ARIES-Pathways Project Meeting Minutes
28-29 May 2008
University of California, San Diego, CA
Documented by L. Waganer
Ref: Agenda and Presentation Links: Meeting Agenda
Welcome - Prof. Jerry Kulcinski welcomed the ARIES team to the University of Wisconsin – Madison. He discussed the evolution of engineering in a changing world and the research areas the University are currently involved in. Laila El-Guebaly covered the logistics of the meeting. The University provided snacks and refreshments for the group. Les Waganer reviewed the meeting agenda.
Prof. Stewart Prager attended our meeting and kindly agreed to summarize the recent and future FESAC activities. He noted the last FESAC report on the "Priorities, Gaps, and Opportunities: Towards a Long-Range Strategic Plan for MFE" was published in October 2007. A new panel has been formed to critically evaluate the major alternate magnetically confined concepts, such as stellarator, spherical torus, RFP, and compact tori (FRC and spheromak). No ranking, just evaluation of the scientific issues and needs for each concept. For the present, FESAC is assessing individual key elements of the fusion program. In the future, they may plan integrated program studies. They will continue to look at scientific issues on the pathway to commercial fusion energy.
ARIES Pathways Technical Working Groups
Summary of TRL Methodology & Interim Report - Mark Tillack reviewed the purpose of the Technical Readiness Level methodology - provide a quantitative set of metrics to determine the maturity of a technology to be applied to a product. The clarity of the levels of maturity will aid in communicating between technologists, developers, and program managers. Metrics are a key element in R&D planning as it allows progress to be planned and measured. TRLs were adopted by ARIES in December 2007 as a helpful tool to assess and plan fusion research and development. TRLs were developed by NASA for this purpose. This useful tool was soon adopted by DoD and recently by parts of DOE. GAO also is a strong advocate of this methodology.
Mark presented three general criteria categories to assess technology readiness for commercial fusion energy production: 1) Power Management, 2) Safety and Environmental Attractiveness, and 3) Reliable and Stable Plant Operations with subcategories under each topic. Definitions for all nine TRL levels have been created for each subcategory. Key to progressing to each level is the level of fidelity of the technology (breadboard, prototype, or demo) and fidelity of the testing environment (laboratory, relevant, or operational). As a framework, two different baseline sets of technologies for the demo fusion power plant have been defined - modest extrapolation and advanced concept. The Working Groups then assessed each technology area (e.g., power conversion) for the two baselines as to the current TRL. This is a measure of how much more development is necessary to achieve a demo power plant for each baseline concept.
This approach is compatible with the FESAC approach of identifying gaps and opportunities. It is hoped that the two approaches can be melded together to help each other achieve the mutual goal of a low risk fusion power system.
Discussion of ARIES-Pathways Plans - - Farrokh Najmabadi noted that the ARIES-Pathways program is nearing the end of the first phase and will soon commence the second phase. We need to identify and quantify (using metrics) the needed R&D for viable fusion energy production. What current facilities can be used for and what new ones are needed? There is a new change in the fusion program. OFES wants to develop a strategic plan for fusion research. Community workshops will be an integral part of this strategic planning. Al Opdenaker would like ARIES to help facilitate this process. Detailed designs are not needed now. Developing the plan is the next necessary step and ARIES should be an integral player. We should adopt the FESAC themes as our primary criteria. During integration, the TRLs should address subsystem/component technologies including hardware and software for major components, e.g., a blanket or a divertor.
We need to complete the interim report very shortly. Everyone should work with Mark to make sure it is finished quickly. We also need to start applying the TRL methodology to subsystems under the FESAC themes. As a start, Farrokh asked Rene and Said to begin putting together a draft of TRL definitions for the subsystems involved under the FESAC Theme C (harnessing fusion power). An example subsystem (e.g. blanket) should be selected to illustrate how to apply the TRL methodology in this case. Next, we have to assist Al Opdenaker working with FESAC to adopt and utilize the TRL methodology to help quantify the current state of fusion R&D, determine the necessary steps to sufficiently mature the needed technologies, and develop a quantitative framework for the strategic plan. We need also to complete the systems code to help quantify the leverage and importance of the key parameters.
