ARIES Documents -- Meetings ArchiveARIES Project Meeting, March 20-21, 2001
Documented by L. Waganer
University of Califonia, San Diego
Attendees: C. Baker, E. Cheng, S. Dean, B. Dove, L. El-Guebaly, L. Lao (GA), S. Malang, T.K. Mau, R. Miller, E. Mogahed, F. Najmabadi, R. Raffray, D. Steiner, D-K. Sze, M. Tillack, L. Waganer, X. Wang
Guests: K. Kleefeldt (FZK), S. Malang (FZK), G. Marback, (CEA-Cadarache), S. Nishio (JAERI), A. Sagara (NIFS)
Encl: ARIES Action Item List
Administrative and General Topics
Bill Dove informed the team that he would like to see significant system design effort directed to the IFE work this year, hopefully with positive reportable results to help justify and support the budget. He attended the Heavy Ion Symposia that just preceded this meeting. Good work was reported, but more needs to be done through our team. Bill noted that next year, three-fourths of the Design Studies budget would be devoted to IFE work. On the other hand, our team is to be commended on the quality of the work and results to date on the ARIES-RS and AT designs. Our results are being widely used by the community to plan future experiments and assess the feasibility of future energy options. We must quickly complete and document ARIES-AT so we can move on to the IFE work.
Farrokh Najmabadi summarized the status of the ARIES-AT project. The definition of the ARIES-AT plasma physics has progressed to allow the systems analyses and engineering groups to finalize on the recommended design point. Three consistent plasma equilibrium cases have been developed, analyzed, and provided for systems code and heating and current drive analyses. Three full strawmen code results have been developed that represent the optimal plasma design space. One of these baseline cases will likely be selected as the representative design point for development of the engineering design and economic assessment. The final design will be completed this fall and might be documented in an IAEA document, as well as individual papers for the October 2000 14th ANS Topical on Fusion Energy.
Farrokh noted the Neutron Source study interim results are largely in hand with a few items being finalized. Don Steiner is gathering and editing the interim report of this activity. Farrokh reported positive feedback on Don's presentation of the findings at a recent FESAC meeting.
Farrokh explained that the team's involvement in IFE work has been moved forward so that the kickoff of the team IFE activity will begin at the ARIES meeting at Madison in June with the existing ARIES team members meeting with the new IFE members at that time. The new IFE team members will involve people from LLNL, GA, and Univ. of Wisconsin (UW) who have been working on IFE related designs and systems. NRL will also be helping with the design and performance of IFE targets. The specific areas being investigated are assessment of candidate chamber designs and driver interfaces, with specific emphasis on integrated, self-consistent assessments. The candidate chamber concepts will likely be dry walls, film-protected walls, and liquid walls.
Next year, the MFE work will be scaled down considerably. Some systems assessment work will continue, collaboration with EU is possible, and a proof-of-principle experimental design might be initiated.
The date for the June meeting at the UW was adjusted to accommodate a VLT meeting in Washington. It was decided to hold the meeting starting at 1:00 PM CDT on Monday, 19 June, and continue through mid-afternoon on Wednesday, 21 June (three-day meeting). Monday morning will be devoted to separate ARIES-AT engineering and physics meetings. Monday afternoon and Tuesday morning will be plenary sessions for the final wrap-up of ARIES-AT. Tuesday afternoon and Wednesday will be devoted to the kickoff of IFE work. The meeting will adjourn in mid-afternoon to allow connection with late afternoon flights.
Tentatively, the next meeting will be scheduled for PPPL starting on Monday morning, 25 September, through the end of the day on Wednesday, 27 September (again a three-day meeting.)
It was also mentioned that several people are intending to present ARIES papers at the upcoming SOFT and ANS symposia. All abstracts should be submitted to F. Najmabadi for coordination. The ARIES-ST papers are being reviewed for publication in a FED journal. The IAEA papers are being edited for final publication.
