(!) __ iiiiiiiii ______ --______ IKJENERAlATOMI,CII_

Jül-1575 GA-A15270 UC-77

PROPERTY CHANGES IN GRAPHITE IRRADIATED AT CHANGI.NG IRR·ADIATION TEMPERATURE

by

R. J. PRICE (General Atomic Company) G. HAAG (Kernforschungsanlage, Jülich GmbH)

Prepared under the Umbrella Agreement for Cooperation in Gas-Cooled Reactor Development between the United States and the Federal Republic of Germany.

Work supported in part by Contract DE-AT03-76ET35300

for the San Francisco Operations Office Department of Energy

JULY 1979

,--------- NOTICE --------, This report was prepared as an account ofwork sponsored by the United States Govemment.

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Price: Printed copy $4.50; Microfiche $3.00

@ __ iiiiiiiiiiiiiiiiiiiii _____________ IIK»ENERAlATOMI~

Jül-1575 GA-A15270 UC-77

PROPERTY CHANGES IN GRAPHITE IRRADIATED AT CHANGING IRRADIATION TEMPERATURE

by

R. J. PRICE (General Atomic Company) G. HAAG (Kernforschungsanlage, Jülich GmbH)

Prepared under the Umbrella Agreement for Cooperation in Gas-Cooled Reactor Development between the United States and the Federal Republic of Germany.

Work supported in part by Contract D E-ATOJ-76ETJ5JOO

for the San Francisco Operations Office Department of Energy

GENERAL ATOMIC PROJECT 6400

JUL Y 1919

CONTENTS

ABSTRACT . . . . .

1.

2.

3.

4.

5.

6.

INTRODUCTION

PROPERTY CHANGES IN ISOTHERMALLY IRRADIATED GRAPHITE

2.1.

2.2.

2.3.

Transient Irradiation-Induced Property Changes . . . . . . . . ....•..

Irradiation-Induced Dimensional Changes

Other Irradiation-Induced Changes

RULES FOR COMBINING ISOTHERMAL CURVES

3.1. Rule 1 - Vertical Transposition at Equal

3.2.

3.3.

Fluence

Rule 2 - Horizontal Transposition at Equal Property Value . . . . . . . . . . .

Rule 3 - Horizontal Transposition at a Scaled Fluence

EXPERIMENTAL DATA

4.1. Dimensional Changes

4.2. Young's Modulus

4.3. Thermal Conductivity

4.4. Thermal Expansivity

SUMMARY AND CONCLUSIONS

REFERENCES . . . . . . . .

FIGURES

1. Alternative rules for transposing isothermal plots of

v

1-1

2-1

2-1

2-1

2-2

3-1

3-1

3-1

3-2

4-1

4-1

4-8

4-8

4-17

5-1

6-1

graphite dimensional change versus fluence 3-3

2. Lifetime fluence of H-451 and simi.1ar graphites as a function of irradiation temperature . . . . . . . .. 3-6

3. Schematic illustration of the application of trans-position rules to property changes in near-isotropic graphite: temperature increase . . . . . . . . . . . . . 3-7

Hi

FIGURES (cont.)

4. Schematic illustration of the application of transpos-ition rules to property changes in near-isotropic graphite: temperature decrease . . . . . . . . . 3-8

5. Irradiation-induced dimensional changes in H-45l graphite: isothermal curves (data from Ref. 2) . . 4-2

6. Irradiation-induced dimensional changes in H-451 graphite: temperature change data, axial orienta-tion (data from Ref. 2) ......... . ... 4-3

7. Irradiation-induced dimensional changes in H-451 graphite: temperature change data, radial orienta-tion (data from Ref. 2 ) . . . . . . . . . . . . . 4-4

8. Irradiation-induced dimensional changes in AS2-M-500 graphite: isothermal curves (data from Ref. 6) . .. 4-5

9. Irradiation-induced dimensional changes in AS2-M-500 graphite: temperature change data, axial orienta-tion (data from Ref. 7) ................ 4-6

10. Irradiation-induced dimensional changes in AS2-M-500 graphite: temperature change data, radial orienta-tion (data from Ref. 6) • . . . . . . • • . . .. •. 4-7

11. Irradiation-induced dimensional changes in Dragon grade 95 graphite: isothermal changes (data from Ref. 4). . . . . . . . . . . . . . . . . . . . . . . . . 4-9

12. Irradiation-induced dimensional changes in Dragon grade 95 graphite: temperature change data (data from Ref. 4) . . . . . . . . . . . . . . . . .. 4-10

13. Irradiation-induced dimensional changes in semi-isostatically pressed graphite matrix material: isothermal changes (data from Ref. 4) ......... 4-11

14. Irradiation-induced dimensional changes in semi-isostatically pressed graphite matrix material: temperature change data (data from Ref. 4 ) ... 4-12

15. Irradiation-induced changes in Young's modulus of AS2-M-500 graphite: isothermal changes (data from Ref. 7) . . . . . . . . . . . . . . . .. • .• 4-13

16. Irradiation-induced changes in Young's modulus of AS2-M-500 graphite: temperature change data (data from Ref. 7) ...................... 4-14

17. Irradiation-induced changes in the room temper-ature thermal conductivity of H-451 graphite: isothermal curves (data from Ref. 2) .......... 4-15

iv

FIGURES (cont.)

