Use of Tungsten Material for the ITER Divertor
T. Hirai
1, S. Panayotis
1, V. Barabash
1, C. Amzallag
2, F. Escourbiac
1, A. Durocher
1, M. Merola
1, J. Linke
3, Th. Loewenhoff
3, G. Pintsuk
3,
M. Wirtz
3, I. Uytdenhouwen
41 ITER Organization, Route de Vinon sur Verdon, F-13067 Saint Paul lez Durance, France 2 Claude Amzallag Materials expert, 42100 Saint-Etienne, France
3 Forschungszentrum Jülich, 52425 Jülich, Germany
4 The Belgian Nuclear Research Centre, Boeretang 200, 2400 Mol, Belgium,
Disclaimer: The views and opinions expressed herein do not necessarily reflect those of the ITER Organization
Contents
1. Introduction - ITER W Divertor Design and Extended Requirements 2. Technology R&D - High Heat Flux Test Results
3. W Monoblock under Thermal Loads - Finite Element 4. Characterization of W Monoblock Materials
5. Summary
ITER Divertor
• To absorb radiation and particle heat fluxes from the plasma while allowing neutral particles to be exhausted to the Vacuum System
• To minimize the influx of impurities to the plasma
• To provide shielding to reduce heat and neutron loads in the vacuum vessel and ex-vessel components
• To house diagnostics
One of 54 divertor cassettes
8.5 ton/cassette (W: 10 % of mass)
Change from CFC to W Divertor and Extended Requirements
W armour divertor (W divertor) was implemented in the baseline since end of 2013
Extended Requirements:
Increase of design heat load 10 MW/m2 to 20 MW/m2 at W monoblock surface Leading-edge protection by design;
Higher performance armour-heat sink joints;
Higher operation temperature at W surface
Design cycle numbers of stationary loads at W monoblock surface 5000 cycles at 10 MW/m2 and 300 cycles at 20 MW/m2
DT operation
DT operation with 1st W divertor (max 0.1 dpa in W)
W Divertor Design – Protect Leading Edge
Optimize tilting of Vertical Targets and Dome to protect inter-cassette leading edges
Individual monoblock shaping in high heat flux areas to protect leading edges
Outer baffle shaping to mitigate W melting at downward VDE impact Strategy: minimum changes compared
with the CFC divertor
~28 mm
Chamfer depth 0.5 mm
Qperp
~ 3o
Ref. T. Hirai et al Fus. Eng. Design 88 (2013) 1798–801 ; S. Carpentier-Chouchana et al Phys. Scr. T159 (2014) 014002. M. Merola, et al., SOFT2014, M. Merola, ISFNT2013.
Neutronics Confirmed W Divertor Design
Neutronic analysis confirmed W divertor design met requirements of neutronic response (1st set divertor exposed to 18% of ITER machine end-of-life fluence)
1. Nuclear heating: Higher component temperatures due to additional heat Included in thermo-mechanical analysis
2. Radiation damage: Degradation of thermo-mechanical properties Acceptable in this low dpa range for all materials
3. He production: critical in re-welding of pipes
No issue (<1appm for divertor radial pipe)
4. Activation: concern of contact dose, radwaste, activated corrosion products:
Updated material specifications for all materials
Updated impurity contents in material specifications, e.g. 316L(N)-IG
Ref.: R. Villari, et al., Fus. Eng. Design 88 (2013) 1798–801.
W monoblock Technology R&D Requirements
~2 m
Full-scale OVT and IVT PFU
(1) Technology Development and Validation
: Demonstration of fitness-for- purpose of proposed technology by small-scale mock-ups manufacturing and demonstration of its High Heat Flux (HHF) performance(2) Full-scale demonstration
: Demonstration of full-scale-prototype manufacturing in compliance with ITER procurement quality requirements and demonstration of its HHF performanceHHF tests for small-scale and full-scale PFU straight part
• 5000 cycles at 10 MW/m2 (10s/10s)
• 300 cycles at 20 MW/m2 (10s/10s)
~ 62 (or 87) mm for 5 (or 7) monoblocks
Ref.: T. Hirai, et al., Phys. Scr. T159 (2014) 014006.
