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ARIES Documents -- Meetings Archive

ARIES Project Meeting, 5-6 December 2000

Documented by L. Waganer

Agenda and Presentations

Attendees:
(ANL)
Billone
(Boeing)
Waganer
(DOE)
Dove
(FPA)
-
(GA)
Goodin, Petzoldt, Schultz
(INEEL)
Petti (by phone)
(LANL)
-
(LBNL)
Lee, Yu
(LLNL)
Meier, Latkowski
(MIT)
-
(NRL)
Sethian
(PPPL)
Jardin
(RPI)
-
(SNL)
Olson
(TSI)
-
(UCSD)
Mau, Miller, Najmabadi, Pulsfier, Raffray, Tillack, Wang, Zaghloul
(UW)
El-Guebaly, Haynes

Action Item List


Administrative

Peer Review -- Farrokh Najmabadi mentioned a draft copy of the recent ARIES Peer Review had high praise for the scope and high quality technical work accomplished by the ARIES team. However, it was recommended the team improve their outreach with release of formal final reports, improved usability of the ARIES web site, more special purpose technical exchange meetings, and formal reviews of completed or nearly completed studies. A limited implementation of these recommendations have already been initiated or accomplished. More detailed plans will be available upon release of the final peer review document.

Documentation -- Partially in response to the recommendation to document the prior final reports, Farrokh Najmabadi is compiling ³final² reports of the prior ARIES studies (-RS and ­ST) and is working on completing formal documentation of the older studies, such as Pulsar and Starlite. The older related papers are more difficult to convert as formats have changed since they were written. Farrokh is preparing to release the ARIES Neutron Study. Final drafts of the ARIES-AT are due to Farrokh by the end of December 2000. He needs formal titles and authors ASAP.

Next Meeting/Conference Call -- The next meeting was selected to be off-site near LLNL. This meeting will be on 5-6 March 2001 (full day meetings) [rescheduled to 8-9 March]. The next meeting will be at or near NRL (or Washington DC) on the first week in June 2001. The next ARIES conference call will be 9 January 2001.

Other Meetings -- An ARIES Tritium Town Meeting may be held in conjunction with the 5-6 March ARIES meeting (probably following the ARIES meeting.) The US/JA Reactor Design Workshop is tentatively planned to be held in Kyoto, JA on 29-31 March 2001. The meeting will concentrate on recent MFE work, but some IFE work may be presented. Therefore the ARIES contributions will likely concentrate on the ARIES-AT results with some early IFE results. Farrokh requested possible contributors send him suggested topics and titles ASAP. A one-day short course on ARIES-AT is to be presented at MIT.

Inputs to APEX -- Rene Raffray reported that he made an invited presentation at the last November APEX meeting summarizing the ARIES-ST and ARIES-AT blanket designs. Subsequently, APEX has selected the ARIES-AT blanket as the focus of their Task IV activities for the next 7 months. APEX considers higher wall loading and heat flux parameters and would like to assess the critical issues and performance limits of the ARIES-AT design.

Budget and Work Scope -- Final budget allocations for Advanced Design activities including the ARIES project are not available. Shifts in monies for several areas are being discussed along with work scope changes. Thus, no firm FY2001 work scope is presently defined for the ARIES group. Until that scope is defined, all task leaders (and contributors) should begin to document the results and findings of drywall chamber and supporting technologies (gain curves, spectra, etc) to be published in an interim progress report. Schedule for completion of that interim IFE progress report is not defined, but progress will be reported in the January 2001 conference call.

New Concepts to be Considered -- Craig Olson suggested the ARIES group consider evaluating the rep-rated Z-Pinch. It was thought the concept would be a viable candidate, but in light of the uncertainty of the project budget, no long-range plans can be formulated at this time.


