Use of Tungsten Material for the ITER Divertor

Transcription

1 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 4 1 ITER Organization, Route de Vinon sur Verdon, F Saint Paul lez Durance, France 2 Claude Amzallag Materials expert, Saint-Etienne, France 3 Forschungszentrum Jülich, 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 Slide 1

2 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 Slide 2

3 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) Slide 3

4 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/m 2 to 20 MW/m 2 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/m 2 and 300 cycles at 20 MW/m 2 DT operation DT operation with 1 st W divertor (max 0.1 dpa in W) Slide 4

5 W Divertor Design Protect Leading Edge Strategy: minimum changes compared with the CFC divertor Optimize tilting of Vertical Targets and Dome to protect inter-cassette leading edges Outer baffle shaping to mitigate W melting at downward VDE impact Chamfer depth 0.5 mm ~ 3 o Q perp Individual monoblock shaping in high heat flux areas to protect leading edges ~28 mm Ref. T. Hirai et al Fus. Eng. Design 88 (2013) ; S. Carpentier-Chouchana et al Phys. Scr. T159 (2014) M. Merola, et al., SOFT2014, M. Merola, ISFNT2013. Slide 5

6 Neutronics Confirmed W Divertor Design Neutronic analysis confirmed W divertor design met requirements of neutronic response (1 st 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 Ref.: R. Villari, et al., Fus. Eng. Design 88 (2013) Updated impurity contents in material specifications, e.g. 316L(N)-IG Slide 6

7 W monoblock Technology R&D Requirements (1)Technology Development and Validation: Demonstration of fitness-forpurpose 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 performance HHF tests for small-scale and full-scale PFU straight part 5000 cycles at 10 MW/m 2 (10s/10s) 300 cycles at 20 MW/m 2 (10s/10s) ~ 62 (or 87) mm for 5 (or 7) monoblocks ~2 m Full-scale OVT and IVT PFU Ref.: T. Hirai, et al., Phys. Scr. T159 (2014) Slide 7

8 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 Slide 8

9 W monoblock - Heat Flux Test Results 5000 cycles at 10 MW/m 2 and 300 cycles at 20 MW/m 2 (EU mockups tested at the electron beam facility FE200) Water flow Macro-crack (self-castellation) appeared at the middle Macro-crack started from top surface and often reached at Cu interlayer Water flow A06 Cross section WMMU A05 6 Loaded area Ref.: T. Hirai, et al., J. Nucl. Mater. 463 (2015) ; G.Pintsuk, et al., Fusion Eng Des 88 (2013) 1858.; G.Pintsuk, et al., SOFT2014; Slide 9

10 W monoblock - Heat Flux Test Results EU mock-ups W monoblock technology for 20MW/m 2 loads is available in EU-DA 9 EU small-scale mock-ups (test at IDTF) macro-cracks Water flow Water flow 5000 cycles at 10MW/m cycles at 20 MW/m 2 8 EU small-scale mock-ups (test at FE200) macro-cracks and surface modification P13 A06 P10 A05 Water flow Water flow 5000 cycles at 10 MW/m cycles at 20 MW/m 2 Ref.: T. Hirai, et al., J. Nucl. Mater. 463 (2015) Slide 10

11 W monoblock - Heat Flux Test Results JA mock-ups W monoblock technology for 20MW/m 2 loads is available in JA-DA 6 JA small-scale mock-ups (test at IDTF) no macro-cracks and surface modification KMM1 KAL KAT MAL1 MAL2 KMM2 Water flow Water flow 5000 cycles at 10 MW/m cycles at 20 MW/m 2 KAT4 KTL3 KAT2 KAL1 4 JA full-scale prototype PFUs (test at IDTF) no macro-cracks and surface modification Water flow Ref.: T. Hirai, et al., Phys. Scr. T159 (2014) ; T. Hirai, et al., J. Nucl. Mater. 463 (2015) MW/m cycles and 20MW/m cycles (required) (additional) cycles Slide 11

