Scoping the Potential of Mobile Tiles for and IFE Power Plant

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Scoping the Potential of Mobile Tiles for and IFE
Power Plant

• Lance Snead, Hsin Wang, Jim Kiggans
• Oak Ridge National Laboratory
• Igor Sviatoslavsky, Mohamed Sawan,Carol Alpine,
  Greg Sviatoslavsky
• University of Wisconsin

Presented at the HAPL Meeting PPPL, Princeton,
NJ December 12-13, 2006
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Basic Idea
Fundamental problem with graphite is solved by
limiting residence time of graphite tile in
chamber and post-processing tile in vacuum
furnace. -- Post processing restores graphite
properties -- Post processing removes
tritium -- Erosion mitigated by limiting time in
chamber ----gt lets consider recycling the
tiles. Material and Design Intermediate
quality graphite tile similar to matrix nuclear
graphite (good thermal conductivity, very high
fracture toughness.) Tile rides on rail from
top of reactor to bottom, through furnace,
inspect, back to the top of the reactor.
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The original twisted biscuit
LAF Rail Na Coolant
Side View View Face Changes With Twist of Oval
Rail
Chamber Support Composed Of Twisting Metallic
Oval Rail
Top View With Oval Rail Graphite Breeder
Multiplier
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900C
2 dpa
600C
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Tritium Outgas Property Recovery (1200-1300C,
hours)
3T
remove
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replace
Recycle Re-fabricate (1100-1200C)
Fresh C Be Li2O
bad
Inspection Storage
good
Tritium Outgas Property Recovery (1100-1200C,
hours)
3T
remove
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Geometric Description

• The chamber is 10 m in radius.
• Tiles are 15 cm X 15 cm X 6 cm
• Tiles are supported on oval cooling
• channels. As the tiles move down on the
  cooling channels, they twist such that at
  mid-plane they face the target 15 cm X 15 cm.
• The tiles are inserted at the top, 105
• tiles at 1 m radius, 105 tiles at 2.5 m
  radius and 210 tiles at 5 m radius.
• There are 25,200 identical tiles in the chamber
  at any one time.
• At replacement time, the tiles slide down on the
  cooling channels and are removed at the bottom.
• Blankets are located behind the tiles
• as shown in the figure.

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Neutronics Assessment and Assumptions

• Neutronics calculations assess breeding potential
  as a function of ceramic breeder content and
  lithium enrichment
• Used HAPL target spectrum in 175 neutron, 42
  gamma groups
• 4 cm graphite tiles with coolant rails (75 C,
  10 FS, 15 Na)
• 1 m blanket made of 80 C/breeder mixture, 10
  FS, 10 Na
• Assessed replacing FS/Na in tiles and blanket by
  SiC/He
• A zone consisting of 85 FS, 15 He used behind
  blanket to represent reflection from shield/VV
• Lithium silicate (Li4SiO4) used as ceramic
  breeder (breeder potential nearly the same for
  different ceramic breeders)
• Required local (1-D) TBRgt1.15 for tritium
  self-sufficiency

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Local TBR No Breeding Materials
FW tiles 75 graphite 10 structure
15 coolant Blanket X Li4SiO4 (80-X)
graphite 10 structure 10 coolant

• Largest TBR achieved with high breeder content /
  low Li enrichment
• Achievable TBR not adequate
• Replacing FS/Na by SiC/He is not Helpful

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Local TBR Addition of Be2C
FW tiles 55 graphite, 20 Be2C, 10 FS, 15
Na Blanket X Li4SiO4, Y Be2C, (80-X-Y)
graphite, 10 FS, 10 Na Be2C content was limited
to 20

• Adding 20 Be2C in FW tiles and blanket results
  in 15 increase in TBR
• Largest achievable local TBR is 1.108 with 50
  Li4SiO4, 20 Be2C, 10 C, 10 FS, 10 Na in
  blanket and 30 lithium enrichment. This value is
  getting close to the goal value of 1.15

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Further TBR Enhancement

• Increasing Be2C content in blanket
• Tiles 55 graphite, 20 Be2C, 10 FS, 15 Na
• Blanket 10 graphite, 30 Be2C, 10 FS, 10 Na,
  40 ceramic breeder
• Local TBR 1.16
• Increasing Be2C content in FW tiles
• Tiles 45 graphite, 30 Be2C, 10 FS, 15 Na
• Blanket 10 graphite, 30 Be2C, 10 FS, 10 Na,
  40 ceramic breeder
• Local TBR 1.18
• Adding ceramic breeder in FW tiles
• Tiles 35 graphite, 30 Be2C, 10 FS, 15 Na,
  10 ceramic breeder
• Blanket 10 graphite, 30 Be2C, 10 FS, 10 Na,
  40 ceramic breeder
• Local TBR 1.19
• It is possible to achieve adequate tritium
  breeding with the mobile tiles design with proper
  composition optimization keeping in mind
  constraints on material content

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Cooling the Tiles is of Paramount Importance

• The target energy in the form of ions, neutrons
  and x-rays impacts the tiles and is conducted to
  the back through the graphite.
• At this point the energy has to be transferred to
  the coolant channel.
• Radiating the energy is not adequate since it
  causes the front temperature to be excessive
  (2700 oC).
• A scheme for conducting the energy is shown in
  the figure. Graphite felt lines the inner channel
  of the tile facing the target.
• A linkage built into the cooling channels, when
  engaged applies forces on the the tile and
  compresses the graphite felt allowing the energy
  to be conducted to the cooling channel.

