend facilities to resolve all the identified challenges. The initiatives and facilities were elaborated for clarity and were related to the technology gaps.

ARIES Pathways Technical Working Groups

TWG Goals, Approach and Output - Mark Tillack reviewed the flow diagram of the ARIES Pathways tasks, highlighting the role of the Technical Working Groups (TWG). Mark said it was difficult to identify and plan a development program when the exact end configuration or embodiment is not known. The TWGs need to identify their long term objectives, highlight key issues, define the methodology to resolve the issues, and establish priorities on the resolution of the issues. The definition of metrics is the key to being able to evaluate, assess, and develop the R&D plans.

Mark supported the FESAC Panel results and felt the TWG teams needed to make sure they addressed all of the findings, but we do not need to mimic the panel results. We are trying to address issues and establish a methodology to develop a R&D pathway. We need a set of groundrules and metrics to establish our methodology, and we need it now.

What Is A Technical Readiness Level and How Is It Used? - Les Waganer explained the NASA and DOE origin and use of the Technical Readiness Levels (TRL) as an objective measure to convey the maturity of a particular technology. It is widely used to judge if a technology is ready to implement on a new or existing product with acceptable program risk. The GAO saw great benefit with the use of TRLs to make sure new programs had acceptable risk using new technologies. Les then explained and showed examples of the 9 TRL levels. The Air Force Research Laboratory has adopted a TRL calculator to help judge the TRL levels of evolving hardware and software technologies. Les recommended that the ARIES project adopt the use of TRLs to help evaluate the technology readiness of the many fusion technologies. GNEP is currently using the TRL methodology on their technology development plans.

Thermal Power Management TWG Direction and Plans - Mark Tillack mentioned that Siegfried Malang composed a detailed memo on systems integration R&D needs using the dual-cooled lead lithium blanket concept. Tillack and Stromsoe are working on high-temperature compatibilities between various blanket and heat transfer systems. Alan Turnbull is concentrating on the power handling issues. We should concentrate on identifying the issues before we start defining the report outline and writing text.

Report on Tritium Management TWG - No input was supplied to Lee Cadwallader, so this topic was not reported.

Summary of Plant Operations TWG - Les Waganer summarized the Plant Operations TWG purpose, scope, and members. The group needs to develop the operational requirements, devise a developmental plan, and consider the implications of Integrated Health Management Systems on plant operations. Les Waganer and Lee Cadwallader have partially completed the Plant Operations draft report, but this section of the report may have to be revised based on new project guidelines.

ARIES-Pathways Systems Code Development

Status of Systems Code Development - Zoran Dragojlovic reported that he, Rene Raffray, and Leslie Bromberg have been working to provide a better engineering model for the TF coils. They have a new algorithm that yields results that are within a few percent of the coils in ARIES-AT. Initially, very simplified models were used with poor matching of the existing data. The present approach uses more sophisticated finite element modeling and is yielding better results for the coil shape and thicknesses.

Zoran is also defining the central solenoid and the PF coil algorithms for geometry and material volumes for costing. The PF coil configuration is still in preliminary definition, but will be revised with a more refined configuration from Chuck Kessel.

Farrokh Najmabadi recommended that Zoran benchmarks all his TF and PF algorithms and data to the ARIES-AT and ARIES-RS designs to confirm the validity of the analysis and methodology.

Restructuring Systems Cost Accounts and Algorithms - Les Waganer summarized all his previous work on revising and recasting the commercial fusion power plant cost accounts in a more functional format. He previously revised the Land and Land Rights (20), and Structures and Site Facilities (21). In the September 2007 meeting, he presented the detailed breakdown of the remainder of the plant accounts 22-26. But it was recommended that he define a more functional view.

At this meeting, Les illustrated the revised plant cost breakdown in a more functional manner. The Power Core Plant Equipment (22) is broken down into 13 major systems, such as Neutronic Conversion and Capture. It was suggested this item be changed to Fusion Energy Conversion and Capture. Les then examined each subcategory and explained the rationale for the new organization of the cost accounts. This new format was adopted by the ARIES team.

Les then provided more definition of the power core algorithms, such as the materials cost database. Farrokh suggested adding a column for ITER cost data. Additional costing data has been added for the dual cooled blanket and divertor. All costs have been revised to reflect 2007 cost values, per the Gross Domestic Product Price Level Deflator.

