Transcript Document 7138514

Materials Issues in High Power Accelerators with
Comparisons to Fission and Fusion Reactors
L. K. Mansur
Oak Ridge National Laboratory
Massachusetts Institute of Technology
ANS Student Chapter and
Nuclear Science and Engineering Department
February 22, 2006
1
Materials Issues in High Power Accelerators
with Comparisons to Fission and Fusion
• Introduction
– Accelerator systems
– Materials topics
– The Spallation Neutron Source
• Radiation effects--most pervasive issue
– Brief review/tutorial
• Metallic alloys
• Ceramics
• Polymers
– Damage conditions and materials choices
• Design-specific issues
– Cavitation erosion in pulsed liquid metal targets
– Beam stripper foils
– …
• Comparisons with Fission and Fusion Reactors
• Summary
2
High Power Accelerator Facilities
• Spallation neutrons
–
–
–
–
–
–
Neutron scattering
Transmutation of nuclear waste
Energy amplification
Isotope production
In operation: SINQ, LANSCE, ISIS, …
Under construction: SNS, J-PARC, …
• Radioactive ion beams
– ISOL (proton)
– Fragmentation (heavy-ion)
• Particle physics
– Muon and neutrino production
– …
3
Nuclear Spallation
• In a high atomic mass
target each proton
produces up to 30
neutrons, with energies
similar to a fission
spectrum, but with a high
energy tail up to the proton
energy
• Radiation damage rates
in a spallation neutron
source are similar to those
in high flux fission and
fusion reactors
4
How to Focus?
• Limitless materials questions for large accelerator
and reactor complexes. Especially important:
– Where R&D is needed to reduce risk
• Establish new concept viability
• Select or develop materials that could fulfill intended function
• Obtain sufficient information to estimate lifetime
• Qualify materials for applications
– requires more effort than above activities
– need prototypical facilities or conditions
– not always possible for new accelerator types
– usual (regulatory requirement) for fission power reactor
and research reactor applications
– Where demands are above experience-based threshold or
beyond conventional needs for high performance facilities
• Conditions for which there are few (or no) data on materials
• Aggressiveness of service environment
5
Specific Example--Spallation Neutron
Source (SNS)
To begin operation in 2006
Oak Ridge, Tennessee
6
Locations Where Radiation Effects are
Key Concern or Issue to Consider
Protons: 1 GeV, 2 ma
Collimator straight section of
accumulator ring
Ring-to-targetAccumulator
beam transport
ring
(RTBT)
SNS
Ring Injection
Dump, Stripper
Mechanisms and
Magnets
General Radiation
Levels
In Tunnels
Ion
DTL
source
CCL
SCL
Linear accelerator system (linac)
Magnets
Spallatio
Target,
Beam
Window
Moderato
Reflecto
Spare
section
High-energy
beam transport
Target
station
(HEBT)
7
SNS Target Region
Target Module
Outer
Reflector
Plug
Target
Inflatable
seal
Core Vessel
water cooled
shielding
Core Vessel
Multi-channel
flange
Proton
Beam
Spallation Target at SNS
Liquid mercury operating at
90-150 C within two
double-walled type 316LN
stainless steel containers
9
Radiation Doses for Key SNS Locations
(per year)
Spallation target module
peak displacement dose
36 dpa
(~ 2/3 n, 1/3 p)
Ring injection dump peak
dose
7 dpa
(~ 3/5 p, 2/5 n)
RTBT second doublet coil
peak ionizing dose
1 MGy
Ring injection section
magnet peak ionizing dose
0.5 MGy
(1/5 n, 4/5 p)
Coupler
-peak displacement dose
6.3 x 10–9 dpa
(~ 3/4 n, 1/4 p)
-peak ionizing dose
9.5 kGy
10
Radiation Effects in Materials
• Short answer
–Virtually every property can be changed by irradiation
• Long answer
–Dimensions
–Mechanical properties
–Physical properties (electrical, optical, thermal…)
–•••
• Underlying these changes are the production
of defects and defect clusters, alterations in
microstructure (e.g., dislocations, voids,
precipitates) compositional segregation,
electronic ionization and excitation …
11
Historical Perspective on Radiation Effects
• Some radiation effects were observed in minerals in the
19th century, but their origin was not understood
• E. P. Wigner, 1946, Journal of Applied Physics 17
“The matter has great scientific interest because pile irradiation should
permit the artificial formation of displacements in definite numbers and
a study of the effect of these on thermal and electrical conductivity,
tensile strength, ductility, etc. as demanded by the theory.”
