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Stefan WikmanMaterials and Manufacturing 

Materials and Components Qualification for ITER 

Materials & Fabrication

Component development → materials and joints development

Mechanical Testing & Thermal Fatigue Testing

Crack Propagation of Tungsten  CFC tensile tests CFC Un‐irradiated  CFC Irradiated

The work is aimed at Definition of Design Criteria Definition of Acceptance Criteria Qualification According to Codes & Standards Irradiation Campaigns at ITER Relevant doses Assessment of the Effect of Corrosion in the Heat Transfer Systems

WHAT DO WE DO AND WHY?

S. Wikman 2014

S. Wikman

Reactor Main Components (with Demanding Functional Requirements)

Vacuum Vessel In-Vessel systems and Heat Transfer Systems

The JET reactor in action (Culham, UK)

2014

ITERMagnets

• Thermal-hydraulics• Thermo-mechanics• Electro-magnetic loads• Neutron Irradiation• Corrosion and Water Chemistry• Fatigue, Creep• Joining methods• Cryogenic (4K) properties• Non destructive examination• Reproducibility• Metrology and Tolerances• Electronics• Ultra Low Vacuum• Etc etc etc …

Detailed analysis of everything

Tokamak

S. Wikman

Fusion reaction in a power plantThis animation combines reactions from the energy generation process and the breeding of tritium (renewal of fuel).

Magnetic confinementWithout a magnetic field, charged particles move randomly similar to motion of gases. As soon as a magnetic field is switched on, nuclei and electrons of the plasma spiral around the magnetic field lines.

Neutrons from the fusion reaction will still move freely.

Materials are exposed to a very high neutron flux and radiation heat.

Materials Qualification Unique thermal and neutron loads

Several Challenges with the Design of Plasma Facing ComponentsFirst barrier must let neutrons pass through to be absorbed by the coolant water to avoid surface melting.

2014

Stainless Steel 316L Irradiation Effects

S. Wikman 2014

Yield stress at higher temperature irradiation

Typical behavior of metals, irradiation hardening and increased strength in the beginning, but brittle with higher doses. And saturation effect.

S. Wikman 2014

Irradiation softening vs irradiation hardening ‐> find matching bolt materials!!Temperature & dose dependent evolutionLow temperatures speeds up irradiation hardeningIrradiation results in dissolution of precipitates thus lowering the strength (stress relaxation will also occur if the bolts are fastened with pre‐tension)

Material & Joining QualificationChallenges: some bolt materials show opposite behaviour

Irradiation hardening of CuCrZr

Irradiation hardening of CuCrZr after irradiation and testing at 150°C

S Wikman 2014

Material & Joining Qualification

Saturation of the irradiation hardening effect as increase yield load versus dose

Three‐point bend tests at 150°C were performed on notched bars of CuCrZr to show the effect of irradiation hardening and saturation of CuCrZr.The irradiation hardening is saturated at ~0.1 dpa. 

PSI

PSI

S. Wikman

Qualification and assessment of materials influenced by neutron irradiation

HFR (High Flux Reactor)Netherlands

2014

Neutron irradiation tend to damage the lattice structure of crystalline materials Increasing dislocations results in increased strength and hardness, but less energy is needed for failure as toughness and ductility decrease. Neutron bombardment of steels also results in swelling (volume increase) and radiation-induced creep.

Typical material structure (un‐irradiated)

Irradiated

Irradiation causes helium production inside the microstructure eventually forming “He-bubbles (white spots)

Cross-sectional SEM Fracture surface

Effect of He migration to grain boundaries

Nuclear Grade MaterialsTypically clean, low impurity powders with restricted compositionLow Co, NB…

S Wikman 2014

Material & Joining QualificationChallenges Re-welding

He accumulated due to the relatively high n‐ and α‐cross section. He is insoluble in metals generating bubbles, pores and eventually initiation of cracks.

No. 1 Issue: Cracking in the HAZ or its vicinity (irradiation hardening + He accumulation especially in grain boundaries). Due to elevated temperature during welding the release of stresses is increased and gets uncontrolled with helium. Energy input must be minimized when performing re‐welding. Thus, a need for qualification under relevant conditions.

5 appm He, multi grain boundary cracking.‐ Single grain boundary cracks are evidence for He‐bubbles

Present challenges Qualify a welding procedure of re‐welding pipes after years of operation.

