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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 SviatoslavskyUniversity 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

----> let’s 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

Top View With Oval RailGraphite + Breeder + Multiplier

Side View: View Face Changes With Twist of Oval Rail

Chamber Support Composed OfTwisting Metallic Oval Rail

LAF RailNa Coolant

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0

20

40

60

80

100

0.1 1 10 100 1000

Time in HFIR Core (hours)

H451 : Tirr

= 430°C

H451 : Tirr

= 710°C

Snead data, recently unpublished

0.2 dpa 2 dpa

H451 Graphite900°C

600°C2 dpa

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Tritium Outgas& Property Recovery (1200-1300°C, hours)

remove3T

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Tritium Outgas& Property Recovery (1100-1200°C, hours)

Inspection& Storage

Recycle& Re-fabricate(1100-1200°C)

good

bad

remove

replace

Fresh C + Be + Li2O

3T

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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 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) TBR>1.15 for tritium self-sufficiency

Neutronics Assessment and Assumptions

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FW tiles 75% graphite 10% structure 15% coolant

Blanket X% Li4SiO4

(80-X)% graphite 10% structure 10% coolant

Local TBR : No Breeding Materials

Largest TBR achieved with high breeder content / low Li enrichmentAchievable TBR not adequateReplacing 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% NaBlanket X% Li4SiO4, Y% Be2C, (80-X-Y)% graphite, 10% FS, 10% NaBe2C content was limited to 20%

Blanket Composition % 6Li % FS % Na % C % Li4SiO4 % Be2C 7.5 10 20 30 40 50 60 70 80 90

10 10 60 10 10 0.792 0.825 0.894 0.927 0.945 0.957 0.964 0.968 0.971 0.973 10 10 50 20 10 0.883 0.912 0.964 0.983 0.991 0.994 0.994 0.994 0.992 0.990 10 10 50 10 20 0.858 0.892 0.964 0.999 1.018 1.031 1.039 1.044 1.047 1.049 10 10 40 30 10 0.939 0.963 1.001 1.010 1.012 1.011 1.008 1.005 1.000 0.995 10 10 40 20 20 0.949 0.979 1.034 1.054 1.063 1.066 1.067 1.067 1.065 1.063 10 10 30 40 10 0.978 0.998 1.025 1.029 1.027 1.023 1.018 1.011 1.005 0.997 10 10 30 30 20 1.003 1.028 1.069 1.080 1.082 1.081 1.078 1.075 1.070 1.065 10 10 20 50 10 1.008 1.024 1.043 1.044 1.039 1.033 1.025 1.016 1.007 0.998 10 10 20 40 20 1.040 1.061 1.091 1.096 1.094 1.090 1.085 1.079 1.072 1.065 10 10 10 60 10 1.032 1.045 1.058 1.056 1.049 1.040 1.030 1.020 1.009 0.999 10 10 10 50 20 1.069 1.086 1.107 1.108 1.104 1.097 1.089 1.081 1.072 1.063

Adding 20% Be2C in FW tiles and blanket results in ~15% increase in TBRLargest 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% NaBlanket: 10% graphite, 30% Be2C, 10% FS, 10% Na, 40% ceramic breeder

Local TBR = 1.16

Increasing Be2C content in FW tilesTiles: 45% graphite, 30% Be2C, 10% FS, 15% NaBlanket: 10% graphite, 30% Be2C, 10% FS, 10% Na, 40% ceramic breeder

Local TBR = 1.18

Adding ceramic breeder in FW tilesTiles: 35% graphite, 30% Be2C, 10% FS, 15% Na, 10% ceramic breederBlanket: 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

x-rays Burn ions Debris ionsType of deposit. Exponential Uniform UniformDeposit. Depth() 2 10 1Deposit. Time (ns) 1.4 1100 3800Fluence (J/cm2) 0.39 2.98 4.0

Max. Temp. (oC) 1330 1400 1600

• Assuming radiation, to transfer the energy from the tile to the coolant channel exceedsdesirable 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.

