Y3. A17
221
AEG
RESEARCH REPORTS
BMI-1604
UNIVERSITY OF
ARIZONA URSARY
FISSION-PRODUCT-RELEASE MEASUREMENT FROM
CLAD FUEL SPECIMENS
BATTELLE MEMORIAL INSTITUTE
UNIVERSITY OF MICHIGAN
3 9015 08648 8411


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Contract No. W-7405-eng-92
Report No. BMI-1604
UC-25 Metals, Ceramics,
and Materials
(TID-4500, 18th Ed.)
FISSION-PRODUCT-RELEASE MEASUREMENT FROM
CLAD FUEL SPECIMENS
by
Mihkel Kangilaski
Arthur A. Bauer
Frank A. Rough
Ronald F. Dickerson
November 28, 1962
BATTELLE MEMORIAL INSTITUTE
505 King Avenue
Columbus 1, Ohio
ABSTRACT
INTRODUCTION.
TABLE OF CONTENTS
Page
1
1
EXPERIMENTAL, PROCEDURES
Description of Equipment.
Collection and Interpretation of Data
Description of Specimens.
EXPERIMENTAL RESULTS.
Niobium-Clad Specimens
Niobium-Aluminum-Titanium-Clad Specimens
Iron-Chromium-Yttrium-Clad Specimens
Iron-Chromium-Yttrium-Aluminum-Clad Specimen
Iodine Release
DISCUSSION.
1
257
∞
9
1 1
11
14
14
. 16
FISSION-PRODUCT-RELEASE MEASUREMENT
FROM CLAD FUEL SPECIMENS
Mihkel Kangilaski, Arthur A. Bauer, Frank A. Rough,
and Ronald F. Dickerson
Xenon-133 and -135, krypton-85m and -87, and iodine-131, -133, and -135
release from VO2 fuel specimens with four types of metallic claddings was deter-
mined during irradiation in 2200 to 3200 F flowing helium and oxygen. Fission-gas
samples cold trapped from the furnace sweep gas were identified in a gamma analyzer.
Information on iodine release was obtained by monitoring xenon produced by iodine
decay after irradiation and by washing and scrubbing the loop after irradiation to
recover iodine plated out in the system. Uranium contamination of portions of the
loop made it impossible to detect releases below a certain level from the specimens.
Specimens clad with niobium or niobium-29.6 w/o aluminum-33.7 w/o titanium
exhibited release fractions in the range of 10-6 at 2200 F and 10-5 at 3000 and
3200 F. Release values for iron-30 w/o chromium-1 w/o yttrium-clad material at
2200 F were around 2 x 10-2. Material clad with iron-25 w/o chromium-1 w/o
yttrium-4.67 w/o aluminum exhibited a release fraction of 1.6 x 10−3 during irradiation
in 2200 F oxygen and oxygen saturated with water vapor.
INTRODUCTION
An important property of fuel-element cladding materials is their ability to retain
fission products within the fuel element and minimize radioactive contamination of the
coolant. This ability becomes increasingly difficult to secure with higher fuel operating
temperatures. Consequently, the rate of fission-product migration through the cladding
must be considered in selecting cladding materials for elevated-temperature operation.
Such considerations led to the program described in this report. Information was
required on the fission-product retention capabilities of a variety of cladding materials
developed by GE-ANPD for operation at temperatures of 2200 F and above. For this
purpose a program was undertaken to investigate the level of release of iodine and
fission-gas isotopes during irradiation of fueled specimens clad with the materials of
interest.
EXPERIMENTAL PROCEDURES
The experiments were conducted in a loop contained in a beam tube of the Battelle
Research Reactor. Fission gases were collected in a fission-gas trapping system from
the sweep gas which flowed over the specimen. Iodine was collected for analysis by
washing and scrubbing the various components in the loop after completion of the irradi-
ation experiment.
2
Description of Equipment
The specimens were irradiated in a loop contained in an 8-in. -diameter beam tube
of the BRR. The specimen itself was contained in a furnace attached to the end of an
easily removable 2-1/2-in. -diameter beam-hole plug. The furnace and removable plug
are shown in Figure 1. An outer containment can was placed over the furnace to provide
a vacuum seal. Vycor was used as the outer can for the initial experiments with a
vacuum seal being provided by O-rings. A stainless steel can, silver soldered to the
plug, was used in later experiments because of difficulties in maintaining the O-ring
seals.
The furnaces were made from high-purity Norton alumina tubes with platinum-40
w/o rhodium resistance windings using standard laboratory construction procedures.
