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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