A potpourri* of engineering topics

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A potpourri of engineering topics
A collection of various things an assortment,
mixed bag or motley. from the French rotten pot
M. S. Tillack, with help from many others
ARIES Project Meeting 27-28 July 2011
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Topics

1. ARIES-AT, ACT-I and ACT-II blanket radial builds
2. ARIES-AT, ACT-I and ACT-II vertical builds(i.e.,
   coolant routing behind the divertor)
3. Vacuum vessel materials selection
4. Heat transfer enhancement by roughening
5. Tantalum

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Comparison of AT, ACT-I and ACT-II parameters
  ARIES-AT ACT-I ACT-II
Blanket materials SiC/PbLi SiC/PbLi SiC/PbLi
Divertor materials SiC/PbLi W/He W/He
Major radius m 5.2 5.5 6.75
Minor radius m 1.3 1.375 1.6875
Plasma aspect ratio 4 4 4
Plasma elongation 2.2 2.2 2
Plasma triangularity 0.84 0.7 0.7
Normalized BetaN 5.4 4.5 2.75
Toroidal magenetic field T 5.86 5.5 7.25
Greenwald density fraction 1.0037 0.95 0.85
H98 1.349 1.441 1.169
q95 or qcyl 3.552 4.4 4.8
Plasma current MA 12.8 10.58 13.28
Bootstrap fraction 0.91 0.8998 0.6066
Max div heat flux OB MW/m2 14.7 6.7 7.3
FW surface area m2 425.588 504.85 692.63
Max FW heat flux MW/m2 0.282 (ave) 0.274 0.257
Blanket volume m3 266.902 318.136 414.629
Plasma volume m3 308.219 407.739 685.192
Ave. neutron wall load MW/m2 3.294 3.07 2.37
Aux. power into plasma MW 0 45.1 130.3
CD power to plasma MW 35 26.9 121.3
Thermal power MW 1982 2065 2332
Fusion power MW 1755 1806.5 1958.5
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The ARIES-AT blanket concept
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Elements of the SiC/PbLi blanket radial build
Parameter value unit explanation
first wall SiC thickness 1 mm armor, may be W, unrelated to power handling NO CHANGE
first wall SiC/SiC thickness 4 mm minimum for structural integrity, dominated by pressure stress (surface heat fluxes nearly identical in all designs) MHD pressure drop will be different, but gravity loads dominated in ARIES-AT NO REASON TO CHANGE
annular channel depth 4 mm sized for flow rate to provide heat removal and bulk DT, similar surface heat fluxes, but more power in ACT-II
inner box thickness (curved) inner box thickness (straight) 5 8 mm mm required to withstand pressure stress due to MHD Dp. side walls are most challenging.
inner box channel depth 27 cm mainly based on neutronics.
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Thermal hydraulic and MHD considerations for
blanket box sizing

• Two changes with largest impact 15 high
  thermal power, 50 higher B2
• Thermal power
• Keep overall DT fixed (maintain temperature
  windows)
• 15 increase in Pthermal ? 15 increase in flow
  rate
• Need either higher velocity (inboard) or deeper
  channels (outboard)
• Higher velocity may require additional
  structure for pressure stresses(ARIES-AT was
  conservative)
• MHD
• Dp3d k N (rv2/2), where N Ha2/Re saB2/rv
  Dp3d k (s/2) avB2
• a can be reduced in the FW channel ? 50 more
  rib structure
• v can be reduced in the FW channel with larger
  d ? 50 more fluid. But, lower v and larger
  d will impact h

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MHD flow conditioning

• Analogous to ordinary flow conditioning
• But based on completely different physics
• I suggested this to the UCLA group as a useful
  geometry to test and/or model