The furnace components are shown in Figure 2 and consist of an inner tube which is
grooved to hold the wire and an outer tube which is placed over the windings for thermal
insulation. Prior to placement of the outer tube, the wire is first covered with high-
purity Alundum cement. The position of baffles in the furnace is also shown. The speci-
men is placed between the baffles in the inner tube. Two platinum-platinum 10 w/o
rhodium thermocouples are placed directly at the rear of the specimen and exit through
the protection tubes upon which the rear baffles are built.
The platinum-40 w/o rhodium winding was satisfactory for all experiments at
2200 F. However, at 2500 F the windings exhibited extremely short lives, 10 to 20 hr,
in-pile. Previously, a similar furnace had been built and operated out-of-pile under
identical experimental conditions in the absence of a neutron flux. This furnace operated
for 260 hr at 2500 F and for an additional 60 hr at temperatures up to about 3200 F.
The in-pile furnace burned out only after over 10 hr at the latter temperature. Analyses
showed appreciable amounts of silicon in the failed windings, and it was suspected that
this element, formed by transmutation of aluminum, might be responsible for the failure.
However, the amount of silicon formed in the refractory Al2O3 by neutron capture and
decay is negligible compared with the silicon already present as an impurity. It appears
more probable that pickup by the platinum-40 w/o rhodium of silicon already present in
the refractory is enhanced somehow by the irradiation.
As a result of this problem, only one reasonably long-time experiment was con-
ducted at 2500 F and above. This was accomplished with a furnace in which tantalum
was substituted for the platinum-40 w/o rhodium windings.
Helium and oxygen were used as carrier gases at flow rates of 25 to 60 cm³ per
min. The helium was high-purity AEC-type which was passed through a Deoxo unit,
which combines oxygen and hydrogen to form water, and through a molecular sieve to
remove the water vapor. The gas entered the specimen plug, flowed over the outside
of the furnace, where it was preheated, and then flowed down through the furnace tube
over the specimen. A zirconium getter was placed just before the specimen to remove
any additional oxygen contained in the gas. The gas flowed from over the specimen into
the gas-trapping system. Flow was maintained by a vacuum pump at the end of the
trapping system. Exhaust gas was released through a stack system.
1-30
N78968
FIGURE 1. SPECIMEN PLUG WITH FURNACE IN PLACE WITHOUT OUTER CONTAINMENT CAN
3


FIGURE 2. FURNACE COMPONENTS
N80972
5
Collection and Interpretation of Data
Traps for fission gases were removed for analysis every 4 hr except at the start
of an experiment when they were removed more often. The traps contained activated
charcoal maintained at liquid-nitrogen temperatures. A sketch illustrating the basic
trapping system is shown in Figure 3. The gas flows through a bypass line when the
trap is removed. Trapping times were varied to obtain gas samples of a convenient
activity to analyze and ranged from 1 to 30 min. To test the efficiency of the activated-
carbon traps a second trap was placed behind the first trap. Analysis of the second
trap showed that some leakage through the first trap did take place. This amounted to
about 10 per cent for trapping times of 15 min. For trapping times of 5 min, no notice-
able leakage was detected.
When the released activities became high a different trapping technique was used.
In such cases, a gas sample of known volume was obtained in a small vial and analyzed.
All traps were counted in a 100-channel gamma analyzer with a sodium iodide
crystal. Counting times were varied from 1 to 5 min, depending on activity of the trap.
Analyses were made for xenon-133 and xenon- 135 and for krypton-85m and krypton-87.
Krypton-88 and xenon-135m were detected, but quantitative analysis of these isotopes
was not attempted because of overlap in the gamma-energy spectrum.
Results of the gas analyses were calculated as R/B values, where R is the number
of atoms release per second, and B is the number of atoms produced per second by
fission and precursor decay at equilibrium. Thus, R/B is the fractional release of a
particular isotope. The B, or production, values are calculated from the fission rate
based on uranium-235 content and neutron flux. The R values are obtained by gamma
counting the gas traps.
In order to determine the neutron flux and fission rate, a burnup analysis was
performed on the first specimen after the experimental run. For this purpose
cesium-137 analysis was considered unreliable because of the high temperatures in-
volved, while a niobium-95 analysis could not be run because the specimen was clad
with niobium. Consequently, a cerium-144 determination was performed for the burnup.
The burnup results indicated an effective neutron flux of 0.5 x 1012 nv, with the reactor
running at 75 per cent power during the experiment. However, the reactor ran at various
power levels during subsequent experiments. The fluxes, consequently, were adjusted
from this value on the basis of the reactor power during a particular experiment.