• The full scope of radiation effects in materials was only
appreciated after high neutron flux fast spectrum
reactors were operated in the 1950’s and 1960’s
• Targets of high power accelerators experience roughly
the same levels of damage as the highest flux fission
reactor cores and first walls of future fusion reactors
12
Origins of Radiation Effects in Materials
• Displacement of atoms (nuclear stopping)
–Dominant damage process for metals
–Significant for ceramics, semiconductors
–Can be significant for polymers (usually neglected)
–Dose unit--displacement per atom, dpa
–One dpa is the dose at which on average every atom in the
material has been energetically displaced once
• Ionization and excitation (electronic stopping)
–Generally can be neglected for metals
–Important for polymers, ceramics, semiconductors
–Dose unit--Gray, Gy, the dose for absorption of 1 J/Kg
13
Origins of Radiation Effects in Materials
• Transmutation reactions
–Transmutation products, especially He and H from protonand neutron-induced reactions, exacerbate damage
–Customary unit of measure is appm transmutant per dpa,
e.g., appm He/dpa, appm H/dpa
• Typical highest damage rates--10-6 dpa/s, >103 Gy/s
–High power accelerator target 100 appm He/dpa
–High flux reactor core
0.2 appm He/dpa
–Fusion reactor first wall
15 appm He/dpa
14
Displacement Damage Occurs in Cascades
•
pka energy
•
200 keV
10 keV
~ avg. fission
•
Particle (e.g., beam proton or
spallation neutron) transfers its
energy to the primary knock-on
atom (pka)
High energy particles, e.g., GeV
protons or fusion neutrons may
produce atomic recoils at much
higher energies than fission
neutrons
Large-scale atomic simulations
demonstrate that subcascade
formation leads to similar defect
production
50 keV
~ avg. fusion
10 nm
Molecular Dynamics Simulations of peak
damage state in iron cascades at 100 K
R. E. Stoller, ORNL
15
Time and Energy Scales for
Radiation Effects by Displacement Damage
Time
Energy
Cascade Creation
10-13 s
Unstable Matrix
10-11 s
Interstitial Diffusion
10-6 s
Vacancy Diffusion
100 s
Microstructural
Evolution
106 s
Neutron or Proton
105 - 109 eV
Primary Knock-on Atom
104 - 105 eV
Displaced Secondary
102 - 103 eV
Unstable Matrix
100 eV
Thermal Diffusion
kT
16
Hierarchy of Reactions Leading to Property
Changes in Metallic Alloys
Displacement of Atoms
Diffusion and Aggregation of Defects
Evolution of Microstructure
Embrittlement, Swelling, Irradiation Creep
What is it? Why is it important?
17
Radiation-induced Swelling
• Volume increase accounted for by a
distribution of nanoscale cavities
• Interstitials absorbed at dislocations;
vacancies absorbed at cavities
• Transmutation helium and other gases
stabilize cavities and enable swelling
• Up to tens of percent at tens of dpa in “offthe-shelf” structural alloys
• Theory and critical experiments have led to
knowledge of mechanisms and to the
design of swelling resistant alloys
18
Low Swelling Alloys Have Been Designed by
Combining Theory/Mechanism Experiments
Austenitic
Stainless
Steel
19
Importance of Swelling
• Significant concern between 0.3 and 0.6 Tm
• Overall dimensional increase of components
• Sensitivity to gradients in dose, dose rate and
temperature can lead to distortions
• Fabricated geometries not preserved
• Cavity distributions possible easy paths for fracture
• May place limits on component lifetimes in fission
and fusion reactors
• May affect particle transport and thermal hydraulics
in fast reactors
• Not expected to be a problem in components
operating < 0.3 Tm (e.g., SNS or J-PARC target)
20
Radiation-induced Creep
• Shape change in response to applied stress, or
relaxation under constraint
• Vacancies and interstitials partition asymmetrically
– to differently oriented dislocations
– between dislocations and other sinks for defects (cavities, grain
boundaries, …)
– because of short time unequal stochastic fluctuations in
absorption of vacancies and interstitials
• Occurs at all temperatures of interest
• At high temperatures, T > 0.55 Tm, it is overwhelmed
by thermal creep
21
Radiation-Induced Creep
Two manifestations of the same phenomenon
Relaxation of stresses (shown below)
Continuing dimensional change
22
Importance of Radiation-induced Creep
• Relaxation of engineered stress distributions
• Dimensional instability in shapes and sizes--linear
dimension changes of several percent at high doses
• May be beneficial in relaxing stresses produced by
radiation-induced swelling
• Could be a significant problem for tight tolerance
geometries, e.g., in fast neutron reactors
• Could affect particle transport and thermal
hydraulics
• Not expected to be a problem in liquid metal
accelerator targets with open structure (e.g., SNS or
J-PARC target)
23
Radiation-induced Embrittlement
• Hardening and loss of ductility
• Caused by vacancy and interstitial clusters,
dislocation loops, precipitates and cavities that
restrict deformation by dislocation glide
• Simultaneous weakening of grain boundaries
– by radiation-induced solute segregation and
precipitation at grain boundaries
– by accumulation of transmutation products on grain
boundaries, especially He from (n, α) reactions
24
Failures Can be Caused by Embrittlement
• Micrographs of tungsten
compression specimens
• Irradiated with 800 MeV
protons and compression
tested to 20% strain at room
temperature
• (a) before irradiation, (b)
after 3.2 dpa, (c) after 14.9
dpa, and (d) after irradiation
to 23.3 dpa.