S. Wikman 2014

Carbon Fibre Reinforced Carbon 

CFC a plasma Facing MaterialExposed to neutron irradiationExposed to high heat fluxRequires high thermal conductivity and strength

Background to decision to not use CFC in ITER

CFC un‐irradiated CFC Irradiated

NB31Pabs = 1.63 GW/m2

CFC is a good example with visible irradiation effects

CFC un‐irradiated CFC irradiated

Decision by ITER to scrap CFC development and go for 100% Tungsten

Tungsten needs optimization for high heat loads to replace CFC

2013S. Wikman

Laser Sintered Surfaces (oriented structure)

Hot Rolled W typically cracks along grain boundaries after thermal shocks.Laser/EB Textured W has a potential for crack mitigation

Aim: Avoid this as much as possible

S. Wikman

Encapsulation of cooling pipesembedded in 316L powder andHIP:ed

Loading of HIP

Background Prototype Manufacturing – ITER BlanketsStarted 20 years ago and still not finalized

HIP:ed prototype

2014

Early prototype (Sweden 1995)Manufacturing conditions still being assessed

2014

Complex coolant water geometry for the internal circuits

S. Wikman

First Wall Panels are attached to Shield Blanket Modules

Shield Blanket Module Ongoing workOperational life time assessment

Over the years the plasma operationwas optimized changing boundaryconditions and design

Be tiles

CuCrZr SS pipesSS drilledstructure

Very complex and lengthy manufacturing

Water flow

CuC1

Inner Waterbox

2014S. Wikman

Several Diffusion Bonding steps (HIP)

Qualification of PM-HIP 316L(N)-IG for the FWPs

15

• Completed a study and fabrication of mock-ups on powder metallurgy 316L(N)-IG and CuCrZr-IG

• The strength of powder 316 was superior to forged 316• Characterization of powder CuCrZr is comencing• Irradiation campaign under preparation

Figure:

Specimen:

Magnification

Etching:Description

Figure:

Specimen:

Magnification

Etching:

Description

Figure:

Specimen:

Magnification

Etching:

Description

Solid/powder boundary

Powder

Solid

500 (A4 print)

11255-40

40 % NaOH, electrolytic

11255-40

500 (A4 print)

40 % NaOH, electrolytic

11255-40

120 (A4 print)

40 % NaOH, electrolyticPowder 316L(N)-IG

Forged 316L(N)-IG Powder 316L(N)-IG

Powder CuCrZr-IG

S. Wikman

New Materials DevelopmentComplex component “printing”

2014S. Wikman

Demonstration that Additive Manufacturing can be utilized for fusion components and to improve thermo hydraulic conditions.

Laser sintered corner

ITER Test Blanket Modules (where new fuel is produced from neutrons)

Very complex assembly using conventional manufacturing techniques!

S. Wikman 2014

Movie 3

Only to manufacture one cooled wall structure is time consuming

EUROFER and ODS Steels shall operate at 650 °C -> creep important!

Additive manufacturing has a potential here!

2014

Corrosion mitigation is a major design criteria for operational life time• 37 water reactions due to radiolysis

• Activated Corrosion Products from coolant water interfaces and impurity accumulation in crevices is an issue due to the complex geometries

A fusion reactor as ITER provides unique cyclic water chemistry

Assessment of Water Coolant Interfaces under ITER Operational Conditions

Electrochemical potential is following the plasma

Extensive work in progress to assess CuCrZr at coolant water interfaces

The water chemistry determines the operational life time of a reactorThe Coolant Water is Influenced by Irradiation 

S. Wikman

2014

Operational Life Time of a Component

Assessment of corrosion data by StudsvikITER operational conditions (long exposure times)

Crevice corrosion under applied load

Crevice corrosion

(15-18 months)

S. Wikman

2014

Erosion corrosion assessment of CuCrZr and CuCrZr/316L(N)-IG joints

Samples had to be replaced after first trial at 250 °C (too high T and after 180 h the water was green)

Repeated for 110 °C and 150 °C and specimens taken out and measured and weighedafter 180 h, 1180h, 2180 h and 4180 h

S. Wikman

2014S. Wikman

2014S. Wikman

Life time assessment

2014

Up to 150 °C the erosion is acceptableOxidizing conditions are mainly relevant for last few years of ITER operationITER IO decision was taken to lower inlet water Temp from 110 °C to 70 °C

250°C is not a high temperature for PFC’s and CuCrZr not suitable for higher temperatures (be careful with design)!

Repeated experiments are ongoing with reducing water chemistry (without active plasma) to complete the assessment of operational life time.

