Critical issues & challenges in the engineering of DEMO divertor - PowerPoint PPT Presentation

Critical issues & challenges in the engineering of DEMO divertor target J.-H. You, E. Visca, Ch. Bachmann, & EUROfusion Divertor Project Team J.-H. YOU et al. | IAEA Divertor Workshop | 29 Sep. – 2 Oct. 2015 |

DEMO divertor in EUROfusion Vertical target (ITER) Technical boundary conditions (DEMO) Power to exhaust: 259 MW in total Power deposited in PFU: 112 MW Particle flux: ~10 24 /m² ∙ s Heat flux stationary: max. 10MW/m² transient: max. 20 MW/m² neutron irradiation W: 3 dpa/fpy, Cu: 6 ‐ 10 dpa?/fpy Plasma ‐ facing unit (ITER) Number of pulses stationary: 5000 cycles? armor transient: 300 cycles? Replacement period: 2 fpy heat sink Plansee

EUROfusion work package ‘Divertor’ Missions  assure the envisaged power exhaust goal for DEMO  deliver holistic design concept for the DEMO divertor  develop feasible technology for high performance target (NB. irradiation) Approaches  water ‐ cooling for the early DEMO, helium ‐ cooling as long ‐ term option  reliable cooling capability as paramount requirement (also for slow transient)  advanced novel Target design concepts vs. baseline model (ITER ‐ like)  design study as well as technology development incl. HHF tests  dedicated (structural) design rules tailored for the joined PFCs

Design rationale: cooling condition Estimated cooling capability of Target 60 ‐ max. surface heat flux: 20 MW/m² ‐ heat flux peaking factor: ~1.6 50 Critical heat flux (MW/m²) ‐ envisaged margin to the CHF: ~1.5 ‐ local critical heat flux: ~48 MW/m² 40 30 ‐ tube diameter: 12 mm 150 °C 20 160 °C ‐ pressure: 5 MPa Pressure: 5 MPa 180 °C 10 Tube diameter: 12 mm 200 °C ‐ temperature: 150 °C Swirl (Tong ‐ 75) 220 °C ‐ velocity: 16 m/s 0 10 12 14 16 18 20 Water velocity (m/s) You, Fus. Eng. Des (submitted)

Target heat sink: performance of irradiated CuCrZr alloy Design stress limits over temperature local fracture due to S d exhausted ductility S e plastic flow localisation 3S m ratchetting Allowable operation temp. range according to elastic design rules: 250 °C – 300 °C  Impracticable for DEMO divertor ITER SDC ‐ IC Annex A You, Nucl. Fusion (2015)

Target heat sink: performance of CuCrZr tube Predicted temperature profiles in the cooling tube (coolant: 150 °C) 10 MW/m² 15 MW/m² 18 MW/m² Max. temp. at top 263 °C 316 °C 348 °C Mid ‐ temp. at side 172 °C 181 °C 187 °C Min. temp. at bottom 150 °C 150 °C 150 °C max ° C Critical material issues for the heat sink mid irradiation creep  high ‐ temperature strength neutron embrittlement  toughness/non ‐ ductile structural design You, Nucl. Fusion (2015)

Target heat sink: design with novel design rules Tensile test curves of CuCrZr Structural design scheme T>250°C : recovery of embrittlement  S e , S d criteria: no issue  3S m criterion: only for elastic design  plastic design rules (LCF, creep ‐ fatigue) T<200°C: negligible uniform elongation  S e criterion not satisfied T>150°C : total elongation exploitable (strain ‐ controlled loading!)  employ a non ‐ ductile design rule for 150 °C < T < 250 °C You, Nucl. Fusion (2015) Fenici, et al., J. Nucl. Mater. (1994) You, Nucl. Mater. Energy (2015)

Target heat sink: design with novel materials W f -Cu composite tube Wwire-reinforced Cu composite 200 mm v. Müller, You (IPP) You, Nucl. Mater. Energy (2015)

Target heat sink: design with novel materials Particulate W-Cu composite W p -Cu composite mock-up W CuCrZr W p /Cu 22×24×150 mm³ W p /Cu composite block with a W armor tile (5 mm thick) You, Brendel et al., J. Nucl. Mater. (2013) v. Müller, You (IPP)

Target heat sink: design with novel materials W/Cu laminate W/V laminate W laminate pipe (1000 mm) Water ‐ cooled mock ‐ up (W/Cu) Helium ‐ cooled mock ‐ up (W/V) Reiser, Rieth (KIT)

Target heat sink: design with novel materials Barrett et al. (CCFE) Highly porous Cu felt layer ‐ thermal conductivity: ~15 W/m  K ‐ elastic modulus: <1GPa