Titanium-0.58 w/o cobalt dosimeter wires were also included with the specimen
in some of the runs. The fluxes indicated by these wires were in general agreement
with those based on the burnup analysis corrected for reactor power level.
Data were also sought on iodine release, in particular iodine-131, iodine-133,
and iodine-135. The latter two isotopes are precursors to xenon-133 and xenon-135,
for which gas-trap analyses were obtained during irradiation.
For this purpose gas trapping was continued after shutdown of the furnace and
retraction of the specimen plug out of the neutron flux in the beam hole. In this manner,
only the xenon-133 and xenon-135 which formed by decay of iodine-133 and iodine-135
Activated-
carbon
D₁
Valve
V-I
Valve
V-2
+
Main gas line
Gas in
DISCONNECT POINTS
6
Disconnect here to
remove trap
+
Valve
V-4
Valve
V-3
AE-43291
D₂
Main gas line
Gas out
FIGURE 3. SIMPLIFIED SKETCH OF ANALYTIC FISSION-GAS TRAP ILLUSTRATING
7
were collected, permitting a calculation of the amounts of iodine which had plated out
in the tubing of the loop. Subsequently, individual parts of the furnace and specimen
plug were washed out separately, including all tubing leading to the gas-trapping system.
The stainless steel tubing and alumina furnace parts were washed in 1N HC1, while
copper tubing in the system was washed in IN NH4OH. Two washings were made of
each part.
The resulting solutions were then analyzed by gamma counting and radio-
chemical techniques for iodine-131, iodine-133, and iodine-135.
Description of Specimens
For these experiments, eight different UO2 fuel specimens were supplied by
GE-ANPD. The specimens were clad with four different materials and are described
in Table 1.
TABLE 1. DESCRIPTION OF EXPERIMENTAL SPECIMENS
Cladding Composition,
w/o
Total
Total
Cladding
Thickness,
Specimen Run
UO2. g Uranium-245, go mils
Specimen
Dimensions, in
Diameter Length
100 Nb
A
1
4.87
0.32(a)
10(b)
0.210
1.69
B
6
5.17
0.33(a)
10(b)
0.210
1.69
C
8
4.83
0.31(a)
13
0.216
1.69
D
9
4.90
0.31(a)
13
0.216
1.69
Nb-29.6 Al-33.7 Ti
E
2,5
4.7
0.41(a)
13
0.216
1.69
Fe-30 Cr-1 Y
F
3,10
0.51
0.42
7-10
0.035
19
G
4
0.52
0.43
7-10
0.035
21
Fe-25 Cr-1 Y-4.67 Al
H
7
0.63
0.51
7-10
0.035
(a) Fuel consisted of fully enriched UO2 dispersed in depleted UO2; all other specimens contained
enriched UO2 only.
(b) 6 mils was machined off the as-received specimen diameters.
The niobium- and niobium-aluminum-titanium-clad specimens were cylinders with
approximately 1/4-in.-thick end caps. These specimens were fueled with a dispersion
of fully enriched UO2 in depleted UO2. The remaining specimens, clad with iron-
chromium-base alloys were in wire form, the wire being wrapped around a tube made
of the same alloy as the cladding. The fueled core in these wires was enriched UO2.
Two of the as-received niobium-clad specimens were machined to obtain surface
samples for analysis of uranium content. The uranium in the niobium was less than the
0.01 w/o detection limit.
The test conditions for each experiment are shown in Table 2. A majority of the
specimens were exposed at 2200 F with helium as the sweep gas. However, tests were
also run at 2500 F, and one specimen was irradiated briefly at 3200 F. Also, oxygen
and oxygen saturated with water vapor at room temperature were employed as the sweep
gas in two experiments involving specimens clad with iron-chromium-base alloys. The
neutron flux varied in direct proportion to the power level, being 0.5 x 1012 at 75 per
cent power.
8
TABLE 2. EXPERIMENTAL CONDITIONS
Reactor Power
Time
Cladding Composition,
Temperature,
Level, per cent
of
Run Specimen
w/o
F
Sweep Gas
of full power
Run, hr
1
A
100 Nb
2200
He
75.0
168
2.
