ARIES Project Meeting Minutes
4-5 April 2011
Documented by L. Waganer
Ref: Agenda and Presentation Links: Meeting Agenda
Welcome/Agenda - - Les Waganer welcomed the ARIES team to the Bethesda Doubletree hotel. Les reviewed the day and half agenda that was quite full of useful information.
Next meeting and call - Tentatively, the next meeting could be on a June or July date. Les Waganer will poll the team for the best dates. The next conference call will occur in the next 3-4 weeks.
Plans and General Scope
Status and Update of the ARIES Project - Farrokh Najmabadi mentioned the need to prepare two technical papers for the upcoming IAEA Technical Meeting on Power Plant Designs, June 8-10 in Vienna. The June or July ARIES project meeting will be critical to make sure the analysis of the new parameter space is complete and correct. It appears the choice between the conservative technology and advanced technology has more influence on economics than the conservative physics and advanced physics cases. Therefore those two technology choices will be the most important to complete.
Updates of the Fusion Budget - Al Opdenaker noted some reorganization is occurring in OFES, but Al will remain as our Program Manager. He remarked that he enjoyed participating in our meetings. Al mentioned the FY11 budget is nearly the same as the prior year and the FY12 is out and will probably be the same or less.
ARIES Task Results
Update on Self-Consistent Plasma Modeling of ARIES Baseline Design Points - Alan Turnbull reviewed a proposal to perform a self-consistent analysis of the ARIES proposed design points. This type of analysis has been performed in the past, but this new effort will use improved tools and contain the current physics understanding from DIII-D and other relevant experiments. He noted the core transport is relatively stiff. Alan outlined his optimization procedure using IMFIT starting with the previous ARIES design point leading to a more self-consistent optimal operating point. He followed with several examples of possible conditions. He hopes to achieve a consistent pedestal and steady-state heating and current drive scenario with data on beta, q-profile and cross-section.
Disruption Heat Loading and Progress on Time-Dependent Modeling - Chuck Kessel described the nominal, nominal-transient and off-normal transient types of heat load events. He then described each of these events in more detail with some indication of the level of severity. He anticipates time-dependent modeling of the ARIES plasmas with the use the Tokamak Simulation Code (TSC).
Future work would produce results that could be used for heat loading analyses of the first wall and divertor. Chuck expects to obtain time-dependent simulations from TSC runs that yield disruption and mechanical data for analysis. Discharge simulations might show plasma evolution and flat-top configurations. He believes the aggressive and conservative plasma strawmen are available for analysis.
Edge Plasma and Divertor Modeling for ARIES - Marv Rensink explained his goals for edge/divertor modeling of the ARIES design points. His presentation focused on the role of impurity radiation to disperse plasma power by spreading the heat flux over flat divertor plates and side walls. His assumption is that the edge plasma model is a 2-D fluid with classical parallel transport and anomalous radial transport. Two impurity models of fixed concentration and individual charge states were used. He believes there is a substantial operating window for highly-radiating SOL plasmas. He showed examples of heat flux on divertor plates including both particles and radiation. He thought the ARIES-AT geometry with fixed-concentrations of impurities would detach the plasma from the divertor plates. He also showed how the divertor radiation varies with impurity species. Laila noted that the divertor geometry does not resemble the latest ARIES divertor design with tilted plates.
Marv summarized how the simulations could demonstrate a highly radiative fraction in the SOL-divertor. The spatial distribution of radiation could be a problem; however the detached plasma operating regime might work.
ELM Loading Conditions and Component Responses - Mark Tillack and Chuck Kessel collaborated on this presentation, but Mark presented it by explained the basics of the ELM processes as applied to the ARIES plasmas. Ninety percent of the ELM energy goes to the divertor with the remainder to the FW. The ELM energy to the divertor is toroidally symmetrical in the high heat flux region of the divertor with the power scaling up in 0.5 ms and down in 1.5 ms time intervals. Mark provided two ELM heat flux specifications for the divertor (no radiation and a steady-state power distribution), but we do not know which specification might be correct. Mark provided some graphical illustrations of the ELM heat flux limits for tungsten and CFC armors from ITER.
Mark showed equations for the peak divertor and wall temperatures with differing assumptions. He mentioned that high-cycle fatigue is another concern.
Mark summarized that unmitigated ELMs, without radiation, would vaporize the divertor unless a factor of 30-60 reduction in ELM power is realized. Even with radiation, a factor of 3-6 reductions is needed to keep the divertor from melting. He hoped the LLNL edge simulation analyses would help characterize the effect. He noted that R&D is underway in the materials program on crack growth in the materials of interest. The new ARIES first wall concept is more ELM-tolerant and a pure steel wall may be acceptable if the frequencies of ELMs could be increased.