The Status and Future of Fusion
Prof. Ray Fonck attended our meeting to provide a status of the US Fusion Program and answer questions about the future of fusion. Ray mentioned that there was a lot of concern about stopping the NCSX experiment. But the more important task is to establish a strategic plan for the US fusion effort to develop fusion. He feels there is no means to assess our current status and guide the US toward the end goal of fusion energy. In the near term, he foresees primarily developing the plasma and engineering science knowledge and in the future, continuing more into the development of a fusion energy program. The alternate concepts are now under review. There is a need for an integrated plasma science. He would like to see a 15-20 year strategic plan and this is where the ARIES group can be helpful. The team would sort out (evaluate) the technology options as an independent broker.
Workshops are being planned to help the community provide inputs into the strategic planning process. Basic Energy Sciences have successfully used this process in their planning. Ray thought there would be four plans: tokamaks, alternate concepts, IFE, and HEPD stewardship programs. He said the planning process would be a roll backward from a "credible fusion power plant".
ARIES-Pathways Systems Code Development
System Code Updates - Zoran Dragojlovic told the group that he had corrected the power flow logic and parameters and corrected the scrape off layer thickness in the ARIES Systems Code. He added the nuclear energy multiplication in the power flow logic and analysis area. He also accounted for the cryogenic power for the magnet cryogenic systems. Zoran found a significant error in Account 26, Special Materials, and determined it was due to the 2.5 factor between total liquid metal coolant and the amount within the immediate power core. For the base case, he changed the coil conducting material from YBCO to Nb3Sn.
Zoran again presented the parametric charts for the COE versus the main influencing parameters. One trend is that the low cost of magnets significantly decreases the COE sensitivity to TF coil magnetic field strength. Zoran continued to discuss data mining or neural networking as a means to uncover and identify key plant parameters and operational regions of interest.
Discussion on Systems Code - Farrokh Najmabadi emphasized that the new systems code will be used to establish a new direction, one that is more productive with insight for R&D priorities. Currently we are taking the code results too literally - need to see the big picture parameters, such as Bn magnitude. Do not try to extrapolate the current status and content, but try to explore new limits. We may need to write both a physics code and an optimizer code.
Preliminary ARIES-RS-DCLL Systems - Laila El-Guebaly has developed a preliminary ARIES-RS radial build for the special case of DCLL with LiPb/He manifolds and stabilizing shells. It is especially critical to locate the shells so they are effective in stabilizing the plasma while not degrading the breeding to a significant extent. Any impact to the design by incorporating these features will be noted. Laila reviewed the prior baseline ARIES-RS design highlights along with the underlying design requirements, such as 1.1 overall TBR and 200 dpa damage limit to ferritic steel. She then compared the prior design with the new DCLL design parameters, with the significant changes noted, such as LiPb with 90% Li enrichment, location of W shells, toroidally continuous LiPb and He manifolds. The new IB radial build is 12-cm thicker than the prior baseline and the OB radial build is 5-cm thicker. By optimizing the vacuum vessel water- and filler-content, the design point moves to more water in the OB. The divertor now has a slightly thinner radial build.
Laila suggested the locations for the vertical stabilizing shells and the outboard kink shells and recommended Chuck Kessel review these locations. The discrete kink shell might be behind the OB first wall. The vertical stabilizing shell is toroidally continuous and can be separated into upper and lower segments.
Laila then reviewed the impact of implementing the DCLL in ARIES-RS. Some dimensions were modified; allowable wall load went down, the pumping power increased greater than 10 fold and the energy multiplication went down. Based on these factors, the COE will have to be larger for the DCLL version without compensating changes.
Laila outlined future work to improve and document the DCLL version. She will send the radial build to Chuck to generate the new physics parameters for ARIES-RS-DCLL, and then Zoran can evaluate the economics of this system.
