Major Materials Challenges for Major Materials Challenges for DEMODEMOMajor Materials Challenges for Major Materials Challenges for DEMODEMO

R.J. Kurtz1 and G.R. Odette2

1Pacific Northwest National Laboratory2University of California, Santa Barbara

Harnessing Fusion Power WorkshopLos Angeles, CAMarch 2 - 4, 2009

Fusion Materials Sciences ChallengesFusion Materials Sciences Challenges

0.1 µm

Challenge: Understand mechanisms controlling performance limiting materials phenomenaEnvironment: Heat flux: 1-15 MW/m2; Neutron fluence: 10-20 MW-y/m2; Transmutation: ~2000 appm He/8000 appm H; High time dependent thermal and mechanical stresses.

Approach: Use full suite of experimental-computational tools to model life-limiting degradation phenomena in the fusion environment.Goal: Experimentally validated, physics-based models to predict performance and improve existing materials and design better ones.

Transmutants and atomic defects lead to accelerated non-equilibrium mesoscale evolutions and damage accumulation over long time > 108 s.• Voids, bubbles, dislocations and phase

instabilities (damage).• Dimensional instabilities (swelling and

irradiation-thermal creep).• Complete loss of strain hardening capability.• High-low temperature He embrittlement.• Fatigue, creep-fatigue, crack growth.• Corrosion, oxidation and impurity

embrittlement (W, V).

Bulk PhenomenaBulk Phenomena

He embrittlement,Thernal Creep,Corrosion

Temperature

Dimensional Instability

Life

tim

e

Materials Design Window

Hardening, Fracture

N. Ghoniem & B.D. Wirth, 2002

High He may narrow or even close the window

High heat, neutron fluxes and mechanical loads result in:

Materials Degradation in the Fusion Materials Degradation in the Fusion EnvironmentEnvironment

Neutron irradiation drives microstructural evolution - property changes.

Fatigue, fatigue crack growth, thermal creep creep-fatigue.Effect of chemical interactions - corrosion, oxidation.

>10≥0.4He Embrittlement

>100.3 - 0.6Volumetric Swelling

>10<0.45Irradiation Creep

>10.3 - 0.6Phase Instabilities

≥0.1<0.4Hardening & Embrittlement

Dose Level, dpa

Temperature Range,Fraction of Melting Point

Damage Phenomenon

fusionSiC

ODS steel

RAF/M steel

S.J. Zinkle ,OECD NEA Workshop on Structural Materials for Innovative Nuclear Energy Systems, Karlsruhe, Germany, June 2007, in press

Comparison of Gen IV and Fusion Comparison of Gen IV and Fusion Structural Materials EnvironmentsStructural Materials Environments

A common theme for fusion and advanced fission is the need to develop high-temperature, radiation resistant materials.

IFMIF

Spallationneutrons

Fusionreactor

ITER

10

15

10

16

10

17

10

18

10

19

10

20

10

21

10

5

10

6

10

7

10

8

10

9

Magnetic

Inertial

( )Ion Temperature K

1955

1960

1965

1970-75

1975-80

1980s

1990s

Breakeven

Ignition

Extrapolation to fusion regime is much larger for the fusion materials than for plasma physics program.Lack of an intense neutron source emphasizes the need for a coordinated scientific effort combining experiment, modeling and theory to a develop a fundamental understanding of radiation damage.

Fusion Materials Relies Heavily on Modeling due Fusion Materials Relies Heavily on Modeling due to Inaccessibility of Fusion Operating Regimeto Inaccessibility of Fusion Operating Regime

He and Displacement Damage Levels

Steels

Theory and Modeling of Materials Theory and Modeling of Materials Performance Under Fusion ConditionsPerformance Under Fusion Conditions

Integration of modeling-theory-experiments-database development is a critical challenge in bridging the multi-physics-length-time scales.

• Microstructural evolution in a high-energy neutron, He-rich environment.

• Resulting in degradation of performance sustaining properties and stability.

• Effects of He are critical.

• Success - simulations and experiments show high-energy fusion damage events are similar to multiple, lower-energy events - provides fission-fusions dpa damage scaling.