ARIES-AT

System Code Results

Ron Miller said that he was planning to post a final ARIES-AT strawman data set on the ARIES web site on 7 December 2000. The basic machine geometry and performance parameters are nearly identical to prior results. The plant factor was changed to 85% to agree with the Les Waganerıs result of a plant availability of 87.8%. Costing for the advanced Brayton power conversion system has been determined to be similar to the cost of the advanced Rankine cycle previously used in the ARIES design concepts. The cost of the current drive system has been updated. The implications an LSA rating of 1 was discussed with the rating of 1 being retained. The resultant cost of electricity (COE) for the ARIES-AT is predicted to be 47 mills/kWh in 1992 dollars.


ARIES-IFE Study Presentations

Ssytems Analysis and Integration

System Uncertainties -- Ron Miller gave Don Steinerıs presentation on the impact of off-normal shots on the IFE power plant performance and safety. The initial task was to identify those off normal and initiating events that could contribute to an event of consequence to the plant. The emphasis of the investigation is on off-normal shots that have zero or reduced yield with details for each type of off-normal shot. The next step is to estimate the frequency of occurrence of each type of event. Dave Petti later phoned in a safety presentation (discussed later) that examined examples of events in different frequency ranges. Ken Shultz predicted the need and ability to inspect all targets prior to injection to improve target reliability and performance. Les Waganer noted the laser and HI driver systems could be continuously monitored to anticipate and mitigate or eliminate off-normal events (affirmed by J. Sethian, E. Lee, and S. Yu).

IFE System Analysis -- Ron Miller outlined the high-level cost elements he intends to define and report. It is mandatory the IFE cost basis be comparable to the MFE basis. The IFE chamber is simpler and less expensive than the MFE power core because the confining coils are eliminated. However, there are added costs and complexities attributed to a separate driver facility and target factory. Ron intends to include a more elaborate learning curve methodology similar to that used in the Prometheus study by Les Waganer. Financial assumptions will be updated per Jerry Deleneıs recent work on this subject. Ron said he would assess multiple, identical complete power plants as well as multiple chambers coupled to a single driver and power plant. Ed Lee expressed caution concerning the complexities of a single induction linac coupled to multiple chambers.

Ron is still evaluating several off-the-shelf commercial software packages to evaluate or scope the risk or parameter uncertainties of the IFE power plant systems. He also discussed the desirability of attaining a plant factor in the range of 85-90% to effectively compete with other power producing plants. He noted the most appreciable fission plant factor improvement has been in the area of scheduled planned outages.

Possible Operating Space for Laser IFE -- Wayne Meier showed the wide range of operating space of target gain versus driver energy for both direct and indirect targets for both conventional and fast ignition targets. He is trying to formulate a process to yield a parameter space that would lead to a viable commercial laser IFE power plant. He created a set of equations to the gain curves to be used in his analysis. Then for a constant power system, he examined the major parameter sets while holding several parameters constant. He also illustrated how design constraints (first wall limits might constrain maximum yield or chamber clearing might constrain repetition rate) would limit the design or operating parameter space. Wayne concluded that the operating space depends largely on the target gain versus driver relationship. The chamber is influenced by the target yield and the pulse rate. The results to date only indicate the importance of certain parameters. Final performance optimization will depend on specific design choices.

Drivers

Discussion of Heavy Ion Power Plant Issues and Strategies -- Simon Yu lead a discussion period on the important heavy ion systems issues for a commercial power plant. One important issue is the propagation of the ion beam through the chamber. He examined three methods of beam propagation: preformed channel, self-pinched, and neutralized ballistic focus. Each of these have chamber pressure regimes best suited to their attributes, respectively 1-20 torr, 5-10 mtorr, and less than 5 mtorr. The preformed channel works with large chamber sizes, high chamber pressures, and is expected to have a high probability of accurately hitting the target. The negative features of this approach include the need to have a return current path to the target and the need to have a conducting shell or grid on the target. The higher chamber pressure may be detrimental to the target heating and trajectory accuracy. The self-pinch operates in a lower pressure regime. Accuracy of the beam alignment must be quantified. The ballistic focus needs beam neutralization. The size of the chamber also is limited with this approach. Don Haynes will obtain the HI ID target spectra to quantify the chamber pressure to assure minimal wall erosion and sputtering. This pressure limit will help select a preferred propagation approach. Gas turbulence in the chamber may also influence the proper formation of the beam channels.

