NEEP 541 – Material Properties

Fall 2003Jake Blanchard

Outline Materials in Reactors

Fission Fusion

Material Properties Tensile tests Impact tests Creep tests

Materials in Reactors Fission

Fuel Cladding Moderator Core structure Reflector Control rods Coolant Pressure

vessel shielding

Fusion Fuel Structure Tritium

breeder Coolant insulators shielding

Fission Primary radiation damage is in fuel

and cladding Cladding:

Adequate strength (T, fluence) Corrosion resistance Thermal conductivity Neutronics (low absorption) Available resources Fabricability Inexpensive

Cladding Materials Low thermal

absorption cross section Al Mg Zr Be

High thermal absorption cross section Nb Mo Ta V Ti Steel

Some NumbersMaterial Thermal - Zr Fast - steel

Tmax (C) 380 660Coolant Water SodiumPressure

(atm)130 <1

Clad thickness

(mm)

0.6 0.4

Clad OD (mm)

10.8 6.3

Life (dpa) 20 150

Fusion Structure Requirements Same as fission plus…

Low swelling Low embrittlement

Typical Materials Austenitic steel (316 SS) Ferritic steel (lately ODS FS) Refractory alloys composites

Radiation Effects Radiation hardening (increase in

strength) Embrittlement (decrease in

ductility) Swelling (volume increase due to

voids) Irradiation creep

Tests Tensile tests (modulus, ductility,

strength) Tube burst tests (creep) Impact tests (ductility, fracture

toughness)

Tensile Tests

Understanding the Tensile Test 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 Engineering stress=eng=P/A0 True Stress=true=P/A Before necking, A~ A0 Engineering strain==(L-L0)/L0 True strain=

1lnln

00LL

LdLL

Ltrue

Stress-Strain Curve

True Stress – True Strain

Combined

When does necking start? Plastic Instability (dP=0)

20

0

0

0

00

0

AdAA

LdL

AA

LL

LAALAdAd

AddAAddP

Volume is conserve

d

Plastic Instability

true

true

dd

dLdL

AdAd

AdA

AdAA

LL

LdL

LL

LdL

ALAL

200

0

0

00

Necking occurs when slope of true stress-true strain curve=true

stress

Plastic Instability suppose

n

CCCn

CCndd

C

C

nn

n

n

n

1

1

1

111

11

1

Hardening

Impact Testing Test for ductility Measure energy absorbed during

fracture

Typical Results DBTT=ductile to brittle transition

temperature

T

E (J)Upper shelfLower

shelf

irradiated

DBTT

40

Creep Tests Apply load and measure

deformation as a function of time

time

Creep strain

primary secondary

tertiary

Study creep rupture with a tube burst test

p

2R

L

Burst Test Analysis

tpR

pRLRLdptL

h

h

2)sin(20

p

hh

Slice cylinder vertically

Burst Test Analysis

tpR

pRRt

axial

axial

2

2 2

axialaxial

Slice cylinder horizontally (picture is shown cut away vertically as well)

Burst Test Analysis Uniaxial (1-D tensile test) Constant stress

tK

Kdtd

n

n

Burst Test Analysis

zrijij

ijij

zzrr

zzrr

n

S

Sdtd

dtd

Kdtd

;31

232121

*

*

21222*

21222*

**

Burst Test Analysis

0231

22

31

2231

31

zz

z

zr

S

tpRS

tpR

tpR

tpRS

Burst Test Analysis

tpR

zzrr

23

2221

21

*

21

222*

21222*

Burst Test Analysis

0

23

43

23

43

223

23

23

1

1

11*

dtd

tpRK

dtd

tpRK

dtd

tpR

tpRKSK

dtd

z

nn

nn

r

n

rnr

Burst Test Analysis 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