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 |

armor heat sink

Plansee

Plasma‐facing unit (ITER) Vertical target (ITER)

DEMO divertor in EUROfusion

Technical boundary conditions (DEMO) Power to exhaust: 259 MW in total Power deposited in PFU: 112 MW Particle flux: ~1024/m²∙s Heat flux stationary: max. 10MW/m² transient: max. 20 MW/m² neutron irradiation W: 3 dpa/fpy, Cu: 6‐10 dpa?/fpy Number of pulses stationary: 5000 cycles? transient: 300 cycles? Replacement period: 2 fpy

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

EUROfusion work package ‘Divertor’

10 20 30 40 50 60 10 12 14 16 18 20

Critical heat flux (MW/m²) Water velocity (m/s) Pressure: 5 MPa Tube diameter: 12 mm Swirl (Tong‐75) 150 °C 160 °C 180 °C 200 °C 220 °C

‐ max. surface heat flux: 20 MW/m² ‐ heat flux peaking factor: ~1.6 ‐ envisaged margin to the CHF: ~1.5 ‐ local critical heat flux: ~48 MW/m² ‐ tube diameter: 12 mm ‐ pressure: 5 MPa ‐ temperature: 150 °C ‐ velocity: 16 m/s

Design rationale: cooling condition

Estimated cooling capability of Target

You, Fus. Eng. Des (submitted)

Target heat sink: performance of irradiated CuCrZr alloy

local fracture due to exhausted ductility

Sd

plastic flow localisation

Se

ratchetting

3Sm Design stress limits over temperature 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

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 Predicted temperature profiles in the cooling tube (coolant: 150 °C) Critical material issues for the heat sink irradiation creep  high‐temperature strength neutron embrittlement  toughness/non‐ductile structural design

°C max mid

You, Nucl. Fusion (2015)

Target heat sink: design with novel design rules

Structural design scheme T>250°C: recovery of embrittlement  Se, Sd criteria: no issue  3Sm criterion: only for elastic design  plastic design rules (LCF, creep‐fatigue) T<200°C: negligible uniform elongation  Se criterion not satisfied T>150°C: total elongation exploitable (strain‐controlled loading!)  employ a non‐ductile design rule for 150 °C < T < 250 °C Tensile test curves of CuCrZr

You, Nucl. Fusion (2015) You, Nucl. Mater. Energy (2015) Fenici, et al., J. Nucl. Mater. (1994)

Target heat sink: design with novel materials

Wf-Cu composite tube 200 mm

• v. Müller, You (IPP)

You, Nucl. Mater. Energy (2015)

Wwire-reinforced Cu composite

CuCrZr Wp/Cu W

Wp/Cu composite block with a W armor tile (5 mm thick)

You, Brendel et al., J. Nucl. Mater. (2013)

Particulate W-Cu composite

Target heat sink: design with novel materials

Wp-Cu composite mock-up

22×24×150 mm³

• v. Müller, You (IPP)

W/Cu laminate

Target heat sink: design with novel materials

W laminate pipe (1000 mm) W/V laminate

Reiser, Rieth (KIT)

Water‐cooled mock‐up (W/Cu) Helium‐cooled mock‐up (W/V)

Highly porous Cu felt layer ‐ thermal conductivity: ~15 W/mK ‐ elastic modulus: <1GPa

Target heat sink: design with novel materials

Barrett et al. (CCFE)

Chromium block/tungsten armour

• v. Müller, You (IPP)

Target heat sink: design with novel materials

Chromium block HHF test mock‐up Temperature range at center line (10MW/m2, Cr: 2mm, 200 °C) 3mm W: 725 ‐ 1172 °C (> DBTT) 2mm Cr: 345‐ 725 °C Tube CuCrZr: 200 ‐ 323 °C LCF lifetime (Cu interlayer) > 5000 cycles at 10 MW/m² 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 Rp0.2: 165 ‐ 140 Mpa

Low activation target concept

Stamm, JNM (1998)

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

Target: design concepts under development

Details on the subproject ‘Target’ will be presented at ICFRM‐17

W/Cu laminate Functionally graded Wf/Cu composite (200 mm long tube)

Target: advanced design concepts (water-cooled)

Cr block (high dpa region) Wp/Cu composite (low HHF region) Thermal break ITER‐like

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)?

Target: advanced design concept (helium-cooled)

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.) 1st phase mock‐up fabrication in 2015, HHF test campaigns in 2016

Pintsuk, Fus. Eng. Des. (2013)

20 MW/m² (4 mm) 15 MW/m² (2 mm) LCF life at W surface 86 cycles 617 cycles

ITER divertor target HHF fatigue test 20 MW/m² 300 load cycles

Li, You, Fus. Eng. Des. (2015)

Target: tungsten armour cracking

Temperature (20 MW/m²) Thermal stress (HHF/cooling) Plastic strain (5th cycle) Recrystallized (4 mm)

During cooling During HHF loading J-integral at different crack lengths Crack: 1.5 mm Crack: 3.5 mm Crack: 5.5 mm Crack: 1.5 mm Crack: 3.5 mm Crack: 5.5 mm During HHF loading During cooling Stress fields at different crack lengths

Li, You, Fus. Eng. Des. (2015)

Target: tungsten armour cracking

Li, You, Fus. Eng. Des. (2015)

Target: tungsten armour cracking

During cooling During cooling 15 MW/m² 18 MW/m²

Li, You, Fus. Eng. Des. (2015)

Target: tungsten armour cracking

ErOx ErOx/W ZrOx ZrOx/W Du, You, Composite Sci. Tech. (2010) In-situ synchrotron tomography Riesch, You, Acta Mater. (2013)

Bending test (single-fiber composite) Microstructure

Target: W wire-reinforced W composite for armour

Work package ‘Divertor’: work breakdown structure

Melting point<500°C Radioactivity/Tritium Availability/Cost Strength at 300°C Ductility at 200°C Water corrosion

Solid elements at RT with thermal conductivity > 50 W/mK

Target heat sink: material requirements

Ta

X

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