Target heat sink: design with novel materials Chromium block/tungsten armour for 400 ° C < T < 800 ° C CTE: 9 ‐ 10 × 10 ‐ 6 /K E : 280 ‐ 255 GPa  : 76 ‐ 63 W/m  K DBTT: 250 ‐ 300 ° C Rp 0.2 : 165 ‐ 140 Mpa Temperature range at center line Chromium block HHF test mock ‐ up (10MW/m 2 , Cr: 2mm, 200 ° C) 3mm W: 725 ‐ 1172 ° C (> DBTT) 2mm Cr: 345 ‐ 725 ° C Tube CuCrZr: 200 ‐ 323 ° C LCF lifetime (Cu interlayer) v. Müller, You (IPP) > 5000 cycles at 10 MW/m²

Low activation target concept Stamm, JNM (1998)

Target: design concepts under development Target concepts Coolant Armor Interlayer Heat sink Design logics ITER ‐ like water W Cu CuCrZr Baseline design. To be (ENEA) evaluated for DEMO Thermal break water W Porous Cu CuCrZr Reduce heat flux (CCFE) felt concentration & stiffness Composite water W W wire /Cu Enhance high ‐ temp. (IPP) composite strength & toughness Chromium water W Cu Cr block Lower DBTT & (IPP) CuCrZr tube low activation (Dome) Functionally water W W/Cu FGM CuCrZr Enhance joining quality graded (CEA) W laminate 1 water W Cu W/Cu Enhance high ‐ temp. (KIT) laminate strength & toughness W laminate 2 helium W Cu? W/V Enhance high ‐ temp (KIT) laminate strength & toughness Details on the subproject ‘Target’ will be presented at ICFRM ‐ 17

Target: advanced design concepts (water-cooled) ITER ‐ like W/Cu laminate Thermal break Cr block (high dpa region) W f /Cu composite W p /Cu composite (200 mm long tube) (low HHF region) Functionally graded

Target: advanced design concept (helium-cooled) He-cooled target in WPDIV classified as long ‐ term option: basic R&D for FPP an alternative design concept based on W/Cu laminate tube → DBTT within the allowed temperature range of irradiated Eurofer(ODS)?

Summary Water ‐ cooling as near ‐ term design option (He ‐ cooling: long ‐ term) Cu ‐ base materials for Target heat sink, Eurofer steel for Cassette body 150 ° C as local inlet temperature at strike point Envisaged goal of max. heat flux density to exhaust: 20 MW/m² Critical material issues identified for heat sink & armour Advanced novel design concepts + baseline model Non ‐ ductile structural design rules (toughness/plastic strain) Technology development (materials, joining, etc.) 1 st phase mock ‐ up fabrication in 2015, HHF test campaigns in 2016

Target: tungsten armour cracking ITER divertor target Recrystallized HHF fatigue test (4 mm) 20 MW/m² 300 load cycles Pintsuk, Fus. Eng. Des. (2013) Plastic strain (5 th cycle) Temperature (20 MW/m²) Thermal stress (HHF/cooling) 20 MW/m² (4 mm) 15 MW/m² (2 mm) LCF life at W surface 86 cycles 617 cycles Li, You, Fus. Eng. Des. (2015)

Target: tungsten armour cracking Stress fields at different crack lengths J -integral at different crack lengths During HHF loading During cooling During HHF loading Crack: 1.5 mm Crack: 1.5 mm During cooling Crack: 3.5 mm Crack: 3.5 mm Crack: 5.5 mm Crack: 5.5 mm Li, You, Fus. Eng. Des. (2015)

Target: tungsten armour cracking Li, You, Fus. Eng. Des. (2015)

Target: tungsten armour cracking During cooling During cooling 18 MW/m² 15 MW/m² Li, You, Fus. Eng. Des. (2015)

Target: W wire-reinforced W composite for armour Microstructure Bending test (single-fiber composite) In-situ synchrotron tomography ErO x ZrO x ErO x /W ZrO x /W Du, You, Composite Sci. Tech. (2010) Riesch, You, Acta Mater. (2013)

Work package ‘Divertor’: work breakdown structure

Target heat sink: material requirements Solid elements at RT with thermal conductivity > 50 W/mK X Melting point<500 ° C Radioactivity/Tritium Ta Availability/Cost Strength at 300°C Ductility at 200°C Water corrosion You, Nucl. Fusion (2015)

Cassette: revised model (2015) Baffle: attached to the breeding blanket Strongly reduced size (54 Cassettes) Gain in tritium breeding ratio: 1.13  1.19 Nuclear heating power: 147 MW