Simon noted the final focus and chamber interface issues. The final focus magnets operate a high field and require significant neutron shielding to achieve a life of plant capability. High temperature superconductors would not help in this situation. Vacuum pumping must also be considered in the integrated design to achieve the proper beam conditions and drift compression. Simon also noted the buildup of metals on the wall from the ID hohlraum debris. Laila El- Guebaly and Rene Raffray will examine possible target metals to determine their effect on the chamber wall.

Heavy Ion Driver Model Update -- Wayne Meier summarized the current status of his HI driver model. He is modifying the code to vary previously fixed variables, including ion mass, total beam energy and minimum pulse duration. The code will have the option to cost near-term and long-term (commercial) drivers. The updated code will incorporate improved emittance growth and chromatic aberration models. Revised front ends models are being developed by LBNL. Preliminary results from this code are expected by mid-January.

Target and Chamber Physics

Direct Drive Heavy Ion Fusion Target -- Ken Schultz presented some of the features and predicted performance of the DD HI target Max Tabak, LLNL, originally postulated over 15 years ago. Max Tabak recently reanalyzed his original design because the performance codes and databases have changed in the interim. The original target, when analyzed with the new code and databases, will now not ignite. However, he has redesigned his design and it now has a gain of 150 and a yield of 265 MJ with driver energies of 1.76 MJ for 4 GeV Pb ions. A stability analysis has not been accomplished and it is thought the design many be fairly sensitive. The output spectra ions will be D, T, C, Br, and Pb. The target radius is 2.8 mm to the outside of the Pb converter, which is a 25-mm-thick shell. The Pb shell should provide thermal protection through the chamber, however it will not be as reflective as gold. This target might be compatible with wetted or liquid wall concepts of a lead or lead mixture coolant. This target might be difficult for the dry wall to accommodate. Mass fabrication is feasible, but permeation of tritium might be difficult.

Drive symmetry for the direct drive target requires 60 beams. Beam transport of that many beams is a challenge. The larger beam spot size of 6 mm is more attractive than the 1-1.7 mm for the comparable indirect drive target.

Parametric Results from Gas-Filled Chamber Analysis -- Don Haynes presented his analysis of the gas filled chamber with spectra from the 160 MJ NRL DD target. He found that a 250 mtorr Xe chamber pressure would suffice in protecting the chamber wall material as compared to the SOMBRERO 500 mtorr pressure. Don also investigated Xe pressures at 50 and 100 mtorr levels. At the pressures considered, the Xe chamber gas absorbs most of the target x- rays.

In a trade of Xe chamber gas and wall temperatures (without knockon ions being considered), the gas pressure was much more important to the survivability of the wall than the steady state wall temperature. He also found the knock-on ions were very important as they contribute 18 MJ to the total ion energy of 43 MJ. When the knock-on ions were considered, the chamber pressure should be increased and the effect of the wall temperature was somewhat stronger. The knock-on ions tended to penetrate deeper into the wall armor material.

With the wall temperature at 1450°C and 0.5 torr Xe chamber gas, the surface heat flux limits the carbon wall armor radius to 4 m without knock-on ions and 4.5 m with knock-on ions. The wall designers suggested that the wall could be run at a much lower temperature, perhaps as low as 600°C. For the next meeting, a series of comparisons would be run at three temperature levels.