18. Irradiation-induced changes in the room temperature thermal conductivity of H-451 graphite: temperature change data (data from Ref. 2) ............. 4-16

19. Irradiation-induced changes in the thermal expan-sivity of AS2-M-500 graphite: isothermal curves (data from Ref. 7) . . . . . . . . . . . . . . . . . • . 4-18

20. Irradiation-induced changes in the thermal con-ductivity of AS2-M-500 graphite: temperature change data, axial orientation (data from Ref. 7) ....•.. 4-19

21. Irradiation-induced changes in the thermal expansivity of AS2-M-500 graphite: temperature change data, radial orientation (data from Ref.7) .......••. 4-20

v

ABSTRACT

Design da ta for irradiated graphite are usually presented as families

of isothermal curves showing the change in physical property as a function

of fast neutron fluence. In this report, procedures for combining iso-

thermal curves to predict behavior und er changing irradiation temperatures

are compared with experimental data on irradiation-induced changes in

dimensions, Young's modulus, thermal conductivity, and thermal expansivity.

The suggested procedure fits the data quite weIl and is physically realistic.

vi

1. INTRODUCTION

Standard irradiation tests for obtaining design data on graphite are

carried out as nearly as possible at a constant temperature, and the test

data are presented as families of isothermal plots showing the change in

property as a function of fast neutron fluence. Such isothermal test data

can be applied directly to the fuel element blocks in a base load HTGR,

but in other systems graphite may be irradiated at widely varying tempera-

tures. Large thermal fluctuations would occur in the fuel elements of a

pebble-bed HTR utilizing the OTTO cycle, a prismatic block HTGR operating

with axial push-through, or a fission-fusion hybrid power system using a

breed-burn cycle.

Changing irradiation temperature presents a problem to designers who

must choose a method for combining isothermal design plots to predict the

property changes accurately. In this report, possible approaches to the

problem are outlined, and experimental data obtained from Kernforschungsanlage

Jülich, General Atomic Company, and the literature are reviewed. A method

for predicting property changes in graphite irradiated at changing tempera-

ture is suggested.

1-1

2. PROPERTY CHANGES IN ISOTHERMALLY IRRADIATED GRAPHITE

When we11-crysta11ized graphite is irradiated with fast neutrons,

interstitials and vacancies are created which coa1esce into clusters

of various shapes and sizes within the crystal1ites. These clusters

change the dimensions and intrinsic physical properties of the crystallites.

In addition, these crystallite dimensional changes cause interactions

between the crystallites. This may alter the internal stress pattern and

the porosity of the polycrystal1ine aggregate. The final effect on the

bulk properties is due to a combination of property changes within the

crystallites and interactions between the crystal1ites.

2.1. TRANSIENT IRRADIATION-INDUCED PROPERTY CHANGES

Irradiation-induced changes in some properties (for example, thermal

conductivity) are dominated by small defect clusters within the crystallites.

Such clusters rapid1y bui1d up to an equilibrium concentration which depends

on the irradiation temperature. As a result, irradiation reduces the thermal

conductivity of graphite to a saturation level which decreases with increas_

ing irradiation temperature. This type of property change is transient in

the sense that it is easily annea1ed out at temperatures above the irradia-

tion temperature.

2.2. IRRADIATION-INDUCED DIMENSIONAL CHANGES

Irradiation-induced dimensional changes in graphite are more complex.

At irradiation temperatures below about 300°C, the dimensional changes are

controlled by sma1l defect clusters within the crysta1lites and, 1ike the

changes in thermal conductivity, they are easily annea1ed either by post-

irradiation healing or by irradiation at a lügher temperature (Ref. 1).

In contrast, dimensional changes created by irradiation at higher tempera-

tures are produced by a combination of 1arge defect clusters within the

2-1

crystallites and inter-crystalline interactions. These high temperature

dimensional changes are difficult to anneal out and may be described as

non-annealable or cumulative, in contrast to the annealable or transient

property changes described above.

2.3. OTHER IRRADIATION-INDUCED CHANGES

The changes in other properties, such as Young's modulus and thermal

expansivity, are produced by a combination of within-crystallite and

inter-crystallite changes. A multiplicity of mechanisms is responsible

for the complexity of the irradiation behavior of graphites. In most

cases, the isothermal curves which depict property values as functions of

neutron fluence do not have simple mathematical forms, and different iso-

therms do not have the same shape. The curves can be expressed mathe-

matically only as complicated empirical or semi-empirical equations which

include temperature and fluence.

