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Title: Materials for Vacuum Vessel OF Fusion Grade Machine


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 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
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 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

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
ITER Vacuum Vessel
24
Main Vessel
25
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
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
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
37
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