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Materials for Vacuum Vessel OF Fusion Grade Machine

Materials for Vacuum Vessel OF Fusion Grade Machine. Ranjana Gangradey Institute For Plasma Research. PART -I. Structure of Vacuum Vessel. +. +. +. =. Inner shell- 40 to 60 mm thick. Rib structure 30 to 40 mm thick. Outer shell- 40 to 60 mm thick. Port structure 40 mm thick.

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Materials for Vacuum Vessel OF Fusion Grade Machine

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  1. Materials for Vacuum Vessel OF Fusion Grade Machine Ranjana Gangradey Institute For Plasma Research

  2. PART -I

  3. Structure of Vacuum Vessel + + + = Inner shell- 40 to 60 mm thick Rib structure 30 to 40 mm thick Outer shell- 40 to 60 mm thick Port structure 40 mm thick 40° sector Main structural Material 316 Special grade

  4. Shielding blocks & Connecting ducts Shielding block Connecting duct SS 304 Primary shielding SS 304 with 2% boron Ferromagnetic inserts SS 430

  5. The Stainless Steels • Austenitic stainless steels (SSs) of 304 and 316 type are the main structural materials of the basic machine. • Reasons • They are qualified in many national design codes. • Have adequate mechanical properties • Good Resistance to corrosion • Weldability • Forging and casting potential • Industrially available in various forms • Can be manufactured by well established techniques • Widely used in high technology area • There is extended data base in un-irradiated condition from cryogenic to elevated temperature

  6. Stainless steel as structural material of Fusion reactor • Requirement • Degradation of properties during irradiations, mechanical and thermal loads and environmental effects should not result in loss of structural integrity of the components. • Both base metal and welded joints should with stand the irradiation doses within the range of operating temperature. • SS components are exposed to vacuum , to liquid helium, to deareated, demineralised water in cooling channels. Hence material must be compatible to these requirements. • Good weldability of the material in a wide range of thickness is required. • Vacuum vessel being the first safety barrier and for safety of machine, its structural integrity must be guaranteed. • Good strength and fatigue resistance and fracture toughness after neutron irradiation are essential requirements.

  7. On the basis of the service experience of Fission Reactors and R&D results obtained in Fast Breeder reactor and Fusion programs 316LN( Low Carbon and Controlled Nitrogen) steel is thought to be the most suitable material to resist high dose of irradiation, relatively high loads and direct contact with water

  8. Background For Selection of Type SS required for Fusion machine • Selection 316L(N) for Fast Breeder Reactors (316LN-FBR) • Reasons • The proposed grade has an optimal combination of main alloying elements carbon, nitrogen, nickel, chromium, manganese and molybdenum with tight specification for their allowable range. The narrow specification provides an optimal microstructure and a good control of the heat to heat variation of mechanical properties. • The tight control of the carbon and nitrogen content provide a the satisfactory resistance to stress corrosion cracking of the base metal and welds, and adequate level of material strength • 316LN-FBR has better strength and ductility and design allowable strength is higher than in other SS grades. • less prone to delayed reheat cracking than Ti or Nb stabilized steels. • less sensitive to irradiation embrittlement than 304 steel. • SS316LN-FBR has comprehensive data base including heat to heat variation and product size.

  9. SS FOR FUSION MACHINE • With the data available for SS316LN for fast breeder reactors for a fusion machine minor modifications required are to cope for radiological safety limits and with rewelding requirements. • In ITER R&D material development programe the following points were considered • Irradiation embrittlement in the temperature range 250-300 deg C • Material characterization after manufacturing cycle including the effect of neutron irradiation • Fracture toughness of the material irradiated in between 250-300 C. • Welding of the irradiated stainless steel

  10. SS 316 LN-ITER GRADE(IG) • Chemical Composition • Main allowing elements;-Ni,Cr,Mo,Mn,C,N Any change results in different kind of steel. Produces Significant Change • P,S,Si  Inherently present in the steel as a consequence of metallurgical process. Changes produce change in material properties and quality of steel. The amount is controlled to produce required quality of steel. • Ti, Ta,Nb,Cu,Co,B Impurities in the Ore Scrap No significant effects on material properties. Lowest level defined by industrial process. • the activation is dominated by isotopes of Mn54,Mn56,Fe55,Co57,Co58,Co60, Ni57, Cr51 produced by transmutation of elements produced in steel Fe,Ni,Cr,Co,Mn,Nb • Content of all the above elements except Co, Ni cannot be changed without affecting steel properties • Required quantity ~ 1600 to 1700 tons for double wall vacuum vessel • Ports  ~1400 tons

  11. SS 316 LN-ITER GRADE(IG) Cobalt • Reducing the Co content from 0.25 % to 0.05% decreases the total decay heat in vacuum vessel by ~20%. • Cobalt is one of the main components of activated corrosion products in water cooling systems cooling systems. Niobium • Niobium produces long lived isotopes which become important for the decommissioning and waste disposal of in vessel components. For vacuum vessel the content has been kept as 0.01%. Boron • SS 316LN-FBR grade boron is less than 20 wppm. Neutronic calculations show that decreasing the boron content to 10 wppm will reduce 31% helium generated. Welding can be successfully carried out if He content is less than 0.5 –1.0 appm.

