Prepared for Presentation at
2 nd EU-US DCLL Workshop
November 14-15, 2014, Los Angeles
Yutai Katoh
Leader, Fusion Materials & Nuclear Structures
Materials Science and Technology Division
Oak Ridge National Laboratory
With contributions from:
L.L. Snead, T. Koyanagi (ORNL)
R.J. Shinavski (Rolls-Royce HTC)
S. Sharafat (UCLA), B. Williams (Ultramet)
T. Nozawa, K. Ozawa (JAEA)
ORNL is managed by UT-Battelle for the US Department of Energy

• FCI is among key components for liquid metal-cooled/bred fusion blankets
– Proposed by Malang (1991) and adopted in conceptual blanket designs.
– Mitigates MHD pressure drop
– Enables high temperature operation
– Makes DCLL concept attractive
• Two important FCI functions in
DCLL
– Thermally insulate steel structures from Pb-Li
– Electrically insulate Pb-Li from steel structures
2 Katoh on SiC FCI for Fusion DCLL Blankets
Temperature Profile for
Model DEMO Case s
FCI
= 5 S/m
Smolentsev
20 S/m
100 S/m

Sharafat and Katoh,
Discussion summary from 8th IEA
International Workshop on SiC/SiC
Ceramic Composites for Fusion
Applications, 2009, Daytona Beach.
1.
Minimize Impact on Tritium Breeding
2.
Adequate thermal insulation
– K th
= 2~5 W/m-K for US DCLL TBM
3.
Adequate electrical insulation
– s el
= 5~100 S/m for US DCLL TBM
4.
Compatibility with Pb-Li
– Up to 470
º
C for US DCLL TBM, >700
º
C for DEMO
–
In a flow system with large temperature gradients
5.
Leak Tight for Liquid Metal / disconnected porosity
–
Pb-Li must not “soak” into cracks or pores, must remain isolated in small pores even if cracked
6.
Mechanical integrity
– Primary and secondary stresses must not endanger integrity of FCI
7.
Retain Requirements 1 – 5 during operation
– Neutron irradiation in D-T phase ITER, and extended to DEMO
– Developing flow conditions, temperature & field gradients
–
Repeated mechanical loading under VDE and disruption events
3 Katoh on SiC FCI for Fusion DCLL Blankets

2007
Present Status
(Radiation-resistant SiC/SiC)
Insufficient unirradiated insulation
(5-10 W/m-K)
Thermal insulation
Substantial change during irradiation
May meet requirement (<~ 20 S/m)
Electrical insulation
Controllability questionable
Radiation effect unknown
Static testing underway
Chemical compatibility
Results so far promising
Liquid metal leak tightness
No serious concern
Cracking stress likely limits
D
T
Mechanical integrity
Stress induced by differential swelling may dictate secondary stress
4 Katoh on SiC FCI for Fusion DCLL Blankets
R&D Goal
(Property-adjusted SiC/SiC)
Maintain 2 - 5 W/m-K throughout operation
Validate radiation effect model
Establish control scheme
Address radiation effect
Perform validation
Perform validation
Survive
D
T > 200K throughout operation
Determine differential swelling effect and irradiation creep
Confirm other radiation effects

5 Katoh on SiC FCI for Fusion DCLL Blankets

Property
Thermal conductivity
Electrical conductivity
Pb-Li compatibility
Leak tightness, BOI
Strength, flexure
Young’s modulus
M’, 500°C, BOL
2D SiC/SiC
>~2 W/m-K irradiated
10 – 100 S/m
Good
Good
~200 MPa m
-cracking
200 GPa
~400K
Porous SiC + CVD SiC
Highly tailorable
Highly tailorable
Good
Good
~100 MPa
200 GPa
~200K
M
 