The complexity of the damage mechanisms and the property change curves

complicates the problem of formulating rules for combining isotherms to

predict behavior under changing temperatures. This problem is discussed

in the next section.

2-2

3. RULES FOR COMBINING ISOTHERMAL CURVES

Simple empirica1 procedures have been suggested in the literature

(Refs. 2 through 4) for transposing isothermal dimensional change curves.

Cords and Zimmermann (Ref. 5) have described a semi-empirica1 model in

which irradiation-induced property changes are described by combinations

of rate processes and switch functions. While this model has the potential

for constructing property change curves for varying temperatures, detailed

procedures have not been deve1oped.

The schematic plots in Fig. 1 i11ustrate three alternative empirical

ru1es to account for the dimensional changes in a typica1 nuc1ear graphite

irradiated first at 600°C, then at 1000°C. Figure l(A) shnws camplete

isothermal dimensional change-versus-f1uence plots for 600°C and 1000°C.

Figures l(B), (C), and (D) show three alternative ways of joining the

1000°C isotherm to the 600°C isotherm fo11owing a step change in tempera-

ture to 1000°C after aperiod of exposure at 600°C.

3.1. RULE 1 - VERTICAL TRANSPOSITION AT EQUAL FLUENCE

Vertica1 transposition at equa1 f1uence is the simp1est of the three

procedures, see Fig. l(B). At the point of temperature change, vertical1y

shift the 1000°C isotherm by an amount (Y2 - Y1) to join the 600°C isotherm

at the same f1uence. Point A corresponds to point (xl' Y2) on the isotherm,

see Fig. l(A). No theoretica1 justification has been proposed for ru1e 1.

3.2. RULE 2 - HORIZONTAL TRANSPOSITION AT EQUAL PROPERTY VALUE

Rule 2, horizontal transposition at equal property value, is illus-

trated in Fig. l(C). At the temperature change point, the 1000°C isotherm

3-1

is shifted horizontally a distance (x1

- x2)

to join the 600°C isotherm

for the same dimensional change value. In this case, point A corresponds

to point (x2 , Y1) on the isotherm. Rule 2 has same justification when

applied to cumulative-type properties, such as high temperature dimensional

change, if it is assumed that a given dimensional change corresponds to il

given state of irradiation damage. The main drawback of rule 2 is that

the procedure is sometimes mathematically impossible, as would be the case

if the temperature change occurred near the minimum in the 600°C isotherm.

3.3. RULE 3 - HORIZONTAL TRANSPOSITION AT A SCALED FLUENCE

Rule 3 is proposed here as a method which fits the fuJlest range of

properties and fluence situations. It may be described as horizontal

transposition at a scaled fluence.

Although different dimensional change isotherms da not have identical

shapes, all eventually cross the zero dimensional change line. The fluence

where this happens (x3

and x 4) [see Fig. 1(A)] can conveniently be regarded

as defining the "usable lifetime" of the graphite at a given temperature.

This makes it possible to define the "scaled fluence" as the actual fluence,

y, divided by the lifetime fluence, L(T). The scaled fluence, y(T)/L(T),

characterizes the fraction of the graphite lifetime which has been used up

at temperature T. The usable lifetime of a graphite component can then

be predicted from a "cumulative damage rule." The graphite reaches the

end of its life when:

2:lill. L(T)

( 1 )

Figure 1(D) illustrates the application of the scaled fluence concept

to the present problem. The 1000°C isotherm is shifted horizontally until

point A (corresponding to a fluence of x1

• x3

/x4

on the original isotherm)

falls at a fluence of x1

. At this point the scaled fluence at 600°C equals

the scaled fluence at 1000°C.

3-2

W I

W

U.J (!:)

2 « :z: (..)

....J

« 2 o cn 2 w :iE o

.,. .. ·~A (xl-x2)

\--'\

lOOO°C ISOTHERM

(A) ISOTHERMAL CURVES

,,--

X4 I

(B) RULE 1: VERTICAL TRANSPOSITION AT EQUAl FlUENCE

NEUTRON FLUENCE

(Cl RULE 2: HORIZONTAL TRANSPOSITION AT EQUAlPROPERTY VAlUE

(0) RUlE 3: HORIZONTAL TRANSPOSITION AT SCAlED FlUENCE

Fig. 1. Alternative rules for transposing isothermal plots of graphite dimensional change versus fluence

However, this procedure usually leaves a gap of 6y between the two

isotherms. This gap is assumed to be progressively reduced according

to this expression:

y = y* + 6y exp (- ~ ) ( 2)

where y is the predicted property value, y* is the property on the trans-

posed 100QoC isotherm, y is the fluence measured from the temperature

change point, and T is a time constant.

