development of low activation structural materials...development of low activation structural...

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Development of Low Activation Vanadium Alloys for Nuclear Fusion Reactors

Materials Challenge for Clean Nuclear Fusion Energy

Development of Low Activation Structural Materials

T. MurogaNational Institute for Fusion Science, Oroshi, Toki,

Gifu 509-5292, JapanSymposium on Materials Challenges for Clean Energy

June 21-25, 2009, NIST, USA

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Roadmap of Fusion Energy Development for Japan

Operation

ITER

DEMO

IFMIF

D-T

ConstructionDesigning Operation

Fission reactors and charged particle irradiation

100-150dpa

2020 2030 2040

Plasma Performance

Materials Performance under Irradiation50dpa Power Generation

IFMIF : International Fusion Materials Test Facility

3


Nuclear Fusion as a Clean Energy Source

Nuclear fusion is a clean energy source from the CO2 emission standpoints

One of the very limited candidates of major energy source in the future

From radiological standpoint, nuclear fusion is a clean energy source relative to nuclear fission

No high level radioactive waste is produced

Neutron-induced radioactivity of the components (low to middle level waste) and tritium are the only radiological issues

Neutron-Induced radioactivity is an issue for :

(1) Maintenance of in-vessel components (lifetime of maintenance tools)

(2) Waste disposal or reuse

(3) Potential hazard

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Structural Materials for Fusion Blankets

Blanket is the key component of fusion reactorsEnergy conversion (neutron to heat)Tritium production (Li + n T)

The structural materials need to have high temperature strength, resistance to neutron irradiation and compatibility with coolants.

Fusion DEMO Reactor(FFHR)

Neutrons

Reactor CoreD+T He+14.1 MeV n

Blanket

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The Concept of Low Activation Materials

“Low Activation Materials” is defined as :

The materials in which neutron irradiation-induced radioactivity decrease to a level where economical waste disposal or recycling in the next fusion plant (possible zero emission) is feasible in <50 years of cooling.

Use of Low Activation Materials can increase largely the attractiveness of fusion system as a clean energy source

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Element Restriction for Low Activation

There is strong element restriction for low activation materialsNi, Cu, Al, Mo, Nb cannot be used as alloying elementsAl, Ag, Nb Mo should be strictly controlled to ~ppm levels

None of the commercially-established materials can be used for the low activation structural components

no limit design dependent <0.1%

Classification of the elements by the restriction for low activation

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Radioactivity of Fusion Candidate Materials

Three candidate materials are under development for fusion application as low activation materials

Reduced activation Ferritic/Martensitic steelVanadium alloysSiC/SiC composites

The candidate materials satisfy the recycling limit

Contact dose of fusion structural materials after shutdown of a reactor

10-2

10-1

100

101

102

103

10410

-5

10-4

10-3

10-2

10-1

100

101

102

103

104

105

10-2

10-1

100

101

102

103

10410

-5

10-4

10-3

10-2

10-1

100

101

102

103

104

105

316SS�SS316LN -IG�Low activation ferritic�F82H�Vanadium alloy�NIFS -HEAT -2�SiC (no impurity�

Radioactivity (Sv/h)

Cooling Time after Shutdown (Years)

FFHR -Li BlanketFirst WallNeutron 1.5MW/m 2

30 years�foperation

Full-hands-on recycling

Full-remote recycling

10-2

10-1

100

101

102

103

10410

-5

10-4

10-3

10-2

10-1

100

101

102

103

104

105

10-2

10-1

100

101

102

103

10410

-5

10-4

10-3

10-2

10-1

100

101

102

103

104

105

10-2

10-1

100

101

102

103

10410

-5

10-4

10-3

10-2

10-1

100

101

102

103

104

105

10-2

10-1

100

101

102

103

10410

-5

10-4

10-3

10-2

10-1

100

101

102

103

104

105


Radioactivity (Sv/h)



Contact Dose (Sv/h)


FFHR -Li BlanketFirst WallNeutron 1.5MW/m 2

30 years�foperation

Full-hands-on recycling

Full-remote recycling

V- 4Cr- 4Ti �NIFS-Heat�

Reduced Activation Ferritics �F82H)

SS -316 Pure SiC/SiC

Pure V-4Cr-4Ti

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“Low Activation” would also be the Future Key Phrase for Nuclear Fission Systems

Disposal of Light Water Reactor in-vessel components The activity can be reduced by three orders using low activation materials

Low Activation Concrete is already investigated in nuclear fission communityReduction of Eu and Co levels for satisfying clearance level

SS316

10-410

-310

-210

-110

010

110

210

310

410

510

610-5

10-4

10-3

10-2

10-1

100

101

102

103

104

105

106

107

10-410

-310

-210

-110

010

110

210

310

410

510

610-5

10-4

10-3

10-2

10-1

100

101

102

103

104

105

106

107

Contact dose (Sv/h)

Cooling time after shut-down (years)

V-alloy

Activation by152Eu and 60Co

Cooling Time (y)

Conventional Concrete

Low Activation Concrete

Clearance ZoneR

elat

ive

Rad

ioac

tivity

Radioactivity after 60 y operation of PWR

Radioactivity of concrete after 20 y operation

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Operation Temperature and Efficiency