2 s 
PLS

E
1
  
Sharafat
6 Katoh on SiC FCI for Fusion DCLL Blankets

Zinkle, ICFRM-14
DoE funded SBIR with Hyper-Therm HTC examining the feasibility of
SiC/SiC composites for flow channel inserts
Benefits:
SiC/SiC composites produced from near stoichiometric SiC fibers and a CVI SiC matrix have demonstrated excellent stability under neutron radiation similar to monolithic
CVD SiC
SiC/SiC composites possess pseudoplasticity because reinforcing fibers provide a high strain to failure
(compared to monolithic ceramics). An insensitivity of the mechanical properties to temperature also exists
Two properties identified do not meet requirements:
1. Unacceptably high through thickness thermal conductivity (15-
23 W/m/K in 800ºC-ambient prior to irradiation) would result in too high of a heat loss and/or insufficient thermal protection of the ferritic steel flow channel; 2. High interlaminar shear stresses at corners due to through thickness thermal gradient may cause matrix cracking and Pb-Li permeability
Solutions:
1. Architectural construction of the SiC/SiC composite to reduce throughthickness thermal transport
FEA modeling indicates fluted core SiC/SiC can achieve equivalent through thickness thermal conductivity of 1.4 W/m/K
Two fluted core technology demonstrators
2. Eliminate interlaminar shear stresses at corners of FCI insert by using continuous inner electrical
FCI with minimal temperature drop through-thickness
Outer
Thermal
FCI
& outer architechurally designed thermal
FCI composed of
Inner
Electrical
FCI non-rigidly attached corners (Smolentsev and Malang )

Ultramet
– Department of Energy SBIR Phase-II (DE-FG02-05ER84193):
Flow Channel Inserts for Dual-Coolant ITER Test Blanket Modules
Ultramet (Materials and Structures)
B. Williams, M. Wright
Digital Material Solutions (Design and Modeling)
S. Sharafat, A. Aoyama, N. Ghoniem
DOE (COTR)
G. Nardella
Objective: Demonstrate the feasibility of a silicon carbide, open-cell-foam-core flow channel insert that will:
• Provide thermal insulation between high temperature liquid Pb-17Li tritium breeder and structural material
• Provide electrical insulation between the Pb-17Li and structural material to mitigate magneto-hydrodynamic effects
10 mm
•
•
Open-cell SiC Foam SiC Foam/SiC Facesheet SiC Foam/SiC Facesheet FCI Prototype Segment
Results:
Development Specimen (100 x 100 x 300 mm long)
•
•
Comprehensive thermomechanical modeling was performed and correlated with experimentally derived performance.
At 700 o C the composite structure exhibited low thermal (~ 3 to 6 W/m-K) and electrical conductivity (< 0.1 S/m).
• Immersion testing of development specimens in PbLi for
100 hours at 0.7 MPa and 600 °C resulted in no metal ingress.
• FCI prototype segments up to 100 x 100 x 300 mm long were
Electrical Conductivity Thermal Conductivity successfully fabricated along with a segment joint coupling
FCI prototype thermal testing showed a high thermal gradient across the wall at steady-state with 600 °C ID and 453°C OD.
Immersion testing of a FCI prototype in PbLi at 560 °C, at ambient pressure, for 6 hours resulted in no metal ingress.

• Thermal conductivity of 2D SiC/SiC composites falls around 2 - 3
W/m-K (HiNicalon™ Type-S) to 4 - 6 W/m-K (Tyranno™-SA3).
• Thermal conductivity of irradiated SiC/SiC exhibits very weak temperature dependence at T < T
9 Katoh on SiC FCI for Fusion DCLL Blankets irrad

Shinavski
Shinavski
• Recent SBIR effort by Hypertherm HTC demonstrated fabrication and effectiveness of fluted panels for improved insulation.
10 Katoh on SiC FCI for Fusion DCLL Blankets

Temperature [ºC]
800 600 400 200 100
1.E+03
20
1.E+03
*Youngblood/GE
Hi-Nicalon-S/PyC(150nm), In-Plane
1.E+02
Graphite AXQ-1F (x1/1000)
1.E+02
T irr
1.E+01
Hi-Nicalon-S/PyC(ML ~100nm)
1.E+01
Tyranno-SA3/PyC(150nm)
Tyranno-SA3/PyC(50nm)
1.E+00
1.E+00
*Youngblood/GE
Hi-Nicalon-S/PyC(150nm)
Rohm&Haas CVD SiC
High Resistivity Grade
1000 500
Temperature [ºC]
200 100
1.E-01
Hi-Nicalon-S/PyC(ML ~100nm)
1120ºC / 8.1 dpa
20
Hi-Nicalon-S/PyC(ML ~100nm)
800ºC / 1.4 dpa
Unirr.
1.E-01
1.E-02
*Youngblood, 2005, Fusion Materials 37, 3.
1.E-03
1.E-02
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
1000/T[K]
1000/T[K]
• “Intrinsic” electrical conductivity for 2D SiC/SiC appeared to be 2 – 20
S/m through-thickness at RT - 800 °C.
• Neutron irradiation slightly increased electrical conductivity to 10 – 20
S/m.
11 Katoh on SiC FCI for Fusion DCLL Blankets

s
Direction of unperturbed field s
SiC
(T)
1/T s bp

PyC
S/W Nicalon-S ML (~100 nm)
P/W Tyranno-SA3 PyC (~150 nm)
P/W Tyranno-SA3 PyC (~50 nm)
Through-thickness conductivity due to interphase bypass: s bp
   f ia s
PyC
  Efficiency of short-circuit conduction
(related with probability of inter-connection) f ia