S. Wikman

No region with large grain sizes

40mm

Problems with CuCrZr for “solid” trial phase

40mm

Regions with large grain sizes

Chaotic grain growth observed with batch to batch differences

Large grains give significantly lower mechanical properties

Main reason:The necessary HIP temperature at 1040°C to obtain CuCrZr/316L(N)-IG jointscritical temperature for CuCrZrfollowed by 980°C + the cooling rate (hard to tell what the plant actually achieves as that is “in-house knowledge”)

2014S. Wikman

CuCrZr composition:99% Cu0.7% Cr 0.3% Zr

Tensile tests after heat treatment (1040°C + 980°C + WQ + 580°C)The tensile properties are higher than ITER requirements, but too high scattering associated with the maximal elongation.

These properties strongly depend on the cooling rate.

0

50

100

150

200

250

300

350

400

0 5 10 15 20 25 30

Engineering strain (%)

Engi

neer

ing

stre

ss (M

Pa)

M2-1 M2-2

M6-1 M6-2

M9-1 M9-2

M9-3 M9-4

D12-HIP-1 D12-HIP-2

M14-1 M14-2

R0,2 = 175MPa (ITER)

Rm = 280MPa (ITER)

Strain rate = 1 10-4s-1, 20°C

Examples CuCrZr “solid” trial phase

2014S. Wikman

Tensile tests after HIP: Scatter and mechanical properties under control

CuCrZr “powder” trials

Results at RT

0

50

100

150

200

250

300

350

400

0 5 10 15 20 25 30 35Engineering strain (%)

Engi

neer

ing

stre

ss F

/S0

(MPa

)

11-10111-10011-07111-072

Powder heat treated under H2

ITER R0,2 20°C

ITER Rm 20°C

Powder without treatment

Strain rate = 10-4s-1

Powder Metallurgy superior for CuCrZr to mitigate chaotic grain growth

2014S. Wikman

S. Wikman

316LN Large piece manufactured via Powder Metallurgy

2011-2012 Prototype – Toroidal Field Coil Radial PlatePowder HIP approach was one candidate for the tender

TF and PF Conductors:• Qualification of mechanical properties of materials and welds at cryogenic temperatures 4K

2014

Carpenter Powder Products, SwedenBodycote HIP, SwedenMetso, FinlandSIMIC, Italy

Irradiation needs

S. Wikman 2014

• Reference testing of the materials performed via Framework contract with Tecnalia Spain

Irradiation Conditions Material DPA DPAXM19 0.1 dpa 250 ○C 0.3 dpa 250 ○CXM19/316L(N)‐IG joint 0.1 dpa 250 ○C 0.3 dpa 250 ○CSS660 0.1 dpa 250 ○C 0.3 dpa 250 ○CNiAl Bronze 0.1 dpa 250 ○C 0.3 dpa 250 ○CInconel 718 0.05 dpa 250 ○C 0.3 dpa 250 ○CCuCrZr/316L(N)‐IG Joint (HIPed and Explosion Bonded joints)

0.1 dpa 250 ○C 0.7 dpa 250 ○C

316L(N)‐IG jointsPowder HIP to solid plate

0.1 dpa 250 ○C 0.7 dpa 250 ○C

CuCrZrPowder HIP

0.1 dpa 250 ○C 0.7 dpa 250 ○C

316L(N)‐IGPowder HIP

0.1 dpa 250 ○C 0.7 dpa 250 ○C

316L(N)‐IG jointsPowder HIP to CuCrZr powder HIP

0.1 dpa 250 ○C 0.7 dpa 250 ○C

In-pile creep relaxation testingMaterials Pre-stress 0.1 DPA 0.3 DPA References

Un‐irradiatedXM-19 σ/YS → 30 % 3 3 2

σ/YS → 50 % 3 3 2σ/YS → 70 % 3 3 2σ/YS → 90 % 3 3 2

Alloy 660 σ/YS → 30 % 3 3 2σ/YS → 50 % 3 3 2σ/YS → 70 % 3 3 2σ/YS → 90 % 3 3 2

NiAl-Bronze σ/YS → 30 % 3 3 2σ/YS → 50 % 3 3 2σ/YS → 70 % 3 3 2σ/YS → 90 % 3 3 2

Total No. Specimens 36 36 24

Hot Cell LaboratoryTensile tests at 250 ºC + RT;Fatigue tests 250 ºC + RT;Fracture tests 250 ºC + RT;Charpy tests at RT;Visual inspection of fractured surfaces presented as pictures.

Similar for TMB materialsSuch as EUROFER but at ~500C to 650°Cand up to 3 dpa

Weldability of irradiated 316L pipes

S. Wikman 29

Non Destructive TestingJoining (TIG, EB, Laser welding, diffusion bonding)Technical Support

Upcoming work on materials assessment

Framework Contract 2014/2015

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