Don also replaced the Xe chamber gas with Kr and reported the changes. A slightly higher pressure of Kr is required for the same stopping effectiveness. Parametrically, he investigated the effect of changing the wall thermal conductivity at two chamber radii. Different forms of carbon have differing thermal conductivities. For each radius, there is a thermal conductivity that keeps the erosion of the wall below the level of a monolayer of erosion per shot. Don suggested we consider the inclusion of another armor material that might be more durable and conductive to help the survivability of the first wall.

Don suggested he could make additional analysis runs with a non-gold-coated DD NRL target. Also a larger target yield, perhaps the 160 MJ NRL target scaled up to the proper size for a 1000 MWe plant, would be more appropriate. Scaling the pressure down to or near to zero pressure would be enlightening.

Chamber Nuclear Analysis

Chamber Nuclear Performance -- Laila El-Guebaly reported an assessment of nominal material assumptions for the dry wall chamber (SiC/SiC blanket with LiPb coolant and breeder, and carbon armor over 1-cm-thick first wall.) She also used the NRL 160 MJ target at a repetition rate of 6 Hz to yield 1000 MW fusion power. (These parameters will have to be increased to attain a 1000 MWe power plant.) The average neutron energy for IFE was in the range of 12.4 MeV as compared to 14 MeV in MFE. She postulated a first wall thickness of 1 cm, a blanket thickness of 44 cm, and a shield thickness of 55 cm that would meet the nuclear requirements of the chamber. She found the first wall absorbed a significant fraction of the nuclear heating. She also presented two cases for chamber radii of 4 and 6.5 meters that illustrated a three-fold difference in peak nuclear heating, neutron wall loading, and first wall lifetimes, assuming a finite first wall fluence limit. These parameters varied as 1/r2 .

Activation Analysis for Gold Coating/Hohlraum -- Laila conducted an activation analysis for both the NRL DD and the HI ID targets with the same set of basic chamber and targets. The target coating was Au for the DD target and Au/Gd for the ID target. The more massive HI ID target produced much more heavy metal debris in the chamber, 70 tonnes/y as compared to 5 kg/y for Au DD target. Almost immediately an 8-micron-thick layer of Au or a 1- mm-thick layer of Au/Gd material will plate the first wall, with the remainder of the metals melting and running down to the bottom of the chamber. Thus all neutronic and thermal analyses should consider the metallic coating an integral part of the wall. The gold plated wall will qualify as Class A and C low level waste. However, the Au/Gd coated wall cannot be classified as low- level waste. Laila recommended replacing Gd with some other hohlraum material or separate Tb out of the waste stream and dispose of it as high-level waste.

Scoping Study Results of Safety and Environmental Attractiveness of Target Materials -- Jeff Latkowski assessed a range of feasible materials that might be considered for the target. Neutron activation analyses were performed on all materials from lithium to bismuth. Weekly batch irradiation was assumed for the materials over the lifetime of the plant. Three criteria was assumed: (1) one half of the accident dose of 10 mSv, namely 5 mSv, (2) the contact dose of 114 Gy per hour (equivalent to 30 MGy over the life of the plant), and (3) a waste disposal rating of <1 after 30 years of operation. A simple MELCOR model was used to estimate the accident release fractions. The particulate results indicate that the particle size determines the amount of the release fraction. All considered elements passed the particulate test except for seven materials for 5 mSv criteria.

Safety and Environmental Analysis

Status of ARIES-IFE Safety and Environmental Studies -- Dave Petti, via a phone link, reviewed the safety and environmental activities for the ARIES-IFE study. The activities were to minimize radiological inventories, implement radiological confinement in IFE systems, identify and analyze accident scenarios, and assess waste management scenarios for considered system configurations. Dave stressed the need for two strong boundaries, emphasizing that the building walls should not be one of these boundaries. Moreover, the enclosed nuclear volume should be minimized as much as possible. Penetrations are a key concern as potential release pathways. He would prefer to have passive safety systems rather than relying on active systems for safety.

Dave talked a great deal about the rouge pellets or driver beams as accident initiators. He discussed frequency and probability of occurrence, comparing those frequencies of commonly known systems. Dave also mentioned the consequences of such abnormal events.