Comparison of 10 and 50 Comparison of 10 and 50 keV displacement keV displacement cascades in ironcascades in iron

100K, iron

50 keV

10 keV

5 nm

Comparison of Materials Issues Fission Comparison of Materials Issues Fission vs. Fusion Reactor Systemsvs. Fusion Reactor Systems

• Big pot and pipes• dpa < 0.15, He ≈ 0• T ≈ 300°C • Heat flux ≈ 0• Coolant Pure H2O• Issue: embrittlement limits on start-up

thermal shock events

• Intricate, large-scale, interconnected multifunctional structure with gradients, startup/shutdown and other transients, dimensional instabilities, continuous time-dependent stress redistributions.

• dpa ≈ 200, He ≈ 2000 appm• T ≈ 400 – 600 °C • Heat flux ≈ 1 – 15 MW/m2

• Coolant: He, Li, …..• Issues: possibly too many to count or

even know.

Yield strength and strain hardening constitutive laws.Various types of ‘ductility’.Fatigue crack growth rates.Fracture toughness.Irradiation and thermal creep rate.Thermo-mechanical fatigue limits .Creep-fatigue interactions.Environmentally assisted cracking.Bulk corrosion, oxidation & compatibility.Void swelling rates.Creep rupture times and strains.Creep crack growth rates.Flaw distributions.

Some Properties NeededSome Properties Needed

Controlled by synergistic interactions between a many variables

Unirradiated

Irradiated365 C, 7.4 dpao

Fe-9Cr

Combinations of many environmental and material variables control in-service microstructural and property evolution in complex non-equilibrium alloys.

Enormous degrees of freedom, many inherently multi-scale interacting (time - length) mechanisms - critical outcomes often depend on small differences between large competing effects (e.g., void swelling).

Data must be extrapolated - thereforemust be modeled - and uncertaintiesmust be estimated.

In-Service Property ChangesIn-Service Property Changes

0

100

200

300

400

500

600

700

0 1 2 3 4 5 6

F82H(300ºC)

Eurofer97 (300ºC)

√dpa

ITER TBM

Ductile

Brittle

Low-Activation Structural Materials Low-Activation Structural Materials for Fusionfor Fusion

None of the current reduced or low activation fusion materials existed 15 years ago.

Low activation is a must!!

Impact of He-Rich Environment on Impact of He-Rich Environment on Neutron Irradiated MaterialsNeutron Irradiated Materials

A unique aspect of the DT fusion environment is large production He and H.

He (and H?) has significant potential to create damage and cause loss of structural integrity:- High-temperature creep embrittlement.- Intermediate-temperature swelling.- Low-temperature loss of fracture toughness.

0

200

400

600

800

1000

0 10 20 30 40 50

F82H

Eurofer 97

T91

optimax

optifer

F82H(SP)

T91(SP)

optimax(SP)

F82H, Eurofer (n-irr)

Δ

T

c ( )ºC

dpa

neutron only

100 ( / )appmHe dpa

100 ( / ) appmHe dpa

Cc

≤ 1.1

Data Y. Dai

Ductile

Brittle

Huge DBTT Shifts!

Brittle intergranular fracture

High He

Low He

He Embrittlement: Unresolved He Embrittlement: Unresolved QuestionsQuestions

What is the sequence of events after He generation that controls its fate?

How does He diffuse?How and where is He trapped?How does He behave and what does it do at various trapping sites?

Can nanofeatures in advanced ferritic alloys stably trap He in very fine bubbles?

Voids in F82H at 500°C, 9dpa, 380 appm He

Science-Based High-Temperature Science-Based High-Temperature Design CriteriaDesign Criteria

Empirical high-temperature design methods are not applicable to fusion applications and damaged materials.

Thermo-mechanical challenges of first-wall/blanket & divertor structures are unprecedented even without radiation damage.

RAFM Steel

Poor creep-fatigue strength (cyclically soften)

Science-Based High-Temperature Science-Based High-Temperature Design CriteriaDesign Criteria Need new models of high-temperature

deformation and fracture:•Creep-rupture. •Creep-fatigue interaction.•Creep crack growth•Complex time-dependent stress states and multiple failure paths.