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Estimating the Tile Surface Temperature
Assuming radiation, to transfer the energy
from the tile to the coolant channel
exceeds desirable temperatures at the surface.
For example, assuming the coolant channel is at
200 oC, the maximum tile surface temperature is
2700 oC. Conduction is needed to transfer heat
from tile to the coolant rails. Tile
temperature is critically dependent on the
contact conductance between tile and coolant
rails. This tile thermal conductivity and
contact conductance can only be guessed at
currently, though there are potential engineering
improvements which can be considered.
Graphite felt in the space between the tile and
the coolant channel, when compressed, provides a
conduction path. Assuming a coolant temperature
at 400oC, a conductivity for the graphite felt of
1 W/mK, a thickness of 0.1 cm, resulting
temperatures are shown below.

• x-rays Burn ions Debris ions
• Type of deposit. Exponential Uniform Uniform
• Deposit. Depth(m) 2 10 1
• Deposit. Time (ns) 1.4
  1100 3800
• Fluence (J/cm2) 0.39 2.98
  4.0
• Max. Temp. (oC) 1330 1400
  1600

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Progress Toward Measuring Thermal Contact
Conductance
Estimation of the thermal contact resistance
is a critical path issue for the mobile
tiles and will be a strong function of
temperature and interfacial pressure

15C
30C
IR Thermal Camera

• 256 x 256 InSb focal plane
• detector array
• Temp. resolution 0.015C
• Spatial resolution 7.5 mm
• Frame speed 130 frames/sec

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Progress Toward Measuring Thermal Contact
Conductance
Flux via electrical resistance delivered to
mandrel of load frame
Top Specimen 25mm x 5mm diameter
TC for measure of ambient Temperature
Bottom Specimen 5mm x 5mm diameter
Sample Pair sat atop hemispherical tungsten
carbide support
Estimation of the thermal contact resistance is
a critical path issue for the mobile tiles will
be a strong function of temperature and
interfacial pressure
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Progress Toward Measuring Thermal Contact
Conductance
The cover is place on the furnace and the heating
elements placed in the top 4 slots to help induce
heat flow. A sapphire widow is placed over the
opening to retain heat while allowing for the
capture of the thermal image
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Test Set Up w/IR Camera
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Test Schedule / Process

• System tested at RT, 50, 100, 150, 200 C and 1,
  25, 50, 75 MPa
• For these initial runs the top specimen was
  aluminum alloy and the bottom specimen a lower
  conductivity steel
• Data was taken at RT with and without the
  sapphire window
• There was a 20 minute interval between heat
  cycles
• For Example, lets say data was collected at 50 C
  for the 4 pressures. The furnace would cycle on,
  and allowed to heat to 100 C (10C/min). Once at
  100 C, it was left there for 8 minutes, at which
  time the flux source was turned on. After 4
  minutes, data collection began for the 4
  pressures, after which time, the furnace began to
  heat up to 150 C.
• This continued up to 200 C, till all the data was
  collected.

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Raw Data w/Curve Fit
Test System Data
The linear approximations were obtained using the
5 mm closet to the interface for the top specimen
and 3mm for the bottom specimen. The true
location of the interface itself (the vertical
line) is very subjective and sensitive to the
calculation of the interface TCC.
Flux was determined for both top and bottom
specimens using (dT/dx)Kmatl, then averaged to
get Qave. Qave/dTinterface TCC (mW/mm2-C)
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Thermal Contact Conductance of Model Al/Steel
System
200C
150C
100C
50C
20C
Additional optimization to the analysis
program would be helpful, but system appears
ready for application to a mobile tile
graphite/metallic interface.
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Fabricating Test Tiles - A Next Step ?
Properties and property evolution in-reactor
can only be estimated for this graphite-ceramic.
Assuming preliminary designs suggest promise,
property measurement on prototypic materials will
be required.

• Mix Be2C powder ( ESPI Metals)
• Graphite powder, and carbon binder
• Dry mixture
• Hot press powder to 1100 C (low
• temperature to avoid vapor hazard)
• Carbon binder will bond powders
• together under pressure

Interior of ORNL Brew hot press showing graphite
die
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next
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Sawicki JNM 1989
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Saeki JNM 81 Neutron irradiation to 3E19 n/cm2,
250-400
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JT-60 tile
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Local TBR No Breeding Materials
FW tiles 75 graphite, 10 structure, 15
coolant Blanket X Li4SiO4, (80-X)
graphite, 10 structure, 10 coolant
FS structure, Na coolant
SiC structure, He coolant

• Largest TBR achieved with high breeder content /
  low Li enrichment
• Achievable TBR not adequate
• Replacing FS/Na by SiC/He is not Helpful

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Degradation in Thermal Conductivity
For graphite held in the 600-1000C range,
thermal conductivity will slightly degrade and
density somewhat. Some recovery during furnace
anneal will occur.
Burchell data
2 dpa