S. A. Maloy, et al., J. Nucl. Mater., 2005
(LANSCE irradiations)
25
Irradiation-induced Hardening/Loss of Ductility
•
•
•
Yield stress and strain-to-necking vs displacement dose for AISI 316L
stainless steel (solution annealed, 20% cold-worked, e-beam welded)
Filled and empty symbols--test temperatures of 25 and 250 º C, respectively
Data from fission reactor irradiations (Ttest = Tirrad = 250 º C) are included
J. Chen, et al.,
J. Nucl. Mater. 2005
(SINQ irradiations)
26
Importance of Embrittlement
• Can lead to structural failure of components
• Possible crack formation and loss of vacuum or
coolant integrity
• May necessitate early replacement of components
• A significant issue for fission and fusion reactors
• Primary radiation effects issue for liquid metal target
containers (e.g., SNS and J-PARC targets)
27
SNS Target Radiation Damage
dpa/SNS year
appm He/SNS year
103
Vertical position (cm)
20
102
10
101
0
Axial position (cm)
Axial position (cm)
Displacements
Helium production
Maximum dpa rate is ~ 21 dpa/SNS year (~36 dpa/year)
(SNS year = 5,000 h)
28
Moderator Vessel Radiation Damage
dpa/SNS year
appm He/SNS year
Vertical position (cm)
7
10
4
1
0.1
0
Axial position (cm)
Axial position (cm)
Displacements
Helium
•Maximum dpa rate is less than 8 dpa/SNS year
•Maximum He production less than 50 appm He/SNS yr (~6 appm He/dpa)
29
Reflector Radiation Damage
Damage rate
dpa/SNS year
Vertical position (cm)
Geometry
1
0.1
10-2
Axial position (cm)
Maximum displacement rate of ~7 dpa/SNS y in Al 6061, less in steel and Be
Maximum He ~40 appm He/SNS y in Al 6061 and ~30 appm He/SNS yr in Be
30
Materials R&D on Ductility of
Stainless Steels
100
DATABASE*
EC316LN(p)**
80
HTUPS316(p)**
EC316LN(n)**
HTUPS316(n)**
*Fusion program database for 316 SS,
irradiated and tested at 0 ~ 200 oC
**ORNL data for LANSCE irradiation
***LANL data for LANSCE irradiation
Type 316 LN
stainless steel
recommended for
SNS target
module
Uniform elongation, %
316L(p)***
60
40
One SNS year
20
Remove 1st target
0
0.0001
0
0.01
1
dpa
100
31
Radiation Can Affect Ceramics through
Three Types of Processes
• Permanent defect production by knock-on collisions
and nuclear reactions
–Displacement damage
–Transmutations
• Displacement production via ionization (radiolysis)
processes
–Occurs in SiO2, alkali halides, etc.