1
2 f i
 Volume fraction of interphase which is aligned in favor of conduction s
PyC

Interphase conductivity
In interphase-dominated condition: s tt comp
   s ip comp s tt meas.
[S/m]
5.5
( ± 0.8 for 8 samples)
4.5
2.6
s ip meas.
[S/m]
200 s ip model
[S/m]
T=RT

250 ~2.8%
550 ~0.8%
180 ~1.4%
12 Katoh on SiC FCI for Fusion DCLL Blankets

1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0
Katoh, 2010
Thermal expansion:
~4.5x10
-6
K -1
-1
Price (1969,1974)
Blackstone (1971)
Snead (1998)
Snead (2001)
Thermal Expansion
Saturated swelling:
~8x10 -6 K -1 at ~500ºC
0.18%
0.16%
0.14%
0.12%
0.10%
0.08%
0.06%
0.04%
0.02%
0.00%
200 400 600
Temperature / deg.C
800 1000
0
T
M
= 773K
100
Katoh, 2010
Flexural strain due to differential swelling
Typical cracking strain for SiC
Flexural strain due to instantaneous thermal expansion
200 300 400 500
Temperature Difference [K]
• Thermal stress due to
D
T s th

2


1
E
  
 D
T
• Swelling-induced stress s sw

2

1
E
  

D 
D
T sw
 D
T
• In presence of D T, secondary stress induced by differential swelling is likely more intense than instantaneous thermal stress.
• Understanding irradiation creep may change situation.
13 Katoh on SiC FCI for Fusion DCLL Blankets

• Need to understand whether matrix microcracking relates to failure (= failure criteria)
• The permeation studies to date have been performed on asfabricated specimens
•
If the fully-ceramic structural reliability is challenging, what are mitigation strategies?
300
250
200
150
100
50
0
0
S = 10 MPa, POF = 1E-6
S = 20 MPa, POF = 1E-6
S = 30 MPa, POF = 1E-6
S = 40 MPa, POF = 1E-6
S = 50 MPa, POF = 1E-6
Leak
18J
SA3
Data
18J
HNLS
Data
2
No-Leak
4 6 8
Weibull Modulus
10 12 14
14 Katoh on SiC FCI for Fusion DCLL Blankets

• Expand upon the success of previous SiC foam/SiC facesheet
FCI work and address two primary areas:
– Develop an internal filler material (carbon or oxide aerogel) to allow the
FCI to continue functioning in the event of SiC facesheet damage.
– Continue design optimization and prototype component fabrication such that testing can be performed in a representative, flowing PbLi environment.
Detailed solid model of FCI ( A ) and shell model of facesheet alone ( B )
Cut end view of aerogel-filled SiC foam specimen
(nominally 30 cm long, 6 x 6 cm ID, 8 x 8 cm OD) showing the ID and OD SiC coating and foam internal structure.
15

16

Example of FCI modeling results for first principal stress and strain, and surface temperature.
17

A B
Views of aerogel-filled foam specimens (nominally 30 cm long, 6 x 6 cm
ID, 8 x 8 cm OD) on the reactor coating stand following the first SiC facesheet deposition run.
18

Increased-length Phase II demonstrator, composed of three, nominally 30 cm
FCI sections linked together using CVD SiC-coated graphite couplings.
19

– Insulating properties are adequate for use in DCLL.
– Likely survive
D
T largely exceeding 200K.
– Solid transmutation effects on insulating performances and corrosion resistance
– Note that extent of concern strongly depends on high energy tail of fusion neutron spectra (e.g. FW vs. most other blanket portions)
– Failure criteria and acceptable failure probability need to be established
20 Katoh on SiC FCI for Fusion DCLL Blankets

21 Katoh on SiC FCI for Fusion DCLL Blankets

Shinavski
• Hypertherm HTC developed
PyC/SiCN multilayer interphase replacing PyC/SiC.
• Interphase becomes insulating when Si-N bond dominates.
• Insulating interphase should lower through-thickness composite conductivity below the matrix SiC conductivity.
22 Katoh on SiC FCI for Fusion DCLL Blankets
Shinavski

Katoh, submitted
Intermittent cooling
T
M
=773K
D
T=400K
T
M
=773K
D
T=200K
B
0
= 3E-7 dpa -1 MPa -1
Typical cracking limit
• Swelling-coupled creep was found for SiC
  tr

D tr s
E n
L
0 n = 1
D tr
~42 at 300ºC
~66 at 500ºC
~120 at 800ºC
23 Katoh on SiC FCI for Fusion DCLL Blankets
• Largest magnitude of secondary stress is anticipated upon cooling after swelling saturation is reached.
• DT = 300K will be close to the cracking limit for SiC.