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2. Vertical Build coolant circuits 1, 2, and 4
in ARIES-AT
1
2
4
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Contribution of cooling circuits to vertical build
Circuit purpose Thermal power (MW) Mass flow rate (kg/s) Flow behind divertor? Avoidable?
1 series flow through the lower divertor and inboard blanket region 501 6100 lower No
2 series flow through the upper divertor and one segment of the first outer blanket region 598 7270 upper Yes, with He divertor
3 flow through the second segment of the first outer blanket region 450 5470 no
4 series flow through the inboard hot shield region and first segment of the second outer blanket region 182 4270 upper and lower No, but flow area could be reduced
5 series flow through the outboard hot shield region and second segment of the second outer blanket region 140 1700 no
A. R. Raffray, L. El-Guebaly, S. Malang, I.
Sviatoslavsky, M. S. Tillack, X. Wang, and The
ARIES Team, "Advanced power core system for the
ARIES-AT power plant, Fusion Eng. and Design 80
(2006) 7998
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Flow area and depth of manifolds

• Assume same nominal velocity as blanket 11
  cm/s(MHD pressure drop is extremely uncertain)
• Assume R3.5 (rough approximation)
• Constant v?B to avoid MHD effects(need to tailor
  channels for changing B higher v at larger R)

Circuit Mass flow rate (kg/s) Volume flow rate (m3/s) Flow area (m2) Channel depth (m)
1 6100 0.610 5.5 0.25
2 7270 0.727 6.6 0.3
4 4270 0.427 3.9 0.18

• Note LM flow through a pebble bed should be
  avoided

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3. Vacuum vessel material selection

• Recent history
• Issue raised by Malang a couple of months ago
  Ferritic steels suffer from low-T embrittlement
  and PWHT issues.Austenitic steels (316) will not
  meet class C.
• Engaged Team members in email discussions.
• Materials community took interest in this topic,
  highlighting it as an important near term issue
  for the program (Kurtz, FNS-PA July 2011)
• Report by Malang distributed, report by Rowcliffe
  expected.
• A review and assessment is underway
• Requirements
• Material choices
• Activation (El-Guebaly)
• RD needs

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Vacuum vessel material choices

• ITER chose SS316 due to
• Easy fabrication, welding of thick elements, no
  post-weld heat treatment required
• No impact on the magnetic field (not
  ferromagnetic)
• Compatible with water coolant (typical conditions
  are T lt 150 C and p lt 1 MPa)
• No embrittlement by neutron irradiation, even at
  irradiation temperatures lt 200 C
• But 316SS can not be used in a power plant due
  to
• Relatively high neutron activation, even at the
  low fluence at the VV
• Potential for swelling, even at low neutron doses
• Material choices considered for ARIES
• Standard austenitic steel (for example SS 316)
• Modified austenitic steel (for example, Ni
  replaced by Mn)
• Ferritic steels (either with 2 3 Cr, or 14
  18 Cr)
• Ferritic/Martensitic steel (F82H, Eurofer)
  (typical 8-9 Cr)
• Simple ferritic steel (Fe with small amounts of
  C, Mn, Si, widely used in industry)
• Others (Inconel, Cu-alloys, Al-alloys,)

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Comparison of material options
Material choice Advantages Disadvantages
Simple carbon steels as widely used in the industry Low cost Easy welding No PWHT required Reduction of ductility by low temperature irradiation may require periodic in-situ annealing. Suitable coatings or effective water chemistry required to avoid corrosion.
Ferritic steel with higher chromium content Relatively low cost No problems with welding No PWHT required Reduction of ductility by low temperature irradiation may require periodic in-situ annealing. Probably corrosion resistant only if Cr content gt 10 .
Austenitic steel with Ni replaced by Mn Can be qualified as low activation material, waste class A Probably no impact of irradiation on ductility and swelling Probably no problem with welding Probably no PWHT required Large development/qualification effort may be required. Fabrication (hardness?) and corrosion resistance unknown.

