Fracture and Creep in an All-Tungsten Divertor for ARIESJake BlanchardUniversity of Wisconsin – MadisonAugust 2012

IntroductionThe ARIES Project is exploring the

feasibility of using tungsten as a structural material for plasma-facing components

For now, we are assuming the material is pure tungsten, but alloys may be necessary

This talk addresses two key failure modes that must be addressed by these designs◦Fracture◦Thermal creep

The Design

Major Input ParametersParameter Value Units

Surface Heat 11 MW/m2

Volumetric Heating 17.5 MW/m3

Coolant Pressure 10 MPaBulk Coolant Temperature

600 C

Crack Location

Crack-Free Stress State

Finite Element Model with Crack on Coolant Channel Surface

0 0.1 0.2 0.3 0.4 0.5 0.60

2

4

6

8

10

12

14

16

c/a=2c/a=6c/a=10

Crack Depth (mm)

Stre

ss In

tens

ity (M

Pa-m

1/2)

Fracture Results

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.550

1

2

3

4

5

6

7

8

c/a=2c/a=6c/a=10

Crack Depth (mm)

Stre

ss In

tens

ity (M

Pa-m

1/2)

Results for Crack on Previous Slide

Results for Crack Perpendicular to Cracks Shown

Results for Crack in Notch (at shutdown)

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.550.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

c/a=2

Crack Depth (mm)

Stre

ss In

tens

ity (M

Pa-m

1/2)

Crack Face

Effect of Transients

Surface Temperature

Temperature 2.5 mm below surface

Vary nominal heat flux by +/-20% and apply 20 cycles

No discernible variation below surface0 0.01 0.02 0.03 0.04

1994

1995

1996

1997

1998

1999

2000

2001

Time (s)

Tem

pera

ture

(oC)

0 0.01 0.02 0.03 0.041715.30

1715.32

1715.34

1715.36

1715.38

1715.40

Time (s)

Tem

pera

ture

(oC)

Surface Effect of “Small” ELM

Assume 1.95 MJ deposited on divertor surface over 1.2 milliseconds

Melt layer is 20 microns thick

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 11000

1500

2000

2500

3000

3500

4000

Surface

Depth = 17.7 um

Depth = 26.6 um

Time (ms)

Tem

pera

ture

(oC

) Melt Temp.

Thermal CreepAdd Thermal Creep Model for Tungsten

Creep rates are excessive at 11 MW/m2

Nominal Heat Flux

Reduced Heat Flux

0 5000 10000 15000 200000

1

2

3

4

5

6

Time (hr)

Dis

plac

emen

t (m

m)

0 5000 10000 15000 200000.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

Total CreepThermal CreepPressure Creep

Time (hr)

Cree

p St

rain

(%)

Design Modifications

0.0

1.0

2.0

3.0

4.0

5.0

6.0

Heat Flux

Pressure

Normalized Parameter Value

Nor

mal

ized

Cre

ep

Stra

in

0 5000 10000 15000 200000

0.00020.00040.00060.00080.001

0.00120.0014

BaselineReduced Notch

Time (hr)

Cree

p St

rain

Varying Surface Heating or Coolant Pressure

Reducing Notch Depth

ConclusionsWe have not identified any

“show-stoppers” with respect to an all-tungsten divertor for ARIES

Many uncertainties are still unresolved