The progressive approach to the new isotherm is physically

reasonable for "transient" properties such as the thermal conductivity,

where following a temperature cahnge, the concentration of irradiation-

induced defect clusters is expected to move toward the dynamic equilibrium

coneentration characteristic of the new irradiation temperature. The time

constant, T, in Eq. 2 is taken to be equal to 1 x 1021

n/cm2

, equivalent

fission fluence for graphite damage. This value appears to fit the avail-

able data reviewed in the follo~ing section. For simplicity, it is assumed

that lifetime L(T) and time constant T are the same for all properties and

for all near-isotropic graphites. A plot of L(T) versus irradiation tem-

perature is shown in Fig. 2. This plot is derived from the dimensional

crossover point for radial specimens of H-451 graphite irradiated at high

temperatures, combined with UKAEA data on near-isotropic graphites irradiated

at low temperatures (Ref. 6).

The application of the three different transposition rules to changes

in dimensions, thermal conductivity, and Young's modulus of a typical near-

isotropie graphite is illustrated in Figs. 3 and 4 for a temperature increase

and temperature decrease, respectively. In the case of dimensional changes

there is not mueh difference in the behavior predieted by the three rules,

except that rule 2 yields no solution when the temperature is stepped up.

For thermal eonductivity changes, the same situation occurs. In addition,

rule 1 predicts no change in conductivity following either an increase or

a deerease in temperature. However, this disagrees with observations

3-4

reported in the next section. Für Young's modulus changes, only rule 3

predicts büth a decrease in modulus when the temperature rises and an

increase when the temperature drops.

3-5

6

3

5 Cl C,!J Z ~ t..J ~ W W

N N E

E u -t..) 4 t:: -t:: N N N N 2

I I 0 0

x x UJ W t..J t..J 3 z 2: w w :::J :::) \ ...J ...J ~ ~

\ z 2: Cl Cl

\ a::

er: 2 I-I- :::) :::) , w w Z 2: , I-I- en U) , oe( oe( ~ ~

o 200 400 600 800 1000 1200 1400

IRRADIATION TEMPERATURE rC)

Fig. 2. Lifetirne fluence of H-451 and similar graphites as a function of irradiation temperature

3-6

w I

--.J

ISOTHERMAL

DIMENSIONAL CHANGE

600°C

THERMAL CONDUCTIVITY 1000°C

600°C

YOUNG'S MODULUS

600° C --+ 10000 C 1\

r~-------------------J ~-------------------, RULE 1 RULE 2 RULE 3 (EQUAL FLUENCE) (EQUAL PROPERTY) (SCALED FlUENCE)

600°C

L

10000 C

1000°C

NO SOLUTION

600°C

NO SOLUTION

1000° C

NEUTRON FLUENCE

1000°C

Fig. 3. Schematic illustration of the application of transposition rules to property changes in near-isotropic graphite: temperature increase

w I

00

1000"C ..... 6000 e ,---- -,

RULE 1 RULE 2 RULE 3 ISOTHERMAL (EOUAL FLUENCE) (EOUAL PROPERTY) (SCALED FLUENCE)

DIMENSIONAL CHANGE

600D e ~ 6000 e

THERMAL CONDUCTIVITY 1000D C 6000 e

600G e 600Ü C ~ 600DC

600"C 600°C 1000°C 6000 e

YOUNG'S MODULUS 1 000° C V-

NEUTRON FLUENCE

Fig. 4. Schematic illustration of the application of transposition rules to property changes in near-isotropic graphite: temperature decrease

4. EXPERIMENTAL DATA

4.1. DIMENSIONAL CHANGES

During irradiation tests on H-451 graphite at General Atomie Company

(Ref. 2), several axial and radial specimens were interchanged between a

high temperature cell and a low temperature cell, while companion speeimens

were irradiated isothermally. The temperatures were 650° to 700°C and

1030° to 1070°C, and both axial and radial speeimens were used. Figure 5

shows the isothermal dimensional changes. Figure 6 shows the temperature

change data for axial specimens. The dashed lines are predictions based

on rule 3 (horizontal transposition at a scaled fluenee). To make the

transposition, the 650° to 700°C isotherm had to be extrapolated based on

the known behavior of other graphites. Figure 7 shows similar data for

the radial direetion. The rule 3 transposition fits the data reasonably

weIl. Rule 2 (horizontal transposition at equal dimensional change) would

fit almost as weIl, whereas rule 1 (vertical transposition at equal

fluence) would underpredict the changes following step-down.

An extensive series of tests were made at KFA on near-isotropie piteh

eoke graphite AS2-M-500 (Ref. 7). Speeimens were shifted between irradia-

tion eells with nominal temperatures of 400°, 600°, 700°C, and 1000°C.