12
28
Contents
1. Introduction - ITER W Divertor Design and Extended Requirements 2. Technology R&D - High Heat Flux Test Results
3. W Monoblock under Thermal Load - Finite Element 4. Characterization of W Monoblock Materials
5. Summary
W monoblock - Heat Flux Test Results
5000 cycles at 10 MW/m2 and 300 cycles at 20 MW/m2 (EU mockups tested at the electron beam facility FE200)
Ref.: T. Hirai, et al., J. Nucl. Mater. 463 (2015) 1248–1251.; G.Pintsuk, et al., Fusion Eng Des 88 (2013) 1858.; G.Pintsuk, et al., SOFT2014;
Water flow
Cross section WMMU 15-15
Macro-crack (self-castellation) appeared at the middle Macro-crack started from top surface and often reached
at Cu interlayer
L o a d e d a re a
A06 A05
28 6
Water flow
W monoblock - Heat Flux Test Results EU mock-ups
9 EU small-scale mock-ups (test at IDTF) macro-cracks
5000 cycles at 10MW/m2 + 75 cycles at 20 MW/m2
8 EU small-scale mock-ups (test at FE200) macro-cracks and surface modification
5000 cycles at 10 MW/m2 + 300 cycles at 20 MW/m2 P13
P10
A06
A05
W monoblock technology for 20MW/m
2loads is available in EU-DA
Ref.: T. Hirai, et al., J. Nucl.
Mater. 463 (2015) 1248–1251.
Water flow Water flow
Water flow
Water flow
W monoblock - Heat Flux Test Results JA mock-ups
6 JA small-scale mock-ups (test at IDTF) no macro-cracks and surface modification
W monoblock technology for 20MW/m
2loads is available in JA-DA
MAL1 MAL2 KMM2
KMM1 KAL KAT
5000 cycles at 10 MW/m2 + 300 cycles at 20 MW/m2
Water flow
Ref.: T. Hirai, et al., Phys. Scr. T159 (2014) 014006. ; T. Hirai, et al., J. Nucl. Mater. 463 (2015) 1248–1251.
4 JA full-scale prototype PFUs (test at IDTF) no macro-cracks and surface modification
KAL1 KTL3 KAT2
KAT4
Water flow
10 MW/m2 5000 cycles and 20MW/m2 300 cycles (required) + 700 (additional) cycles
Water flow
W Monoblock Surface Temperature vs Heat Flux
Tsurf measurement during JA full-scale prototype PFUs at electron beam facility IDTF
Measurements (two-color pyrometer)
Heat Flux Test Result Summary
Macro-cracks Macroscopic behavior
Not observed after 5000 cycles at 10 MW/m2 nor 1000 cycles at 15 MW/m2 test*
Observed typically after thermal cycles at 20 MW/m2 test
Not observed after 1000 cycles at 20 MW/m2 from JA suppliers with W plate materials
Macro-cracks started from loaded (hot) surfaces and showed ductile fracture surfaces around initiation site and brittle surfaces close to cooling pipe
Surface modification (roughening; local melting) microscopic
Observed at 20 MW/m2; not observed at 10 and 15 MW/m2
aT. Hirai, et al., Journal of Nuclear Materials 463 (2015) 1248–1251. bG. Pintsuk et al., Fusion Eng. Des. 88 (2013) 1858 ; cG. Pintsuk et al., presented at SOFT, 2014, San Sebastian Spain ; dK. Ezato et al., presented at SOFT, 2014, San Sebastian Spain ; e S. Suzuki et al., presented at ISFNT-11 2013, Barcelona Spain ; f P. Gavila et al. presented at SOFT, 2014, San Sebastian Spain ; gP. Lorenzetto et al 2012 Technology R&D activities for the ITER full-tungsten divertor 24th IAEA Fusion Energy Conf. (San Diego, USA, Oct. 8–13 2012).