Zinkle, ICFRM-14
Objective, using silicon carbide, open-cellfoam-core develop FCI prototype that:
• Provides thermal insulation between high temperature liquid Pb-17Li tritium breeder and structural material
• Provides electrical insulation between Pb-17Li and structural material to mitigate MHD effects
Results:
• Comprehensive thermomechanical modeling was performed and correlated with experimentally derived performance.
• At 700 o C the composite structure exhibited low thermal (~ 3 to
6 W/m-K) and electrical conductivity (< 0.1 S/m).
• Immersion testing of development specimens in PbLi for
100 hours at 0.7 MPa and 600ºC resulted in no metal ingress.
• FCI prototype segments up to 100 x 100 x 300 mm long were successfully fabricated along with a segment joint coupling
• FCI prototype thermal testing showed a high thermal gradient across the wall at steadystate with 600ºC ID and 453°C OD.
• Immersion testing of a FCI prototype in PbLi at 560°C, at ambient pressure, for 6 hours resulted in no metal ingress.
Electrical Conductivity
Thermal Conductivity
SiC Foam/SiC Facesheet
FCI Prototype Segment
(100 x 100 x 300 mm long)
24

Program Team
Ultramet:
Brian Williams (PI), Jim Selin
Digital Materials Solutions:
Shahram Sharafat, Nasr Ghoniem, Aaron Aoyama
UCLA:
Sergey Smolentsev, Tomas Sketchley, Neil Morley
DOE Technical Monitor:
Barry Sullivan

The program was clearly successful in continuing to establish the feasibility of Ultramet ’ s SiC foam-based FCI for use as electrical/thermal insulation in DCLL blankets.
• High electrical/thermal insulation performance was demonstrated using development specimens and 30 cm long SiC foam/SiC facesheet components filled with vitreous carbon and silica aerogels to enhance insulation behavior were successfully fabricated.
• For the first time, a component was tested for electrical insulating performance in flowing
PbLi for one month, and components were tested in static PbLi at both high pressure and temperature.
•
Although dynamic testing of a 30cm FCI segment in flowing PbLi performed using the magnetohydrodynamic PbLi loop MaPLE at UCLA was shown to be highly complex in terms of the test procedure and data interpretation, the results were very promising.
• Monitoring of the temperature and flowrate in the loop for 30 days did not reveal any significant changes that would indicate metal ingress and deterioration of the FCI electroinsulating properties, and analysis of the MHD pressure drop indicated that the
FCI performed as required, reducing the MHD pressure drop in the PbLi flow to a level that matched 3D theoretical predictions. Extrapolation of these results to actual blanket conditions, suggested a pressure drop reduction factor in the range of 50-100.
26 Katoh on SiC FCI for Fusion DCLL Blankets

• Thermochemical and thermomechanical survivability of FCI segments under worstcase-scenario conditions was performed at UCLA in static PbLi at high pressure
(1MPa) as well as high temperature (700˚C) for 100 hours.
• The test proved to be very demanding because specimens were subjected to a sudden initial temperature change from room temperature to 400˚C (submersion of ambient temperature FCI into 400˚C PbLi). An FCI segment would not encounter this thermal shock in actual use. However, the testing provided useful information under off-normal conditions for specimens with differing aerogel filler materials, with and without dense SiC facesheets.
• One specimen exhibited no metal ingress wheras other specimens exhibited varying degrees of ingress (no specimen exhibited full ingress). It is speculated that ingress in some areas may be caused by mechanical failure of the aerogel
(exposed to high pressure), rather than chemical reactivity with the PbLi, and that use of higher density aerogels may reduce or eliminate metal ingress in all areas as long as thermal/electrical conductivity remains within requirements.
• Based on these results, UCLA recommends continued development, testing, and analysis of the SiC foam-based FCI for use as electrical insulation in DCLL blankets.
Although significant progress has been made, additional FCI materials/processing development and testing is clearly required to optimize performance of this critical component.
27 Katoh on SiC FCI for Fusion DCLL Blankets