(Speeimens shifted by 200°C or less are exeluded from this review because

data scatter masks the temperature change effects.) Figure 8 shows the

isothermal dimensional changes in axial and radial speeimens plotted as

functions of neutron fluence. Figure 9 shows the results of step-up and

step-down experiments on axial specimens and Figure 10 shows equivalent

data for radial specimens. In Figs. 6, 7, 9, and 10, the dashed lines are

the rule 3 predictions. Agreement between the data and the predieted

behavior is reasonably good; however, extrapolation of the 410° to 450°C

isotherm was necessary. Beeause the experiments were conducted in a region

where the dimensional change curves are almost linear, any one of the

three transposition rules would give similar predictions.

4-1

o

-1

-2

w (!J -3 2:

o

-1 I-

-2 t-

w -3 t-C!l z

UJ C!l z « ::c t..)

-l « z o CI:)

z UJ ~

o a: « UJ z -l

o

-0.5

-1.0

-1.5

o

-0.5

-1.0

-1.5

o

H-451 GRAPHITE " RADIAL ORIENTATION , , , , ,

&11070 Cf', /

" / " ,., .... _-"

~ 1030 o

--- 675°~1050°C(PREDICTED)

o 675°~1050°C(MEASURED)

\

H-451 GRAPHITE RADIAL ORIENTATION

1030-1070

\ \

\

~680 ~

"-. .

fi 700

_ - - 1050o~67!f C(PREDICTED) '. "-~ 1050o~675° C(MEASURED)

2 4 6 8 10

FAST NEUTRON FLUENCE X 10-21 (n/cm2, EFFGD)

12

Fig. 7. Irradiation-induced dimensional changes in H-451 graphite: temperature change data, radial orientation (data from Ref. 2)

4-4

w C!l Z

o

-1

-2

oe( -3 :::c u -I oe( Z 0 o CI)

2: W :E o ~ -0.5 w 2: ....J

-1.0

• 410°-470°C

• 570° -640° C

• 720°-760°C

T 950 0 -1030°C

o 41 0° -470° C -1.5 0 570°-640° C

Ö 720°-760°C

V 9500 -1030°C

-2.0 o 2 3

AS2-M-500 GRAPHITE AXIAL ORIENTATION

AS2-M-500 GRAPHITE RADIAL ORIENTATION

4 5

FAST NEUTRON FLUENCE X 10-21 (n/cm 2, EDN)

Fig. 8. Irradiation-induced dimensional changes in AS2-M-500 graphite: isothermal curves (data from Ref. 6)

4-5

LU (!)

2:

o

. -0.5

-1

~ -1.5 ;z « ::c u -' « ;z o -2 CI) ;z LU ::2: o a::

~ -0.5 ;z -l

-1

-1.5

2 o

• 720-730 ,. ~. ~ .

'\'! . • 4,,950-1030

'" " ''-.

AS2-M-500 GRAPH ITE RADIAL ORIENTATION

" --- 440 Ü ~ 990°C (PREDICTED) ''-. • 4400 ~ 990°C (MEASURED) ~.,

_.- 725° ~ 990°C (PREDICTED) • '" -=-......... . • 725° ~ 990°C (MEASURED) •• ........ .::::

---o

-'-o

1005°~ 430°C(PREDICTED)

1005°~ 430°C(MEASURED)

1005°~ 770°C(PREDICTED)

1005°~ 770°C(MEASURED)

2 3

950-1030

AS2-M·500 GRAPHITE RADIAL ORIENTATION

4 5

FAST NEUTRON FLUENCE X 10-21 (n/cm2, EON)

Fig. 10. Irradiation-induced dimensional changes in AS2-M-500 graphite: temperature change data, radial orientation (data from Ref. 6)

4-7

A third set of temperature change data on gilsocarbon-based graphite

(Dragon grade 95) and semi-isostatically pressed graphite matrix material

was published by Delle, et al. (Ref. 4). In these experiments, the

irradiations were taken almost to the point of minimum dimensional change.

Isothermal curves for the grade 95 graphite are shown in Fig. 11 and the

results of the temperature change experiments are shown in Fig. 12. Similar

data for the matrix material appear in Figs. 13 and 14. The rule 3 predic-

tions fit the observations fairly well, with the exception of the graphite

specimens whose temperature was shifted from 900°C to 1200°C (Fig. 12).

Although rules 2 and 3 predict continued shrinkage, expansion was actual1y

observed. In the rest of the cases (for example, the 1200°C ~ 800°C shift

in the graphite specimens, and the 900°C ~ 1300°C shift in the matrix

specimens), rule 3 transposition matches the data better than either

rules 1 or 2.

4.2. YOUNG'S MODULUS

Reference 6 contains data obtained by KFA on the effects of systematic

changes in irradiation temperature on the dynamic Young's modulus of

AS2-M-SOO graphite. Isothermal data are shown in Fig. 15, and data für the

percent change in Young's modulus for temperature changes exceeding 200°C

are shown in Fig. 16. The data are in very good agreement wHh rulc 3

predictions, whereas rules 1 or 2 do not fit the observations.