Addressing Lingering Cost Questions - Les Waganer addressed some topics that have been of recent concern. Les believes the previous ARIES enriched lithium cost estimates that were generally based on the 1982 UWTOR-M enriched lithium cost estimates and are no longer valid. There is no current large-scale production cost basis for enriched lithium. He had proposed a cost of $1000/kg for 90% enriched lithium as a placeholder plus a graph of an ever increasingly more difficult (and costly) enrichment process. References from prior mixing experiments indicated no difficulty in obtaining and sustaining a mixture of Li and Pb, although Lee Cadwallader mentioned that Li and Pb might separate if allowed to stagnate. Les provided reference costs for commercial natural lithium and lead.
Les presented some ARIES-AT subsystem costs to illustrate the Main Heat Transfer and Transport (MHTT) is thought to be too high. He showed his new proposed algorithms compared to the prior costing algorithms for single and multiple fluid MHTT systems. He also emphasized that the current MHTT is inadequately defined and a more thorough documentation is needed to correctly portray the system definition. For instance, the current pumping power is only defined for portions of the loop within the power core and nothing is defined for the BOP portion of the MHTT loop.
Les noted that Laila El-Guebaly has been encouraging the ARIES project to implement additional cost factors for nuclear-grade or safety-related systems. Les cautioned about which categories of costs would be related to the 10th of a kind plant.
Les said the Turbine-Generator Plant Equipment costs previously were incorrectly related to the primary fluid rather than the turbine fluid or type and the efficiency of the thermal conversion. He recommended a new set of algorithms that accounted for cycle type and efficiency and were scaled from the nominal thermal power of the ARIES plants. Ken Schultz and Puja Gupta provided gas turbine-generator plant cost algorithms for a nominal 48% efficient system with a 95% learning factor. Les scaled these data to ARIES-AT parameters with an 88% learning curve suggested by Energy Technology Systems Analysis. The resultant estimated cost was consistent with Les' new algorithms, which should be used.
Finalized Systems Code Modifications & New Aggressive Strawmen Suggestions - Lane Carlson presented an overview of recent improvements to the ARIES Systems Code (ASC). New (April 2011) strawmen were issued after the meeting for the aggressive technology/aggressive physics and the aggressive technology/conservative physics. Lane has just added multi-parameter filtering capability to the VASST GUI to enable easier analysis of data sets. He is also improving the DCLL blanket definition module. He then enumerated his completed action items since the January 2011 meeting. He still needs input from Tom Rognlien on edge power flows and he needs consensus on the new April 2011 strawmen. He noted the generic radial build format that would easily be adapted for new configurations. Lane also addressed Laila's, Les' and Mark's suggestions on code improvements. He then discussed new topics to be addressed in the near future.
Lane showed the Strawman ACT-I parameters for the aggressive physics case as compared to the Kessel Jan 2011 presentation with a series of charts and graphs. He concluded that the aspect ratio (A) is reduced, the major radius drops, the TF at the plasma drops, the plasma current increases and the max field at the TF coil increases. Lane then presented a chart of the averages of the main parameters, but it was concluded this data was not meaningful as the data was not coupled. Lane presented the ACT-I best data sets. The ACT-II data for the conservative physics case was also presented which had much higher COE values and Lane was asked to investigate the reason for the higher COE values. Lane also had geometric images for the two strawmen cases. Lane discussed a chart that limited the heat loads on the divertor, but it was a moderately weak effect on COE.
Lane showed the live-action link VASST multi-filtering functionality that would allow visualization of various parameter filters being imposed. Les and Lane previewed the ability to exercise VASST via Skype the previous week.
In summary, Lane will continue to make corrections and improvements in ASC, the strawmen will be issued to the team, scans will continue to be used and the DCLL blanket module will be completed.
Comments on ARIES-ACT 3/2011 Strawmen - Laila El-Guebaly commented that the DOE Annual Energy Outlook for 2011 significantly modified the overnight costs of many of the electrical energy sources, with nuclear and coal both rising 37%. If the ARIES estimates were reasonably accurate, tokamak fusion plants are now lower than coal and nuclear, (but in reality, we are probably underestimating the fusion costs). For the same fixed charge rate (FCR), the COE from the ACT strawmen results in early 2011 are slightly below the previous ARIES-AT value with LSA of 4. Note that the FCR has been reduced recently to be consistent with GEN IV.