E
Nb-29.6 Al-33.7 Ti 2200 and 2500
He
77.5
220
3
F
Fe-30 Cr-1 Y
2200
He
82.5
109
4
G
Fe-30 Cr-1 Y
2200
He
82.5
4
5
E
Nb-29.6 A1-33.7 Ti
2500
He
97.5
10
6
B
100 Nb
2200 and 2500
He
97.5
26
7
H
Fe-25 Cr-1 Y-4.67 Al
2200
O2 and H2O-
97.5
245
saturated 02
∞ ∞
8
9
UA
C
100Nb
D
100 Nb
2200 and 2500
2500, 3000,
He
100
66
He
96.5
110
10
F
Fe-30 Cr-1 Y
and 3200
2200
He and O2
98.0
85
The times of test depended upon a number of factors. Tests were generally run
long enough to make certain that equilibrium releases were being observed and then
were stopped. A few tests were discontinued when it was believed that a specimen was
defective or had failed during the test. In some cases, tests were terminated by a
furnace failure.
EXPERIMENTAL RESULTS
The results of fission-gas trapping are given in the following paragraphs in terms
of release fractions or R/B values. The results are presented in graphical form. In
the majority of the experiments, the release fractions for all four isotopes for which
analyses were made fell within fairly well defined limits, and within the limits of
accuracy of analysis no differences in release fractions were apparent among the four
isotopes. Consequently, the range within which the release fractions fell are generally
shown. In those cases where excessive scatter or deviations from this general behavior
were observed actual data points or identifications of isotopes showing unique behavior
are given.
Data are also presented for three iodine isotopes. From these data inferences
concerning release fractions for iodine are drawn.
Before proceeding to the exceptional results with clad specimens, a supplementary
experiment should be described, since the results have a significant bearing on the re-
lease fraction which can be detected. This experiment was run after completion of all
specimen tests. The experiment was conducted because the insignificant difference in
release fractions for a number of niobium-clad and niobium-aluminum-titanium speci-
mens suggested that the primary source of release might be contaminant uranium in
various parts of the furnace and specimen plug rather than from the specimen. A blank
run was made without a specimen at 2200 F under conditions identical to those employed
in testing specimens. Fission-gas analyses showed that the amount of gas generated
within the loop was sufficient to account for the release fractions obtained for a number
9
of the specimens. Consequently, for these experiments it can only be concluded that
the release fraction is less than the number obtained.
Niobium-Clad Specimens
Four specimens, clad with niobium, were exposed to irradiation for fission-gas
release studies. Release for three of these specimens is shown in Figure 4. The fourth
specimen was apparently defective. It was exposed at 2500 and then 2200 F, exhibiting
release fractions on the order of 10-2. Data are not shown for this specimen.
The first specimen was exposed at 2200 F for a total of 168 hr (Run 1, Speci-
men A). During the first 11 hr of the experiment, an air leak developed in the loop
system and the specimen was removed and examined visually and macroscopically in
the BMI Hot-Cell Facility. No evidence of damage to the cladding was noted so the
specimen was reinserted and the test continued. Release fractions are shown in
Figure 4a. After 101 hr, another air leak developed, and the release of fission gases
increased rapidly and then leveled off. The high background associated with argon
activity, the argon being introduced with the air, made it impossible to analyze for any
isotope other than xenon-135 during this final 67-hr period.
After removal from the loop, the specimen was examined in the hot cells and it
was found that it had split into two pieces. The specimen diameter had increased from
0.210 in. to 0.213 in. and the cladding appeared oxidized. It was uncertain whether the
specimen broke during irradiation or during removal from the loop. However, it appears
certain that the increased release fraction during the last period of operation was a re-
sult of oxidation of the specimen.
The release fractions recorded for the first 101 hr of operation are of the order of
magnitude that can be accounted for on the basis of fission-product production in and
release from the furnace parts rather than from the specimen. Consequently, it must
be concluded that the release fraction shown in Figure 4a represents maximum values,
with the release fraction from the specimen itself probably being significantly lower.
A second specimen was exposed at 2200 F for 42 hr and then at 2500 F for 24 hr
(Run 8, Specimen C). Results are shown in Figure 4b.
Results are shown in Figure 4b. No increase in release ac
companied the increase in temperature from 2200 to 2500 F. As with the previous
specimen, the release fractions observed can be accounted for on the basis of fission-
gas generation by contaminant uranium in the system rather than release from the
specimen.
A final niobium-clad specimen was exposed at 2200 F for 11 hr then at 2500 F for
65 hr, at 3000 F for 30 hr, and at 3200 F for roughly 4 hr (Run 9, Specimen D). Re-
lease fractions for the xenon and krypton isotopes as can be seen in Figure 4c increased
slightly with increasing temperature but as with the previous specimens the source of
the fission gases is believed to be principally uranium impurity in the furnace parts.