–Does not occur in Al2O3, BeO, AlN
• Radiation-induced conductivity (RIC)
–Transient excitation of valence electrons into conduction
band
32
Electrical Conductivity in Fine Grained 99.99%
Pure Alumina Cable (CR 125)
Loss of electrical insulation under typical
accelerator conditions
is not of concern
33
Basics of Radiation Effects on Polymers
• Comparatively low doses can change properties
–Why? Typically very high molecular weight—therefore,
a large fraction (tens of percent) of molecules can suffer
at least one event in doses of order 10 kGy
• Predominant changes are chain scission and crosslinking (other changes: release of small molecules,
altering chemical composition, i.e., gas formation;
modification in types of bonding, …)
• For a given polymer, radiation type and temperature,
either cross-linking or scission usually dominates
• Cross-linking increases molecular mass, lowers
solubility and can improve mechanical properties
• Scission generally degrades properties
• Sensitivity depends on irradiation conditions and
environment. In vacuum dose endurance than in air by
an order of magnitude. Improvement at higher T.
34
Mechanical Properties
of Polymers
(dose to reduce
elongation by 25%)
K. J. Hemmerich, Med. Dev.
& Diag. Ind. Magazine, Feb. 2000
Consider Polymers for Use Only in
Secondary Radiation Fields
• Radiation effects become significant over the range from
~ 1 kGy to 103 kGy, depending on the material
• Acetal, polypropylene, and PTFE (teflon) should be
avoided except for very low dose applications
• Top performers include PI (polyimide)
• High performance fluoropolymers like “Viton” are in an
intermediate range (“Viton” is a general name for different formulations.
Specific data must be consulted.)
• “Harden” magnets, electronics, insulators—For example,
avoid conventional insulation in favor of polyimide
(Kapton) or ceramic insulation
36
Approximate Radiation Dose Limits
• People << 1 Gy (Sv)
• Polymers: 102 to 107 Gy
• Semiconductors: ~1013 n/cm2, ~102 Gy (1016 to 1017
for SIC JFETs at 300˚C)
• Glass: 1020 n/cm2 (>10% dimension change); 108 Gy
(optical darkening saturates)
• Ceramics:
– ~109 Gy, ~ 1020 n/cm2 (radiolysis-sensitive ceramics)
– >1021 n/cm2 (> 1 dpa) for most oxides, carbides and
nitrides
• Metals: > to >> 1021 n/cm2 (> 1 dpa); can ignore
ionizing radiation; alloys tailored for radiation
resistance > 50 dpa
37
Examples of Design-Specific Materials Issues
1) Cavitation Erosion in Hg;
2) Beam Stripper Foils; 3) IASCC
• Cavitation erosion (pitting) is expected in short
pulse/high power/liquid Hg target
• Observed in simulations (but not yet in actual target)
– Origin of effect
– Potential problem
– Research to characterize and mitigate damage
• LANSCE accelerator (WNR facility) tests
• Vibratory horn
• High repetition pulse experiments
• Surface carburization treatment
• US, Japanese, European collaboration
38
Rapid Heating and High Thermal Expansion
Lead to Large Pressure Pulse in Mercury
• Peak energy deposition in Hg for a single pulse = 13
MJ/m3
– Peak temperature rise is only ~ 10 K for a single pulse, but rate of
rise is ~ 107 K/s
• An isochoric (constant volume) process
because beam deposition time (0.7 ms)
<< time required for Hg expansion
– Beam size/sound speed ~ 33 ms
• Local pressure rise is 34 MPa
(340 atm compared to static
pressure of 3 atm)
39
Cavitation Bubble Collapse
Leads to Pitting Damage
• Large tensile pressures occur due to reflections
of compression waves from steel/air interface
– These tensile pressures cavitate the mercury
– Damage is caused by violent collapse of cavitation bubbles under
subsequent interaction with large compression waves
Damage in region with large
pits for bare 316SS-LN
diaphragm after July 2001
LANSCE-WNR tests
40
Summary of Pitting Erosion Tests
WNR 2.5 MW
WNR 0.4 MW
MIMTM 316SS-CW
250 mm Drop Test - Lower Position
MIMTM Curve Fit: MDE = C N^1.27
WNR 1.1 MW
WNR 3.1 MW w/ Kolster
250 mm Drop Test - Upper Position
Ultrasonic Horn (Pawel et al.)