Stabilizing Shells for ARIES-RS-DCLL System - Chuck Kessel discussed the purpose of the vertical stabilizing shell and the kink stability shell. Elongated plasmas are naturally unstable to vertical motions, but a conducting shell can slow the instability and active feed back coils can stabilize the vertical plasma motions. To achieve high beta plasmas, a conducting shell is needed to stabilize the plasma to kink modes. Again conducting shells slow the kink motion and active feedback coils can control the kink instability. This is an evolving technology and defining parameters are difficult to estimate.
Chuck referenced a generic vertical stability study and scaling laws from ARIES-AT and -RS. Feedback control was invoked in these cases. Chuck also discussed the difficulty of designing a workable kink stability shell and feedback control coils for power plant-sized plasma.
Lifecycle Waste Disposal and Decommissioning Costs for ARIES Systems Code - Laila El-Guebaly noted that all ARIES power plant studies have stressed use of low-activation materials to minimize long-lived radioactive products. Still, there are design-to-design changes in these radioactive materials and their quantities. The use of LSA cost factors helped to quantify the perceived cost of these waste materials. Laila then reviewed the factors and the cost of waste disposal, primarily in the US. The NRC categorizes the waste as Class A (~$20/ft3), Class C (~$2,000/ft3), and High Level Waste (>$20,000/ft3). Laila also reviewed the worldwide radioactive repositories status (no HLW facilities other than in the US). There are several US LLW repositories, but they are getting full and have lots of restrictions. Fusion has the advantage of only generating LLW. Laila explained the breakdown of the fusion LLW sources and classes (A or C).
Decommissioning of the plant will start at the end of operational life and may take 6-10 years to complete. Funds for decommissioning will be assessed as an annual charge that goes into a fund. It is estimated that fusion studies should set aside 1.0 mill/kWh for the SiC system and 1.5 mill/kWh for the FS system to fund the decommissioning process.
Advanced Magnet Technology for Future Fusion Machines - Leslie Bromberg prefers HT Superconductors because they have higher critical current, Jc, up to 30 Tesla than LT SC. He also thinks Hastelloy is the preferred coil structural material. He believes that a large user base will develop using HT SC, probably YBCO that will mature the processing and fabrication of the conductor material and coil fabrication. An advanced production process using Ion Beam assisted Deposition can quickly produce single crystal films. Large scale production will drive the cost of the material down to or below the cost of copper. Farrokh Najmabadi suggested that Leslie develop costing algorithm for all the coil components with all considered options and materials. Also, develop cost algorithms for the coil subsystems including the cryostat, refrigeration subsystem, anti-torque structure, thermal supports, and power supplies. Leslie cautioned that the US magnet base program is withering away.
ARIES-Pathways Task Results
Thermal Effects of Disruptions on a Bare FS Wall - Rene Raffray explained how he analyzed the off-normal thermal loads with the RACLETTE code. The disruption energy density is 28-45 MJ/m2 over 1-3 ms, which will be at least four times as high as ITER's. VDE's deposit up to 60 MJ/m2 in 0.2 sec. ELMS, in a thermal quench mode, deposit ion controlled or uncontrolled modes, energies of 0.77 or 3.8 MJ/m2, respectively. Rene showed the vapor pressure and thermal properties of FS first wall material. Rene then presented example disruption case for bare FS without W coating. He also conducted a parametric study of the maximum phase change thickness of FS first wall and concluded that only a few events per first wall lifetime can be tolerated. He also did a case for VDE thermal loads - not even one event is acceptable. ELMs may occur more frequently and with 10-100 events will result in a not-acceptable evaporation loss of first wall material. There is a definite need to actively control disruptions, VDEs, and ELMs for the case of bare FW.
Documentation and Recommendations on Costing Algorithms (Waganer) - Time was running short and this presentation would require a lot of time and discussion. It was recommended to postpone this presentation until a dedicated conference call can be held.
Updates on Helium-Cooled Flat Plate Divertor Design and Analysis - Xueren Wang reviewed his prior presentation of a divertor plate concept that would accommodate 10 MW/m2 heat flux. but it had high thermal stresses. He raised the side wall temperature and decreased the thermal stresses. The plate design is good because it reduces the number of assembly pieces. He considered uniform nuclear heating across the 5 cm thick plate, which is not correct. Laila will provide the radial distribution of the heating.
