Shuhei NogamiTohoku University, Japan
AcknowledgementM. Rieth, P. Lied (KIT), G. Pintsuk (FZJ), T. Hirai (IO), J.H. You (IPP),
M. Fukuda (QST), R. Kasada, A. Hasegawa (Tohoku U.), Y. Hatano (U. Toyama)
1
Outline
1. Introduction
2. Tungsten-based materials as an armor
3. Copper-based materials as heat sink and cooling pipe
4. Irradiation projects of materials for divertors
5. Issues for evaluation and prediction of structural strength and lifetime
6. Summary and Conclusion
Introduction
3
Requirements of Divertors
n Requirementsü Removal of waste material (helium) from plasmaü Cooling capability --- thermal conductivity (W, Cu, etc.), coolant (water, etc.) ü Structural reliability --- strength, ductility, corrosion resistance, etc.ü Long-term operation for DEMOü Assessment of time-dependent degradation (neutron irradiation damage, etc.)
for DEMO
You et al., DVM, Mittweida, 2017
4
Damage and Degradation of Divertors
n Damage and degradation of materials and jointsü Degradation of physical and mechanical properties by
--- surface modification (melting and fuzz, etc.)--- macro-, micro-cracking (thermal fatigue, etc.)--- displacement damage (embrittlement, etc.)--- transmutation (Re, Os, and He, etc.)
Pintsuk et al., FED, 2013
Wirtz et al., NME, 2016
5
Damage and Degradation of Divertors
n Damage and degradation of materials and jointsü Volume change
- plastic strain accumulation (ratcheting, etc.)- creep deformation- swelling (voids, bubbles etc.)
ü Tritium issues- accumulation in materials and interfaces- interaction with defects by neutron irradiation
Merola et al., FED, 2015
Ogorodnikova et al., JNM, 2018
6
Neutron Irradiation Effects
ü Heat--- Steady state (stationary): 10 MW/m2
--- Slow transient: 20 MW/m2
--- ELM (fast transient): a few ten GW/m2
ü Neutron --- 15 dpa in W and 60 dpa in Cu (after 5 years)ü Ions (D, T, He) --- 1023 ions/m2/s
Reactor ITER DEMO
Material W Cu W Cu
Component replacements up to 3 5 year cycle
Av. neutron fluence [MWa/m2] Max. 0.15 5
Displacement damage [dpa] 0.7 1.7 15 60
TransmutationHe [appm] negligible 16 10 600
Re [%] 0.15 3Bolt et al., JNM, 2002 & JNM, 2004 and Robinson et al., UWFDM-1378, 2010
Acceptable or negligible
in ITER
7
OFHC-CuCuCrZr
W-based
Limitation of Structural Strength and LifetimeDetermined by Synergistic Loads
Helium(transmutation)
Helium(from plasma)
Sputtering
Solidtransmutation
Hydrogen(transmutation)
Tritium(from plasma)
Irradiationdamage
Oxidation(Accident)
Fatigue
Strength
Ductility
Recrystallization
Creep
Plastic deform.Ratcheting
Thermalconductivity
CorrosionErosion
Surfacemodification
8
Issues on Assessment of Structural Strength and Lifetime
ü DEMO needs an assessment of long-term structural reliability and lifetime.
ü Synergistic loads, time-dependent phenomena, gradient, distribution, and anisotropy of loads and material properties, should be considered.
ü Especially, consideration of neutron irradiation effects is important.
ü Material properties database and handbook and criteria and rules for the assessment of structural strength and lifetime are required.
ü However, lack of enough (experimental) data and knowledge is significant issue at present.
Tungsten-based materialsas an armor
10
Lifetime Limitation due to Degradation of W
20 MW/m2
10 s
1800oC x 1 h
1500oC x 1 h
1300oC x 1 h
1100oC x 1 h
As-received
Longitudinal cracks
Grain ejection (only near large cracks)
Cracks around resolidified layer
Before HHF load
After HHF load
Recrystallizationembrittlement
Low temperaturebrittleness
Rieth et al., JNM, 2019
Low temperature brittleness (low fracture toughness and high DBTT), recrystallization embrittlement, and neutron-irradiation-induced embrittlement will limit the lifetime.