MIMTM Kolsterized 316SS
Mean Depth of Erosion (microns)
1.E+04
MIMTM device
data used for
extrapolation
because 100
pulse damage is
slightly worse than
1 MW equivalent
in-beam damage
1.E+03
1.E+02
1.E+01
1.E+00
Two weeks
at 60 Hz
1.E-01
1.E-02
1.E-03
1.E-04
1.E-05
1.E+02
1.E+03
1.E+04
1.E+05 1.E+06
1.E+07
1.E+08
1.E+09
Number of Cycles
Extrapolating--estimated mean depth of erosion in SNS at 1 MW for 2 weeks < 50 mm
Fission, Fusion, and Spallation Involve Major
Efforts on Radiation Effects in Materials
• Working groups
– Basic radiation effects research
– High power accelerator targets
– Fission reactor internals and PVs (Generation IV)
– Fusion reactor first walls & high dose components
• Need more deliberate coordination of work (where it makes
sense)
– Understand life-limiting mechanisms
– Select or develop materials to meet applications
– Utilize key facilities for experiments
– Pool knowledge
– Make better use of sparse resources
42
High Energy Accelerator Radiation Damage
Compared with Fission and Fusion Reactors
• Highest particle energies
– Spallation ~1 GeV; fusion and fission  14 MeV
• Instantaneous damage rates
– 10-2 vs. 10-6 dpa/s for pulsed beams (time average
approximately 10-6 dpa/s for all)
• He and H transmutation rates
– Spallation
– Fusion
– Fission
~ 500 appm H/dpa
100 appm He/dpa
10
“
0.2
“
• Other transmutations higher for spallation
43
Similarities in Accelerator, Fission and
Fusion Materials Technologies
• Performance limits dictated by
– Radiation effects
– Strength and toughness vs temperature
– Long-term microstructural and phase stability
– Compatibility with special purpose fluids
• Fusion--Heat transfer/isotope breeding
• Fission--Heat transfer/neutron moderation
• Spallation--Heat transfer/neutron production
• More experimental data required to support designs
• No prototype facilities available
• Lifetime projections by modeling and analysis
44
More Similarities in Accelerator, Fission
and Fusion Materials Technologies
• Reliance on similar advanced alloys--austenitic, ferriticmartensitic, high nickel alloys
• Future need for higher performance materials including
mechanically alloyed steels
• Mechanisms of radiation response
• Furnish radiation test bed for the other technologies
45
More Similarities in Accelerator, Fission and
Fusion Materials Technologies (continued)
•
•
•
No prototype facilities available for Fusion, Gen IV
Reactors, or Liquid Metal Pulsed Targets
Most irradiations conducted in a few key facilities:
HFIR and ATR
JMTR and JOYO
HFR
BOR 60
LANSCE
SINQ
Require compatibility with special purpose fluids
– Liquid metals in contact with irradiated structural materials-Fusion, SFR, LFR, Spallation
– Water coolant in contact with irradiated structural materials-ITER, SCWR, Spallation
– Gas coolant in contact with irradiated structural materials-Fusion, NGNP, GFR
46
Key Operating Conditions
Technology
Parameter
Fluid
Fusion
Fission
(Gen IV)
H2O, He, Li, H2O-SC, He,
PbLi, FLiBe Na, Pb, PbBi
Particle
Energy
< 14 MeV
He/dpa
Stresses
Spallation
Hg, Pb,
PbBi, H2O
10
< 2 MeV
(most n’s)
0.1 - 50
< 1 GeV
(p and n)
50 - 100
Moderate,
slow var.
Moderate,
slow var.
High,
pulsed
47
Overlap in Temperature for Fusion, Generation IV
Fission Reactors and Spallation Facilities
Operating Temperatures and Radiation Effects
Gen IV
SCWR
Fusion
ITER DEMO
Spallation
Example: Austenitic SS
0
SNS
Trans.
NGNP (VHTR)
A-SSTR2
SS Temp.
Limit
500
Irradiation Creep
1000
Swelling
1500 T, ºC
He Embrittlement
Low T Embrittlement (Self-defects, He, H)
48
Current Alloy Systems Have Limitations
• Austenitic stainless steels (300 series)
- thermal creep temperature limits
- inherently poor swelling resistance at high doses “off the
shelf”. Compositionally tailored low-swelling variants are
available (An important success of materials R&D).