The designs of the four ACT strawmen are still evolving and Laila recommended a list of placeholder parameters and guidelines to be used. She asked if there were any updates to the SiC/LiPb first wall and blanket design. She outlined the design suggestions and groundrules for the He-cooled thermal shield between the VV and the superconducting TF coils (much like the ITER thermal shield). Laila reviewed the continuing project debate over the cost of enriched lithium as a component in the LiPb coolant. The market value for natural LiPb is higher than predicted by L. Waganer. The Li and Pb mixing process and cost of liquid metal purification is also an ongoing open question. Boron data from Ceradyne, Inc. shows a large cost for any enrichment with concave curve for the enrichment cost, neither straight (as in UWTOR-M) nor convex (as L. Waganer proposed). This suggests more costly LiPb (relative to Waganer's prediction) by a factor of 2 or more, depending on the enrichment.
Laila continues to advocate including cost adders of 1.5 for nuclear-grade materials and 2 for safety-related systems. The project team agrees, but obtaining a reasonable cost estimate for a new fusion nuclear system is proving to be very difficult. Lee Cadwallader volunteered to check with INL if he could recommend other values.
Defining an ARIES RAMI Process - Tom Weaver stressed that Reliability, Availability, Maintainability and Inspectability (RAMI) have become a part of the ARIES culture, yet we lack formal procedures and processes to implement RAMI in a significant manner. The aerospace community has embraced this discipline and has an outstanding set of tools and processes available for implementation with minimal modifications.
Neutron Wall Loading Update - Laila El-Guebaly showed the new ARIES-ACT FW and divertor configuration with detailed specifications. She also illustrated the difference between the old and the new wall and divertor positions relative to the plasma (new surfaces are more conformal). This very fine segmentation of the 3-D NWL model with millions of particle histories enabled smaller statistical errors. Additionally, there are three neutron source sampling options (uniform, nested and exact). Laila illustrated inboard and outboard NWL results for the first wall and the divertor regions using the 3-nested source distribution. The current NWL peaks are 3.3 MW/m2 at the IB midplane, 4.7 MW/m2 at the OB midplane and 2 MW/m2 at the divertor dome. For input to the ASC, the peak to average NLW is 1.68.
Fracture of Divertor Structures - Jake Blanchard reminded the team that the WWII Liberty ships were plagued with fracture problems. These fracture failures were related to low temperatures that enabled crack growth. Flaws in the elastic materials are manifested as small sharp cracks where fracture can occur when the stresses exceed the material allowables. Fracture occurs when the stress intensity factor, K, exceeds the critical value, (KIC - fracture toughness). Jake showed microstructures of ductile and brittle materials after shearing. Jake noted there is a strong temperature dependence in the toughness of tungsten. He also noted cracks in ductile materials will deform at the crack tip and lessen crack growth. Irradiated materials tend to become more brittle with increased exposure. Fatigue also contributes to crack growth and failure rates. Detection is related to crack sizes and detection methods.
Jake presented some initial analysis work on the ARIES divertor modules. He concluded we must include fracture in our design analysis, particularly for materials with limited ductility (e.g., tungsten). Presently, he is analyzing the pressure loads on the divertor tubes, but in the future, thermal stresses will be added. His initial studies computed the stress intensities for pressurized cylinder axial cracks, which are a function of the crack depth.
Elasto-Plastic Creep Modeling for the First Wall with Tungsten Armor - Xueren Wang explained he is creating a simple thermal creep model for the FW of the DCLL blanket to compare ANSYS results to experimental creep data (EROFER 97 steel). With the temperature of the tungsten pins around 680°C, thermal creep is not significant until the temperatures exceed 1500°C. The model assumes F82H structural material, which is analyzed by using EUROFER 97 data (that should be similar). Irradiation-induced creep is not presently evaluated due to lack of credible data (Arnie Lumsdaine is seeking applicable data). Xueren mentioned the structural criteria for time-dependent elasto-plastic creep analysis including creep rupture curves for EUROFER 97 steel. Xueren noted the allowable creep rate per hour corresponds to the 1% creep limit (structural criteria #1). With his ANSYS code, he modeled the thermal loads during fabrication and operation. The maximum local creep strain of the F82H at 1000 hours is ~ 0.17% at the upper sharp corner of the I-section. This local strain could be reduced with the addition of a small fillet. Plastic strains are also maximized at this same location.
Xueren summarized that a fully time-dependent elasto-plastic creep analysis has been done on the first wall for 1000 hours and a longer time period is recommended for future analysis. There was also some discussion about the frequency power core shutdowns/startups and the allowable rate of temperature change, which resulted in a related action item.
