Transcript Structural Materials Performance and Mechanical Integrity under the Effects of Radiation and

#4
Structural Materials
Performance and Mechanical Integrity
under the Effects of Radiation and
Thermo-mechanical Loadings
in Blankets and PFCs
S. Sharafat – FNST Aug 2009 - UCLA
1
The Grand Thermo-mechanical Challenges In
Developing Fusion Test Reactor Structures
 The mechanical loads in combination with high temperatures and
intense neutron and particle radiation fields and chemically reactive
environments could lead to severe degradation of performance sustaining
properties, internal damage, macroscopic cracking, corrosion-erosion and
inherent dimensional instabilities due to irradiation creep and possibly
swelling of Fusion Structural Materials.
 The unprecedented demands on fusion structures derive from severe time
varying thermal-mechanical loading of complex, large scale and highly
interconnected heat transfer-energy conversion structures.
 Non-irradiation environments typically require 10–20 years for
development of incrementally improved structural materials.
 Neither the materials, nor the requisite computational tools, nor the
underlying knowledge base is currently sufficient for reliable integrity
and lifetime assessments of fusion reactor structures.
S. Sharafat – FNST Aug 2009 - UCLA
2
Radiation Damage Based Challenges
In Developing Fusion Test Reactor Structures
 Radiation tolerant structures including the synergistic effects of radiation damage and
nuclear transmutants are required:
Major Radiation Damage Phenomena
Synergistic Effect Example
Workshop on Science Applications of a Triple Beam Capability for
Advanced Nuclear Energy Materials , Cochairs Michael and Wayne
E. King (LLNL), April 2009
S. Sharafat – FNST Aug 2009 - UCLA
3
Thermal-mechanical Challenges for
Fusion Test Reactor Structures
 Accumulation of radiation damage due to atomic damage is minimal at
high temperatures, with the exception of irradiation creep.
 Stress driven growth and coalescence of cavities due to formation of
helium bubbles at grain boundaries at high temperature can severely
degrade creep rupture properties (impact of field gradients).
 Even without radiation damage the challenges of developing a FW
structure are unprecedented, particularly because of interaction of
various synergistically interacting phenomena:
 High-cycle fatigue and fracture growth due to flow induced vibrations
 Low-cycle thermal mechanical fatigue resulting in cyclic softening
 Irradiation creep and possible radiation damage induced dimensional strains
and stress redistribution
 Thermal creep, creep rupture, creep-fatigue interactions and crack growth
 Microstructural instabilities and softening due to thermal aging
S. Sharafat – FNST Aug 2009 - UCLA
4
Objectives and Required R&D
 OBJECTIVES:
(1) Establish the feasibility of designing, constructing and operating a fusion energy
system with materials and components that can survive the fusion environment and
meet safety, environment and performance criteria.
(2) Meet the enormous challenge of developing material systems and multifunctional
structures for predictably operating reliable, safe, and long-lived first wall, blanket and
divertor structures.
 REQUIRED R&D:
Develop underlying knowledge base and computational tools for reliable integrity and
lifetime assessments of fusion reactor structures, which include:
o
Revolutionary experimental methods to understand the interplay between high
performance demands and eroding in-service property limits
o
Synergistic effects of radiation damage, transmutation products, and thermomechanical loading in structures (including associated gradients)
o
Establish Essential Databases:
• Properties for Engineering Design
• Materials Production, Component Fabrication, and Joining
• Reactor Assembly and Integration Technology
S. Sharafat – FNST Aug 2009 - UCLA
5
Radiation Resistant Materials alone can no longer address the larger challenge of
Material Systems and Multifunctional Structures
Material Properties
& Fundamental Interactions
CONCEPT
DEVELOPMENT
DESIGN OF
SUBSYSTEMS &
INTEGRATION
INTO POWER
PLANT
COMPONENT &
SUBSYSTEM
MANUFACTURE
Material Technology or
Component Technolgy
MATERIALS
SCIENCE
AND
ENGINEERING
Properties for Engineering Design
Specifications of
Operating
Conditions/Limits
(e.g. corrosion)
OPERATION
TEST REACTOR
CONSTRUCTION
S. Sharafat – FNST Aug 2009 - UCLA
(after D.T. Hoelzer) 6
#6
Fabrication and Joining of
Structural and Functional Materials
S. Sharafat – FNST Aug 2009 - UCLA
7
Fabrication and Joining Issues
 Multifunctional fusion structures are very complex and
involve the use of many different materials, including
structural alloys, ceramics and composites, breeding and
neutron multiplying media, coolants, and thermal-electrical
insulators, which need to be fabricated and assembled
or joined into components, such as divertors or blankets.