12 W Monoblock Surface Temperature vs Heat Flux T surf measurement during JA full-scale prototype PFUs at electron beam facility IDTF Measurements (two-color pyrometer) Slide 12

13 Heat Flux Test Result Summary Macro-cracks Macroscopic behavior Not observed after 5000 cycles at 10 MW/m 2 nor 1000 cycles at 15 MW/m 2 test* Observed typically after thermal cycles at 20 MW/m 2 test Not observed after 1000 cycles at 20 MW/m 2 from JA suppliers with W plate materials Different performance of W materials in thermal cycling at 20 MW/m 2 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/m 2 ; not observed at 10 and 15 MW/m 2 * For mock-ups using W-plate materials a T. Hirai, et al., Journal of Nuclear Materials 463 (2015) b G. Pintsuk et al., Fusion Eng. Des. 88 (2013) 1858 ; c G. Pintsuk et al., presented at SOFT, 2014, San Sebastian Spain ; d K. Ezato et al., presented at SOFT, 2014, San Sebastian Spain ; e S. Suzuki et al., presented at ISFNT , Barcelona Spain ; f P. Gavila et al. presented at SOFT, 2014, San Sebastian Spain ; g P. Lorenzetto et al 2012 Technology R&D activities for the ITER full-tungsten divertor 24th IAEA Fusion Energy Conf. (San Diego, USA, Oct ). Slide 13

14 W Materials in HHF-Tested mockups W materials in accordance with ITER Material Specification for W (based on ASTM B760) Minimum W content: 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/cm 3 : 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 Difference due to production routes e.g. W powder size, deformation process (forging and rolling), deformation rate and temperature, Different production routes different microstructures different mechanical properties (depending on material and orientation) Note: ITER-grade W does not exist. Forged bar Rolled plate Slide 14

15 Macro-crack appearance at W Monoblock Coolant temp o C DBTT Creep Re-crystallization Temp [ o C] 10 MW/m 2 Melting point 15 MW/m 2 20 MW/m cycles No macro-cracks Crossing DBTT; without exposure to high temp (below re-crystallization) 1000 cycles Crossing DBTT; without remarkable exposure to high temp (up to re-crystallization) Crossing DBTT; exposure to high temp (well above re-crystallization) Frequent macro-cracks 300 cycles No macro-cracks* * For mock-ups using W-plate materials Macro-cracks due to cyclic exposure to high temperature, which causes fatigue, creep damage, progressive plastic deformation, recrystallization Slide 15

16 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 Slide 16

17 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 mm 3 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 200 o C Coolant parameters: T coolant = 100 o C, heat transfer coefficient for pipe with swirl tape 100 kw/k.m 2 x z y Armour thickness 12 [mm 3 ] Slide 17

18 FE Analysis: Temperature and Stress Distribution 20 MW/m 2 at 10s [ o C] σ y-direction at 10s [MPa] 6 mm Rect Stress in y-direction (σ 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. T_surf [ o C] 0s 6 10s 20s σ y-direction at 20s [MPa] Slide 18

19 Mechanical Properties of W Materials Mechanical properties, e.g. yield strength (YS) and tensile strength (UTS), ductility, depend on temperature Plate t= 12 mm Bar 36x36mm 2 x L Plate t= 12 mm New data 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 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 Slide 19

20 FE Analysis: Time Evolution of T surf and σ y-direction 2 nd cycle Creep & recrystallization range T surf above 1500 o C after 2 s at 20 MW/m 2 (rectangular wave form) σ y-direction [MPa] 20 MW/m MW/m 2 : 6 mm : Rect Remark: rectangular waveform is more conservative than foreseen plasma loads in terms of thermal stress. σ y-direction : compressive stress in heating phase and tensile stress after heating σ y-direction / YS Stress/ YS > 1 Stress/ YS > 1 σ y-direction normalized by temperature-dependent-yield strength (YS) indicate plastic deformation in the heating phase Fatigue involving plastic strain Time [s] Slide 20