DBTT and TRxx will be a critical factor for the
operation window
Neutronirradiation
embrittlement
11
Development of Tungsten Materials for DEMO
Stre
ss, σ
Test temperature, Tt [oC]
Yield stress (Unirradiated)
Fracture stress(Unirradiated, Irradiated)
Yield stress (Irradiated)
DBTT(Unirradiated)
DBTT(Irradiated)
--- need to increase recrystallization resistance--- need to increase fracture toughness and to lower DBTT
à need to increase strength and ductility--- need to increase neutron irradiation tolerance
12
Operation Window Determined by DBTT and TRxx
Nogami et al., FED, 2018, Bonk et al., IJRMHM, 2016, and Bonnekoh et al., IJRMHM, 2018
Increase in deformation ratio can make the DBTT lower.
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
200 300 400 500 600 700 800 900 1000 1100
Char
py a
bsor
bed
ener
gy [J
]
Test temperature [oC]
Pure WAs-received
L-S direction
Plate, 4 mm thick, (Rieth, Reiser)Plate, 7 mm thickRound-blank, 175 mm dia. x 29 mm thick, (Rieth)
t = 4 mm à ds = 19 μmt = 7 mmà ds = 22 μm
t = 29 mmà ds = 63 μm
13
Operation Window Determined by DBTT and TRxx
300
350
400
450
500
550
600
650
700
0 300 600 900 1200 1500 1800
Vick
ers h
ardn
ess
Annealing temperature [oC]
Annealing time = 1 h
Pure W foil(t = 0.2 mm)
Pure W plate(t = 7 mm)
Pure W platet = 6 mm)
Warm-rolled foil w/o SRHot-rolled plate with SR
Nogami et al., ISFNT-14, 2019 and to be published in the FED
High DBTTHigh TRxx
Low DBTTLow TRxx
Increase in deformation ratio can sometimes make the TRxx lower.
DBTT TRxx
14
Operation Window Determined by DBTT and TRxx
ü Optimization of deformation ratio is required to obtain acceptable combination of DBTT and TRxx.
ü A method with no increase in the deformation ratio should be considered.
Rieth et al., JNM, 2019
Second-phaseDispersion
Alloying
Grain Refining
15
Modification of Tungsten Materials
Rieth et al., JNM, 2019
ü There are a lot of approaches to modifytungsten.
• Doped W (dispersion-strengthened W,grain-stabilized W)
• W binary alloys by solid solute elements• Ternary and multi-component W alloys• W composites
16
Potassium Doped Tungsten-Rhenium Alloy
200 400 600 800 1000 1200 1400
T / oC
Pure WDBTT TRxx
K-doped W
K-doped W-3%Re
W-3%Re
1600
Reduction of DBTT and increase in TRxx were simultaneously achieved by K-doping and Re-additionwith no increase in the deformation ratio
Nogami et al., FED, 2019
Still
brit
tle
350
400
450
500
550
900 1100 1300 1500 1700 1900 2100 2300
Vick
ers
hard
ness
, HV
Test temperature [oC]
As-received, L x S surfacePure W, Plate, 7 mmK-doped W, Plate, 7 mmW-3%Re, Plate, 7mmK-doped W-3%Re, Plate, 7mm
As-received
Higher TRxx
Lower DBTTHigher USE
17
Tungsten Fiber Reinforced Tungsten
Mao et al., Composites Part A, 2018
Wf/W compositewith Y2O3 interfaceby FAST
MatrixInterfaceFiber
Elastic deformation
Matrix crackingPropagation of cracks to interface
Rupture of fibersPull-out of fibersFriction at interface
(c) Ultimate strength (fiber bridging)
(d)
PseudoDuctility
Mass Production à ?
19
Development of Tungsten Materials for DEMO
--- need to increase recrystallization resistance--- need to increase fracture toughness and to lower DBTT
à need to increase strength and ductility--- need to increase neutron irradiation tolerance
Stre
ss, σ
Test temperature, Tt [oC]
Yield stress (Unirradiated)
Fracture stress(Unirradiated, Irradiated)
Yield stress (Irradiated)
DBTT(Unirradiated)
DBTT(Irradiated)
20
Irradiation Effects on Tungsten
Microstructural Change
Koyanagi et al., JNM, 2017
ü Irradiation-induced microstructure dependent on the irradiation conditions (temperature, dose, dose rate, and transmutation etc.)