 Fabrication of complex fusion reactor structures and
components is an enormous challenge in that
performance and reliability criteria of fusion components
are unprecedented.
Holtkamp,2009
Divertor vertical target qualification
prototype (EU).
 There are 2 primary weld/joint concerns:
1. Structural integrity (will the weld withstand thermo-mechanical and chemical loads)
2. Leakage of coolant (probability of leakage is ~10 times higher than weld failure)
(1) Weld Integrity: Welds, joints, or coated materials need to
withstand the hostile fusion environment (temperatures, radiation
fluxes, transmutation products, field gradients, etc.) as well
as, if not better than the base structural materials:
If the weld or joint fails it does not matter how well the
base materials perform.
(2) Leakage: Even if the weld holds thermo-mechanically,
if it leaks as little as a pin hole, the entire TBM module
might have to be removed and/or even replaced
S. Sharafat – FNST Aug 2009 - UCLA
EU Helium Cooled Pebble Bed
(HCPB) TBM Concept
8
Major Joining Challenges
Eurofer Weld Microstructure
 WELDS AND JOINTS:
The microstructure at/or near welds, bond joints, and coatings almost
always differs from base material ( different properties).
 Invariably fabrication and joining alters the microstructure of the nearby
host material, which is subject to the same harsh fusion environment as the base material
 BOND COATS:
– Low-Z (Be) or high-Z (W) armor on FW/Divertor
require joining/coating of multilayered components.
– Beryllium is chemically active and forms stable,
strong and brittle intermetallic compounds,
which reduce the mechanical performance (ductility
and toughness):  relatively low bonding strength.
SEM image
and EDX line
profiles at a
X-sectional
surface of Be
and FMS bond.
Lee, FED2009
 Preventing de-bonding of similar and dissimilar metal
joints made of different materials such as Ferritic Steel
and W or Be may be difficult due to large coefficient of thermal expansion mismatches and
the formation of brittle interlayer phases; also a challenge: Austenitic/Ferritic steel pipe weld.
 ADDITIONAL FUSION ENVIRONMENT CHALLENGE:
Accumulation of He/H in bonded joint interfaces, along with significant time-dependent
stresses, inelastic strains and displacements, spatially dependent thermal expansions,
thermal and irradiation creep, and potential swelling (Be) are but a few of the scientific and
technical challenges that must be overcome for reliable functioning of multilayered
and simply bonded fusion components (& coolant chemistry: corrosion subcritical cracking).
S. Sharafat – FNST Aug 2009 - UCLA
9
Objectives and R&D
 OBJECTIVES:
• The First Wall (FW) of the US DCLL TBM (2009) alone has tens of meters of Diffusion
Bond. In addition internal rib structures, top and bottom caps, manifolds, and back
plates have to be joined using a variety of welding techniques, such as EB and LW.
• A FW Beryllium coating would add a total bond coat area of over 0.8 m2.
• The structural integrity as well as the leak-tightness of the welds and bonds plays a
very significant role in the reliability of fusion components.
• Lack of any knowledge of the synergistic effects of irradiation damage, He and H
accumulation, and coolant chemistry (He and PbLi) on welds, joints, and bond coats
requires a significant uptick in scientific and technical efforts to develop fully
functioning joining techniques.
 Required Key Bonding R&D:
1. Assessment of PWHT* on HAZ* of TIG* for Eurofer97 and/or F82H;
2. Creep performance of HAZ before and after PWHT;
3. Effect of irradiation on PWHT of weld materials (HAZ, TIG, or EB welds);
4. Impact of pulsed operation resulting in high temperature irradiation followed by
relatively long periods of cold non-neutron environments;
5. Potential radiation induced segregation and/of phase instabilities in HIP joints,
6. Knowledgebase of multi-layered (Be-steel, W-FMS) bonding strengths.
7. Impact of synergistic effects of irradiation damage, He/H production, and coolants.
8. Detailed characterization of joint properties has not been done systematically but
will be necessary for code qualification and licensing.
*PWHT: Post Weld Heat Treatment; HAZ: Heat Affected Zone; TIG: Tungsten Inert Gas
S. Sharafat – FNST Aug 2009 - UCLA
10
STRUCTURAL CHALLEGES
BACKUP SLIDES
S. Sharafat – FNST Aug 2009 - UCLA
11
Radiation Damage Challenges In Developing
Fusion Power Reactor Structures
 Radiation induced microstructural evolutions, which are controlled by the combination
of many variables and synergistic interactions between displacement-induced defects
and transmutation products (He & H), are a major source of property degradation,
internal damage, and failure.
