TECHNOLOGICAL DRIVERS & OPERATIONAL WINDOW OF AN ACTIVELY - - PowerPoint PPT Presentation

TECHNOLOGICAL DRIVERS & OPERATIONAL WINDOW OF AN ACTIVELY COOLED DIVERTOR

SEPTEMBER 2015

First IAEA Technical Meeting on Divertor Concepts | Mehdi Firdaouss

| PAGE 1 CEA | 10 AVRIL 2012

OUTLINE

Introduction

 Physics requirements  General material requirements

Present water cooled divertor

 Water cooled divertor concepts  Limits of the main concept  Integration issues  Industrialization issues

Summary

IAEA TM DIVERTOR CONCEPTS | SEPTEMBER 2015 | PAGE 2

ITER-GRADE DIVERTOR: TECHNOLOGICAL REQUIREMENTS COME FROM PLASMA PHYSICS

IAEA TM DIVERTOR CONCEPTS | SEPTEMBER 2015 | PAGE 3

Main role of the divertor is to sustain power coming from the plasma:

 Steady state: 10MW/m²  Slow transient: 20MW/M²  ELMS/disruptions

Other requirements come also from this interaction with the plasma

 Sputtering cause by particles impact  Misalignment due to low incidence angle

These requirements coming from the plasma physics have a direct effect on the divertor concepts

Thermal properties Erosion sensitivity & thickness Machinability

MATERIAL REQUIREMENTS FOR ACTIVELY COOLED ITER-GRADE DIVERTOR

IAEA TM DIVERTOR CONCEPTS | SEPTEMBER 2015 | PAGE 4

No single material can endorse the three roles -> need for an assembly Armor material Material properties

• high melting temperature
• good bonding

characteristics

• high thermal conductivity
• resilience to thermal shock
• machinability

Vacuum and plasma compatibility

• low tritium retention
• low chemical and

sputtering erosion

• low hydrogen

embrittlement

• low affinity to hydrogen /
• xygen
• low plasma perturbation

Heat sink material Material properties

• compatibility with water

cooling

• low corrosion
• high thermal conductivity
• low electric conductivity
• good bonding

characteristics

Structural material Material properties

• high mechanical properties
• low electric conductivity
• availability

EXAMPLE OF THE HEAT SINK MATERIAL REQUIREMENTS A simple 1D thermo- mechanical model is used to sort different material heat removal capability

IAEA TM DIVERTOR CONCEPTS | SEPTEMBER 2015 | PAGE 5

Li-Puma et al., Fus. Eng. Des. 88 (2013) 1836-1843

* heat removal capability = heat flux density * thickness

Operating temperatures ranges also indicated for Cu alloys and Eurofer

 Lower limit is the DBTT of the material  Max limit is strength loss due to thermal softening, overaging and irradiation creep (in particular for CuCrZr)  Temperature of the coolant has also to be limited to keep margin to the critical heat flux

WATER COOLED DIVERTOR CONCEPTS Best compromise:

 W as plasma facing material  CuCrZr as heat sink material  316L IG as structural material

Three main concepts, showing the trade-off between W thickness and erosion / surface temperature:

Coating W

 Compatible with any shape of PFC  Very sensitive to erosion

Flat tile / EAST

 Good bonding

Monoblock / ITER / EAST / WEST

 Minimization of the CuCrZr quantitiy

IAEA TM DIVERTOR CONCEPTS | SEPTEMBER 2015 | PAGE 6

Technology difficulty Performances Design constrains

THERMAL PERFORMANCE OF THE MONOBLOCK: PRESENT STATUS Considering the requirements (in particular with 8mm W thickness), the geometry is optimized as its best in terms of manufacturability and thermal lifetime From the HHF tests on different supplier (from Europe, China, Japan…)

 10 MW/m² is achievable  At 15MW/m² surface modification without loosing the power handling capabilities  The 20 MW/m² limit is more challenging, as a macro crack (“self- castellation”) appears for some of the tested monoblocks

However synergistic effects (impact of transients and plasma wall interactions) might decrease these

• perational limits.

Lower mechanical stress and therefore better thermal lifetime may only come with changing requirements (W thickness) and/or material (cooling tube / compliance layer / W alloy)

IAEA TM DIVERTOR CONCEPTS | SEPTEMBER 2015 | PAGE 7 W thickness 8mm

• M. Merola et al., Fus. Eng.
• Des. 2015

INTEGRATION BRINGS ADDITIONAL CONSTRAINS The PFC has to be connected to the water cooling circuit an heterogeneous bonding between CuCrZr and Stainless steel has to be done (generally by electron beam welding).