• Ferritic/Martensitic Steels
- good swelling resistance up to high doses
- low temperature radiation hardening
- thermal creep temperature limits
• High nickel alloys
- thermal creep resistance up to high temperatures
- severe embrittlement at low to moderate doses
• Refractory Alloys
- adequate swelling resistance up to high doses
- fabrication, joining difficulties
- “low” temperature embrittlement
- poor oxidation resistance
49
High Power Accelerators, Advanced
Fission and Fusion Reactors
• Diverse irradiation environments for materials
• Strong underlying commonality in fundamental
radiation effects and in performance limiting
phenomena
• Many other issues in common: similar advanced
alloys selected, lack of prototype facilities, related
compatibility issues, …
• Work more as one community to better support the
three technologies and to form scientific basis to
develop better materials
50
Acknowledgements
• Materials--T. S. Byun, Yong Dai, Jim DiStefano,
Ken Farrell, Martin Grossbeck, John Haines,
John Hunn, Stuart Maloy, Steve Pawel, Bernie
Riemer, Joe Strizak, Steve Zinkle
• Radiation damage calculations--Phil Ferguson,
Franz Gallmeier, Monroe Wechsler
• Carbon stripper foils--Mike Plum
51
Physics of radiation effects in materials
• W. Schilling and H. Ullmaier, “Physics of Radiation Damage in Metals,” Chapter 9,
Volume 10B, Nuclear Materials, Part 2, B. R. T. Frost, ed., Materials Science and
Technology: A Comprehensive Treatment, R. W. Cahn, P. Haasen, and E. J.
Kramer, eds., VCH publishers, Germany, 1994.
• L. K. Mansur, "Mechanisms and Kinetics of Radiation Effects in Metals and Alloys,"
A chapter in the book, Kinetics of Non-Homogeneous Processes, edited by G. R.
Freeman, Wiley-Interscience, New York 1987, pp. 377-463.
Materials issues in nuclear technologies
• W. Sommer, et al. “Materials Selection and Qualification Processes at a HighPower Spallation Neutron Source,” Mater. Char., 43 (1999) 97-123
• G. S. Bauer and H. Ullmaier, “Materials Related Work for the ESS Target
Stations,” J. Nucl. Mater. 318 (2003) 26-37
• Y. Dai, et al., “The Second SINQ target Irradiation Program,” J. Nucl. Mater. 43
(2005) 33-44
• S. J. Zinkle, “Overview of the US Fusion Materials Sciences Program,” Fusion Sci.
and Tech. 47 (2005) 821-828
• L. K. Mansur, “Materials issues in high power accelerators,” Nucl. Instr. Meth. A (in
press)
• L. K. Mansur, et al., “Materials for Fusion, Generation IV Fission Reactors and
Spallation Neutron Sources--Similarities and Differences,” J. Nucl. Mater. 329-333
(2004) 166-172
• L. K. Mansur, R. K. Nanstad, A. F. Rowcliffe, and R. L. Klueh, “Survey of Metallic
Materials for Irradiated Service in Generation IV Reactor Internals and Pressure
Vessels,” ORNL/TM-2005/519 (draft out for comments)
53
Approximate Radiation Dose Limits
• Fast fission reactor spectrum: 1x1010 n/cm2
~2 rads ~ 0.8x10-11 dpa (equal contributions
from gamma ray and neutron pka ionization)
• Mixed spectrum reactor: 1x1010 n/cm2 ~ 40
rads ~ 0.8x10-11 dpa (ionization dose mainly
due to gamma rays)
(precise values depend on reactor design
and material)
54
Irradiation-Assisted Stress
Corrosion Cracking
• For water-cooled stainless steel or nickel-based
alloys in radiation fields, need to consider IASCC
• Damage based on irradiation embrittlement (above)
may not be worst case for water-cooled structures
• Discuss dpa limits, fabrication and chemistry
•
•
•
•
First reported in Boiling Water Reactors (BWRs) in 1962
Observed in 300 series stainless steels and high nickel alloys
Earlier, components affected were either small (bolts, springs), or
designed for replacement (control blades, instrumentation tubes)
Recently, more structurally significant components of reactor cores
such as core shrouds have also been degraded
55
Some Facts About IASCC
•
•
•
•
•
•
An intergranular cracking phenomenon
Requires displacement damage, water, stress
Threshold in BWRs ~ 0.5 dpa
Threshold in PWRs ~ several dpa
Most available data in range 270-370 C
Decreasing T may decrease prevalence; there is