10 100 800600

1000

1500

2000

2500

3000

COMPRESSION HOLD-TIME

SYMMETRICAL HOLD-TIME

TENSION HOLD-TIMEZEROHOLD-TIME

EUROFER 97 T=550°C Δεt=1.0%

, NUMBER OF CYCLES TO FAILURE N

f

TIME PER CYCLE, S

J. Aktaa & R. Schmitt, FZK, 2004

Cyclic loading far more damaging

Grain boundary

1

10

100

1000

Un-implanted 200 appm He

316 SS @ 750°C & 100 MPa

Schroeder and Batflasky, 1983

Thermal creep test at 800°C and 138 MPa for 14,235 h

Nanoclusters possess long-term stability at temperatures > 200°C higher than the upper temperature limit of advanced RAF/M steels.

Superior Creep Strength of ODS Steels is Superior Creep Strength of ODS Steels is Due to the Presence of Stable NanoclustersDue to the Presence of Stable Nanoclusters

SANS:r = 1.61 nm,f = 0.69%,N = 3.9x1023 m-3

J12YWT: 12Cr-3W-0.4Ti-0.25Y2O3

RAF/M Steel

NFA

RT tensile strength 1 - 2 GPa

ORNL

Materials Design Strategy to Manage Materials Design Strategy to Manage High He and Displacement DamageHigh He and Displacement Damage

• Trapping at a high-density of nanofeatures is key strategy for management of He.

NFA

Bubbles

Dislocations

Voids

GB creep cavity

Loops&voids

GB bubbles

TMS

NF

Climb-glide

IG fracture

Ductile Fracturea b

G. R. Odette, M. J. Alinger and B. D. Wirth, “Recent Developments in Irradiation Resistant Steels”, Annual Reviews of Materials Research V38 (2008) 371-403

F82HMA957

NFADuctile fracture

J. Henry ICFRM13 STIP 320°C ~19 dpa

1700 appm He

Breaking the High Strength-Low Breaking the High Strength-Low Toughness/Ductility ParadigmToughness/Ductility Paradigm

Increased strength is accompanied by reduced toughness (cracking resistance) and ductility.

Strength is increased by alloying, processing and radiation damage.

Low toughness and ductility reduce failure margins.

The benefits of simultaneously achieving high-strength and high ductility/ toughness would be enormous.

Toughness or Ductility

Stre

ngth

Theoretical Strength ~E/50

Future Materials

Current Engineering Materials

Fundamentals of Material-Coolant Chemical Fundamentals of Material-Coolant Chemical Compatibility in the Fusion EnvironmentCompatibility in the Fusion Environment

The traditional approach to corrosion is empirical.

Correlations do not capture basic physics and have limited predictive capability.

Opportunities: Controlled experiments

combined with physical models utilizing advanced thermodynamics & kinetics codes.

Integrated experiments using sophisticated in situ diagnostic and sensor technologies.

M. Zmitko / US-EU Material and Breeding Blanket Experts Meeting (2005)J. Konys et al./ ICFRM-12 (2005)

Role of Neutron Sources in Fusion Role of Neutron Sources in Fusion Materials ScienceMaterials Science Overcoming radiation damage degradation is the key rate-controlling

step in fusion materials development.• Additional factors such as joining are important, but critical

radiation effects data is needed to evaluate feasibility. Evaluation of radiation effects requires simultaneous displacement

damage (~200 dpa) and He generation (~2000 appm He).• Data without high fusion relevant dpa and He/dpa of limited value.

Evaluation of mechanical properties for a given material at a given temperature requires a minimum volume of ~10 cm3 with flux gradients < 20%/cm.• Innovative small-volume neutron sources would be useful but do

not replace the need for a moderate-volume intense neutron source.

Conclusions - IConclusions - I

Materials and structures are a fusion power feasibility issue. Fusion materials research has led to high-performance reduced-

activation materials with radiation a resistance window to ~30 dpa/~300 appm He.