Different performance of W materials in thermal cycling at 20 MW/m2
* For mock-ups using W-plate materials
W Materials in HHF-Tested mockups
W materials in accordance with ITER Material Specification for W (based on ASTM B760)
Minimum W content: 99.94 wt% : accepted – similar for all W monoblock
Maximum impurity content (C, O, N, Fe, Ni, Si): 0.01 wt% : accepted - similar Density (ASTM B311): ≥ 19.0 g/cm3 : accepted - similar for all W monoblock Hardness HV30 (ASTM E92): ≥ 410 : accepted - similar for all W monoblock Grain size (ASTM E112): grain size number 3 or finer at perpendicular to
deformation direction : accepted – different
Microstructure (grain orientation/size) : accepted – different
Different production routes different microstructures different mechanical properties (depending on material and orientation)
Difference due to production routes e.g. W powder size, deformation process (forging and rolling), deformation rate and temperature, …
Rolled plate Forged
bar
Note: “ITER-grade W” does not exist.
Macro-crack appearance at W Monoblock
DBTT
Re-crystallization Creep
Temp [oC]
Melting point
Macro-cracks due to cyclic exposure to high temperature, which causes fatigue, creep damage, progressive plastic deformation, recrystallization
Coolant temp.
70-120oC
…
20 MW/m2
Crossing DBTT; exposure to high temp (well above re-crystallization)
300 cycles
Frequent macro-cracks
……
15 MW/m2 10 MW/m2
Crossing DBTT; without exposure to high temp (below re-crystallization)
Crossing DBTT; without remarkable exposure to high temp (up to re-crystallization)
1000 cycles
5000 cycles No macro-cracks
No macro-cracks*
* For mock-ups using W-plate materials
Contents
1. Introduction - ITER W Divertor Design and Extended Requirements 2. Technology R&D - High Heat Flux Test Results
3. W Monoblock under Thermal Load - Finite Element 4. Characterization of W Monoblock Materials
5. Summary
Thermo-Mechanical Analysis: Assumptions
Objectives: to understand stress-strain in W monoblock related to macro-crack appearance
Model: 3D Elasto-plastic model
Material Properties of W, CuCrZr-IG, OFCu: temperature dependent, elastoplastic behavior (SDC-IC Appendix A)
Geometry: rectangular shape 28 x 28 x 12 mm3 with OFCu interlayer (OD/ID=17/15), CuCrZr-IG pipe (OD/ID=15/12), armour thickness 6 mm
Boundary Conditions: mechanical constraint at bottom surface; radiation at 200oC Coolant parameters: Tcoolant = 100oC, heat transfer coefficient for pipe with swirl tape 100 kW/K.m2
12 28
28
x y z
[mm3]
Armour thickness
FE Analysis: Temperature and Stress Distribution
Stress in y-direction (σσσσ
y-direction) is dominant at loaded surface
Max σ
y-direction at the middle Stresses vary in time
Note: Joint shall be validated by design-by-experiment.
Stresses around joint are indicative. Stresses at loaded W surface are in-sensitive to joint area.