ü The lack of data from high temperature and high dose neutron irradiation tests
21
Irradiation Effects on Tungsten
Irradiation Hardening
Fukuda et al., JNM, 2014
ü No positive and negative effects of the K-doping and dispersion of La2O3 particlesü Suppression of hardening by Re-addition due to the suppression of formation of
voids and dislocation loopsü Significant hardening after the formation of precipitation
Hasegawa et al., JNM, 2016 & Fukuda et al., Mater. Trans., 2012
22
Irradiation Effects on Tungsten
Irradiation Hardening
ü Significant hardening caused by irradiation-induced precipitation in W-26%Re (χ-phase and σ-phase)
ü Effect of Re on the irradiation hardening could be positive and negative, which is dependent on the irradiation conditions.
Nemoto et al., JNM, 2000, Hasegawa et al., JNM, 2011, Hasegawa et al., JNM, 2016
23
Irradiation Effects on Tungsten
Swelling
W-25%Re
Pure W
ü No voids in W-25%Re induced suppression of swelling, although a large fraction of second phase precipitate was observed.
EBR-IITirrad = 430-1100 oCφt = 1 x 1022 n/cm2 (9.5 dpa) (E > 1 MeV)
Matolich et al., Scr. Metal, 1974
24
Irradiation Effects on Tungsten
Effect of Neutron Spectrum
Hasegawa et al., JNM, 2016 and Katoh et al., JNM, 2019
ü Thermal neutrons cause solid transmutations via (n, γ) neutron capture reactions, resulting in accumulation of Re, Os, and Ta, etc.
ü Higher energy neutrons like 14 MeV neutrons cause gas transmutationsvia (n, α) and (n, p) reactions, resulting in accumulation of He and H.
25
Irradiation Effects on Tungsten
Effect of Neutron Spectrum
Hasegawa et al., JNM, 2016 and Katoh et al., JNM, 2019
26
Irradiation Effects on Tungsten
Effect of Neutron Spectrum
Fukuda et al., JNM, 2016Dickinson, Trans. Am. Soc. Met., 1959
ü Significant hardening by precipitation in the non-irradiated conditionsü Higher irradiation hardening produced in the mixed-spectrum fission reactors, HFIR
and JMTR, compared to the fast breeder reactor JOYO
27
Irradiation Effects on Tungsten
Strength and Ductility
EBR-IITirrad = 371-388 oC
φt = 0.4-0.9 x 1022 n/cm2
(E > 1 MeV)
Steichen et al., JNM, 1976
ü Increase in the strength and decrease in the ductility (elongation and reduction in area), especially at low temperature range
28
Irradiation Effects on Tungsten
Strength and Ductility
ü As a recent result from the J-US PHENIX project, K-doping and Re-addition showed a positive effect on the suppression of ductility loss, even at low temperature, accompanied by the positive effects on the non-irradiated thermo-mechanical properties.
Miyazawa et al.,ICFRM-19, 2019
29
Pure W
W-10%Re
Irradiation Effects on Tungsten
DBTT
FRJ2 and HFRTirrad = 252-302 oC
(1 dpa ~ 5 x 1025 n/m2)
Krautwasser et al., 12th International PLANSEE Seminar, 1989
ü Lower DBTT of W-10%Re in the non-irradiated condition compared to the pure Wü Increase in DBTT with increase in irradiation doseü Higher DBTT of W-10%Re in the non-irradiated condition compared to the pure W
30
Irradiation Effects on Tungsten
Thermal Properties
JMTRTirrad = 57 oCφt = 3.37 x 1019 n/cm2
(E > 1 MeV)
Fujitsuka et al., JNM, 2000
Pure W
W-5%Re
W-10%Re
W-25%Re
ü Change in thermal diffusivity was dependent on the content of Re and temperature
31
Irradiation Effects on Tungsten
Effects of Helium by Transmutation
Annealed at 1250 oC for 1 hà Nano bubbles (1 nm) in matrix
Annealed at 1300 oC for 1 hà Nano bubbles (4 nm) at dislocation loops and sub-grain boundaries
Annealed at 1800 oC for 1 hà Nano bubbles (10 nm) at sub-grain boundaries
Annealed at 2100 oC for 1 hà Nano bubbles (10 nm) in matrix after recrystallization
Cyclotron12 MeV alpha with degraderTirrad = 52 oCφt = 600 appm
Chernikov et al., JNM, 1994
DislocationHe bubble
Grainboundary
Helium implantation at 52 oC to 600 appm
ü No significant swellingü No segregation of helium to grain boundaries