4.3. THERMAL CONDUCTIVITY

During irradiation experiments by General Atomic Company (Ref. 2) some

specimens of H-451 graphite were interchanged between irradiation tempera-

tures of 1350°C and 600° to 650°C. The thermal conductivity of the

irradiated specimens was measured at room temperature. Isothermal irradia-

tion results are shown in Fig. 17 and temperature shift data are shown in

Fig. 18. The observations agree very weIl with rule 3 predictions. In

contrast, rule 1 would predict no change in conductivity after the tempera-

ture change and rule 2 would give no solution in the temperature rise case.

4-8

+1

DRAGDN REF. 95 GRAPHITE

RADIAL DRIENTATION

+0.5

~ UJ

0 t!J Z « :::c Co)

..J

« z Cl -0.5 CI)

z UJ :iE Cl a: « -1.0 UJ z ::::i \

-1.5

-2 L-____ ~ ______ L-____ ~ ____ ~ ______ ~ ____ ~ ____ ~

o 2 3 4 5 6 7

FAST NEUTRON FLUENCE X 10-21 (n/cm2, EDN)

Fig. 11. Irradiation-induced dimensional changes in Dragon grade 95 graphite: isothermal changes (data from Ref. 4)

4-9

U.J t!J

o

-0.5

-1

~ -1.5 ::z: u ....J

« z o CI:)

z UJ ::2: o a: « U.J

o

z -0.5 ....J

-1

-1.5

o

DRAGON REF 95 GRAPHITE RADIAL ORIENTATION

o o 810

815 o

o 1200 1185 /

870 o v O 0\ ,/, 540 865 ~ 590 fC

., () ./ 0 , -...;; _ -- /' 560 ',-.".

---900° ---+ 560°C (PREDICTED)

o 900 0 ---+ 5600 C (MEASURED) ---- 900 0 ---+ 1200°---+ 800 DC (PREDICTED)

o 9000 ---+ 1200c---+ 800 D C (MEASURED)

DRAGON REF 95 GRAPHITE RADIAL ORIENTATION

1200"---+ 550°C (PREDICTED)

1200°---+ 550°C (MEASURED

1200"---+ 780 -> 1200°C (PREDICTED)

\l 1160

1200°-> 780 ---+ 1200°C (MEASURED) • /

2

\l ' /\ 1155 ",/

I' /' • 815' ..,..,' / \l '--

1180 '~740 t1

L:::.. • - L:::.. 515 L:::.. --_ 1170 L:::.. - -tr- -

585 550

3 4 5 6

FAST NEUTRON FLUENCE X 10-21 (n/cm 2/EDN)

Fig. 12. Irradiation-induced dimensional changes in Dragon grade 95 graphite: temperature change data (data from Ref. 4)

4-10

~ !

~ L.U (!J

2: c:( :x: w .....J c:( 2: o (/)

2: L.U

:2: o cx: c:( UJ 2: .....J

o

-1

-2

-3

-4

'\

"

o

105 GRAPHITE MATRIX

900°C

1200°C

" " 1350°C / (ESTIMATED) "-.. ............... ~ - --2 3 4 5 6 7

FAST NEUTRON FLUENCE x 10-21 (n/cm 2, EDN)

Fig. 13. Irradiation-induced dimensional changes in semi-isostatically pressed graphite matrix material: isothermal changes (data from Ref. 4)

o

-1

-2

~ -3 z « :I: (.)

105 GRAPHITE MATRIX

- - - 9000 .... 1350° .... 9000 C (PREDICTED)

o 900° .... 1350':"'" 9000 e (MEASUREO) - • -1200° .... 1350° e (PREOICTEO)

o 1200° .... 1350° C (MEASUREO)

\ .,.,...-\ /' \ /

\ 1360 /

\ I 9600 9300

.'. 1340 'J .'" ........ 0 ./ .""",-.-.",..

1315 1370 o 0 ...J

« z o _41.----J.-..---'----L---L---L--L----J ü3 I\. Z LU :E Cl a: « w z ~

-1

-2

-3

-4 o

/ 01180 I

d 1160

___ 1200° ..... 850°C (PREDICTED)

o 1200° ..... 850°C (MEASURED)

2 3

/'

4

~."...- - -- --- --

0830

5

o 830

o 855

FAST NEUTRON FLUENCE X 10-21 (n/cm2, EON)

Fig. 14. Irradiation-induced dimensional changes in semi-isostatically pressed graphite matrix material: temperature change data

(data from Ref. 4)

4-12

AS2-M-500 GRAPHITE

100

o o 2 3 4 5

FAST NEUTRON FLUENCE X 10-21 (n/cm2, EDN)

Fig. 15. Irradiation-induced changes in Young's modulus of AS2-M-500 graphite: isothermal changes (data from Ref.7)

100 AS2-M-500 GRAPHITE • // (CLOSED SYMBOLS: AXIAL

80 OPEN SYMBOLS: RADIAL) 1015°C / ~

9/' 430°C ./ °

60 1015°C ,,~/ 1015°C

- 0'''''''' o /' --_ .............. CI) • '-' _ 1015°C ::;) ...J 40 720°C ::;) _,0 430° ~ 1015° C Cl (MEASURED) Cl :iE 430° ~ 10 15

c C (PAEDICTED) CI) 20 (!)