• G. Piatti, P. Schiller, Thermal and Mechanical
  Properties of the Cr-Mn (Ni-free) Austenitic
  Steel for Fusion Reactor Applications, J.
  Nuclear Materials vol. 141-143, p. 417-426 (1986)
• Y. Suzuki, T. Saida and F. Kudough, Low
  activation austenitic Mn-steel for in-vessel
  fusion materials, J. Nuclear Materials vol.
  258-263, Part 2, p. 1687- 1693 (Oct. 1998)

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Comments on low-Cr FS and FM steel

• Post-weld heat treatment (PWHT) is required for
  low-Cr content and ferritic/martensitic steels.
• Welding would be needed after initial fabrication
  and after any maintenance rewelding.
• Friction stir welding is a low-temperature
  alternative to TIG welding, and may eliminate the
  need for PWHT.
• However, these are high-performance steels
  developed for in-vessel service. Would we want
  to use them in the vacuum vessel?
• Higher fabrication cost.
• Lower development cost (already under development
  for blanket).
• Tailored for high temperature operation, not
  below 200 C.

• Glenn Grant and Scott Weil, Friction Stir
  Welding of ODS Steels Steps toward a Commercial
  Process, Workshop on Fe-Based ODS Alloys Role
  and Future Applications, UC San Diego La Jolla,
  CA (Nov 17 18, 2010).
• (http//www.netl.doe.gov/publications/proceedings/
  10/ods/Glenn_Grant_FSW.pdf)

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4. FW heat transfer enhancement (He cooling)

• Since the time of ARIES-ST, we took credit for
  1-sided roughening
• 2x higher h assumed
• Friction increased on only one wall (assumed no
  effect on other walls)
• Large margin on 5 pumping power requirement when
  using desired bulk velocity. Typically Re105
• Limited effort was given to design the roughness,
  determine exact values of h and dp, and establish
  design consistency.

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Several types of 2d and 3d structures are
possible roughness, ribs, scales, dimples, pins
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Enhancement beyond 2x comes with increasing
friction factor penalty

• (Re104 for most of these data)

• P. M. Ligrani and M. M. Oliveira, Comparison of
  Heat Transfer Augmentation Techniques, AIAA
  Journal 41 (3) March 2003.

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Roughness on side and back walls affects h

• P. R. Chandra, C. R. Alexander and J. C. Han,
  Heat transfer and friction behaviors in
  rectangular channels with varying number of
  ribbed walls, International Journal of Heat and
  Mass Transfer, Volume 46, Issue 3, January 2003,
  Pages 481-495.

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Dimpling works at high Re (we need 105)
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CFD studies could be performed for our particular
design conditions
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Performance metrics
Roughening features have corresponding heat
transfer factor (j) and friction factor (f) Hold
two of the 3 ratios on left constant to evaluate
the performance of each roughness Holding
Pumping Power and Area Constant
R. L. Webb and N. H. Kim (2005) Principles of
Enhanced Heat Transfer
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5. Tantalum

• Assessed in previous IFE and MFE studies high
  temperature capability, industrial experience,
  good database.
• Used in the current ARIES divertor design due to
  its high ductility, even after irradiation.
• If W alloys do not succeed, then is Ta-alloy or
  some compound structure employing Ta a reasonable
  option?

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Tantalum characteristics vs. W

• Melting temperature (hence temperature window)
  3290 vs. 3695 K
• Activation, afterheat a concern, but better than
  W
• Transmutation becomes 10 W after 10 MW-yr/m2
  (LIFE)
• Thermal neutron absorption may be problematic
  for TBR
• Thermal conductivity 57 vs. 173 W/m-K
• Hydrogen inventory strong getter at 1000 C,
  outgases at 1500 C
• Hydrogen hardening and embrittlement
• Oxygen and nitrogen chemistry impurity control
  required
• Raw material cost 300/kg vs. 200 for W

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Tantalum temperature windows
Allowable plastic strain for Ta is gt15 at room
temperature and gt5 at 700 ºC (based on Steven
Zinkle emails). Not much literature on this, and
no information on fracture toughness. Should we
press for more information?