fracture and creep in the all-tungsten aries divertor
DESCRIPTION
Fracture and Creep in the All-Tungsten ARIES Divertor. Jake Blanchard University of Wisconsin – Madison (presented by Mark Tillack). Japan/US Workshop on Power Plant Studies and Advanced Technologies 26-27 February 2013. Introduction. - PowerPoint PPT PresentationTRANSCRIPT
Fracture and Creep in the All-Tungsten ARIES Divertor
Jake BlanchardUniversity of Wisconsin – Madison
(presented by Mark Tillack)
Japan/US Workshop on Power Plant Studies and Advanced Technologies
26-27 February 20131
2
Introduction
The ARIES Project is exploring the feasibility of using tungsten as a structural material for plasma-facing components
For this analysis, we assumed 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
3
We examined the ARIES plate divertor design
Temperature distributions were simulated using ARIES design loads with simplified convection cooling
q”=11 MW/m2
q’’’=17.5 MW/m3
P=10 MPa
Tcoolant=600 ᵒC
Max. Tarmor= 2000 ᵒC
Max. Tstructure=1310 ᵒC
Min. Tstructure=725 ᵒCoC
Stresses in uncracked structure identify regions of concern
MPa MPa
X- Stress Distribution when Hot (MPa)
x
• During operation: tensile stress along the cooling channel, compressive stress in the grooves.
• High tensile stress occurs at the base of the grooves after cool-down, resulting from plastic deformation.
x
X- Stress Distribution after Cool-down (MPa)
tension
6
Simulated cracks were introduced in high-stress regions
Crack-Free Stress State
2. Coolant channel surface
1. Base of grooves
7
Stress intensity should remain below the fracture toughness
B. Gludovatz, S. Wurster, A. Hoffmann, R. Pippan, “Fracture Toughness of Polycrystalline Tungsten Alloys.” 17th Plansee Seminar 2009, Vol. 1.
(unir
radia
ted)
8
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
(MPa
-m1/
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=2
c/a=6
c/a=10
Crack Depth (mm)St
ress
Inte
nsit
y (M
Pa-m
1/2)
Crack on coolant surface (hot)
Crack in notch (at shutdown)
2c
a
Stress intensities for crack perpendicular to coolant flow direction
Crack Face
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)
Z- Stress Distribution when Hot (MPa)
Lower stress intensities are obtained
Conclusions on fractureStress intensity is highest at full
power.
Critical crack is in the notch between “tiles” under shutdown conditions.
This may change if thermal creep is taken into account.
Fatigue (growth rate) has not yet been explicitly included.
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Thermal Creep
12
Thermal analysis predicts temperatures in the 1100 – 1300 oC range in the W structure
q”=11 MW/m2
q’’’=17.5 MW/m3
P=10 MPa
Tcoolant=600 ᵒC
Max. Tarmor= 2000 ᵒC
Max. Tstructure=1310 ᵒC
Min. Tstructure=725 ᵒC
• While structural temperatures are only ~0.4 T/Tm data indicate that pure tungsten can creep at these temperatures.
• Power law creep model was added to ANSYS analysis to evaluate creep behavior
oC
1300 C
1300 C
Large uncertainties exist in creep strain rate data• Most W creep data is for higher temperatures and
lower stress
• Limited available data for temperatures/stresses of interest
13
A. Purohit N. A. Hanan S. K. Bhattacharyya E. E. Gruber “Development of a steady state creep behavior model of polycrystalline tungsten for bimodal space reactor application.” Argonne National Lab., IL 1995
14
Using the more conservative data, excessive creep deformation is obtained
Mid Channel Displacement
Time (hr)
Dis
pla
cem
ent
(mm
)
15
q”=6.7 MW/m2
q’’’=17.5 MW/m3
P=10 MPa
Tcoolant=600 ᵒC
Max. Tarmor=1433 ᵒC
Max. Tstructure=1310 ᵒC
Min. Tstructure=714 ᵒC
• Reducing the surface flux to a value of 6.7 MW/m2 reduces the maximum armor temperature to 1433 oC
• Structure temperatures where creep occurs are in the 900-1000 oC range
Additional studies were performed using reduced heat flux
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Creep behavior of tungsten armor over two year exposure
0 5000 10000 15000 200000.0000
0.0002
0.0004
0.0006
0.0008
0.0010
0.0012
0.0014Total CreepThermal CreepPressure Creep
Time (hr)
Cre
ep S
train
Creep Strain After Two Years
Pt. A
Total Creep Strain along with Pressure Only and Thermal Only Creep at Pt. A
•Creep from combined thermal and pressure loads is considerably greater than sum of the individual components
•Thermal creep rate is initially high, but slows as stress is relieved. Pressure creep rates are constant.
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0 5000 10000 15000 200000
0.001
0.002
0.003
0.004
0.005
0.006
0.007
baselineq +20%q +10%q -10%q -20%
Time (hr)
Cre
ep S
train
(m
m/m
m)
Sensitivity of Creep Rates to Changes in the Thermal and Pressure Loads
0 5000 10000 15000 200000
0.0005
0.001
0.0015
0.002
0.0025
base-lineP +20%P +10%P -10%P -20%
Time (hr)
Cre
ep S
train
(m
m/m
m)
Creep Sensitivity to Surface Heat Flux
Creep Sensitivity to Coolant Pressure
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Results show creep rates are very sensitive to changes in temperature and stress
0.0
1.0
2.0
3.0
4.0
5.0
6.0
Heat Flux
Pressure
Normalized Parameter Value
Norm
alize
d C
reep S
train
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Reduce Tile Notch Depth by 1 mm
3 mm
•Reducing the notch depth increases minimum wall thickness to 3 mm (from 2 mm) reducing pressure stress in wall with some increase in thermal stress.
•Two year creep strain is reduced by 23% and rate is also significantly reduced.
0 5000 10000 15000 200000
0.0002
0.0004
0.0006
0.0008
0.001
0.0012
0.0014
Baseline
Reduced Notch
Time (hr)
Cre
ep S
train
20
Remove Notch Completely
0 5000 10000 15000 200000
0.0002
0.0004
0.0006
0.0008
0.001
0.0012
0.0014
BaselineSolid Wall 3.5mmSolid Wall 4mm
Time (hr)
Cre
ep S
train
•Removing alleviates stress concentrations and lowers surface temperature. Thermal stresses increase however.•Two year creep strain is reduced by 7% for a 3.5 mm wall and 15% for a 4 mm wall.•4 mm wall reduces maximum surface temperature by 162 oC vs baseline.
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Conclusions on creepCreep appears to be a significant
problem for design heat fluxes above 10 MW/m2.
Design changes can alleviate the problem to some extent, but
Materials with higher creep strength are needed (compared with pure W).
Reliable data are essential.
Data NeedsFracture toughness of tungsten
(alloy)◦As-manufactured, at temperature◦Irradiated
Crack growth rates (da/dN)Creep ratesCreep rupture dataCreep-fatigue interaction data