_,0 7200~ 1015°C (MEASURED) 2 720° ~ 1015°C ::;) (PREDICTEO) Cl >- 0 2

100 LU '\1 (!)

2 430°C 430°C cl: • '\1 ."."..- 755°C :I: 80 u ~. 6 I- " _---6-2 LU /' ",-: ........ --u

60 / ",,/ l::. AS2-M-500 GRAPHITE CI: LU ~ i " 755°C A (CLOSED SYMBOLS: AXIAL

• / OPEN SYMBOLS: RADIAL)

40 A,fl 1020° ~ 755°C (MEASUREO)

1 020° ~ 755° C (PREDICTEO) 20 .,'\1 1020° ~ 430°C (MEASUREO)

0 0 2 3 4 5

FAST NEUTRON FLUENCE X 10-21 (n!cm 2, EDN)

Fig. 16. Irradiation-induced changes in Young's modulus of AS2-M-SOO graphite: temperature change data (data from Ref. 7)

4-14

~ I

E ---~ u ° N N

I-

~

>-I-> i= u ::J 0 z: 0 U .....J

150

100

50

0

150

100

50

o o 2 4

H·451 GRAPHITE AXIAL ORIENTATION

900°·940ü C 600o·630°C

H·451·GRAPHITE RADIAL ORIENTATION

6 8 10

FAST NEUTRON FLUENCE X 10-21 (n/cm2, EFFGD)

12

Fig. 17. Irradiation-induced changes in the room temperature thermal conductivity of H-451 graphite: isothermal curves (data from Ref. 2)

4-15

150 ~

_ 100 ::.:::

)

H-451 GRAPHITE RADIAL ORIENTATION

E -~ l \ \ 8 1~0

u \ "...----/' 'c-... N

t-« 50 ~ \ /

''-8 CI w a:: ::J (/.)

« LU :lE >-t-> t-u

o

::J 150 I-CI z CI U .....J "I « , :lE ,

~ 100 ~ "

600

f

:r: ......

I

t- .......

1350)

50 I-

o I 1 o 2 4

, ,

--- 600"-+ 1340°C (PREOICTED)

o 600u-+ 1340°C (OBSERVED) I I

H-451 GRAPHITE RADIAL ORIENTATION

I

-- 1350°-+ 650°C (pREDICTED)

6. 1350u-+ 650°C (OBSERVED)

"'-650 &----

I I I

6 8 10 12

FAST NEUTRON FlUENCE X 10-21 (n icm 2, EFFGD)

Fig. 18. lrradiation-induced changes in the room temperature thermal conductivity of H-451 graphite: temperature change data (data from Ref. 2)

4-16

4.4. THERMAL EXPANSIVITY

During the KFA experiments (Ref. 7), the thermal conductivity of some

AS2-M-500 specimens was measured. The isothermal data are plotted in

Fig. 19, and the temperature change data in Figs. 20 and 21. Again,

rule 3 transposition shows fairly good overall agreement with the data.

However, rule 1 transposition fails to predict the rise in thermal expan-

sivity when the irradiation temperature is dropped from 1020° to 430°C,

and rule 2 transposition is impossible in some cases.

4-17

+20

+10

0

~ -10 >-I-

> CI:)

2:

+20 AS2-M-500 GRAPHITE

.430 AXIAL ORIENTATION

+10 .1015

1015 • __ 430o~1015°C (PREDICTED)

0 • 430o~1015° C (MEASURED) , \ " --- 720o~1015° C (PREDICTED) ~ ~ • 720"-+1015° C (MEASUR ED)

>- -10 ~ I-> " CI) " .1015 z

........ --..J

-10 ... 755 X X X 1020c~ 755° C (PREDICTEO)

• 1020o~ 755°C (MEASUREO) -20 *** 1020o~ 430° C (PREDICTEO)

~ 1020o~ 430°C (MEASUREO)

o 2 3 4 5

FAST NEUTRON FLUENCE X 10-21 (n/cm 2, EON)

Fig. 20. lrradiation-induced changes in the thermal conductivity of AS2-M-SOO graphite: temperature change data, axial orienta-tion (data from Ref. 7)

4-19

+20 r---------------------------------------AS2·M·500 GRAPH ITE RADIAL DRIENTATION

o

~ -10 > CI)

z oe( a.. ~ -20 ....J oe( :2 a:: w ::t: -30 ~

w c.!J Z oe( +10 ::t: c...J

~ Z W

~ 0 w a..

