First Wall and Fusion Materials

8/2/2019 First Wall and Fusion Materials

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FIRST WALL AND FUSION

MATERIALS

ByVinay Menon

Scientist SCPrototype Divertors DivisionIPR


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ITER DESIGN


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Any part of the tokamak that directly faces the plasma is knownas the first wall or more broadly classified as Plasma FacingComponents (PFCs)

The Plasma Facing Components constitute- First Wall- Divertor / Limiters


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LOADS FOR PLASMA FACINGCOMPONENTS


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Considerations for selection ofPFCs

High melting point

Plasma contamination

High strength

Low activation

Other issues specific to tokamaks like tritiumretention etc.


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LIMITERS

A solid surface, which defines the edge of the plasma

Limiter plays a number of roles in the operation ofTokamak: - it

1) protects the wall from the plasma when there aredisruptions, runaway electrons, or other instabilities.

2) localizes the plasma surface interaction and particlerecycling

Three types of Limiters:1) Poloidal limiter2) Rail limiter3) Toroidal limiter


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TOROIDAL LIMITER OF TORE SUPRA

Tore Supra Tokamak uses a Toroidal limiter as its plasma facingcomponent. It does not have a Divertor configuration.


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POLOIDAL LIMITERS OF SST 1


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DIVERTORS

One of the main fuctions of the divertor system is to exhaustmajor part of alpha particle power as well as He impuritiesfrom the plasma

Apart from that it adds stability to the plasma as opposed tothe closed limiter type of configuration


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Candidate Materials as PFCs

Beryllium

At no 4, MP 1278 Cusable for low heat flux regions eg first wall.Advantages: Low radiated power,Disadvantages : low MP, Toxicity, high reactivity withwater vapour to form Hydrogen

TungstenAt No. 74, MP 3410 Cusable for medium heat flux regions at the divertortargets like dome with heat loads


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DIVERTOR LAYOUT

The ITER Divertor is divided into 54 cassettes The cassette concept employed for the divertor is

fundamental for the maintenance stategyminimizing maintenance time and allowing shortRH intervention times and high reliability.


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POWER CONDUCTED INTO THE DIVERTOR


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1) PFCs

intercept high energy plasma

particles withstands all loads likeNeutronic Loads, ThermalLoads & ElectromagneticLoads

consists of an armour made

of either carbon fibrereinforced carbon composite(CFC) or tungsten (W).

2) Cassette Body

used as a support structure formounting Divertor Targets

facilitates supply of water toDivertor Targets for heat removal

acts as a neutron shield for thevacuum vessel

DIVERTOR ASSEMBLY


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COMPONENTS OF DIVERTOR

Divertor cassette body (CB) (SS316 L(N)-IG)o Complete Cassette Body is made by SS316 L(N)-I Type 3o Fabrication - CAST, HIPed, Wrought Plate weld

Inner & outer vertical targets (VTs)o Baffle area (W) + CFC + Heat sink(CuCrZr) + support structure

(SS316L(N))+ Cooling Channel (SS316L(N)) Domeo Dome is made of SS316L(N)

Cooling pipeso SS316L(N)-IG Type 2

Supporting structure (SS316L(N)) Link (nuts, hinges, pins etc.)

Super alloy e.g. Nickel Inconel.


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DESIGNATION OF SS316L(N)-IGX 316Type of Steel LLow carbon content (N)Controlled nitrogen content IGITER Grade XProgressive Number indicating the procurement specification 316(N)-IG1 for the modules of the primary wall should have a cobalt content


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Cooling Channel Design

The ITER Design consists of- Armor (to sustain high heat loads)W / CFC- Heat sink (for improved conduction)CuCrZr alloy- Coolant Channel - CuCrZr Tube- Support Structure - SS 316 LN (IG)


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1 Hot Isostatic Process Joining Monoblock with CuCrZr tube Joining CFC/W tiles with CuCrZr plate Joining CuCrZr plate with SS316L(N) plate

2 Electron beam/ laserwelding

Joining CFC/W tiles with CuCrZr plate Joining CuCrZr plate with CuCrZr plate

Joining CuCrZr tube with SS316L(N) tubeusing nickel adapter

3 Electron/Laser beamsurface modification

Modification of inside surface of hole inmonoblock geometry

4 Machining Tungsten and Tungsten alloy machining

CFC machining5 Coating/Casting Activation of CFC surface

Deposition of OFHC copper layer Tungsten deposition on CuCrZr/SS316L (N)

Various Techniques used for fabrication of DivertorTargets


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Water Cooled TargetsConcepts


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WHERE ARE WE NOW?


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HELIUM COOLED DIVERTORS

1. About 15% of the total Fusion thermal power has to be removed by the Divertor.

2. Water as a coolant Offers a very high htc compared to He

Technology is well established

Reacts explosively with Be

Other safety concerns

3. Helium as a coolant Chemical and neutronic inertness

Compatible with materials such as beryllium, lithium, and lead that are anticipated for future fusionpower plants.

Easily integrated into a gas turbine cycle power cycle

Operation at higher temperatures Low heat exchange capability

4. Operation with high coolant exit temperature allows for higher efficiency in power plantconversion


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Materials and anticipated temperatureranges required for a high temp helium

cooled divertor

Component Material Min Temperature Max Temperature

Tiles W600 C (DBTT)

(irradiated)

2500 CMelting temperature -

3410 C

High heat fluxand Helium

Containmentstructures

W- alloy600 C (DBTT)

(irradiated)

1300 C

(Re-crystallization)

Structure andManifolds

W- alloyODS steel

600 C (DBTT)400 C (DBTT)

1300 C(Re-crystallization)

700-750 Cstrength limits


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The HEMJ concept

(e) Uses jet impingement toenhance htc

Inlet/outlet temp 600/700 C

max heat flux - 10Mw/m2

effective htc - 31kW/m2 K

Operating Pressure 10 MPa

(e)

a) The HETS concept - High

efficiency thermal shield: initiallydeveloped for water, is nowadopted for use with He as acoolant.

Operates at 10 MPainlet/outlet 600/669C,max heat flux 10 MW/m2

b) T-Tube concept for ARIES-CS (USA) - uses slotimpingement to enhance htc,

operates at 10 MPa, inlet/outlet 600/680C Max heatflux 10 MW/m2 effective htc 30 kW/m2K


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Other Major considerationsin material selection

Low ActivationDecommissionability

Very high heat loads for materials

facing the plasma

Damage to the structure caused by

high-energy neutronsIFMIF facility

Production of tritium in situ

Helium embrittlementSputtering on surface & poisoning of plasma by heavy ions


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International Fusion MaterialsIrradiation Facility (IFMIF)


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THANK YOU!

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First Wall and Fusion Materials