TECHNOLOGICAL DRIVERS & OPERATIONAL WINDOW OF AN ACTIVELY COOLED DIVERTOR First IAEA Technical Meeting on Divertor Concepts | Mehdi Firdaouss SEPTEMBER 2015 CEA | 10 AVRIL 2012 | PAGE 1
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 Main role of the divertor is to sustain power coming from the plasma: Steady state: 10MW/m² Slow transient: 20MW/M² Thermal properties ELMS/disruptions Other requirements come also from this interaction with the plasma Sputtering cause by particles impact Erosion sensitivity & thickness Misalignment due to low incidence angle Machinability These requirements coming from the plasma physics have a direct effect on the divertor concepts IAEA TM DIVERTOR CONCEPTS | SEPTEMBER 2015 | PAGE 3
MATERIAL REQUIREMENTS FOR ACTIVELY COOLED ITER-GRADE DIVERTOR Armor material Heat sink material Structural material Material properties Material properties Material properties • high melting temperature • compatibility with water • high mechanical properties • good bonding cooling • low electric conductivity characteristics • low corrosion • availability • high thermal conductivity • high thermal conductivity • resilience to thermal shock • low electric conductivity • machinability • good bonding characteristics Vacuum and plasma compatibility • low tritium retention • low chemical and sputtering erosion • low hydrogen embrittlement • low affinity to hydrogen / oxygen • low plasma perturbation No single material can endorse the three roles -> need for an assembly IAEA TM DIVERTOR CONCEPTS | SEPTEMBER 2015 | PAGE 4
EXAMPLE OF THE HEAT SINK MATERIAL REQUIREMENTS Li-Puma et al., Fus. Eng. Des. 88 (2013) 1836-1843 A simple 1D thermo- mechanical model is used to sort different material heat removal capability * 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 IAEA TM DIVERTOR CONCEPTS | SEPTEMBER 2015 | PAGE 5
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 Design constrains Performances Technology difficulty 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
THERMAL PERFORMANCE OF THE MONOBLOCK: PRESENT STATUS Considering the requirements (in particular with 8mm W thickness W thickness), the geometry is optimized as its best in 8mm 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 operational limits. M. Merola et al., Fus. Eng. Des. 2015 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
INTEGRATION BRINGS ADDITIONAL CONSTRAINS 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 ) The PFC has to be connected to the water cooling circuit an heterogeneous bonding between CuCrZr and Stainless steel has to be 10mm done (generally by electron beam welding). > 1mm grain size ~0.3mm 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 IAEA TM DIVERTOR CONCEPTS | SEPTEMBER 2015 | PAGE 8
TOWARDS THE INDUSTRIALIZATION: CLOSE LINK WITH INDUSTRY REQUIRED Examples of a manufacturing of water cooled PFC TPL of Tore Supra Divertor of W7-X Flat-Tile concept with CFC-armoured Flat-Tile concept with CFC-armoured 890 Targets , ~18000 tiles 622 Fingers, ~13000 tiles Series Expected Realized Modification Acceptance criteria TPL 6 batches / 4 years 6 batches / 5 years relaxed after 3 batches Pre-series 60 fingers / 4 years Re-validation of the Divertor W7-X 6 batches / 4 years 6 batches / 5 years 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. IAEA TM DIVERTOR CONCEPTS | SEPTEMBER 2015 | PAGE 9
WEST: A PROJECT IN SUPPORT TO THE ITER DIVERTOR ITER Divertor Technology Test of scale 1 target (~14% monoblocks WEST vs ITER total ) in a tokamak with relevant heat Monoblock loads under plasma conditions. Identical geometry and shape Test the industrialization capabilities of several supplier, in close link with the DAs Assembling Identical technology in charge of procuring the ITER divertor targets (EU, Japan). Thermal hydraulic Identical WEST will benefit to both industrial and DA conditions toward the success of ITER IAEA TM DIVERTOR CONCEPTS | SEPTEMBER 2015 | PAGE 10
DEVELOPMENT OF QUALIFICATION AND CONTROL FACILITIES 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 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 M. Missirlian et al., proceedings of ISFNT-12 repairing process IAEA TM DIVERTOR CONCEPTS | SEPTEMBER 2015 | PAGE 11
SUMMARY 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 12
SPARE SLIDES IAEA TM DIVERTOR CONCEPTS | SEPTEMBER 2015 | PAGE 13
OPERATING TEMPERATURE RANGE – DEMO AND BEYOND S.J. Zinkle & J.T. Busby, Mater. Today 12 (2009) 12-19 CEA | SEPTEMBER 2015 | PAGE 14
KNOWLEDGE DATABASE REQUIREMENT – DEMO AND BEYOND Complimentary: R. Kurtz, PNNL A. Möslang, KIT 1 st DEMO Blanket 2 nd DEMO Blanket Adv. DEMO <20 dpa ~50 dpa >100 dpa Data base need Li ceramic Li ceramic Li ceramic Materials FM-ODS FM-ODS FM-ODS RAFM RAFM RAFM SiC SiC SiC Be Be Be W W W Irradiation effects Hardening/Embrittlement Phase stabilities Creep & fatigue Volumetric swelling High T He & H effects Adequate knowledge base exists Note: He levels are only for FM steels Partial knowledge base exists No knowledge base CEA | SEPTEMBER 2015 | PAGE 15
EFFECTS ON MATERIAL UNDER NEUTRON IRRADIATION – DEMO AND BEYOND Neutron irradiation affecting Consequences on plasma-material interaction Temperature operation window, less tolerance to Thermal conductivity transient heat loads, erosion yield Chemical composition (transmutation) Hydrogen retention, thermal conductivity indirectly Interstitials, vacancies, dislocations, Hydrogen retention voids Swelling and irradiation creep at Tolerance in PFC alignment will become larger, intermediate temperatures hence power handling capability lower Loss of high-temperature creep Reduced temperature operation window strength 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 CEA | SEPTEMBER 2015 | PAGE 16
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