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H. Greuner, IPP Garching 1 2nd Technical Meeting on Divertor Concepts (IAEA) Nov. 13-16, 2017, Suzhou, China

Strategy and results of high heat flux testing of European DEMO divertor mock-ups

H. Greunera, B. Böswirtha, T. Barrettb, M. Richoud, E. Viscac and J-H. Youa

aMax Planck Institute for Plasma Physics, Boltzmann Str. 2, 85748 Garching, Germany

bCCFE, Culham Science Centre, Abingdon OX14 3DB, United Kingdom cENEA, Unità Tecnica Fusione, ENEA C. R. Frascati, via E. Fermi 45, 0 0 044 Frascati, Italy

dCEA, IRFM, F-13108 Saint Paul Lez Durance, France

Motivation: The successful development of divertor plasma-facing components (PFCs) for DEMO requires high heat flux testing (HHF) to assess the performance and the expected lifetime. • Only HHF loading can generate thermo-mechanical stress similar to the expected operating

conditions in a fusion device • Other test procedures do not consider this complex thermo-mechanical behaviour during

cyclic HHF loading

Max-Planck-Institut für Plasmaphysik


Outline

1) Strategy of HHF testing • Introduction • Heat transfer, CHF of cold and hot-water cooling • Testing procedure

2) HHF testing • GLADIS facility • examples of test results

3) Summary, outlook and conclusion


Status of highly heat flux loaded ITER divertor PFCs Design criteria of W monoblock components: • 10 MW/m² steady-state, 5000 cycles experimentally confirmed,

respectively 30,0001) based on fatigue FEM, 70 °C water inlet, • 300 cycles at 20 MW/m², slow transients up to 10 s • max. 0.1 dpa neutron dose in W The reliability of the world wide developed technologies of W -PFCs has been confirmed by intensive HHF tests up to 5000 cycles

1. Strategy of HHF testing - Introduction

Challenges for DEMO Expected neutron dose during 2 full power operation years: • 4 dpa in W, 13 dpa in CuCrZr cooling tubes, however lower cycle number Embrittlement of materials requires the development of new target concepts according to the specific operation in DEMO Design criteria: • 10 MW/m², nominal steady-state operation,150 °C water inlet, 50 bar, 16 m/s • 20 MW/m², during slow transients up to 10 s

1) M. Merola, ICFRM-18 2017

Typical ITER W monoblock mock-ups (blocks ~ 25 x 28 x 12 mm³)


HHF test strategy of “phase I”

• Experimental validation of the FEM predicted thermo-mechanical behaviour under DEMO relevant heat loads and cooling conditions

• HHF tests of three mock-ups of each concept • Standard test procedure for HHF test facilities (currently only GLADIS involved)

Test procedure: 1. Step: cold-water, low pressure (20°C inlet, 10 bar static, 12 m/s) as “initial assessment” to reduce risks & operational costs of the test facility: 1. screening of each mock- up up to 20 – 25 MW/m², 2. 100 cycles 10 s at 10, 15, 20 MW/m²

Aim: Selection of the most promising target concept(s) for the phase II of target development

2. Step: hot-water, high pressure (130°C inlet, 40 bar, 16 m/s) screening and fatigue tests 3. screening up to 20 MW/m², 4. extended cycling up to 300 (1000) cycl. at 20 MW/m², 10 s for one mock-up of each concept


Heat transfer regimes of water cooling - one-side heated tube -

heating

coolant

Heat flux peaking 1.5 -1.8 on inner wall of cooling tube 20 MW/m² on top → >30 MW/m² at cooling tube

relatively small wall temperature range available for efficient and safe heat transfer safety margin: 1.4 x q’ max wall < CHF (in addition to peaking factor!)