Ron Miller highlighted the cost of electricity (COE) projected for advanced coal and combined cycle natural gas as being in the high 30s to low 40s mill/kWh in the 2005-2020 time frame (referencing the Annual Energy Outlook2000). These represent increases from the AEO99 projections. With a $100/ton carbon tax added, the projections rise into the mid-40s and up to low 60s. In comparison, wind turbine COE is 59 mill/kWh and fission is 70 mills/kWh in 2005 and 48 and 63 respectively in 2020. So these options will represent the competition for fusion for the near future.
Ron informed the team that the ASC systems code is now producing verifiable results, but the graphics are not working properly yet. The modeling of the coils is not quite correct yet, but it is close. The RF current drive modeling has been incorporated. Costing updates for advanced components and systems are not yet complete. Ron posted three cases with normalized betas of 5.59, 6.04 and 6.81. The latest versions were posted on 3/10, with a major plasma radius of 5.2 m and a PFC current density of 45 MA/m2. Conceivably higher field strength toroidal coils could be used with the high temperature superconductor (HTS) that would result in a smaller plasma and power core.
At the major radius of 5.2 m, the projected COE is nearly the same for all three beta normal cases, with the 6.0 case being slightly better; thus the case with a beta normal of 6.0 was chosen as the design baseline case for more detailed assessment.
Power Core Configuration Development and Maintenance Approach - Rene Raffray and Xueren Wang noted that the current configuration used to date has a major radius of 5.04 m. This major radius will be increased to 5.2 m, along with other geometric parameters, to be consistent with the new baseline presented by Ron Miller. The first wall, blanket, divertor, and high temperature shield are using SiC/SiC as the structural material, with LiPb as the coolant and breeding material. The high temperature shield or blanket region II will serve as the structural element that ties all the high temperature components together. The low temperature inboard shield is now integrated with the vacuum vessel as recommended by Les Waganer. Large vacuum vessel doors between TF coils allow modular replacement of the high temperature, life limited power core components. The decision to have the plumbing connections inside or outside the vacuum vessel door has not been made. Coolant routing and plenum designs are proceeding with the criteria of passive drain from all tubes and not exceeding structural temperature limits with a higher bulk exit coolant temperature.
The divertor flow arrangement with large supply and return headers and a restricted flow region near the surface of the divertor has been adopted. Detailed design and analysis of this arrangement is in work. It seems the LiPb can handle the surface heat load, but the SiC wall must be very thin (1 mm or so) to handle the heat flux without exceeding the thermal stresses. Moreover the surface erosion of SiC would be excessive. A suggested solution is to bond a thin layer of tungsten to the surface of the divertor. The divertor would have 3 mm SiC walls except for the plasma-facing surface, which would be 0.5 mm SiC with a W surface protection layer.
The accommodation of two neutral beam ports would be a severe design complication with regard to the outer blanket, shield, vacuum vessel, and maintenance systems. This was brought up later during the heating and current drive system selection.
Vacuum Vessel Design Approach - Les Waganer reviewed the current CAD definition of the power core. In place of the conformal vacuum vessel, he suggested a simplified shape combining the functions of the vacuum vessel and the low temperature shield. The new vacuum vessel is a welded, double walled cylinder with flanges top and bottom to closely house and support the high temperature, replaceable core elements. Outboard are 16 vacuum vessel doors to allow insertion and extraction of the replaceable core elements. Laila raised concerns regarding the ability to reweld the combined components. The vacuum vessel meets a 1 He appm limit for reweldability but the plasma facing surface of the LT shield does not.
Updated Nuclear Parameters, Radial/Vertical Build, and Activation Analysis - Laila El-Guebaly summarized the power core design and nuclear parameters. The design and material choices currently satisfy the desired performance requirements. However, as more details are added, the margins are likely to be reduced. The vacuum vessel materials and composition will be determined in the near future. The final design of the stabilizing shell will be incorporated into the analysis. Laila reviewed the selected inboard and outboard radial builds that were supplied to the systems code. She is in the process of refining the divertor radial build.
Laila reported on the activation analysis being conducted on the ARIES-AT. She noted that SiC activity drops by several orders of magnitude shortly after shutdown. Decay heat drops quickly after one minute following shutdown. Decay heat data is provided for LOFA and LOCA analyses. LOFA is more critical than LOCA. All components are anticipated to meet both Fetter's and NRC Class C waste disposal limits, but none of the ARIES-AT components will meet the IAEA clearance index guidelines.
