-
(!) __ 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.
Neither the United States nor the Department ofEnergy, nor any
oftheir employees, nor any oftheir contractors, subcontractors, or
their employees, makes any warranty, express or implied, or
assurnes any legalliability or responsibility for the accuracy,
completeness or usefulness of any information, apparatus, product
or process disclosed, or represents that its use would not infringe
privately owned rights.
Printed in the United States of America Availab1e from
National Technica1 Information Service U.S. Department of
Commerce
5285 Port Royal Road Springfield, Virginia 22161
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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