Five major radiation damage phenomena:
1. Radiation hardening & embrittlement:
<0.4 TM; > 0.1 dpa
2. Phase instabilities from radiation-induced precipitation: <0.3-0.6 TM;
> 10 dpa
3. Irradiation creep: <0.45 TM; > 10 dpa
4. Volumetric swelling from void formation: <0.3-0.6 TM; > 10 dpa
5. High temperature Helium-embrittlement:
>0.5 TM; > 10 dpa
after S. Zinkle (2005)
S. Sharafat – FNST Aug 2009 - UCLA
12
Radiation Damage Challenges In Developing
Fusion Test Reactor Structures
Fission
(Gen I)
Fission
(Gen II)
Fission
(Gen IV)
Fusion
(Gen I: FNSF)
Structural alloy Tmax
<300 °C
< 350 °C
300–1000 °C
< 550 °C
Max dose (internal
core structures)
~1 - 10dpa
~30 dpa
~30–200 dpa
~ 10 - 100 dpa
Max He concentration
~0.1 appm
~ 3 appm
~3–40 appm
~100 - 1000 appm
Max H concentration
Neutron Energy Emax
~450 - 4500 appm
<1–2 MeV
<1–3 MeV
<1–3 MeV
S. Sharafat – FNST Aug 2009 - UCLA
<14 MeV
13
Challenges for Development of Fusion Test Reactor Structures
 A 500 – 700 m2 First Wall (FW) removes about 10% of fusion power experiencing high
thermal loading from a combination of charged particle and radiation fluxes at ~ 0.5 to
1 MW/m2 PLUS volumetric heating.
 FW is a few mm thick  Reliability of very large, thermally loaded, pressurized (~8
MPa He) thin wall structures, erosion due to sputtering and an ability to survive
disruption induced large and rapid thermal and structural load transients are the major
mechanical challenges.
 Temperature window for TMS is primarily dictated by embrittlement and loss of
ductility below 350 oC and thermal creep strength above ~500 oC, however effects of
high He & H levels may shrink TMS temperature window in both high and low
temperature regimes (due to degradation of fracture toughness).
 Heat flux of the FW comparable to fast reactor fuel cladding, but geometry is much
more complex, plus pressurized coolants (8 MPa He) result in combination of thermal
and primary stresses.
 Stresses also arise from thermal expansions and gradients that occur over large
distances of meters in 3-D (several cm displacement in an unconstrained FW).
 Stresses in FW are time dependent due to irradiation and thermal creep during quasi
steady state operation. Stresses and dimensional instabilities may also arise from
density decreases due to helium bubble and void swelling, or slight density increases
due to precipitation.
 Neutron flux varies spatially  corresponding irradiation creep strain and stress
relaxation also varies with position in the fusion structures.
S. Sharafat – FNST Aug 2009 - UCLA
14
FABRICATION / JOINING
BACKUP SLIDE
S. Sharafat – FNST Aug 2009 - UCLA
15
Fabrication and Joining R&D
 Bonding and welding has been identified as a key fabrication and assembly issue for
TBM.
 Joining R&D falls into two categories (1) manufacturing of structures (FW), and (2)
welding/bonding to form component (TBM). Japan and the EU are developing both,
structure fabrication techniques, based on HIPing and Diffusion Welding, and various
welding techniques, including TIG*, EB (Electron Beam), and LW (Laser Welding).
 Eurofer97 bonds have been irradiated up to 2.5 dpa @ 300°C in Sodium, and F82H
bonds up to 2.5 & 10 dpa @ 275°C in He. Below 300 oC all welds experience shift in
DBTT saturating around 2 dpa. Post Weld Heat Treatment (PWHT) can lower DBTT shift
of welds. Mutliple PWHT of Eurofer97 TIG weld produced the best DBTT results
 HIPed Bonds: The shift in DBTT of HIPed Eurofer97 is similar to that of Eurofer97
base material (base material DDBTT ~100 oC at 2.5 dpa;
~150 C at 8 dpa irradiated at 300 oC).
 EB Welds: Eurofer97 EB welds show shifts in DBTT of about 70 oC – 120 oC for PWHT
welds (2.6 dpa at 300 oC). F82H EB welds exposed to 2.2 dpa at 275 oC (no PHWT)
show a shift in DBTT of ~250 oC. F82H EB weld results are inconclusive (no PHWT) and
can not be compared with the Eurofer97 EB welds.
 TIG Welds: Eurofer97 TIG shows a shift in DBTT from about -25 oC to about +100 oC
(2.6 dpa at 300 oC). TIG welded F82H show an increase DBTT from about -75 oC to
about +50 oC (2.28 dpa and 8.94 dpa irradiated at 300 oC).
*TIG: Tungsten Inert Gas welding is an arc welding process
S. Sharafat – FNST Aug 2009 - UCLA
16