Design Improvements of the Tungsten-based Divertor Concepts - Xueren Wang summarized the design and analysis status of the three types of divertor concepts being evaluated for the FS-based DCLL system. Due to the fracture toughness of the tungsten alloy being used, the lower temperature limit was raised from 700°C to 800°C to avoid embitterment (this modifies the divertor coolant temperature range). Xueren is considering the use of an advanced ODS ferritic steel, such as 13CrYWTi. This material has been tested in similar conditions by experimentalists. Increasing the coolant temperature has reduced the allowable maximum heat flux to keep within the maximum tungsten temperature below 1300°C.
Xueren showed his results of reevaluating the HCPF concept with the 800°C operating temperature. The allowable heat flux has been reduced from 15 to 14 MW/m2. Similar analysis for the HCFP divertor showed the allowable heat flux has been reduced from 11 to 9 MW/m2.
Xueren also adjusted the cooling using a tapered baffle inside the supply and exhaust side of the T-tube. He analyzed the design methods to determine the flow rates and cooling capabilities. His CFD results showed that the plate can handle the ARIES-AT power profile with 10% pumping power. Xueren then showed the HCTT design approaches, but no analysis has been done on this configuration and power profile. Xueren presented designs combining finger and slot jets (fingers can handle higher localized heat fluxes). Laila asked if similar analysis is underway for the He-cooled divertor of the SiC design. Also, what W alloy would A. Rowcliffe recommend for the divertor design?
Tritium and Safety Issues for (Fusion) Power Plants - Lee Cadwallader outlined the issues with routine tritium releases. ITER is a great benchmark for tritium handling and storage as it has to address many of the same issues at the same scale as a power plant. Lee also used fission regulations to scope the fusion plant releases. HTO is the more important parameter as it is more easily ingested. Lee also discussed the allowable tritium inventories within the plant and mitigation approaches including multiple confinement zones. He concluded ARIES would meet the current regulations. Tritium boundaries need to be clearly defined and designed to meet the regulations (example ITER). Lee also noted the VV safety provisions may increase the cost of the N-Stamp vessel by 10 or 20%.
During this presentation, there was some discussion of a new ASME code development for fusion; however OFES is not engaged in this effort.
Adding Impurities to the Core Plasma to Alleviate Plasma Material Interaction Problems - John Sheffield had to leave early, but he orally summarized his presentation. He mentioned several studies that added impurities to increase radiation losses and alleviate plasma material interaction (PMI) problems, see references and prior ARIES studies. As the tokamak experimental facilities increase in power level, the PMI issues become more serious and solutions need to be implemented. John then had some slides that scoped the confinement and power problems that may be reduced by increasing the radiation fraction using injected impurities.
Update on National Academy of Science Review of IFE - Dale Meade had prepared a talk on the on the IFE reviews but due to lack of time, it was not presented. A short summary is presented here. There are currently three ongoing reviews on IFE: National Academy of Science (NAS) Review of IFE, Review of ICF Target Physics for #1, and Review of National Ignition Campaign. EPRI also is reviewing all fusion concepts (MFE and IFE) in a new study. The NAS review is to assess prospects of generating power using ICF, identifying scientific and engineering challenges, cost targets and R&D objectives. The intent is to advise DOE on preparing a R&D roadmap for IFE (primarily for FY2013 planning). An advisory committee has been formed by LLNL to help guide the LIFE project. The LIFE project has three evolutionary design configurations reflecting increasing levels of capability. These three configurations could be separate fusion cores with the first wall changed out. The LIFE laser is expected to achieve 18% efficiency. Liquid lithium is the primary coolant. The LIFE project is embracing RAMI processes. The tritium inventory goal is < 600 gm. The target chamber structural material is HT-9 and is designed with the ASME piping code factors. The LIFE project feels HT-9 achieves adequate economics for the first phase without invoking the use of ODS or SiC materials. Reducing technical and financial risk is crucial to deliver a viable IFE power plant and they feel they have no high risk items. They are using TRL measures to manage risk. Their schedule is to design in 6 yrs, 7 yrs to build, and 7 yrs to qualify and then produce electricity. The question raised by Secretary Chu about the viability of magnetic fusion given the projected ITER cost is being posed to IFE relative to NIF costs.
Action Items - Les Waganer reviewed his list of action items from the January 2011 meeting with verbal feedback provided by the responsible persons. After the meeting, Les transcribed the responses into the January 2011 Action Item List.
During the April meeting, Mark took notes of new action items and compiled these items into a new April 2011 action item list. At the meeting, Mark refined the new action item list with the help of the project team.
After the meeting, Mark and Les combined the January and Action Item List into a single April 2011 Action Item List, which is shown as a link in the meeting agenda list (see April agenda link at the beginning of this set of minutes).