  12. SS 316 LN-IG Mechanical & Thermal Properties of SS 316LN-IG

  13. SS 304B4 and SS 304B7 Chemical Composition For primary Shielding • SS 304B7 with 1.75-2.25 wt. % of boron for the inboard region • SS 304B4 with 1.00-1.24 wt. % of boron for the outboard region • Addition of Boron for neutron shielding • The steel has low ductility & low fracture toughness • Additional elements for vessel application Co 0.05 Nb 0.01 Requirement for a fusion grade machine  1700 tons

  14. SS 304B4 Mechanical & Thermal Properties of SS 304B4

  15. SS 304B7 Mechanical & Thermal Properties of SS 304B7

  16. Ferromagnetic Materials For Vacuum Vessel inserts • An insert of Ferromagnetic material is used in the outboard area inside the double vacuum vessel to reduce the toroidal field ripple. • SS 430 is a suitable material for the ferromagnetic inserts in terms of magnetic , technological, corrosion properties availability and acceptable cost. • SS430 has curie temperature of 660 deg C and saturation magnetic flux density 1.35 T(13500 gauss) • strengths are comparable to SS316 but have lower ductility • lower thermal expansion co-efficient • generally easier to machine Chemical Composition

  17. SS 430 Mechanical & Thermal Properties of SS 430

  18. SS 304 Chemical Composition For Connecting Ducts • Good weldability • Cost consideration • Additional elements for vessel application Co 0.05 Nb 0.01 Requirement  ~ 300 tonns

  19. SS 304 Mechanical & Thermal Properties of SS 304

  20. Filler material for SS/SS welding • Weld metal composition ---- to form duplex structure (austenitic + delta ferrite) to reduce the risk of hot cracking • Specified range of delta ferrite --- 3-7% • Sulphur content ---- 0.005-0.01 to improve weld penetration Chemical Composition of 16-8-2 filler metal for TIG welding

  21. PART- II

  22. VV Manufacturability A Glance at vacuum vessel of Fusion grade machine ( ITER VACUUM VESSEL)

  23. Size - Torus OD 19.4 m - Torus Height 11.3 m - Double Wall Thickness 0.34-0.75 m - Toroidal Extent of Sector 40° - Number of Sectors 9 - Shell Thickness 60 mm - Rib Thickness 40-60 mm Structure double wall Resistance - Toroidal 7.9 µΩ - Poloidal 4.1 µΩ Required Leak Rate  110-8 Pam-3/s Surface Area / Volume (Main vessel) - Interior Surface Area 850 m2 - Interior Free Volume 1090 m3 - Interior Total Volume 1600 m3 Mass (without water) - Main Vessel (without shielding) 1611 t - Shielding 1733 t - Port Structures 1487 t - Connecting Ducts 294 t - Total (not including water) 5124 t ITER Vacuum Vessel

  24. Main Vessel

  25. Parameter Value in mm Fabrication tolerance at factory Sector overall height ± 20 Sector overall width ± 20 Sector wall thickness ± 5 Surface deviations of a 20-degree sector from the reference geometry after fabrication at factory ± 10 Assembly/positioning tolerances at site Mismatch of the sector surfaces at field joints ± 5 Vessel weld distortion due to field/shop welds at the site ± 5 Surface deviations of the torus from the reference geometry after assembly at the pit ± 15 Challenge is in achieving the accuracy and tolerances

  26. RIBS

  27. Segmentation Inboard segment Upper segment segment Lower segment segment Equatorial segment

  28. Inboard Segment: Design details Fragment of outer shell Fragment of the inner shell Inboard housing Intermodular key Centering key

  29. FABRICATION OF A SECTION OF A SECTOR

  30. SEGMENTS UPPER Equatorial LOWER

  31. FABRICATION OF A SECTION POLOIDAL SECTOR

  32. Shielding backup slides • Shielding assembly sequence

  33. What is being aimed – SST-2

  34. FOR ITER Total average neutron fluence at the first wall = 0.59 x (4700 hrs/24x365 ) = 0.31 MW a/m2 = 0.59 x 7800/(24x365) = 0.525( assessed) Neutron flux/cm2/sec = 1.8 x1020/680x104 = 2.64 x1013 neutrons/cm2/sec FOR SST -2 Total average neutron fluence at the first wall For 5,000 hours = 0.2 x (4700/24x365) = 0.107 MW a/m2 & for 78000.178 MWa/m2 For 5,000 hours ~ 0.11 MW a/m2 --------------------------------------------------------------- Neutron flux/cm2/sec = 0.357x10 20/391x10 4 = 0.91x1013 = 1 x1013 neutrons/cm2/sec (0.38 ~0.4 times of ITER SST -2 & ITER ITER total burn time 4700 hrs = 1.69 x107 secs ~2x107 sec, 0.63 FPY 1Gwatt=1x109 joules /sec, 17.6 Mev= 2.8x1012 joules No neutron3.57x1020 /sec

  35. Concept of Fusion machine being aimed at SST-2 Vessel Material requirement Vessel ~ 1600 tons of 316LN (IG) Total Height: 9.55 meter Outer Diameter: 13.8 meter Width: ­­ 5.3 meter Inner shell: 40 mm thick plate Outer shell: 40 mm thick plate Poloidal Ribs: 30 mm thick plate Wall separation: 120 mm at inboard region 320 mm at outboard region

  36. JOIN HANDS TO FACE MATERIAL CHALLANGES THANK YOU

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