also evidence to the contrary
• Can be eliminated by controlling O to < 10 ppb,
and/or H > 200 ppb
– Too much H can also cause cracking
– Crack tips can become acidic without added H
56
Recommendations on IASCC
• Avoid designs and fabrication that increase
stress--e.g., unrelieved residual stresses, sharp
corners, other stress raisers
• Avoid high strength alloys--e.g., CW materials
• Use strictly controlled weld procedures
• Consider control of water chemistry--addition of
hydrogen/removal of radiolytic oxygen and
removal of impurities (e.g., chlorides, sulfates)
• Restrict very long term water-cooled structures in
critical applications under significant stress to
< few dpa; if no chemistry control < 0.5 dpa
• Design for non-routine replacement of
“permanent” structures as far as possible
– 40 years is too long for irrevocable decisions in a complex
irradiation environment
57
H- Beam Stripper Foils
• Multi-Turn Charge-Exchange Injection creates short pulse of
protons in Ring from long pulse Linac
• Two electrons are removed by the stripping foil, injected protons
are merged with previously accumulated beam
• The secondary foil strips the H- and H0 which survive the first foil
58
Need Foil Thick Enough to Strip Electrons
• Average proton in SNS ring will pass through stripper foil 6 to 7x
• Thicker foil runs at higher T, scatters circulating beam, and
increases activation levels
• Select thin foils with low atomic number and low density
0.14
-1,0 = (6.76+.09
10 cm
Nominal
SNS )x
foil
2
0,1 = (2.64+.05
)x 10-192cm
thickness
300 ug/cm
,
-19
-1,1 = (0.12+.06
cm2
97% efficiency
at)x110GeV
-19
0.12
EFFICIENCY
0.1
2
Probability of scattering
per foil traversal
~ Z2 ρ t
0.08
0.06
0.04
Carbon selected--low density, low
atomic number, high melting
point, fabricable in thin sections
H- + H0
0.02
0
200
250
300
350
400
450
FOIL THICKNESS mg/cm2
500
550
600
59
Stripper Foil Damage
• Stripper foils degraded by high temperature
and radiation damage
• Efforts ongoing to develop new types of
carbon stripper foils
LANSCE PSR stripper foils
60
Tradeoff between Stripper Foil and Ring
Injection Dump Capabilities
Small
Foil Size/Thickness
Large
• Less efficient H+ production
• More efficient H+ production
– More power to dump
– Less power to dump
– More radiation damage in dump
– Less radiation damage in dump
• Lower loss and activation
• More losses and activation
– Lower foil temperature
– Higher foil temperature
– Fewer foil hits by stored beam
– More foil hits by stored beam
– Fewer large amplitude particles
– More large amplitude particles
injected into ring
injected into ring
Foil size and thickness optimization problem involves
both materials and accelerator physics/engineering
61
Austenitic Stainless Steels: Fusion and
Gen IV Fission Applications
System
(Coolant)
Component
T
ºC
Max
Dose
dpa
Max
He
appm
Candidate
Alloys
Performance-limiting
Phenomena
ITER
(Water)
First Wall/
Blanket
100
to
300
3
75
316LN
Flow localization and
reduced fracture
toughness. (Performance
beyond 3 dpa)
Fuel
Assembly
280
to
620
15
200
Core
Support/
Internals
280
to
500
0.1
to
20
Advanced
low
swelling
stainless
steels:
D9,
PNC316,
HT-UPS
Flow localization and
reduced fracture
toughness (< 400 ºC).
Helium effects on rupture
life and ductility > 550 ºC.
Void swelling 400-550 ºC.
Helium bubble coarsening
during T excursions.
SCWR
(SC Water)
250
62
Ferritic/Martensitic Steels: Fusion and
Gen IV Fission Applications
System
(Coolant)
Component
T
ºC
Max
Dose
dpa
Max
He
appm
SSTR
(Water)
First Wall/
Blanket
300550
100
>1000
HCLL
(He)
270550
100
>1000
HCPB
(He)
300550
100
>1000
Fuel
Assembly
280620
15
20
Core Support/
Internals
280500
0.1 20
150
Fuel Assemby
300550
SCWR
(SC Water)
LFR
( Pb-Bi )
20
15
Candidate
Alloys
Performance-limiting
Phenomena
Low Activ.
8-9% Cr
FerriticMartensitic
Steels
Flow localization and loss of UE
< 400 ºC. Shifts in DBTT by selfdefects and He. Helium effects
on rupture life and ductility > 550
ºC. Segregation and phase
instabilities effect on fracture >
450 ºC.