High operation temperature is essential for high conversion efficiencyPlant efficiency is influenced also by other factors (e.g. net working rate)

20

30

40

50

200 300 400 500 600 700 800 900 1000

Con

vers

ion

effic

ienc

y / %

Coolant temperature / oC

PWR

BWR

SSTR*

FBR

ARIES-1*

AGR

HTGR

DREAM*

RAF steel

V alloy

SiC ceramicFFHR*

WaterFlibe, Li, Li-Pb

He

*Fusion

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History of Vanadium Alloys for Fusion Reactors

Vanadium alloys were once candidates of FBR core materials in 1970sV-Nb-Cr, V-Nb-Mo, V-Cr-Zr (JP-NIMS) , V-Ti-Cr, V-Cr-Fe (US), V-Ti-Si (Germany)The programs were concluded because of insufficient compatibility with NaVanadium alloys attracted attention for fusion reactors from 1980sLow activation property -- potentiality for recyclingHigh temperature strength, high thermal stress factor

950� 1hr

V-XCr-YTi

The effects of Cr+Ti (wt%) on Ductile-Brittle Transition Temperature of V-Cr-Ti alloys

Fusion materials programs identified V-4Cr-4Ti as the leading candidate

Industrial infrastructure of vanadium alloys are still quite limited

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Impurity Reduction is the Key Issue for V-Alloys

Vanadium is a reactive metal, whose properties are influenced heavily by C, N, O impurities

C, N, O impurities need to be controlled

Contamination from the environment may be an issue

Vanadium alloys must satisfy low activation criteria

Nb, Mo, Al, Ag need to be controlled to 1~10 ppm

Cross contamination by sharing facilities for other purposes may be an issue

Elon

gatio

n (%

)

The effect of O, N and C levels on Elongation

NIFS has promoted a program for development of high purity V-4Cr-4Ti

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Commercial Production Process of Metal Vanadium

C N Nb, Mo (Cross Contamination)

OAl

Ores

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Improvement of the Process

Intermediates Conventional process Improved processC N O C N O

Ammonium Vanadate 12 41 12 41

(Calcination)

V2O5 100-150 20-90 44 10 10-20 44

Al 20-80 10 10-20 10

(Themic reduction)

V-Al-O 180 300-400 800-5000 60 60-120 800-5000

(EB refining)

Metal V 300 400-710 50-150 100 60-160 40-100

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Production of Purified Metal Vanadium

Metal Vanadium with <100wppm O and <200ppm N were produced by improving the production process

0

100

200

300

400

500

0 100 200 300 400 500 600

Laboratory ScaleUS-DOE Program (900, 2200 kg)Conventional (50 kg)Improved (25 kg)

Oxy

gen

/ wpp

m

Nitrogen / wppm

This study

Conventional largeingots ofcommercial vanadium in Japan

Large ingotsby US-DOE

0

O and N levels of metal V produced 125 kg ingots of purified V

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Alloying Technology

Alloying to V-4Cr-4Ti was carried out by EB and VAR methods

Special cares were taken to avoid contamination with O and N from atmosphere and with Nb and Mo by cross-contamination

EB-weldingEB melting from V, Ti, Cr flakes 1st VAR Ingot scaling

2nd VAR Ingot160 kg ingotcanningHot Forging

N and O Nb, Mo (Cross Contamination)

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Resulting Purity of the Alloys

ID C O N B Na Mg Al Si V Cr Mn Fe Ni Cu

NIFS-HEAT-1 56 181 103 7 17 <1 119 280 Bal. 4.12 <1 80 13 4

NIFS-HEAT-2 69 148 122 5 <1 <1 59 270 Bal. 4.02 <1 49 7 2

US832665 170 330 100 3.7 0.01 0.17 355 785 Bal. 3.25 0.21 205 9.6 0.84

US832864 37 357 130 <2 <1 193 273 Bal. 3.8 228 <50

Purification of metal vanadium resulted in low O level relative to US alloys.

US alloy had high Nb level because the infrastructure was common to Nbproduction system

This is a valuable lesson for future manufacturing of low activation V-alloys

ID As Zr Nb P S Ca Co Ag Sn Sb Ti W Mo Ta

NIFS-HEAT-1 1 <10 1.4 16 9 3 2 <0.05 <1 <1 4.13 <1 23 58

NIFS-HEAT-2 <1 2.5 0.8 7 3 12 0.7 <0.05 <1 <1 3.98 <1 24 13

US832665 1.4 <46 60 33 16.5 <0.26 0.30 0.078 0.24 0.17 4.05 25 315 <19

US832864 106 <30 4 3.8 <50

Chemical compositions of V-4Cr-4Ti ingots produced by NIFS and USDOE Programs

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V-4Cr-4Ti Products

Various high purity products were manufactured

26t 6.6t 4.0t1.9t 1.0t 0.5t 0.25t

2d

8d

(mm)

Plates, Sheets, Wires and Rods

Laser weld joint

Thin pipes

W coating by plasma spraying

Creep tubes

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V-4Cr-4Ti Tubing by Drawing

Quality of tubes increased by reducing O levels

O impurity before fabrication ~400 ppm

O impurity before fabrication ~130 ppm

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Welding – Impurity Control is the Key Issue

Welding can results in contamination with C, N, O by two ways(a) Contamination of the weld joints with C, N, O from atmosphere during

the welding(b) In V-4Cr-4Ti, large fraction of C, N, O are stored in Ti-CON precipitates.