σ σσ
σy-direction at 20s σ
σσ
σy-direction at 10s 20 MW/m2 at 10s
6 mm Rect
[MPa]
[MPa]
[oC]
T_surf[o C]
0s
10s 20s
6
Mechanical Properties of W Materials
Mechanical properties, e.g. yield strength (YS) and tensile strength (UTS), ductility, depend on temperature
Ref. ITER Material Property Handbook Ref 1: Southern research report W, 1966
Ref 2: Kotelknikov A.M., Osobotuqoplavkie
Elementy I soedinenia 1969 Ref 3: Anon. USAF ASD- TDR-63-585 report, 1963 Ref 4: Rabenstaine A.S., Marquardt corporation AF report 1962
Ref 5: Kharchenko V.K., IPP info letter 1971
To include temperature variation, thermal stress normalized by temperature dependent material properties
Plate t= 12 mm
Bar □ 36x36mm2x L New data
Plate t= 12 mm
FE Analysis: Time Evolution of T surf and σ σ σ σ
y-direction
σy-direction :
compressive stress in heating phase and tensile stress after heating
20 MW/m2
σσσσy-direction[MPa]σσσσy-direction/ YS
Time [s]
Stress/ YS > 1 Stress/ YS > 1
2ndcycle
Creep & recrystallization range
20 MW/m2: 6 mm : Rect
σy-direction normalized by
temperature-dependent-yield strength (YS) indicate plastic deformation in the heating phase
Fatigue involving plastic strain
Remark: rectangular waveform is more conservative than foreseen plasma loads in terms of thermal stress.
Tsurf above 1500oC after 2 s at 20 MW/m2 (rectangular wave form)
6
Thermal Fatigue of W monoblock
Fatigue hysteresis of W monoblock surface in “Stress vs strain” domain: negative strain range
Total strain is stabilized after limited cycles – no remarkable progressive plastic deformation
20 MW/m2: 6 mm : Rect
1st cycle 2nd cycle 3rd-4thcycle
Plastic stress-strain range at high temperature
Elastic stress-strain range at low Temperature
T_surf[o C]
0s 10s 20s
σ σσ
σy-direction
at middle of loaded surface [MPa]
Total strain
at middle of loaded surface [mm/mm]
W monoblock thermal fatigue: fatigue including plastic strain (low cycle fatigue) at total strain range ~0.3 % at ~1800 oC
~0.3 %
6
Fatigue: General Description
Ref. S.S. Manson, Exp. Mech. 5 (1965) 193–226. ; Ph. Mertens, et al., Journal of Nuclear Materials 438 (2013) S401–S405.
Applicability of universal slope for W materials at high temperature to be confirmed Note: The universal slope was obtained from 29 materials at Troom
Log (cycle number)
Log (strain range)
Low cycle fatigue - Plastic strain range
∆εp = B·Nf-b (Manson-Coffin law)
High cycle fatigue - Elastic strain range
∆εe = A·Nf-b (Basquin law)
Mechanical Fatigue Test : Strain vs cycle number at constant temperature
∆ = .
. + .
Method of universal slope:
correlation tensile properties and fatigue
High ductility is advantageous
D: ductility
E: elastic modulus σu: UTS
Fatigue: Available Data W materials
Universal slope does NOT fit perfectly but fits better by adjusting coefficients
Ref. R.E. Schmunk, et al., JNM 122&123 (1984) 850-854.
Test at 1232oC
recrystallized W (13 mm thick plate)
Total strain, ∆ε t
Cycle, Nf
Fatigue data of W material at high temperature are demanded Due to inappropriate coefficients and/or exponents?
Due to lack of database?
∆ = 3.5
. + .!.!
∆ = ∙ 3.5
. + $. ∙ % .!.!
Creep: General Description
Creep: material resistance under constant stress and at constant temperature
Ref. Norman E. Dowling, ‘’Mechanical behavior of materials: engineering methods for deformation, fracture and fatigue’‘ 1993 Prentice-Hall, Inc.
Stress vs rupture time (tr) Stress vs strain rate
tr, Time to rupture, [h]
εsc, true strain rate [1/h]
σ, true stress [MPa] σ, stress [MPa]
A201 Steel
S-590 Alloy
Creep: Available Data for W materials
T.E. Tietz and J. W. Wilson, “Behavior and properties of refractory metals” Standord University Press 1965; M. Rieth, Nr1951 FZK IMF-I report (2005).