-10

-20

o

I, I ,

I 0 ,,~O _ _ 1015 I 430 ...... -.- • .::::-- 0 I." 0" ......

• / 1015 '" "'

- - - 430°-+ 1015°C (PREDICTED)

o 430"-+ 1015°C (MEASURED) -. - 720°-+ 1015°C (PREDICTED)

o 720"-+ 1015°C (MEASURED)

* * X 1020 X

\1430 V* *

* * * X X X· X

~ 755

X X

X X X 1020"-+ 755°C (pREDICTED)

~ 1020°-+ 755°C (MEASURED)

* * * 1020°-+ 430°C (PREDICTED)

\1 1020°-+ 430°C (MEASURED)

2 3

X

"-" " " 0 1015 , o 1015 ,

AS2·M·500 GRAPHITE RADIAL ORIENTATION

X X

X X

4

X X

755 ~ X

5

X

FAST NEUTRON F LUENCE X 10-21 (n/cm 2, EDN)

Fig. 21. Irradiation-induced changes in the thermal expansivity of AS2-M-500 graphite: temperature change data, radial orien-tation (data from Ref. 7 )

4-20

5. SUMMARY AND CONCLUSIONS

Routine irradiation tests on graphite are carried out at constant

temperature and the resulting design data are presented in the form of

families of isothermal plots showing the change in property as a function

of fast neutron fluence. When service conditions require the irradiation

temperature to change, design calculations must use combinations of iso-

thermal plots to predict the graphite properties. In the present report

three alternative rules for transposing isothermal curves are discussed.

Rule 1: Vertical transposition at equal fluence [Fig. 1(B)]: this procedure is simple, but fails to predict the changes in properties such as thermal conductivity which are controlled by a transient population of small defect clusters.

Rule 2: Horizontal transposition at equal property value [Fig. 1(C)]: this procedure has some justification, but frequently fails to provide a solution.

Rule 3: Horizontal transposition at scaled fluence [Fig. 1(D)]: this procedure provides a physically realistic method which always yields a solution and can be used for transient property changes such as Young's modulus and thermal conductivity.

Experimental data from several programs in which the irradiation

temperature of graphite specimens was systematically changed were reviewed.

Measurements of changes in dimensions, Young's modulus thermal conductivity,

and thermal expansivity are plotted in Figs. 5 through 21.

Overall, the measurements agree weIl with predictions based on the

h h the f1'rst and second rules sometimes t ird transposition rule, w ereas

give rise to false predictions or no predictions at all.

5-1

The suggested procedure for combining i sotherms bv Iwr i Zllnt al

transposition at a scaled fluence is as follllws. Thv flul'llCl'

ACKNOWLEDGEMENTS

General Atomic's contribution to this work was supported by

Contract DE-AT03-76ET-35300 for the San Francisco office of the Depart-

ment of Energy. The contribution from the Federal Republic of Germany

was carried out in the framework of the Project "Hochtemperaturreaktor-

Brennstoffkreislauf" (High Temperature Reactor Fuel Cycle) that includes

the partners Gelsenberg AG, Gesellschaft fuer Hochtemperaturreaktor-

Technik GmbH, Hochtemperaturreaktor-Brennelement GmbH, Sigri Elektro-

graphit GmbH, Rindsdorff-Werke GmbH and is financed by BMFT (Federal

Ministry for Research and Tecnnology) and the State of Nordrhein-Westfalen.

5-3

6. REFERENCES

1. Gray, B. S., et al., "Radiation Annealing in Graphite," Proc. Conf.

on Radiation Damage in Reactor Materials, Vienna, 1969, 11, 523

(IAEA, Vienna, 1969).

2. Price, R. J., and L. A. Beavan, "Final Report on Graphite Irradiation

Test OG-3," USERDA Report GA-A14211, General Atomic Company, 1977.

3. Engle, G. B., "Effect of Temperature History on the Dimensional

Changes of Irradiated Nuclear Graphite," USAEC Report Gulf-GA-A12080,

Gulf General Atomic Company, 1972.

4. Delle, W. W., et a1., "Effects of Changes in Irradültion Temperature

on the Irradiation Behavior of Graphite and Matrix Materials," Extended

Abstracts of the 11th Biennial Conference on Carbon, Gatlinberg, 1973,

(CONF-730601), p. 300 (1973).

5. Cords, H., and R. Zimmerman, "A Model for Irradiation Induced Changcs

in Graphite Material Properties," Proc. Fifth London International

Carbon and Graphite Conference 11, 918 (1978); (Society of Chemic~l

Industry, Landon, 1978).

6. Nettley, P. T., et al., "Irradiation Experience with Isotopic

Graphite," Proc. Symp. on Advanced and High Temperature Gas-Cooled

Reactors, Juelich, 1969, p. 603, (IAEA, Vienna, 1969).

7. Haag, G., unpublished data, General Atomic Company, 1978.

6-1

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