21 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 Elastic stress-strain range at low Temperature σ y-direction at middle of loaded surface [MPa] 6 T_surf [ o C] 0s 10s 20s 3 rd -4 th cycle 2 nd cycle 1 st cycle Total strain at middle of loaded surface [mm/mm] Plastic stress-strain range at high temperature ~0.3 % 20 MW/m 2 : 6 mm : Rect W monoblock thermal fatigue: fatigue including plastic strain (low cycle fatigue) at total strain range ~0.3 % at ~1800 o C Slide 21

22 Fatigue: General Description Mechanical Fatigue Test : Strain vs cycle number at constant temperature Log (strain range) Low cycle fatigue - Plastic strain range ε p = B N f -b (Manson-Coffin law) =.. +. Method of universal slope: correlation tensile properties and fatigue High ductility is advantageous D: ductility E: elastic modulus σ u : UTS High cycle fatigue - Elastic strain range ε e = A N f -b (Basquin law) Log (cycle number) Note: The universal slope was obtained from 29 materials at T room Applicability of universal slope for W materials at high temperature to be confirmed Ref. S.S. Manson, Exp. Mech. 5 (1965) ; Ph. Mertens, et al., Journal of Nuclear Materials 438 (2013) S401 S405. Slide 22

23 Fatigue: Available Data W materials Universal slope does NOT fit perfectly but fits better by adjusting coefficients Test at 1232 o C recrystallized W (13 mm thick plate) Total strain, ε t = = Ref. R.E. Schmunk, et al., JNM 122&123 (1984) Cycle, N f Due to inappropriate coefficients and/or exponents? Due to lack of database? Fatigue data of W material at high temperature are demanded Slide 23

24 Creep: General Description Creep: material resistance under constant stress and at constant temperature Stress vs strain rate Stress vs rupture time (t r ) σ, true stress [MPa] A201 Steel σ, stress [MPa] S-590 Alloy ε sc, true strain rate [1/h] t r, Time to rupture, [h] Ref. Norman E. Dowling, Mechanical behavior of materials: engineering methods for deformation, fracture and fatigue 1993 Prentice-Hall, Inc. Slide 24

25 Creep: Available Data for W materials Creep stress-rupture curves are summarized by Larson-Miller parameter (P L-M ) P L-M correlates T with the time-to-rupture (t r ) at constant stress (σ) tool to predict rupture time P L-M = T (log t r + C) (C = 13~15 for W) 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 Stress [MPa] Pugh; 870 o C-1200 o C; ø 8.8 mm rod Rieth; 1100 o C & 1300 o C; ø 10 mm rod Sell; 1480 o C & 1650 o C; rod P L-M x 10-3 Green; >2000 o C; rod Creep data of W monoblock materials are demanded. P L-M plot for these materials to be confirmed 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). Slide 25

26 Key Parameters for W Monoblock Cyclic thermal load at high temperature: fatigue damage, creep damage and material property degradation due to recrystallization Interaction between creep and fatigue: Damage factor method (ref. SDC-IC and RCC-MR) Fatigue life time [cycles] Creep life time [h] Non-linear rule for accurate prediction could be applied if database are available 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. Slide 26

27 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 Slide 27

28 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 ( o C) 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 ( o C) to examine/ confirm applicability of creep database (Larson Miller plot) for W monoblock materials Recrystallization sensitivity test, annealing test 1300 o C, 1500 o C and 1800 o C. Slide 28

29 W samples for Tensile Tests W monoblock materials that were selected for mock-ups HHF-tested W products HHF tested as EU mock-up EU mock-up JA mock-up JA mock-up JA mock-up Received Material Block size samples in X direction samples in Y direction calib. Square cross section sample (x- and y- direction) Tensile properties at 800 o C; Tensile properties at o C; Creep and low cycle fatigue test; Recrystallization sensitivity test To be completed by first half of 2016 Slide 29

30 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 Slide 30

31 Summary W divertor in baseline since This resulted in extended requirements, e.g. 10 MW/m 2 to 20 MW/m 2. Qualified armour-heat sink joining technologies are available for ITER divertor application. W monoblocks tested at 20 MW/m 2 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. 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. 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. Slide 31