Dave mentioned accident identification and analysis and how it would be applied initially to the SOMBRERO design approach. Such accidents would include loss of vacuum, loss of power, or a pump trip. Some of these can be avoided by system redundancy, but others cannot. Waste management will also be assessed. He mentioned the magnets might not meet the shallow land burial criteria. Assessment of the tritium factory is be evaluated to determine likely tritium inventories and how they can be reduced to safer levels. Different approaches are being investigated to determine the best method of reducing inventories. Segmentation of inventories can also reduce the consequences of a tritium release.

Final Optics Analysis

Final Laser Optics Modeling -- TK Mau said the primary objective of the laser final optics modeling is to quantitatively analyze the effects of damage from x-rays, gamma rays, neutrons, laser radiation, charged particles, and target debris to the quality of the laser beam focusing on the target. The second objective is to define the design windows for the grazing incidence metal mirror (GIMM). Mirror damage can be manifested in beam defocusing, wave front distortion, increased beam absorption, and shorter mirror lifetime. The two general categories of damage are dimensional defects and compositional defects.

Compositional defects can be modeled with Fresnel modeling of reflectivity, considering four elements of the GIMM: metal substrate, mirror coating, contaminant layer, and incident medium. The beam can be analyzed as two polarized waves (Es and Ep). Each of these waves behaves differently when reflected off the mirror. The Al2O3 protective coating is totally reflective for both beams at 90° (tangential) incidence. As the incidence angle decreases, the S-wave decreases to a minimum reflectivity of ~0.1 at 0° (normal) incidence whereas the P-wave becomes totally transmissive at 60° incidence angle and then increases back to the same 0.1 reflectivity at 0° incidence.

TK also described the effects of uniform layers of surface contaminants, such as carbon. This layer affects the reflectivity rather linearly with respect to thickness and non-linearly with respect to incidence angle. TK then combined the surface layer effect with the protective layer to yield a combined effect.

TK is considering purchasing a ray tracing code to analyze the effect of gross surface defects. Microscopically rough surfaces tend to scatter the beams. This effect can be modeled either by perturbation theory or physical optics, depending on the magnitude of the roughness as compared to the beam wavelength.

Update on Target Fabrication -- Dan Goodin reported the results of a target fabrication facility tritium inventory meeting held at LANL on 11/13/00. The conclusion was that the target fabrication facility tritium inventory should be below 250 g releasable and 1 kg total. Work will continue on ID target filling method (hot assembly, cold assembly, and temperature shimmed assembly), capsule buckle pressures, permeation coefficients, and other filling parameters. The assembly of the DD target is much simpler than the ID target.

Dan illustrated a few filling techniques to increase production rate to indicate possible commercial approaches. Future work will include modeling the cooling process, bringing experimental data into analytical buckling pressure and fill time calculations, and inclusion of real engineering data into the models.

Dan also described the present temperature shimmed hohlraum target fabrication process and future mass production approaches. He also described the present status of the fluidized bed process to produce filled capsules.

There is also an experiment to evaluate the effects of radiation heating of the target from the chamber wall. In response to a question about the effect of chamber emissivity on target heating, Dan reported the chamber emissivity does not affect target heating if the chamber wall reflections are diffuse (not specular) as would be the case for a dry wall concept. On the other hand, a highly reflective chamber wall would have specular reflections and the target absorbs less energy. If a dry wall chamber condenses the target coating, such as gold, its first wall may also become highly reflective and behave like the wetted wall concept.

Modeling of Target Radiation Heating -- TK Mau is modeling the gold-coated NRL DD Laser target. He quoted the SOMBRERO report that indicated radiation heating is much larger than convective heating from the chamber gases. The radiation heat load is assumed to be black body radiation from the wall at a temperature of 625°C. The same analysis tools he discussed earlier can be used in this analysis to obtain target reflectivity. He found the target is highly reflective in the IR spectrum with a gold thickness greater than 0.04 _m. The IR reflectivity is insensitive to polymer layer thicknesses in the 1-10 _m range. Target heating is strong in the visible spectrum over all angles of incidence.