Future work will continue to refine the costing algorithms for the remainder of the plant capital cost accounts. Responsible persons will be assigned to each cost account (i.e., Cost Account Manager).

ARIES Pathways Task Results

Determining Heat Loads on Divertors and First Walls - TK Mau reported progress on using the UEDGE code to run representative cases with specific impurity injection values. The model geometry used a single null divertor, such as ITER to solve the equations. The case used an argon impurity level set at 0.05% per ARIES-AT. Orthogonal divertor plate geometries were used. The peak heat flux was estimated to be 17 MW/m2 with 77% of the heat sent to the first wall and 23% to the divertor. Farrokh Najmabadi asked how close is this data to the ARIES-AT reported data. TK did not know. Farrokh recommended that the code be rerun with the ARIES-AT geometry and plasma condition and impurity levels and compare to the ARIES-AT reported data. Then recheck the power distribution between the inner and outer divertor plates.

Taming The Physics For Commercial Fusion Power Plants - In an effort to formulate a comprehensive approach to asking the right questions, Alan Turnbull posed the question, "How are the (plasma) performance and heat loads balanced and controlled (in a commercial tokamak power plant) as the basic engineering control question? This question then was decomposed into a set of more specific engineering questions to be answered which, with selection of a possible solution, could be posed as a set of physics questions. Most of these questions had a common thread of measuring plasma quantities, providing actuators to control these quantities, and formulating an algorithm to determine the actuator levels needed. Alan further elaborated on the metrics, methodologies, and the approaches to all of these issues. In the end, Alan thought there would be many diagnostic and control measurements and real-time data analysis would be needed to control a commercial fusion plant. However, the group agreed that much of this data gathering and analysis would be needed to be done in the developmental machines, but control of a commercial machine has to be much simpler - fewer measurements and minimal real-time analysis. The control algorithms have to be worked on the prior machines; ITER, CTS and to a lesser extent, Demo. Keep it simple for the Demo.

Power Core Engineering: Design Updates and Trade-Off Studies - Rene Raffray provided the status of the engineering and trade-off studies for the Demo Fusion Power Plant. He discussed impact of the SiC vapor pressure and heat of dissociation on the operating temperature of the first wall and blanket. He has evaluated some off-normal thermal loads to assess the impact of disruptions, vertical displacement events (VDEs), and edge-localized modes (ELMs). He showed an example disruption case of a SiC first wall and then illustrated with different disruption scenarios. He also examined the SiC sublimation thickness and the tungsten thickness for different disruption conditions. Several other cases were examined for VDE and ELM events.

Rene summarized that plasma thermal effects on the PFC components are important for all concepts. However, electromagnetic effects inducing stresses in the structure are especially important for concepts with conducting walls (e.g., the DCLL concept with FS structure). For concepts with resistive walls (e.g., with the SiC/SiC structural material), this effect is less severe. Based on the thermal energy deposition and the corresponding loss of armor (due to evaporation and/or melt layer loss), only a few disruptions can be tolerated within the expected lifetime of the first wall. With the increased severity of the VDE, not even one VDE can be accommodated based on the ITER-like parameters of ~ 60 MJ/m2 over 0.2 s. A limited number of ELMs can be tolerated (depending on the energy density), and, overall, a tungsten armor would accommodate the ELMs better than a SiC armor.

DCLL Blanket for ARIES-AT: Major Changes to Radial Build and Design Implications - Laila El-Guebaly noted that the ARIES-AT needs to be redesigned to incorporate the DCLL first wall, blanket, and shielding system. This will entail defining new inboard, outboard and divertor radial builds as well as refining the remainder of the engineering, physics, and economics. Laila then reviewed the baseline ARIES-AT design and illustrated the necessary changes for the DCLL system including the new radial builds. Laila had assessed the inboard breeding and the radiation damage when the IB shield is replaced with the thicker DCLL blanket. She also revised the outboard radial build for the DCLL and calculated the radiation damage and breeding. With these changes, Laila estimated that the TBR should be in excess of 1.1. Likewise the divertor design needs to be revised to be consistent with the DCLL concept. She revised the divertor radial build, assessed the radiation damage, and recommended a revised radial build. The He/LiPb manifolds have not been integrated in the radial build yet. (Action, Raffray, Malang).