32
Neutron Irradiation Effects
ü Heat--- Steady state (stationary): 10 MW/m2
--- Slow transient: 20 MW/m2
--- ELM (fast transient): a few ten GW/m2
ü Neutron --- 15 dpa in W and 60 dpa in Cu (after 5 years)ü Ions (D, T, He) --- 1023 ions/m2/s
Reactor ITER DEMO
Material W Cu W Cu
Component replacements up to 3 5 year cycle
Av. neutron fluence [MWa/m2] Max. 0.15 5
Displacement damage [dpa] 0.7 1.7 15 60
TransmutationHe [appm] negligible 16 10 600
Re [%] 0.15 3Bolt et al., JNM, 2002 & JNM, 2004 and Robinson et al., UWFDM-1378, 2010
33
Irradiation Effects on Tungsten
Retarded Recrystallization
350
400
450
500
550
900 1100 1300 1500 1700 1900 2100 2300
Vick
ers
hard
ness
, HV
Test temperature [oC]
As-received, L x S surfacePure W, Plate, 7 mmK-doped W, Plate, 7 mmW-3%Re, Plate, 7mmK-doped W-3%Re, Plate, 7mm
As-received
ü Dislocation cell structure in the grain of He-implanted pure W was retained even after the at 1500 oC.
ü Only 20 appm He suppressed the recovery and recrystallization of pure W.
Annealedat 1500 oC
HRed and SRedAs-produced
HRed and SRedHe-implanted
HRed and SRedAs-produced
Hasegawa et al., Phys. Scr., accepted
Nogami et al., FED, 2019
34
Irradiation Effects on Tungsten1. Neutron irradiation effects must be considered both in the design
and operation phases of DEMO to manage the structural strengthand lifetime under long term operation.
2. Database of neutron irradiation response of W materials arelimited, even for the pure W (baseline material). Especially, thelack of data from high temperature and high dose neutronirradiation tests is an issue.
3. As a recent result from the J-US PHENIX project, K-doping and Re-addition indicated a positive effect on the suppression of ductilityloss, even at low temperature, accompanied by the positiveeffects on the non-irradiated thermo-mechanical properties.
4. Fusion-relevant neutron sources are necessary to confirm theresponse to the 14 MeV neutron irradiation includingtransmutation.
Copper-based materialsas heat sink and cooling pipe
36
Copper-based Materials for DEMO
uMaterials
ü Oxide Dispersion Strengthened Cupper Alloys (ODS-Cu, DS-alloy)--- Cu-Al2O3 (CuAl25-IG, GLIDCOP)
ü Precipitation hardened Cupper Alloys (PH-alloy)--- CuCrZr à CuCrZr-IG for ITER --- CuNiBe
u Issues--- need to increase strength and toughness--- need to decrease CTE mismatch to W-based material--- need to implement corrosion protection--- need to increase neutron irradiation tolerance
37
Lifetime Limitation due to Degradation of Copper-based Materials
Thermal Fatigue of Pipes and Interfaces20 MW/m2 x 1000 cycles
Pintsuk et al., ICFRM-17, 2015void / crack formation in OFCu
Deformationà crack/pore formation & modification of round shaped geometry
Deformation à local reduction of CuCrZr thickness
38
Lifetime Limitation due to Degradation of Copper-based Materials
Corrosion of CuCrZr
reducing: without active plasmaoxidizing: with active plasma (neutron induced radiolysis)cyclic: radiolysis is partially suppressed
Pintsuk et al., ICFRM-17, 2015
Corrosion rates of CuCrZr was higher than the structural materials of LWR (< 1 μm/year).
39
Lifetime Limitation due to Degradation of Copper-based Materials
Irradiation Damages of PH & DS Cu Alloys
Fabritsiev et al., FED, 1998
ü Irradiation hardeningbelow 300 oC and softening above 300 oC for both PH and DS alloys
Ø PH: Precipitation hardenedØ DS: Dispersion strengthened
40
Lifetime Limitation due to Degradation of Copper-based Materials
Irradiation Damages of PH & DS Cu Alloys
Fabritsiev et al., FED, 1998
ü Ductility loss accompanied by the irradiation hardening with decrease in the irradiation temperature for both PH and DS alloys(<1% by below 0.1 dpa)
ü Irradiation-tolerant Cu-based materials
ü Alternative (non Cu-based) materials
are required for heat sink and cooling pipe.