Blanket Design and Coolant Routing - Rene Raffray presented Igor Sviatoslavsky's material on this subject. The inboard blanket is subdivided into 32 modules, each containing 4 straight, nearly rectangular, coaxial tubes. These 4 tubes are connected to common manifolds at the top and bottom. The coolant first travels down the front channels nearest the plasma, goes back up the rear channels, and then returns slowly back down the central tubes.
The outboard blanket uses 6 tubes per module. The coolant flow is upward through the outer channels and down in the center tubes. The coolant routing is determined to allow passive draining of all tubes and fully utilize the available heat and not overheat the SiC structure. The divertors are the first components to be cooled.
Tritium System and Primary Loop Design - Dai-Kai Sze recommended a liquid-gas contactor system for the tritium recovery process. This approach has acceptable performance and safety risks and minimum material impacts. It should be assumed that the tritium permeation through SiC is virtually zero. However, the tritium bred in the Li has a 2.5 MeV recoil energy that indicates the tritium will penetrate into the SiC, thus the tritium inventory in the SiC might be sizable.
Dai-Kai has not found an acceptable set of materials for the primary heat exchanger. The criteria include high temperature operation (1000-1100°C), compatibility with LiPb and high pressure helium, low tritium permeability, and excellent joining characteristics with SiC.
Material Options for Stabilizing Shells - L. Waganer presented Igor Sviatoslavsky's material on this subject. The resistivity (or conductivity) requirements for the stabilizing shells were specified by C. Kessel to obtain sufficient plasma vertical stability within certain geometry constraints. This would equate to a thickness of approximately 5.5 cm for 400°C tungsten. In addition to tungsten, solid and molten forms of aluminum and copper were evaluated over the range of temperatures being considered. Tungsten cladding was included for both copper and aluminum conductors. The group favored the solid copper conductor shell encased in tungsten and cooled with helium.
High Temperature Superconducting Magnet Design Choices - M. Tillack presented Leslie Bromerg's material. Leslie selected the YBCO HTS material for both the PF and TF coil sets because of low material cost and inexpensive construction technique ($50/kg). It is advantageous to design and construct the TF coils with the local field parallel to the tape structure; namely, the TF coils should use the shell-type structure. The PF coils could use either the pancake or layer wound structure. Both the TF and PF coils would be dominated by structure (85% structural fraction). Leslie recommended that PPPL conduct a stress analysis on the TF and the PF coils.
LOCA and LOFA Analyses - Elsayed Mogahed explained his assumptions and the baseline geometry used in his analyses. He is using the most current ARIES-AT geometry in a 2-D finite element model in r-q midplane for the inboard (IB) and outboard (OB) geometries. The boundary conditions are adiabatic at the inner surface of IB vacuum vessel and radiative at the OB vacuum vessel. Since the analysis is 2-D, no heat is transmitted in the vertical direction. Radiation is the heat transfer mechanism between radial build elements. Decay heat profiles for all core elements are provided as a function of time after shutdown. Elsayed also presented the initial thermal conditions for all core elements. For the LOCA, all coolants in the core were assumed to be absent. This was not the most severe case as there is afterheat in the LiPb, which is removed from the core. Nevertheless, the FS in the IB vacuum vessel exceeds 800°C around 3-8 days. A LOCA of the vacuum vessel water and a LOFA in the LiPb is the most severe accident condition, peaking around 885°C in the IB vacuum vessel. These conditions are predicated upon an initial vacuum vessel operating temperature of 200°C. However, it is likely the vacuum vessel will be operated near room temperature (20-30°C), which would lower the peak temperature of the FS-based components into a safe range for all accident cases. If the vacuum water coolant remains in place; the water would be allowed to boil, the vapors collected and condensed, and returned to the vessel. This would be an efficient heat transfer mechanism to safely remove the afterheat and keep the internal temperatures well within allowables.
Laila thought availability would decrease the decay heat. She will verify that statement and also consider the 20% lower wall loading in the decay heat analysis.
