NEEP 541 – Material
Properties
Fall 2003
Jake Blanchard
Outline

Materials in Reactors

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Fission
Fusion
Material Properties
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Tensile tests
Impact tests
Creep tests
Materials in Reactors
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Fission
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Fuel
Cladding
Moderator
Core structure
Reflector
Control rods
Coolant
Pressure vessel
shielding
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Fusion
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Fuel
Structure
Tritium breeder
Coolant
insulators
shielding
Fission

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Primary radiation damage is in fuel and
cladding
Cladding:
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Adequate strength (T, fluence)
Corrosion resistance
Thermal conductivity
Neutronics (low absorption)
Available resources
Fabricability
Inexpensive
Cladding Materials

Low thermal
absorption
cross section
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Al
Mg
Zr
Be

High thermal
absorption
cross section
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Nb
Mo
Ta
V
Ti
Steel
Some Numbers
Material
Thermal - Zr
Fast - steel
Tmax (C)
380
660
Coolant
Water
Sodium
Pressure (atm)
130
<1
Clad thickness
(mm)
Clad OD (mm)
0.6
0.4
10.8
6.3
Life (dpa)
20
150
Fusion Structure Requirements

Same as fission plus…
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Low swelling
Low embrittlement
Typical Materials

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Austenitic steel (316 SS)
Ferritic steel (lately ODS FS)
Refractory alloys
composites
Radiation Effects
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Radiation hardening (increase in
strength)
Embrittlement (decrease in ductility)
Swelling (volume increase due to voids)
Irradiation creep
Tests
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Tensile tests (modulus, ductility,
strength)
Tube burst tests (creep)
Impact tests (ductility, fracture
toughness)
Tensile Tests
Understanding the Tensile Test
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A0=cross sectional area before test (in
test section)
A=cross sectional area during test
(load=P)
L0=section length before test
L=section length during test
Tensile Tests
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Engineering stress=eng=P/A0
True Stress=true=P/A
Before necking, A~ A0
Engineering strain==(L-L0)/L0
True strain=
L
L
dL
 true  
 ln    ln 1   
L
 L0 
L
0
Stress-Strain Curve
True Stress – True Strain
Combined
When does necking start?

Plastic Instability (dP=0)
dP  d A  dA  Ad  0
d
 dA


A
AL  A0 L0
L A0

L0
A
dL  A0 dA

L0
A2
Volume is
conserved
Plastic Instability
LA
L0 
A0
dL L0 dL L0   A0 dA   dA

 

2
L
L L0
L A 
A
d  dA dL


 d true

A
L
d
Necking occurs when slope of true

d true
stress-true strain curve=true stress
Plastic Instability

suppose
  C n
 
  
C
1
n
d
1  

 
d Cn  C 
1  
 
Cn  C 
1

n
 1 n 1
 1n 1
 
 
C
1
n
Hardening
Impact Testing
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Test for ductility
Measure energy absorbed during
fracture
Typical Results

E (J)
DBTT=ductile to brittle transition
temperature
Lower
shelf
Upper shelf
irradiated
40
DBTT
T
Creep Tests

Apply load and measure deformation as
a function of time
primary
secondary
tertiary
Creep
strain
time
Study creep rupture with a
tube burst test
2R
p
L
Burst Test Analysis
Slice cylinder
vertically
p
h
h

2 htL   p sin(  )RLd   2 pRL
0
h 
pR
t
Burst Test Analysis
Slice cylinder
horizontally
(picture is shown
cut away vertically
as well)
 axial
 axial
2Rt  axial  pR 2
 axial
pR

2t
Burst Test Analysis
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Uniaxial (1-D tensile test)
Constant stress
d
n
 K
dt
n
  K t
Burst Test Analysis
d *
* n
K
dt
1
*
 r    2   r   z 2   z    2
 
2
1
1
2
2
2 2
*
 r      r   z    z   
 
2
d ij 3 d * Sij

dt
2 dt  *
1
Sij   ij    ;     r      z
3
 




1
2
Burst Test Analysis
1
 1  pR pR   pR
 z         
Sr 
3
3  2t
t 
2t
1
pR
S  2    z  
3
2t
1
S z  2 z      0
3
Burst Test Analysis

1
2
2
2
 r       r   z    z    
 
2
*
2
2

1
      
2
*
 
         
2 
 2   2  
3 pR
 
2 t
*
1
2

1
2
Burst Test Analysis
d r 3
 K *
dt
2
 
n 1
3  3 pR 

S r  K 
2  2 t 
d r  3 K  3 



dt
4  2 
d  3 K  3 




dt
4  2 
d z
0
dt
n 1
n 1
 pR 


 t 
 pR 


 t 
n
n
n 1
  pR 


 2t 
Burst Test Analysis
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Negative radial strain means that wall
gets thinner
Zero axial strain means length doesn’t
change
Positive hoop strain means radius
increases
Analysis assumes small strain, constant
stress
For large strain, wall thins and stress
increases, leading to rupture