41
Hybrid Cooling Channel Concept using CuCrZr (High-λ) and RAFM Steel (Irradiation Tolerance)
Asakura et al., Nucl. Fusion, 2017
Target
BaffleDome and Reflector
Irradiation projectsof materials for divertors
43
Irradiation Studies in Japan
JAEA JMTR : Japan Materials Testing Reactor 50MW / 7 x 1014 n/cm2/s
Irradiation temperature control rigCan control the irradiation temperature within ±10 degree C
Specimen Type : Miniature Tensile (SS-J, SS-3) , CVN, PCCVN, DCT, Creep,
Heater
TC
Specimens
Gas gap
Outer canister
Inner canister
Heater line
TC line
Vacume temperature control line
Guide tube
JAEA JOYO : Experimental Fast reactor 140MW / 5.7 x 1015 n/cm2/s
Core map of JOYO
Shielding SubassemblyIrradiation Rig (for fuel)
Inner Reflector
Control Rod
ReflectorOuter Core Fuel
Inner Core Fuel
Irradiation Rig (for material)
MARICO : Material Testing Rig with Temperature ControlThe MARICO is being developed to obtain real time irradiation data,such as swelling,creep and rupture strength,on core materials.Specimen temperatures are controlled with an accuracy of ±4℃ by use of combined gas gap and electrical heater control methods.In the gas gap method the composition of a mixture of helium and argon fill gases is modified to increase or decrease the conductance of the gas between the double-wall cannister.
Schedule ofresuming operation
is uncertain.
Shut-down has been decided and no alternative
is uncertain.
Irradiation studies in Japan promoted by IMR-Tohoku university
HFIR : High Flux Isotope Reactor in ORNL BR2 : Belgian Reactor 2 in SCK•CEN
44
Irradiation Projects of Japan-US Collaboration
Task 3Plasma-Surf. Interac.
Tritium Behavior(TPE, Idaho NL)
Task 2Neutron-irrad. Effects
MicrostructurePhysical Properties
(HFIR, ORNL)
Task 1Heat Load Tests
Heat TransferSystem Evaluation
Material Properties
Tritium Behavior
Neutron-irradiatedsamples
2013 2014 2015 2016 2017 2018
Task 1
Task 2
Task 3
Heat transfer tests & turbulence modeling New divertor design
Heat load tests for non-irradiated samples n-irr. samples
Material selectionCapsule design
Low dose non-shielded n-irr.High dose n-irr. with thermal
neutron shielding
Post-irr.Examination
Device modifications
Retention & permeation meas. of non-irr. samples
Retention & permeation meas. of n-irr. samples
Japan USA
Representative Y. Ueda(Osaka U.) D. Clark (DOE)
Coordinator Y. Hatano (U. Toyama) D. Clark (DOE)
Task 1T. Yokomine(Kyoto U.)
Y. Ueda(Osaka U.)A. Sabau (ORNL)
M. Yoda (GIT)
Task 2T. Hinoki (Kyoto U.)
A. Hasegawa(Tohoku U.)Y. Katoh(ORNL)
L. Garrison (ORNL)
Task 3Y. Oya(Shizuoka U.)
Y. Hatano (U. Toyama)M. Shimada (INL)
D. Buchenauer (SNL)
Japan-US PHENIX Project (2013-2018)PFC evaluation by tritium Plasma, HEat and Neutron Irradiation eXperiments
45
Irradiation Projects of Japan-US Collaboration
Stainless steel
Gadolinium
Aluminum
Garrison et al., FST, 2019
46
Irradiation Projects of Japan-US Collaboration
1200°CSubcapsule
Garrison et al., FST, 2019
Japan-US Collaboration, PHENIX (~2018) and FRONTIER (2019~), will reveal the irradiation response of both
baseline and advanced W materials developed recently.
Issues for evaluation and prediction of structural strength and lifetime
50
Evaluation and prediction of structural strength and lifetime
Key Factors for DEMO
1. Synergistic Loads
2. Time-dependent
3. Gradient, Distribution, and Anisotropy
4. Material Properties Database and Handbook
5. Prediction and Validation, and Criteria and Rules
51
Evaluation and prediction of structural strength and lifetime
Key Factors for DEMO1. Synergistic Loadsü Synergistic loads (heat, neutron,
and ions) result in the complicated degradations and damages.