Two Heat Flux Zone Divertor Design - Xueren Wang summarized the helium cooled divertor design concepts which have been postulated. These concepts were the helium, jet cooled modular divertor, the helium cooled T-tube divertor shown in ARIES-CS design, and helium cooled flat divertor concept for ARIES-TNS. Each of these design concepts were explained and compared. Xueren thought that it would be best to use two designs to cover a two-heat flux zone divertor. The flat plate design was used in the lower heat flux zone and small modules in the high heat flux areas. Designs and fabrication processes of the two zone divertor were shown.
An Analytic Scheme for CD Power Estimate - T.K. Mau outlined his scheme for the current drive power system. . He noted that ARIES-AT used fast wave (FW) for current drive on axis and lower hybrid on the plasma edges. He fixed the reference equilibrium conditions with fixed pressure and current. He used ray tracing methods to analyze the current drive effectiveness. The FW on axis is around 10 % effective.
A Study of the Effects of Source Sampling Methods on ARIES-RS NWL Profiles - Paul Wilson first reviewed Laila's past 3-D NWL results with an approximate neutron source distribution. Prior methods used three nested source sampling regions to improved analysis accuracy. The present 3-D work compares three source distributions: uniform, three uniform sampled zones (prior approach), and sampling of actual source distribution on R, Z grid (from Kessel). Using the latter actual source distribution, a source density distribution and a probability density function were derived. The source mesh cells are sampled uniformly in volume space. The results of all three approaches were compared over the vertical distance. The three region approximate approach had a similar appearance to the actual distribution; however, the uniform approach distribution was not similar. The outboard and the divertor results were very similar and the inboard were somewhat similar. The actual source distribution compared nearly identically (<1% error) to the DAGMCNPX code developed by UW-Madison. His recommendation is to use the actual source data as inboard the errors can be as much as 10%.
Technology Readiness Levels for Plasma Control - Alan Turnbull emphasized that the essential control of the plasma demands measuring plasma conditions and then making changes to properly correct it. Alan then provided a set of definitions for all TRL levels of plasma control, specifically noting the maturity of the plasma control subsystems and the environments they where they will be tested and verified. Some TRL levels can be accomplished in either a dedicated laboratory plasma physics experiment, in one of the current national facilities, or in some new experimental fusion facilities.
Plasma parameters can be broken down into global, shape, kinetic profiles, current density profile, rotational profile, composition profiles, and power handling profiles. Control linkages of these parameters are reasonably well understood to be control functions of other parameters for the Modest Extrapolation scenario. Each of these plasma parameters were discussed as to depth of knowledge, control functions, and maturity (TRL) of closed loop control. Key issues for the Advanced Scenario (from Mark Tillack's interim report) can be achieved by scaling up (improving) rotation and impurity control technologies.
Advisory Committee and Action Items
Advisory Committee Planning - Ken Schultz told the group that we, ARIES, have not effectively used our Industrial Advisory Committee (IAC). The first IAC meeting was held in June 2007, with no meetings or actions since that time. The meeting scheduled for December 2007 was cancelled for lack of a mission for the Committee and the meeting. A small ARIES group met in March 2008 to discuss options to better utilize the committee. The emphasis was to inquire what needs to be demonstrated before the investors would consider fusion had acceptable risk. What development program is necessary? Ken suggested the question, "What will the ARIES Pathways development program have to do to justify the credibility of fusion and prove the readiness to proceed with a Demo with major utility/industry involvement?" Ken proposed a two day meeting in September 2008 to better inform the IAC and then ask them the posed question.
Farrokh acknowledged the changing mission of the ARIES Pathways program. Originally, it was to identify the issues to plant a new fusion power source. But now it seems ARIES-Pathways has evolved to be an advisory team to help develop the US fusion development strategic plan. Maybe our advisory committee needs to have more members with strong fusion and scientific backgrounds, meshed with the utility and power provider expertise. This will take time to solidify our Pathways project goals, select the right members, and to plan a strategy for the committee involvement along with expected results. As a result, the IAC meeting may be held in December 2008.