With these changes, Laila made some qualitative assessments of the COE impact. The radial builds are increased due to the He coolant, blanket segmentation is not allowed for the DCLL blanket (that increased radwaste and replacement cost), < 90% lithium enrichment is needed, cost of Heat Transfer/Transport account may increase by ~$150M, and overall COE is likely to increase by 15-20 mills/kWh. Other design detail changes are needed to make the system fully compatible and integrated.

There was some discussion about where the conducting shell should be located for the ARIES-AT with DCLL blanket system. Rene Raffray asked if the blanket module ferritic steel structure could be conductively linked around the torus to create a conducting shell. (Action, Kessel, Raffray). If this is not workable, where can the conducting shell be located?

DCLL Heat Capture, Transfer and Transport Options - Siegfried Malang described the characteristics of the strawman commercial power plant concept: DCLL blanket, He-cooled divertor target plates, tritium extraction from lead lithium coolant with a permeator, and closed cycle Brayton thermal conversion system. Siegfried identified several important issues for the DCLL blanket, the helium cooled divertor target plates, and tritium extraction system. Siegfried compared the thermal conversion capabilities possible with the different blanket options and the Rankine and Brayton conversion cycles. The advantage of the DCLL is that it is a technology pathway to the higher temperature self cooled liquid metal blankets that can yield higher thermal efficiencies.

Dual-Cooled Blankets and Helium Cooled Divertor Targets - Siegfried Malang summarized the key issues that enable and determine the power plant performance when using DCLL first walls and blanket system. Several detailed technical issues and design approaches determine the expected lead lithium exit temperature, which in turn, determines the thermal efficiency of the power conversion system. Critical blanket developmental areas are the SiC flow channel inserts, the MHD heat transfer capability, fabrication of the FW/blanket structure, and integration of the blanket modules with the plumbing, structural support, (and maintenance provisions).

The rationale for using helium in place of water or liquid metal was explained. The critical issues for the helium cooled divertor target plates include structural materials with high thermal conductivities and a large working temperature window. Transferring the heat from the structure into the heat transfer media requires a highly effective conductive heat transfer mechanism into the helium coolant. Thermal stresses and deformations in the target plates need to be analyzed and controlled within the allowable ranges. Reliability and maintainability of the divertor plates remain a critical issue. Fortunately, there are several design concepts to be considered.

Neutron Streaming Through Divertor He-Access Pipes: 3-D Assessment And Recommendations - Laila El-Guebaly reviewed the design concerns around divertor radial builds, penetrations, and neutron streaming effects. These are especially difficult with helium-cooled divertors. Many of the solutions examined in the ARIES-CS DCLL design will be applicable to the revised ARIES-AT version. Laila illustrated the ARIES-CS helium-cooled divertor system, pointing out the neutron streaming concerns for the design elements. Several coolant shield plug designs concepts were considered. One concept was analyzed for the ARIES-CS with the 3-D neutronics model. The shielding plug will help protect the bulk shield, however the parts of the manifold and vacuum vessel will not be reweldable after lengthy exposure. Inter-coil structure will adequately protect the winding pack. Additional local shielding will be needed to protect other external components. Future divertor design concepts should address these issues and develop a more effective scheme to attenuate the streaming neutrons. For example, a simple pipe with a diameter smaller than 60 cm and several right-angle bends might be a better approach, eliminating the need for the large WC shielding plug and inserts (~ 170 tons for the 24 pipes in the ARIES-CS design).

Impact of Reliability, Availability, Maintainability and Inspectability (RAMI) - Lee Cadwallader explained that availability is the metric that enters in the COE equation. Availability is composed of three elements: Reliability (probability of a system operating properly for extended time periods), Maintainability (probability of returning a failed or end-of-life system to service in a fixed time interval), and Inspectability (productive time lost or gained due to test and inspection).

Some reliability data for reasonably applicable components and systems can be obtained from other non-fission systems, but these may have to be modified for application in the fusion environment. There is also some reliability data available from existing fusion experiments, but these data also need to be adjusted for longer lived components and more severe fusion environments associated with Demo and commercial applications.

How is the availability for a commercial fusion power plant determined? One approach is to do top down allocations for all the major plant systems that would flow down as availability goals for all systems, subsystems and components as recommended by M. Abdou (UCLA). These allocations could be used in specifications for development and procurements. However these allocations may not reflect the real world capabilities. This approach is probably overly optimistic.

