Materials for Vacuum Vessel OF Fusion Grade Machine

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Materials for Vacuum Vessel OF Fusion Grade
Machine
Ranjana Gangradey Institute For Plasma Research
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PART -I
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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
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Shielding blocks Connecting ducts
Shielding block
Connecting duct SS 304
Primary shielding SS 304 with 2 boron
Ferromagnetic inserts SS 430
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• 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

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• 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.

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On the basis of the service experience of Fission
Reactors and RD 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
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• 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.

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• 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 RD 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

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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

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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.

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SS 316 LN-IG
Mechanical Thermal Properties of SS 316LN-IG
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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

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SS 304B4
Mechanical Thermal Properties of SS 304B4
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SS 304B7
Mechanical Thermal Properties of SS 304B7
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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
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SS 430
Mechanical Thermal Properties of SS 430
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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

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SS 304
Mechanical Thermal Properties of SS 304
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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
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PART- II
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VV Manufacturability A Glance at vacuum vessel
of Fusion grade machine ( ITER VACUUM VESSEL)
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ITER Vacuum Vessel
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Main Vessel
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Challenge is in achieving the accuracy and
tolerances
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RIBS
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Segmentation
Inboard segment
Upper segment segment
Lower segment segment
Equatorial segment
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Inboard Segment Design details
Fragment of outer shell
Fragment of the inner shell
Inboard housing
Intermodular key
Centering key
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FABRICATION OF A SECTION OF A SECTOR
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SEGMENTS
UPPER
Equatorial
LOWER
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FABRICATION OF A SECTION POLOIDAL SECTOR
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Shielding backup slides

• Shielding assembly sequence

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What is being aimed SST-2
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SST -2 ITER
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
ITER total burn time 4700 hrs 1.69 x107 secs
2x107 sec, 0.63 FPY
1Gwatt1x109 joules /sec, 17.6 Mev 2.8x1012
joules No neutron?3.57x1020 /sec
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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
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JOIN HANDS TO FACE MATERIAL CHALLANGES THANK YOU
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