Welding results in contamination of matrix with C, N, O

(a) is avoidable by highly controlling the welding atmosphere(b) can be avoided only by reducing the original level of C, N, O in the

material

Base Metal Weld Metal

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TIG Welding with Ultra-High Purity Wire

Weld joint

0 50 100 150 200 250 300 350 4000

100

200

300

Oxygen in weld metal / wppm

NH1 / HP

US / HPNH1 / NH1

0

US / US

DBTT = +60 K / 100 wppm oxygen0

5

10

15

-100-200 0 100Test temperature (C)

US / US47 C

NH1 / NH1-85 C

US / HP-90 C

-145 CNH1/HP

Abs

orbe

d En

ergy

(J)

Plate / WireDBTT

0

5

10

15

0

5

10

15

-100-200 0 100Test temperature (C)

US / US47 C

NH1 / NH1-85 C

US / HP-90 C

-145 CNH1/HP

Abs

orbe

d En

ergy

(J)

Plate / WireDBTT

Alloy Name O level (appm)

US-Large Heat (US) 310NIFS-HEAT-1 (NH1) 180High Purity Wire (HP) 36

Alloy Name O level (appm)

US-Large Heat (US) 310NIFS-HEAT-1 (NH1) 180High Purity Wire (HP) 36

Ultra-high purity wires were used for TIG welding for the purpose of reducing impurity level of weld jointsWith the decrease in the oxygen level in the weld joint, DBTT decreased

Absorbed energy of Charpytests for weld joints

DBTT of weld joints as a function of oxygen level

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Radiation Effects at Low Temperature

Irradiated Vanadium alloys showed plastic instability

Interaction of dislocations with radiation-induced defect clusters (black dot images by TEM) is thought to be the key process

Atom Probe Elemental Mapping showed the black dots are decorated with Ti, O and TiO.

35nm

Ti

O

TiO

11nm

10nm

(Rice 1998)

(Nita 2003)

Elemental mapping of radiation-induced defect clusters by Atom Probe

Change of tensile property and typical microstructure after deformation in V-4Cr-4Ti irradiated at low temperature

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Enhanced Uniform Elongation in V-Cr-Ti-Si,Al,Y

Uniform elongation after irradiation decreased to ~ 0 after irradiation at <400ºC

However, the uniform elongation recovered by addition of Si, Al, Y

Si, Al and Y can scavenge impurity O in V-4Cr-4Ti matrix and suppress the formation of the “decorated” defect clusters

Uniform elongation of V-4Cr-4Ti after neutron irradiation

(Abe, Satou 2003)

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Nano oxide dispersion strengthened (ODS) materials are under development for fusion as advanced options :

Enhanced high temperature strengthImproved radiation damage resistance because of high density of defect sinks

ODS low activation steel : Fe-9Cr-WCollaboration with FBR and SCWR

ODS vanadium alloysODS Cu alloys : Heat sink materials

400nm

Nano Structural Materials for Fusion

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Tens

ile S

tres

s (M

Pa)

Temperature (K)

Ferritic steel

9CrODS steel

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12

Uni

form

Elo

ngat

ion

(%)

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1400

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1400

300 500 700 900 1100

Tens

ile S

tres

s (M

Pa)

Temperature (K)

Ferritic steel

9CrODS steel

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6

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12

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4

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12

Uni

form

Elo

ngat

ion

(%)

Strain (%)

Stre

ss (M

Pa)

TTest = 298 K

TTest = 1073 K

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200

400

600

800V - 1.0 vol% Y 2O3 - 0.7 vol% YN

V - 4.4 wt% Cr - 4.1 wt% Ti

20%

NIFS-HEAT-1

Strain (%)

Stre

ss (M

Pa)

TTest = 298 K

TTest = 1073 K

0

200

400

600

800V - 1.0 vol% Y 2O3 - 0.7 vol% YN

V - 4.4 wt% Cr - 4.1 wt% Ti

20%

NIFS-HEAT-1

ODS V-alloys

9Cr Ferritic Steel vs. 9Cr ODS steel

W, Be, C

CuCrZr to ODS-Cu

Steels

ITER First Wall

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Summary

Materials development is the key to successful development of fusion energy.

Use of “low activation” structural materials can largely increase the attractiveness of fusion reactors as a clean energy source.

High temperature operation is essential for high efficiency energy conversion

Vanadium alloys are attractive candidate low activation structural materials for fusion reactors because of low activation and high temperature strength.

Control of both potentially-radioactive impurities (Nb, Mo, Al, Ag) and interstitial impurities (C, N, O) is essential for vanadium alloy development.

Nano Structural Materials are longer-term advanced options to enhance the operation temperature window and radiation resistance of structural components.

development of low activation structural materials...development of low activation structural...

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