However, the structural materials scientific challenge for DEMO is managing microstructural and property evolution at ~200 dpa, ~2000 appm He.

Physical models of creep and creep-fatigue interactions are needed for development of advanced radiation damaged materials and science-based high-temperature design.

Better fundamental understanding is needed to achieve high-strength and high-ductility and toughness.

A robust theory and modeling activity is vital for understanding the complex physical phenomena associated with development of radiation-resistant fusion materials.

Conclusions - IIConclusions - II

The most critical facility need is an intense neutron source. Irradiations in fission reactors combined with theory and modeling will not be able to fully address needs for DEMO (Workshop on Advanced Computational Materials Science, 2004).

Non-nuclear facilities like corrosion loops and semi-scale thermo-mechanical testing capability to: Address component - system level issues. Identify synergistic failure paths. Verify computational codes for structural integrity and performance assessment.

There is growing evidence that RAF/M steels will have a limited application window for a DEMO reactor.

Tremendous opportunity to design and develop high creep strength, radiation tolerant, thermally stable nanostructured materials that may make fusion power a reality.

Scientific Grand Challenges: Scientific Grand Challenges: Revolutionary Technology AdvancesRevolutionary Technology Advances

Solving the puzzle of the ductile to brittle transition:Breaking the high strength-low toughness paradigm.

Understanding the transport, fate and consequences of helium and displacement damage:

Radiation damage immune alloys for high-temperature, very high-dose service.

Modeling the mechanisms, microstructures and mechanics of high-temperature deformation and damage:

Science based performance life-cycle models for high temperature materials under complex long-term loading.

Greenwald Panel Research InitiativesGreenwald Panel Research Initiatives

Initiative Description

I-1 Predictive plasma modeling and validation

I-2 ITER – AT extensions

I-3 Integrated advanced physics demonstrations

I-4 Integrated PWI/PFC experiment

I-5 Disruption-free experiments

I-6 Engineering and materials science modeling and experimental validation

I-7 Materials qualification facility (intense neutron source)

I-8 Component development and testing program

I-9 Component qualification facility

Guiding PrinciplesGuiding Principles

A science-based approach is the most efficient path for developing and qualifying materials, components and structures for service in the fusion environment.

A robust theory and modeling activity (atomic to component) is vital for understanding the complex physical phenomena associated with development of radiation-resistant fusion materials and this modeling activity must be closely linked to critical experiments.

Development of low or reduced activation materials is essential to meeting the safety and environmental attractiveness goals of fusion.

Developments in related areas such as advanced fission must be leveraged to the maximum extent possible.

Research effort must begin now since structural materials development is a long-term endeavor. The historical precedent is 10-20 y with 150-200 M$ budgets.

Research Thrust IResearch Thrust I

Intense Neutron Source and Non-Nuclear Structural Integrity Benchmarking Facilities• Identify and demonstrate approaches to improve the performance of existing

and near-term materials, components and structures using the full suite of non-nuclear structural integrity benchmarking facilities (thermo-mechanical, corrosion, etc.) and the intense neutron source.

• Identify concept specific issues and demonstrate proof-of-principle solutions.• Refine and validate predictive models of required materials, components and

structural performance.• Service qualification of materials, components and structures for codes,

standards and regulatory requirements.• Qualify large-scale, multi-physics structural and safety computational codes in

preparation for intermediate nuclear facilities and DEMO.• Develop foundation for surveillance of materials, components and structures

including in-service inspection, maintenance and repair.

Research Thrust IIResearch Thrust II

Development and Qualification of Advanced Structural and Functional Materials by Design With Revolutionary Properties• Design of high-performance alloys and ceramics including fabrication and joining

technologies.• Experiments to characterize fundamental radiation damage mechanisms and

thermo-mechanical degradation in next generation fusion materials.• Multiscale (atomic to component level) modeling of the performance of

materials, structures and components in the fusion environment.• Exploration of compatibility with coolants and tritium breeders.• Development of design specific functional and diagnostic materials such as

coatings, insulating ceramics, functionally graded components, etc.