Simulating Material Property Changes of Irradiated Nuclear Graphite

L. Luyken, A. N. Jones, M. Schmidt,

B. J. Marsden, T. J. Marrow

Primarily graphite is used as a moderator

• Slowing down neutrons to thermal

energies

Is also used as a structural component.

• Control rod channels

• Coolant channels

• Reflector bricks

• Fuel Compacts

What Happens to Graphite in a Reactor Core

Components Deform

Material Properties Change

Simple Dose Profile

Why?

Nuclear Graphite is made up of;

Pechinay Bulk Structure (polarised optical image)

Graphite Microstructure

Filler Particles

-Ordered Crystallites

Binder Matrix

- Disordered Crystallites

Porosity

- Calcination cracks- Gas evolution pores

Crystallite Structure.

Crystallite Structure (Image Abbie Jones)

Graphite Microstructure

Mrozowski cracks

Crystal

Damage Mechanism

Standard Model Ruck, Tuck and Buckle

Graphite Structure

Crystallite Structure (Image Abbie Jones)

Damage Mechanism

C

a

a

• Initial Adsorption “unpins” layers

• Intercalate can then penetrate graphite planes.

• Intercalate concentration within microstructure dependant on partial pressure of surrounding atmosphere.

• Bromine can also fill dislocation ribbons and push planes further apart

Widening of Dislocation Ribbons on Intercalation

Simulating Irradiation Damage

-1

0

1

2

3

4

5

0 1 2 3 4

% Br/C%

Str

ain

PGA Perp 1PGA Perp 2PGA para 1PGA Para 2Gilsocarbon 1Gilsocarbon 2EDF

Strain due to Bromination of polycrystalline graphites

-10

-5

0

5

10

15

20

25

30

0 0.01 0.02 0.03 0.04 0.05

% Br/C

% St

rain HOPG in c

HOPG in a

Strain due to Bromination of HOPG

Dimensional Change by Intercalation

(Presented at UNTF 2009)

•Single crystals experience high strain at low bromine concentration

•Polycrystalline graphites experience differing bulk strains depending on orientation of crystals

Tomography at the Swiss Light Source

Experimental Set Up

X-Ray Source Shutter Bromine Rig Camera

Beam Energy: 28KeV (high)

Projections: 1501 (reduces noise)

CCD exposure time: 160ms (fast)

Binning: 2 x 2 (reduces image resolution)

Figure 1 Strain due to bromination of Pile Grade A graphite

Figure 2 Strain due to irradiation of Pile Grade A graphite 

Strain due to Bromination

-1

-0.5

0

0.5

1

1.5

2

2.5

3

3.5

0 100 200 300 400 500 600

time (mins)

Str

ain

(%)

PGA_B3

-10.00

-8.00

-6.00

-4.00

-2.00

0.00

2.00

4.00

0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00 160.00

parallel

perpendicular

Brominating Graphite Microstructure

Filler

Binder

Brominating Graphite Microstructure

Brominating Graphite Microstructure

Brominating Graphite Microstructure

Brominating Graphite Microstructure

Brominating Graphite Microstructure

Brominating Graphite Microstructure

Brominating Graphite Microstructure

Brominating Graphite Microstructure

Brominating Graphite Microstructure

Brominating Graphite Microstructure

Brominating Graphite Microstructure

Binder

However larger regions of the binder matrix

accommodate bromine due to greater open

porosity in this region

Filler

Bromine quickly permeates large

crystalline regions

Filler

Nevertheless the largest deformation vectors are seen in the filler particles

Change in Young’s modulus

)1(

)21)(1(2

vE

Where

E = Young’s modulus

ρ = density

ν = sonic velocity

θ = Poisson's ratio

Experimental Setup

Change in Young’s modulus

PGA Perp

43

43.2

43.4

43.6

43.8

44

44.2

0 200 400 600 800

Time in Bromine (mins)

Tim

e o

f fl

igh

t (u

s)

Time Strain Young’s Modulus

t=0 0% 5.25 GPa**

t=720 0.3 % 5.29 GPa

** literature values vary from 4GPa to 7GPa

Conclusions

• Bromination produces bulk dimensional

• Initially penetrates binder phase due to large amounts of open porosity

• Later quickly fills filler phase

• Largest strains are seen in filler phase

• As with irradiation brominating graphite increases the young’s modulus.

Future Work

• Investigate crystal strains due to bromination.

• Applied for beam time at ILL

• Further develop Young’s modulus experiment to measure bulk strain insitu

• Use laser displacement detector

Thank you

James Perrin University of Manchester

David James University of Manchester

Paul Townsend University of Manchester

Sam Macdonald University of Manchester (Swiss Light Source)

Will Bodel University of Manchester

"This work was carried out as part of the TSEC programme KNOO and as such we are grateful to the EPSRC for funding under grant EP/C549465/1“

Questions?