142.52.01.51.00.50.0

1000

1200

1400

1600

1800

2000

2200

2400

Maximum Tile Surface Temperature as a Function of Graphite Felt Conductivity

Thermal Conductivity of Graphite Felt (W/mK

Coolant ChannelTemp. 400 C

Coolant ChannelTemp. 200 C

)

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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

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20

25

30

0 5 10 15 20 25

Temperature (°C)

Length (mm)

ΔT/ ΔX = -0.476°C/

ΔT/ ΔX = -0.432°C/

ΔT = 3.44°C

• 256 x 256 InSb focal plane detector array

• Temp. resolution: 0.015°C

• Spatial resolution: 7.5 m

• Frame speed: 130 frames/sec

IR Thermal Camera

30°C 15°C

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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

Bottom Specimen 5mm x 5mm diameter

Sample Pair sat atop hemispherical tungsten carbide support

TC for measure of ambient Temperature

• 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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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

Progress Toward Measuring Thermal Contact Conductance

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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 Fit319 vs Brico @ 50 C Ambient

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50

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58

60

0 5 10 15

Distance (mm)

Temperature (C)

1 MPa

25 MPa

50 MPa

75 MPa

Series5

Series6

Series7

Series8Flux was determined for both top and bottom specimens using (dT/dx)Kmat’l, then averaged to get Qave.

Qave/dTinterface = TCC (mW/mm2-C)

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.

Test System Data

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356 vs Exhaust Seat Mat'l (K=40.1)

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120

160

200

240

0 10 20 30 40 50 60 70 80

Pressure (MPa)

TCC (mW/mm2-C)

200°C150°C

100°C

50°C

20°C

Thermal Contact Conductance of Model Al/Steel System

• 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 ?

• 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

• 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.

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next

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Sawicki JNM 1989

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Saeki JNM 81Neutron irradiation to ~3E19 n/cm2, 250-400

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JT-60 tile

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FW tiles : 75% graphite, 10% structure, 15% coolantBlanket : X% Li4SiO4, (80-X)% graphite, 10% structure, 10% coolant

Local TBR : No Breeding Materials

% Li4SiO4 7.5% 6Li 10% 6Li 20% 6Li 30% 6Li 40% 6Li 50% 6Li 60% 6Li 70% 6Li 80% 6Li 90% 6Li 10% Li4SiO4 0.685 0.714 0.777 0.806 0.822 0.832 0.838 0.841 0.843 0.845 20% Li4SiO4 0.774 0.800 0.846 0.861 0.867 0.869 0.869 0.868 0.866 0.863 30% Li4SiO4 0.829 0.851 0.883 0.890 0.891 0.889 0.886 0.882 0.877 0.872 40% Li4SiO4 0.870 0.887 0.909 0.911 0.909 0.904 0.898 0.892 0.885 0.878 50% Li4SiO4 0.901 0.914 0.930 0.929 0.924 0.916 0.908 0.900 0.891 0.882 60% Li4SiO4 0.926 0.937 0.947 0.944 0.936 0.927 0.917 0.906 0.896 0.885 70% Li4SiO4 0.948 0.956 0.963 0.957 0.947 0.936 0.924 0.912 0.900 0.888

FS structure, Na coolant

SiC structure, He coolant% Li4SiO4 7.5% 6Li 10% 6Li 20% 6Li 30% 6Li 40% 6Li 50% 6Li 60% 6Li 70% 6Li 80% 6Li 90% 6Li

10% Li4SiO4 0.810 0.811 0.810 0.808 0.805 0.803 0.800 0.797 0.794 0.792 20% Li4SiO4 0.841 0.841 0.836 0.831 0.826 0.821 0.816 0.810 0.805 0.800 30% Li4SiO4 0.868 0.867 0.860 0.852 0.845 0.837 0.829 0.822 0.814 0.807 40% Li4SiO4 0.892 0.890 0.881 0.871 0.861 0.851 0.842 0.832 0.822 0.813 50% Li4SiO4 0.913 0.911 0.900 0.888 0.876 0.864 0.853 0.841 0.830 0.818 60% Li4SiO4 0.933 0.930 0.917 0.903 0.890 0.876 0.863 0.849 0.836 0.823 70% Li4SiO4 0.950 0.947 0.932 0.917 0.902 0.887 0.872 0.857 0.842 0.827

Largest TBR achieved with high breeder content / low Li enrichmentAchievable TBR not adequateReplacing FS/Na by SiC/He is not Helpful

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0

20

40

60

80

100

0.1 1 10 100 1000

Time in HFIR Core (hours)

H451 : Tirr

= 430°C

H451 : Tirr

= 710°C

Snead data, recently unpublished

0.2 dpa 2 dpa

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

H451 Graphite

900°C600°C

2 dpa

Burchell data