IAEA TM DIVERTOR CONCEPTS | SEPTEMBER 2015 | PAGE 8

10mm

~0.3mm grain size > 1mm grain size

Specifity of ITER/DEMO:

 Need of having inspectable welding (including in service)  Wide use of remote handling  Maintenance will have to be done in a harsh environment

In order to avoid creating leading edges (gaps, grazing incidence angle), assembly tolerances are very strict (±0.3mm in some case), which lead to demanding manufacturing tolerances ( down to ±0.1mm )

TPL of Tore Supra

Flat-Tile concept with CFC-armoured

Divertor of W7-X

Flat-Tile concept with CFC-armoured

 622 Fingers, ~13000 tiles  890 Targets , ~18000 tiles

TOWARDS THE INDUSTRIALIZATION: CLOSE LINK WITH INDUSTRY REQUIRED

IAEA TM DIVERTOR CONCEPTS | SEPTEMBER 2015 | PAGE 9

Examples of a manufacturing of water cooled PFC

Series Expected Realized Modification TPL 6 batches / 4 years 6 batches / 5 years Acceptance criteria relaxed after 3 batches Divertor W7-X 6 batches / 4 years Pre-series 60 fingers / 4 years 6 batches / 5 years Re-validation of the process

For divertor manufacturing, technological difficulty is associated with a small market. Industrial involvement is required. Coming from past experience, a close work with Industry is required to improve this involvement and decrease the risks of delay / failure.

WEST: A PROJECT IN SUPPORT TO THE ITER DIVERTOR

IAEA TM DIVERTOR CONCEPTS | SEPTEMBER 2015 | PAGE 10

ITER Divertor Technology WEST vs ITER Monoblock geometry and shape Identical Assembling technology Identical Thermal hydraulic conditions Identical

Test of scale 1 target (~14% monoblocks total ) in a tokamak with relevant heat loads under plasma conditions. Test the industrialization capabilities of several supplier, in close link with the DAs in charge of procuring the ITER divertor targets (EU, Japan). WEST will benefit to both industrial and DA toward the success of ITER

More than 1E5 individual monoblocks to be manufactured and assembled (rejection rates of the process around 5% as of now) Testing 100% of the PFC has a strong impact on cost and delay DEVELOPMENT OF QUALIFICATION AND CONTROL FACILITIES

IAEA TM DIVERTOR CONCEPTS | SEPTEMBER 2015 | PAGE 11

• M. Missirlian et al., proceedings of ISFNT-12

Optimization of the qualification tests and reception controls to be used is required

 US tests for bonding inspection  Hot He leak test  HHF test  Non destructive thermal tests

A consequence to this approach is the need to have access to repairing process

SUMMARY

IAEA TM DIVERTOR CONCEPTS | SEPTEMBER 2015 | PAGE 12

ITER-grade divertor requirements can be reached with the W monoblock concept in its present prototype state with a good level of thermal performance However, challenging issues remains on several aspects:

 Integration of the individual components  Large scale industrialization

From the past experience, it is necessary to work in close link with Industry to optimize the manufacturing process as well as the test and control processes. The operational window of the ITER-grade divertor is well qualified at lab-scale, and only few optimization can be expected. DEMO will bring additional constraints mainly due to nuclear environment. The use of an ITER-grade Cu-W monoblock at the same operational windows seems very challenging.

IAEA TM DIVERTOR CONCEPTS | SEPTEMBER 2015 | PAGE 13

SPARE SLIDES

OPERATING TEMPERATURE RANGE – DEMO AND BEYOND

CEA | SEPTEMBER 2015 | PAGE 14

S.J. Zinkle & J.T. Busby, Mater. Today 12 (2009) 12-19

KNOWLEDGE DATABASE REQUIREMENT – DEMO AND BEYOND

CEA | SEPTEMBER 2015 | PAGE 15

Data base need <20 dpa ~50 dpa >100 dpa Materials RAFM FM-ODS W SiC Be Li ceramic RAFM FM-ODS W SiC Be Li ceramic RAFM FM-ODS W SiC Be Li ceramic Irradiation effects Hardening/Embrittlement Phase stabilities Creep & fatigue Volumetric swelling High T He & H effects

• Adv. DEMO

2nd DEMO Blanket 1st DEMO Blanket

Adequate knowledge base exists Partial knowledge base exists No knowledge base Note: He levels are only for FM steels

Complimentary: R. Kurtz, PNNL

• A. Möslang, KIT

EFFECTS ON MATERIAL UNDER NEUTRON IRRADIATION – DEMO AND BEYOND

CEA | SEPTEMBER 2015 | PAGE 16

Neutron irradiation affecting Consequences on plasma-material interaction Thermal conductivity Temperature operation window, less tolerance to transient heat loads, erosion yield Chemical composition (transmutation) Hydrogen retention, thermal conductivity indirectly Interstitials, vacancies, dislocations, voids Hydrogen retention Swelling and irradiation creep at intermediate temperatures Tolerance in PFC alignment will become larger, hence power handling capability lower Loss of high-temperature creep strength Reduced temperature operation window Ductile to Brittle Transition Temperature Reduced temperature operation window He, H embrittlement Erosion and dust production will be enhanced

Under neutron irradiation, the temperature operation window will reduce, retention and erosion will increase

CU ALLOYS UNDER NEUTRONS – DEMO AND BEYOND  Neutron irradiation causes hardening and loss of elongation  Other properties also degrades quickly with neutrons, although stabilization seems to appear at ~10dpa  It could be replaced by a RAFM steel, like Eurofer, with a strong impact

• n

the acceptable temperature range and also the maximal heat flux (<10MW/m²).

CEA | SEPTEMBER 2015 | PAGE 17

• M. Li et al., J. Nucl. Mater.

393 (2009) 36

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| PAGE 18 CEA | 10 AVRIL 2012