Chamber Wall Engineering

Impact of Power Cycle Performance of Separately Cooling Chamber Wall -- In response to a question as to the impact on the power cycle of cooling the first wall below the nominal blanket output temperature, Rene analyzed the change in efficiency of the Brayton cycle. Rather than have all the first wall, blanket and shield energy be transferred through the intermediate heat exchanger into the turbine helium working fluid, he modified the cycle to route the helium working fluid through the first wall, effectively preheating the working fluid before the intermediate heat exchanger. The chamber wall helium temperature is dictated by the maximum cycle helium temperature and compression ratio. Approximately 30% of the total power is absorbed in the first wall.

For a temperature drop of ~100-150°C across the first wall and a compression ratio of 4.5, the average wall surface temperature can be held to ~600°C and the power cycle can still achieve an overall efficiency of 50% as compared to the ARIES-AT efficiency of 59%.

Dry Wall Chamber Engineering -- Rene Raffray reported on UCSDıs analysis of the heat deposition on the dry wall chamber first wall armor. Initial material options include C, SiC, and W. There may be some protective gas in the chamber. The first wall is assumed to be 3-mm- thick carbon with 400°C helium in contact to the back face of the wall. An upper bound, admittedly too severe, is to consider all the x-ray, fast ion, and debris ion energy is deposited immediately upon the first wall surface at a radius of 6.5 m. This produces an instantaneous heat spike with very high temperatures, ignoring the heat of fusion and vaporization. The spatial distribution of the photons, fast ions, and debris ions (all arriving simultaneously) was then considered. This temperature spike was a factor of 2.5 lower, but still way above any reasonable solution. The next iteration was to add in the temporal distribution of the energies: first photons, then fast neutrons, and finally debris ions. This brings the thermal spike on the first wall to a maximum of ~1400°C for a flat carbon wall. This may be a feasible solution for a carbon thermal conductivity of 400 W/mK, however, lowering the conductivity to 100 W/mK increases the temperature spike to 1950°C.

The next step is to alter the wall surface from the flat surface to increase the surface area and spread out the deposition of the energy over a greater depth within the first wall (e.g., porous media or fibrous walls.) Work in this area is continuing.

Assessment of IFE Structural and Armour Materials -- Mike Billone reviewed the materials being assessed and developed by the US materials program. There were low activation ferritic steel alloys, oxide-dispersion-strengthened low activation ferritic steels, vanadium alloys, silicon carbide composites, tungsten alloys, graphite, and carbon fiber composites.

First wall issues include surface erosion, tritium inventory buildup, chamber clearing, thermo physical properties, mechanical properties, and dimensional changes during irradiation. Graphite/CFC is sensitive to thermal shock and thermal shock can vary by a factor of 3 within this family. Thermal conductivity for graphite degrades with increasing dpa levels up to a saturation point around 1 dpa. The thermal conductivity of unirradiated CFC decreases with increasing temperature, however the thermal conductivity for irradiated (up to 1 dpa) CFC increases with increasing temperature. These bounding conditions converge on a thermal conductivity of 200-250 W/mK at high temperature (~1200°C).

Upon irradiation, graphite initially shrinks until a fluence of 15-20 dpa is reached and then it begins to swell with increasing irradiation. There is also temperature dependence and an axial or radial dependence. The coefficient of thermal expansion increases with fluence until a fluence of 4 to 8 dpa is reached and then the coefficient of thermal expansion decreases. The behavior of CFCs is dependent on the weave and densification.

Graphites and CFCs are unique in that numerous physical properties changes occur during neutron irradiation and elevated temperature exposure. Graphite, carbon, and CFC all behave differently and all applications need to be examined closely.

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