ü Integrated experiments and calculations are required.
HHF Tests after Neutron Irradiation0.2 dpa in C and 0.15 dpa in W (irradiation campaign PARIDE 3)1 dpa in C and 0.6 dpa in W (irradiation campaign PARIDE 4)Irradiation temperatures were 200 C
Roedig et al., JNM, 2004
Neutron HHF
Creep Fatigue Test Module for IFMIFhttps://www.ifmif.org/
Neutron Creep-Fatigue
52
Evaluation and prediction of structural strength and lifetime
Key Factors for DEMO2. Time-dependentü Degradations and damages caused by cyclic fatigue, creep, ratcheting,
recrystallization, displacement damage, transmutation are time-dependent phenomena.
Merola et al., FED, 2015You et al., FED, 2016 Nogami et al., Phys. Scr., 2017
53
350
400
450
500
550
900 1100 1300 1500 1700 1900 2100 2300
Vick
ers
hard
ness
, HV
Test temperature [oC]
As-received, L x S surfacePure W, Plate, 7 mmK-doped W, Plate, 7 mmW-3%Re, Plate, 7mmK-doped W-3%Re, Plate, 7mm
As-received
1100
o C
Annealing time [h]
550
500
450
400
350
Vick
ers h
ardn
ess,
HV
0 1 10 100 1000 10000
Pure WK-doped WK-doped W-3%Re
Annealing temp. = 1100 oC
Evaluation and prediction of structural strength and lifetime
Key Factors for DEMO2. Time-dependentü Degradations and damages caused by cyclic fatigue, creep, ratcheting,
recrystallization, displacement damage, transmutation are time-dependent phenomena.
Tsuchida et al., NME, 2018Nogami et al., FED, 2019
54
Evaluation and prediction of structural strength and lifetime
Key Factors for DEMO2. Time-dependentü Degradations and damages caused by cyclic fatigue, creep, ratcheting,
recrystallization, displacement damage, transmutation are time-dependent phenomena.
Hasegawa et al., JNM, 2016
Fukuda et al., JNM, 2016
55
Evaluation and prediction of structural strength and lifetime
Key Factors for DEMO
Nogami et al., FED, 2017
3. Gradient, Distribution, and Anisotropyü Gradient, distribution, and anisotropy of applied
heat and temperature, neutron irradiation damage, material properties should be considered.
ZX
Y
W-monoblock
Cooling channel
Plasma facing surfaceR
.D.
Fukuda et al., FST, 2015
56
Evaluation and prediction of structural strength and lifetime
Typical Issues for DEMO4. Material Properties Database and Handbookü Authorized material properties databases and handbooks are required.ü Definition and licensing of materials are required.
57
Evaluation and prediction of structural strength and lifetime
Key Factors for DEMO5. Prediction and Validation, and Criteria and Rulesü Integrated experiments and calculations are required to evaluate the structural
strength and lifetime under synergistic loads.
ü It will be required to additionally apply theoretical predictions and calculation-based predictions.
ü Fusion neutron source are required to clarify the effects of 14 MeV neutron irradiation, including transmutation effects.
ü In service condition monitoring, surveillance, and inspection will be important because all degradations and damages cannot be completely predicted before design and operation.
ü Criteria and rules for design and operation, including for maintenance and replacement, etc., should be established.
58
Summary and Conclusion
1. For a long-term structural reliability and lifetime, synergistic loads, time-dependent phenomena, gradient, distribution, and anisotropy of loads andmaterial properties, material properties database and handbook, predictionand validation, and criteria and rules are the key factors.
2. Neutron irradiation effects must be considered both in the design andoperation phases to manage the structural strength and lifetime under longterm operation.
3. Database of neutron irradiation response of W materials are limited, even forthe pure W (baseline mateiral). The irradiation projects under J-UScollaboration (PHENIX (~2018) and FRONTIER (2019~)) and EUROfusion willreveal the irradiation response of both baseline and advanced W materialsdeveloped recently.
4. Neutron irradiation response of Cu-based materials are severe for long termoperation of DEMO. Drastic modification or alternative materials are required.
5. Fusion-relevant neutron sources are necessary to confirm the response tothe 14 MeV neutron irradiation.