Transcript Major Materials Challenges for DEMO R.J. Kurtz and G.R. Odette

Major Materials Challenges for
DEMO
R.J. Kurtz1 and G.R. Odette2
1Pacific
Northwest National Laboratory
2University
of California, Santa Barbara
Harnessing Fusion Power Workshop
Los Angeles, CA
March 2 - 4, 2009
Fusion Materials Sciences Challenges
Challenge: Understand mechanisms controlling
performance limiting materials phenomena
Environment: 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 experimentalcomputational 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.
0.1
µm
Bulk Phenomena
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).
Lifeti
me
High heat, neutron fluxes and mechanical loads result in:
High He may narrow or even
 Transmutants and atomic defects lead to
accelerated non-equilibrium mesoscale
close the window
Dimension
al
Instability
Hardenin
g,
Fracture
He
embrittlement,
Thernal Creep,
Corrosion
Materials Design
Window
Temperature
N. Ghoniem & B.D. Wirth, 2002
Materials Degradation in the Fusion
Environment
Neutron irradiation drives microstructural evolution - property changes.
Temperature Range,
Fraction of Melting Point
Dose Level,
dpa
<0.4
≥0.1
Phase Instabilities
0.3 - 0.6
>1
Irradiation Creep
<0.45
>10
0.3 - 0.6
>10
≥0.4
>10
Damage Phenomenon
Hardening & Embrittlement
Volumetric Swelling
He Embrittlement
Fatigue, fatigue crack growth, thermal creep creep-fatigue.
Effect of chemical interactions - corrosion, oxidation.
Comparison of Gen IV and Fusion
Structural Materials Environments
S.J. Zinkle ,OECD NEA Workshop on
Structural Materials for Innovative Nuclear
Energy Systems, Karlsruhe, Germany,
June 2007, in press
fusion
SiC
ODS steel
RAF/M steel
A common theme for fusion and advanced fission is the need to
develop high-temperature, radiation resistant materials.
Fusion Materials Relies Heavily on Modeling due
to Inaccessibility of Fusion Operating Regime
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.
He and Displacement Damage Levels
Steels
Spallation
neutrons
ITER
Fusion
reactor
IFMIF
Theory and Modeling of Materials
Performance Under Fusion Conditions
Integration of modeling-theory-experiments-database development is a
critical challenge in bridging the multi-physics-length-time scales.
• Success - simulations and
• Microstructural evolution in a
high-energy neutron, He-rich
environment.
• Resulting in degradation of
performance sustaining
properties and stability.
• Effects of He are critical.
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
keV displacement
cascades in iron
50
keV
10
keV
100K, iron
Comparison of Materials Issues Fission
vs. 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.
Some Properties Needed
Yield strength and strain hardening constitutive laws.
Various types of ‘ductility’.
Controlled by synergistic interactions
Fatigue crack growth rates.
between a many variables
Fracture toughness.
Irradiation and thermal creep rate.
Fe-9Cr
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.
Irradiated
365oC, 7.4 dpa
Unirradiated
In-Service Property Changes
Combinations of many environmental and material variables control
in-service microstructural and property evolution in complex nonequilibrium alloys.
700
600
y (MPa)
400
300
200
F82H(300ΌC)
Eurofer97 (300ΌC)
100
0
0
1
2
3
4
5
6
Γdpa
F82H 5dpa @ 300°C
200
KJc (MPa¦m)
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 - therefore
must be modeled - and uncertainties
must be estimated.
ITER TBM
500
Ductile
235°C
100
0
-200 -100
Brittle
0
T (°C)
100
200
Low-Activation Structural Materials
for Fusion
 Materials strongly impact
economic & environmental
attractiveness of fusion power
- basic feasibility.
 Many materials are not
suitable for various
reasons.
 Based on safety, waste
disposal and performance
considerations, the three
leading candidates are:
RAF/M and NFA steels
Tungsten alloys
SiC composites
Low activation is a must!!