Advanced
8-12 %
FerriticMartensitic
Steels
Flow localization and loss of UE
< 400 ºC. Shifts in DBTT by selfdefects. Effects of long term
aging > 400 ºC (segregation
and precipitation) on mechanical
properties. Off-normal
temperature excursions effect
on microstructure and
properties
63
Mechanically Alloyed Steels: Potential
Fusion and Gen IV Fission Applications
System
(Coolant)
Component
T
ºC
Max
Dose
dpa
Max
He
appm
Fusion
Demo
Plants
(Water/He)
First Wall/
Blanket
300550
100
~ 1000
9Cr martensitic: 12-14Cr ferritic; Y, W,
Ti. High concentration clusters/nano
particles trap He and minimize nonhardening embrittlement.
Fuel Assembly
600900
100
10
Matrix--high T corrosion resistance in
Pb. Cluster/particle dispersion--high
T creep strength, very long term
stability . Microstructural stability
during off-normal events.
Core Support/
Internals
8001000
< 0.5
Core Structure
5001000
80
High T LFR
(Lead)
NGNP
(He)
GFR
(He)
50
8
Potential
Alloy Design Features
Ni-Fe-Cr matrix--oxidation
resistance in He (and void swelling
resistance in GFR). Cluster/particle
dispersion--high T creep strength,
very long term stability (and void
swelling resistance in GFR).
Microstructural stability during offnormal events.
64
1200
Yield strength, MPa
1000
800
DATABASE*
EC316LN(p)**
HTUPS316(p)**
EC316LN(n)**
HTUPS316(n)**
316L(p)***
316****
316LN****
600
SNS R&D on
Irradiated
Yield Strength
and Ductility
of Stainless
Steels
400
*Fusion program database for 316 SS,
irradiated and tested at 0 ~ 200 oC
**ORNL data for LANSCE irradiation
***LANL data for LANSCE irradiation
****ORNL data for HFIR irradiation
200
0
80
Uniform elongation, %
60
40
20
0
0
0.0001
0.001
0.01
0.1
dpa
1
10
100
Radiation-Induced
Conductivity
in Insulators
Radiation Induced
Conductivity in Insulators
conduction
band
shallow trap
valence band
radiation
66
Summary of RIC Data for Oxide Ceramics
 RIC   0  K
d~1.0
SNS Coupler
K depends on
electron trap
concentration
67
d
Basics of Radiation Effects on Polymers
• Although polymers are often classed as cross-linking or
scission (degrading) types under irradiation, our
research has shown that the ratio of cross-links to
scissions depends strongly on LET. Energetic heavy
ions cause much more cross-linking than  or e-,
because of much higher LET and can lead to
reclassification from scission type to cross-linking type
• Range of sensitivity for producing significant
degradation spans more than three orders of magnitude
in dose, for example, for reduction in elongation by 25%:
1kGy PTFE (Teflon)
103 kGy
PI, PS (Polyimide, Polystyrene)
• Sensitivity also depends on irradiation conditions and
environment. Irradiation in vacuum can improve dose
endurance over that in air by an order of magnitude.
Irradiation at higher temperatures can give improvement.
68
Type and Distributions of Microstructural Features
are Strong Functions of Temperature
Not irradiated
Irradiated 300 ºC
Irradiated 500 ºC
Irradiated 700 ºC
69
Radiation-induced Creep
70
SNS Moderators and Inner Reflector
Outer
beryllium
radius
6061 Al
Structure
Decoupled
and
poisoned
hydrogen
moderator
Coupled
hydrogen
moderators
304L SS
shielding
plates
Decoupled
Ambient
water
moderator
Spallation Sources
Transmutation of
nuclear waste
ADS (F, B...)
AFCI (US)
EA (I, E, F)
Neutron Scattering
ISIS (UK)
LANSCE (US)
SINQ (CH)
Tritium production
TRISPAL (F)
APT (US)
SNS (US)
J-PARC (J)
ESS (EU)
Typical Parameters:
Beam power several MW (~1 GeV protons)
Pulse length < 1ms (several 1014 p/Pulse, energy up to 100 kJ)
Repetition frequency 25/50/60 Hz
Thermal n-flux up to 7x1018 n/m2s average
up to 2x1021 n/m2s in pulse
72
Decrease in Elongation of Viton Elastomer
Irradiated at Various Temperatures
SNS Coupler
M. Ito, Radiat. Phys. Chem.
47(1996)607-610
73