20 MW/m² loading in GLADIS


Comparison of heat transfer and CHF - HHF tests versus DEMO requirements -

“cold-water testing”, safe heat transfer, high CHF, corresponds to ~ 30 MW/m² “component load”

Heat load tests > 20 MW/m² on the component should be performed at 20 °C inlet only

• Relatively small temp. diff. to “hot-water” at higher heat loads, about 50 °C only 130°C water-cooling in GLADIS similar to DEMO heat transfer conditions • To avoid onset of CHF, local heat flux at the inner wall should be < 35 MW/m² the heat load on the component should be limited to ~22 MW/m²


2. HHF test facility GLADIS

Technical characteristics: • Power 2 x 1 MW ion sources • Accel. voltage 15 - 50 kV • Heat flux 2 - 45 (90) MW/m² • Neutral beam ∅ 70 mm (80% central q’) • Pulse duration 1 ms - 45 s • Target dim. up to 2 m (0.6 m vacuum lock)

H. Greuner et al. / Journal of Nuclear Materials 367–370 (2007) 1444–1448

Target cooling • Water, RT 8.5 l/s, 25 bar

2015 upgraded to meet ITER and DEMO: • Tin 20 – 230 ±0.5 °C, Tout max. 250°C • Flow rate ≤ 2 l/s , p ≤ 55 bar

Target diagnostics • Water calorimetry, thermocouples or other sensors • Fast one and two-colour pyrometers • High resolution CCD & IR cameras • In 2017: fast IR camera, 5 µm, 640*512, 300Hz FF


Screening tests, hot-water 130°C, 40 bar, 16 m/s

Comparison of measured and calculated surface temperatures for two different target concepts • Thermal break concept (27 mm) → mitigate local heat flux concentration at cooling tube • Wf reinforced Cu tube (22 mm) → enhance high-temp. strength of Cu

10 MW/m² steady state for both concepts o.k., q’ > 15 MW/m² results in recrystallization


Examples of 300 x 20 MW/m² fatigue, hot-water (1)

Thermal break concept, CCFE#3 27 mm

1st pulse 20 MW/m² CCFF #3 300th pulse 20 MW/m² CCFF #3 20 MW/m² loading in GLADIS

Wf reinforced Cu tube concept, IPP#1


W surface images after 20 MW/m² cycling

Thermal break concept, CCFE#3 27 mm Tsurf during loading ~ 2000°𝐶

Thermal break concept, CCFE#6 22 mm Tsurf during loading ~ 1700°𝐶

• Both concepts, no cracks, loss of grains or strongly increased surface roughness • 27 mm mock-ups: recrystallization and grain growth of W surfaces clearly visible • 22 mm mock-ups: much less pronounced

300 pulses 20 MW/m² CCFE # 3 27 mm block width

4 mm

300 pulses 20 MW/m² CCFE # 6 22 mm block width

4 mm


Thin graded interlayer CEA FGM #4

DEMO type ENEA#5 300th pulse 20 MW/m² loading, 130°C

© E2M, IPP 2017

Examples of 300 x 20 MW/m² fatigue, hot-water (2)


Target concepts

Water temp. (°C)

Screening tests (MW/m²)

Fatigue tests 100 x (MW/m²)

Results

Extended cycling 300 x 20 MW/m² (status: 10/11/2017)

DEMO type (ENEA), 3 mock-ups

20 6 – 20 10 successful -

130 6 – 20 20 successful successful

ITER-like (ENEA), 3 mock-ups

20 6 – 20 10, 15 successful -


Thermal break layer (CCFE), 3 x 2 mock-ups

20 6 – 25 10, 15, 20 successful -

130 6 – 20 10, 15, 20 successful successful

W-Cu composite block (IPP), 1 mock-up

20 6 – 22 20 successful (crack at cycle 362)

-

Wf Cu composite tube (IPP), 1 mock-up

20 6 – 20 10 successful -


Thin graded interlayer (CEA), 3 x 2 mock-ups

20 6 – 25 10, 15, 20 successful -

130 6 – 20 10, 15, 20 successful successful

Summary table phase I HHF tests


Summary and conclusion

Summary • Cold water tests of all EU concepts as initial successfully performed • 300 cycles at 20 MW/m² 130°C hot-water of all EU W monoblock concepts successfully

performed • no serious surface or component damage occurred, all 20 tested mock-ups survived • good agreement between FEM predicted and measured surface temperatures • Indication of recrystallization and grain growth of W surface after 20 MW/m² cycling

Outlook • NDE after performed HHF loading • Micrographs of selected mock-ups

• Investigation of recrystallization depth, grain size • Investigation of W/ Cu interface, plastic deformation, delamination, cracks

Conclusion • A number of European manufacturers are able to produce advanced W divertor PFCs for

DEMO application. These water-cooled components are able to withstand up to 20 MW/m² cyclic heat load

• Important R&D progress in the last years

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