Clearance Issues and Radwaste Volume - Laila El-Guebaly summarized the IAEA Clearance guidelines that defined radiation limits for materials, which would allow removing the materials from the waste stream if they met a clearance index of 1 or less after a permissible storage period of 50-100 years. The EU SEAFP plants typically use blankets and shields with large volumes. The coils for these design approaches usually have clearance indices less than 1, but a large mass of the core has a clearance value greater than one. On the other hand, the ARIES-AT design is compact. Thus, all ARIES-AT components have clearance indices greater than one, but the total mass being disposed is reduced relative to typical EU designs.
The goal of "clearing" the OB vacuum vessel and magnet of ARIES-AT would require additional new shielding component on the OB side. The net effect is a 15% reduction in the total volume of waste generated by ARIES-AT. The U.S. Nuclear Regulatory Commission (NRC) regulation is likely to be more restrictive than the IAEA limits. This means the reduction in waste volume using the NRC limits may not be significant (< 15%). Furthermore, if the market for cleared metals does not exist, the design will end up generating more radioactive materials (waste plus cleared metals). Because of the lack of official US guidelines for Clearance and the uncertainty in the market, we should not adjust our designs to comply. We should only report these data for comparison.
Neutron Source Study
Status of Neutron Source Study - Don Steiner reported that the concept definition phase has been concluded. The intent of this phase was to determine if any fusion neutron source applications offered sufficient promise to warrant detailed design and development path consideration. He has gathered the interim results and is compiling them into a report package. Some additional support information has been requested from several contributors. He anticipated that the interim report would be completed in a month.
Don presented a list of general observations regarding neutron sources and their applications. Evaluation metrics are not universally defined or accepted. The neutronic performance is more dependent on the blanket design and processing than on the neutron source. Blanket criticality is one of the most important distinctions. To the first order, the cost of neutrons is similar for all approaches. The estimated cost of electricity from a transmuter is higher than for a pure electrical power generator, but the COE is not the primary product – electricity should be considered as a supplemental income stream.
Ron Miller noted that LANL is comparing the ATW with other concepts. Ron and Don agreed to contact the ATW project to exchange information and data.
Performance of a Transmutation Blanket for Catalyzed DD Fuel Cycle Reactor - Ed Cheng compared fusion-driven and ATW transmutation systems based on fusion equivalent engineering parameters. The ATW parameters were obtained from the ATW roadmap document. Most of the major parameters were similar for the two systems. The ATW quoted a COE of 4 cents/kWh, but this was the price at which they would sell the electricity and did not represent the cost of electricity. The major product was the processed waste.
Ed presented the results of a comparison of catalyzed DD plasma-based transmutation blanket to a DT transmutation blanket. The catalyzed DD has the advantages of no tritium breeding, higher energy multiplication performance, and lower plutonium and minor actinide inventories. The disadvantage of the catalyzed DD blanket is that Li-6 cannot be used to guarantee sub-criticality.
Current Drive and Plasma Rotation Considerations - Tak Kuen Mau described the seed current drive (CD) requirements for the typical AT equilibrium cases for both on-axis and off-axis conditions. TK summarized that for the on-axis CD, the ICRF/FW is the preferred baseline system. For the off-axis CD, LHW would be the choice if rotation was not needed. But since plasma rotation is required for kink stability, he recommended the use of neutral beam (NB) injection for both CD and plasma rotation. The problem is the severe impact on the other power core components. Injection of two beams tangential to the plasma centerline requires two large openings at midplane cutting through first walls, blankets, shields, and vacuum vessel. The group recommended that TK assess the CD system impact to choose an off-axis solution other than NB.
Beta Optimization and Transport Results - Lang Lao summarized the GA study plan to support the ARIES-AT project. He commented that the equilibrium state appears to be sensitive to the current profile, thus current profile may be crucial to maintain the desired equilibrium state. Plasma stability may be limited near the edge by ballooning modes. It was recommended that he look specifically at the PPPL beta = 6.0 case for further analysis.
ARIES 20-21 March 2000 Meeting Action Items
Configuration and Maintenance Approach
Fuel Cycle System and Main Heat Transfer and Transport System
Vertical Stabilizing Shell
Safety and Waste Management