None of the current reduced or low
activation fusion materials existed 15 years
Impact of He-Rich Environment on
Neutron Irradiated Materials
235°C
100
F82H
Eurofer 97
optifer
0
100 200
T91(SP)
T (°C) optimax(SP)
F82H(SP)
Eurofer (n-irr)
Huge
DBTTF82H,
Shifts!
T91
Tc (ºC)
Brittle
0
-200optimax
-100
1000
100 (appmHe/dpa)
800
Brittle intergranular
fracture
Ductile
KJc (MPa¦m)
 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.
F82H 5dpa @ 300°C
200
Data Y. Dai
High He
100 (appmHe/dpa)
Cc Š 1.1
600
Low He
400
neutron only
200
0
0
10
20
30
dpa
40
50
He Embrittlement: Unresolved
Questions
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
Design 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)
100000
Re-entry
vehicle
1000
100
Divertor
Rocket
nozzle
10
1
Service Life (s)
1010
1.0E+09
1.0E+10
1.0E+06
1.0E+07
1.0E+08
105
1.0E+03
1.0E+04
1.0E+05
1
1.0E+00
1.0E+01
1.0E+02
0.1
10-5
1.0E-03
1.0E-02
1.0E-01
First wall
1.0E-05
1.0E-04
Heat Flux (MW/m2)
Plasma disruption
10000
Science-Based High-Temperature
Design Criteria
Need new models of high-temperature
deformation and fracture:
• Creep-rupture.
• Creep-fatigue interaction.
• Creep crack growth
• Complex time-dependent stress states and
Grain boundary
multiple failure paths.
Cyclic loading far more damaging
1000
3000
EUROFER 97
T=550°C t=1.0%
2500
2000
1500
ZERO
HOLD-TIME
316 SS @ 750°C & 100 MPa
TENSION HOLD-TIME
J. Aktaa & R.
Schmitt, FZK,
2004
Time to rupture, h
NUMBER OF CYCLES TO FAILURE, Nf

SYMMETRICAL HOLD-TIME
1000
100
Schroeder and
Batflasky, 1983
10
COMPRESSION HOLD-TIME
600
10
100
TIME PER CYCLE, S
800
1
Un-implanted
200 appm He
Superior Creep Strength of ODS Steels is
Due to the Presence of Stable Nanoclusters
Thermal creep test at 800°C and 138 MPa for 14,235 h
52 nm
J12YWT: 12Cr-3W-0.4Ti-0.25Y2O3
NFA
RAF/M Steel
SANS:
r = 1.61 nm,
f = 0.69%,
N = 3.9x1023 m-3
ORNL
RT tensile strength 1 - 2 GPa
Nanoclusters possess long-term stability at temperatures > 200°C
higher than the upper temperature limit of advanced RAF/M steels.
Materials Design Strategy to Manage
High He and Displacement Damage
• Trapping at a high-density of nanofeatures is key strategy for
management of He.
NFA
Ductile fracture
Loops
&voids
NF
IG fracture
GB creep
cavity
Climb-glide
J. Henry ICFRM13
STIP 320°C ~19 dpa
1700 appm He
Voids
GB
bubbles
NFA
Bubbles
Dislocations
a
Ductile Fracture b
TMS
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
MA957
F82H
Breaking the High Strength-Low
Toughness/Ductility Paradigm
Theoretical Strength ~E/50
Future Materials
Strength
 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.
Current Engineering
Materials
Toughness or Ductility
Fundamentals of Material-Coolant Chemical
Compatibility 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
Materials 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 - I
 Materials and structures are a fusion power feasibility issue.
 Fusion materials research has led to high-performance reducedactivation 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 sciencebased 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 radiationresistant fusion materials.
Conclusions - 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 thermomechanical 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:
Revolutionary 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 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 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 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 nonnuclear 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 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.