On the other hand, existing databases could be used as starting points to construct a bottoms-up availability estimate. This approach is likely to be pessimistic as the existing data base would be used or extrapolated with minimal incentive to improve. In reality, we must design and develop a commercial fusion plant that will be competitive with the targeted competition. This requires a high plant availability, probably better than 90% (ref, Les Waganer's and Ken Schultz's presentations). Mature Gen III fission plants are anticipating availabilities in excess of 93% and Gen IV in the range of 93-95%. Achieving such goals requires allocation to the various plant elements, with qualified consideration of promised and demonstrated availabilities. This, in turn, establishes respective reliability, maintainability, and inspectability goals. (Les Waganer has been recommending inclusion of a very effective Integrated System Health Management system to enable real-time monitoring of all plant systems for health and lifetime predictions to optimize the plant operations and maintenance.) Lee Cadwallader provided a listing of references for the data shown in his presentation.

CFD and Stress Analysis of He-Cooled Divertor Concepts (Xueren Wang) - There was insufficient time remaining for Xueren to make this presentation, so it will be included in the next project meeting.

Status of the Industrial Advisory Committee Involvement

Ken Schultz summarized the major issues to be resolved for commercial magnetic fusion that might be addressed by the Industrial Advisory Committee (IAC). The major issues were: what R&D database is needed to field a Demo? What is the impact (specific metric) of each R&D item? Where/when can each R&D need be resolved? What major R&D facilities are needed?

The Committee met on June 2007 and provided high level guidance for practical (attractive) fusion power systems: 1) economically competitive COE, 2) excellent safety and environmental characteristics, and 3) reliable, available, and stable power. The Committee commented on the prior EPRI Advisory Committee criteria for practical fusion power (see slide #5 for details). They envisioned the Demo must be very similar in size and function to the commercial fusion power plant, based on the need to demonstrate a low risk solution (performance, schedule and cost). The Demo must demonstrate an integrated, prototypical fusion power plant. The first generation plant must be attractive in terms of economics, safety, regulation, and environmental characteristics. It is imperative for the Demo to also demonstrate that there is an existing stable industrial supply chain to support the new energy source.

To enable these goals in a timely and cost effective manner, additional use of advanced modeling and simulation will supplement the more traditional development and testing in physical facilities. Final validation of the complete plant must be accomplished in an integrated, prototypical environment.

Ken Schultz then highlighted the possible options for engagement and utilization of the IAC. The project team was concerned that we are asking the IAC to provide guidance on areas where they have minimal expertise. Instead, we should be concentrating on having the IAC provide more feedback on fusion plant desirable and necessary attributes that would allow the ARIES team to tailor the design concept and developmental pathway toward the most cost effective approach. A small team of Meade, Abdel-Khalik, Najmabadi, Schultz and Waganer will craft an engagement approach for the IAC to support the ARIES-Pathway project.

Discussion of Action Items and Pending Tasks

Farrokh Najmabadi outlined the immediate project tasks to be accomplished:

  1. Top level requirements for the next step facility (fusion power technology demonstration and certification facility)
  2. the Systems Code to understand technical and programmatic tradeoffs, adapt costing model for next step facility, and operate in an optimizer mode
  3. Prepare the Interim Report to include top-level requirements (for next step and demo?), systems code trade studies of power plant studies, and description of new methodology for development pathway.

Working groups (TWGs) need to identify technical issues and employ TRL methodology to benchmark current technical status and developmental needs.

How do we address the integrated burning plasma issues in our current TWG approach?

How do we visualize our development needs, ala, - EU figure?

How do we consider the "certification" issues (Abdel-Khalik?)

Other Action Items derived from minutes

  • A small team of Meade, Abdel-Khalik, Najmabadi, Schultz and Waganer will craft an engagement approach for the IAC to support the ARIES-Pathway project.
  • Chuck Kessel to provide a more simplified PF coil configuration.
  • Zoran Dragojlovic should benchmark all his algorithms and data to the ARIES-AT and ARIES-RS design to confirm the validity of the TF and PF analysis and methodology.
  • TK Mau should rerun the UEDGE code with the ARIES-AT geometry and plasma condition and impurity levels and compare to the ARIES-AT reported data. Then recheck the power distribution between the inner and outer divertor plates.
  • Chuck Kessel and Rene Raffray should determine if the blanket module ferritic steel structure could be conductively linked around the torus to create a complete conducting shell. If this was not workable, where can the conducting shell be located and what is the material?
  • Rene and Siegfried should determine the size, composition, and location of He/LiPb manifolds for the DCLL blanket/shielding system for ARIES-AT.