PL-M = T (log tr + C)
(C = 13~15 for W)
Creep “stress-rupture curves” are summarized by Larson-Miller parameter (PL-M) PL-M correlates T with the time-to-rupture (tr) at constant stress (σ) tool to predict rupture time
PL-M x 10-3
Stress [MPa]
Green;
>2000oC; rod Sell; 1480oC &
1650oC; rod
Rieth; 1100oC &
1300oC; ø 10 mm rod
Pugh; 870oC-1200oC;
ø 8.8 mm rod
Fairly well-aligned
Pure W creep performance is predictable with certain accuracy Small difference between W materials
Note: recrystallization results in negligible difference between W products
Creep data of W monoblock materials are demanded. PL-M plot for these materials to be confirmed
Cyclic thermal load at high temperature: fatigue damage, creep damage and material property degradation due to recrystallization
Key Parameters for W Monoblock
Non-linear rule for accurate prediction could be applied if database are available
Interaction between creep and fatigue: “Damage factor” method (ref. SDC-IC and RCC-MR)
Creep life time [h]
Fatigue life time [cycles]
For longer fatigue life time, select W with higher ductility at high temperature (better performance in low-cycle-fatigue)
For longer creep life time, select W with higher creep performance
Material properties, select W with higher mechanical properties at high temperature and higher recrystallization resistance
For precise understanding on macro-crack appearance (initiation), fatigue, creep and tensile properties and recrystallization resistance of W monoblock materials are demanded.
Contents
1. Introduction - ITER W Divertor Design and Extended Requirements 2. Technology R&D - High Heat Flux Test Results
3. W Monoblock under Thermal Load - Finite Element 4. Characterization of W Monoblock Materials
5. Summary
Characterization of W monoblock Property
Fatigue, creep and tensile properties and recrystallization resistance of W monoblock materials are demanded.
IO launched activity to characterize W monoblock materials selected for mock-ups tested under HHF tests
Objectives
- To understand macro-crack initiation and its correlation to properties of W monoblock materials
- For possible additional acceptance criteria on tensile properties in W material specification
Tensile test at elevated temperature (800-2000oC) to examine difference between W monoblock materials
Fatigue test to examine/ confirm coefficients and exponents of universal slopes (fatigue law), especially low cycle fatigue regime at high temperature
Creep test at elevated temperature (1400-2000oC) to examine/ confirm
applicability of creep database (Larson Miller plot) for W monoblock materials Recrystallization sensitivity test, annealing test 1300oC, 1500oC and 1800oC.
W samples for Tensile Tests
W monoblock materials that were selected for mock-ups HHF-tested
Square cross section sample (x- and y- direction)
To be completed by first half of 2016
• Tensile properties at 800oC;
• Tensile properties at 1400-2000oC;
• Creep and low cycle fatigue test;
• Recrystallization sensitivity test
W products HHF tested as EU mock-up EU mock-up JA mock-up JA mock-up JA mock-up
samples in X direction
samples in Y direction Block size
Received Material
28 + 4 calib.
Contents
1. Introduction - ITER W Divertor Design and Extended Requirements 2. Technology R&D - High Heat Flux Test Results
3. W Monoblock under Thermal Load - Finite Element 4. Characterization of W Monoblock Materials
5. Summary
Summary
W divertor in baseline since 2013. This resulted in extended requirements, e.g.
10 MW/m2 to 20 MW/m2.
Qualified armour-heat sink joining technologies are available for ITER divertor application.
Higher performance for low cycle fatigue (high ductility) and creep resistance at high temperature, higher resistance for recrystallization are preferable.
Mechanical properties data, i.e. fatigue, creep and tensile at higher temperature are demanded for divertor application.
W monoblocks tested at 20 MW/m2 showed non-systematic appearance of macro-cracks, which do not appear to have had an impact on the heat removal performance.
Macro-cracks due to exposure to high temperature. Finite element analysis
indicated high compressive stress (>yield strength) in heating phase. Exposure to high temperature could cause thermal fatigue, creep damage, degradation due to recrystallization.
Characterization of W monoblock: (1) to understand macro-crack appearance and its correlation to W properties; and (2) for possible addition of acceptance criteria in W material specification, i.e. tensile properties, is in progress.
