SLIDE 1
1
2
Irradiation Creep in Graphite
- Due to fast neutron irradiation
- Significantly reduces stresses in nuclear
graphite components
- The difference in dimensions between a
Irradiation Creep in Graphite A Review Barry J Marsden The - - PowerPoint PPT Presentation
Irradiation Creep in Graphite A Review Barry J Marsden The - - PowerPoint PPT Presentation
Irradiation Creep in Graphite A Review Barry J Marsden The University of Manchester Stephen D Preston SERCO Assurance 1 Irradiation Creep in Graphite Due to fast neutron irradiation Significantly reduces stresses in nuclear
SLIDE 2
SLIDE 3
3
Irradiated Unstressed Graphite Changes
- Dimensional
- Modulus
- Coefficient of Thermal Expansion -CTE
SLIDE 4
4
Irradiated Stressed Graphite Changes
- Dimensional
- Modulus
- Coefficient of Thermal Expansion - CTE
- Additional changes to CTE
- Additional changes to modulus
- Modified dimensional change rate
SLIDE 5
5
Irradiation Creep Rate (UK)
- Proportional to stress
- Inversely proportional to creep modulus
γ = Irradiation dose
- CREEP RATE = PRIMARY + SECONDARY
( ) ( )
[ ]
( )
c c cr
E T b E T d d σ β γ σ α γ ε + − = exp
SLIDE 6
6
Coefficients
- Primary and secondary
- Secondary creep coefficient independent of
temperature below 600oC
( ) ( )
T b T β α ,
SLIDE 7
7
Low Dose Creep
- When expressed in elastic strain units
- Common law for tension and compression
- Common creep law for all graphite types
σ εcr
c
E esu =
SLIDE 8
8
2 4 6 8 10 12 14 16 0.E+00 2.E+21 4.E+21 6.E+21 8.E+21 Dose, EDND, n/cm2 Elastic Strain Units
Pluto 300°C (Flux 4E13 n/cm2/s) BR2 300-650°C (Flux 3E14 n/cm2/s) Calder Hall 140-350°C (Flux ~1E12 n/cm2/s) UK Creep law
SLIDE 9
9
Creep Modulus Ec
- Unirradiated Young’s modulus
- Creep rate not changed by pinning
- However modified by:
– Structural changes – Radiolytic oxidation
- UK theoretical pinning / unpinning model
appears to back this up
SLIDE 10
10
2 4 6 8 10 12 14 16 0.E+00 1.E+21 2.E+21 3.E+21 4.E+21 5.E+21 Dose, EDND n/cm2 ESU
Radiolytically oxidised sample 1 Radiolytically oxidised sample 2 Radiolytically oxidised sample 3 Unoxidised in compression Unoxidised pyrolytic Pre-irradiated to a high dose UK Creep law
SLIDE 11
11
USA and Russian low dose data
- Similar laws to the UK but has a different
secondary creep temperature dependence
SLIDE 12
12
1.E-27 1.E-26 1.E-25 1.E-24 200 400 600 800 1000 Temperature °C Creep Coefficient (Kg/cm
2)-1 (neutron/cm2)-1
Russian Graphite EGCR (American Graphite) CGB (American Graphite)
SLIDE 13
13
DRAGON Experience
- Flux dependent creep coefficient (Verginga
and Blackstone)
( )
φ E kT Q / exp cont
SLIDE 14
14
High Dose Creep
- UK rule breaks down
- Tension and Compression different
- Kennedy, Cundy, Kliest
( )
- ∆
∆ − ′ =
- =
m
- crs
V V V V K K E K / 1 µ σ ε
SLIDE 15
15 5 10 15 20 25 30 35 40 45 5 10 15 20 Dose (x10
21 n.cm
- 2 EDN)
ESU
ATR-2E @ 300 °C (in tension) 300°C with x3.3 multiplier (in tension) ATR-2E @ 500 °C (in tension) 500°C with x3 multiplier (in tension) ATR-2E @ 900 °C (in tension) 900°C with x7 multiplier (in tension) ATR-2E @ 550 °C (in compression)
SLIDE 16
16
Creep strain, CTE and Dimensional change
- By observation creep strain modifies CTE
- However, dimensional change appears to be
a function of CTE
- Therefore creep strain should be expected to
modify dimensional change
- Kelly, Burchell model 1994
SLIDE 17
17
SLIDE 18
18
Change in Modulus due to Creep Strain
- For IG-110 graphite a 35% change in
modulus for 0.23% creep strain - Oku -1998
SLIDE 19
19
Main Conclusions
- Creep is important in the design of graphite