However, xenon-133 release appeared to be higher than could be attributed to this source
particularly at 3000 and 3200 F. This higher level of xenon-133 release is consistent
with the advent of detectable diffusion release.
10
Release Fraction
Release Fraction
10-5
10-6
Release Fraction
10°5
10%
107
10-6
30
60
10-7
·2200 F 2500 F
O
30
60
90
Probable rupture
Xe
135
120
150
180
a. Run I with Specimen A
Activity increased by
a factor of 104
90
120
150
180
b. Run 8 with Specimen C
0Xe133
2500 F.
3000F3200 F
10-7
30
60
90
120
150
Irradiation Time, hr
c. Run 9 with Specimen D
180
AE -43292
FIGURE 4. FISSION-GAS-RELEASE FRACTIONS FROM NIOBIUM-CLAD SPECIMENS
11
Xenon-133 releases were also fairly high at the beginning of this particular ex-
periment, although these high values are not shown. It is believed that the specimen
plug, which was reused directly after an experiment in which high release rates were
obtained, was contaminated with iodine-133. The rate of decrease in xenon-133 release
was consistent with this assumption, since the decrease showed an iodine-133 half-life
dependency.
Niobium-Aluminum- Titanium-Clad Specimens
A specimen clad with a niobium-29.6 w/o aluminum-33.7 w/o titanium alloy was
exposed for 205 hr at 2200 F and then for 15 hr at 2500 F (Run 2, Specimen E). No
increase in fission-gas release was noted when the temperature was increased. Re-
sults are shown in Figure 5a. A number of air leaks developed in the loop during this
experiment but these had no effect on the release of fission gases.
The release of fission gases, as with the niobium specimens described previously,
is below the background level of release due to impurity uranium in the system. Thus,
the release fractions reported must be considered maximum values with actual release
fractions less than those calculated.
This same specimen was re-exposed at 2500 F for 10 hr (Run 5, Specimen E).
The release fraction increased steadily during this period as can be seen in Figure 5b,
and it is suspected that the specimen developed a defect as a result of handling. Sub-
sequent metallographic examination in the hot cells revealed evidence of cracking
although it was not certain that these cracks formed during irradiation rather than during
metallographic preparation.
Iron-Chromium-Yttrium-Clad Specimens
Two specimens clad with the iron-30 w/o chromium-1 w/o yttrium alloy were
tested at 2200 F. Within 11 hr after insertion of the first specimen, release fractions of
about 10-2 were obtained (Run 3, Specimen F). It was thought that the specimen might
be defective, and the specimen plug was removed from the flux. However, it was de-
cided to observe release during irradiation for longer periods with the results shown
in Figure 6a. The specimen plug was reinserted into the flux and the specimen tem-
perature reached 450 F. Power was then applied to the furnace and the temperature
was increased in 300 F increments to 2200 F over a 50-hr period. The release fraction
increased steadily and then leveled off at a maximum of 2 x 10-2, as can be seen in
Figure 6a, during operation at 2200 F. The test was discontinued after a total of 109 hr.
One feature in the release behavior was the significantly lower fractional release of
krypton-87 compared with xenon-133 and xenon-135 and krypton-85m. As can be seen
in Figure 6a the release fraction for krypton-87 was lower by about one order of magni-
tude than for the remaining isotopes. This suggests a time-dependent release mecha-
nism. Krypton-87 is the shortest lived of the isotopes, having a half-life of 78 min.
Decay during release would lead to a lower release fraction for this isotope compared
with the remaining longer lived isotopes.
12
Release Rate
Release Rate
10-6
2200 F
10-7
5
104
10-5
10-6
ــــلام
O O
10
50
2500 F
100
150
200
250
a. Run 2 with Specimen E
Xe 135
oxe135
Reading taken 30 minutes
after furnace failure
54
O
5
10
50
100
Irradiation Time, hr
b. Run 5 with Specimen E
150
200
AE - 43293
FIGURE 5. FISSION-GAS-RELEASE FRACTIONS FROM A SPECIMEN CLAD WITH
NIOBIUM-29.6 w/o ALUMINUM-33.7 w/o TITANIUM
250
Release Fraction
Release Fraction
10-3
Release Fraction
10-2
10-3
102
450 to
2200 F
10-4
O
20
40
10-1
60
0
2200 F
80
0
QKr 87
13

a. Run 3 with Specimen F in Helium
Atmosphere changed from
helium to oxygen
20
40
100 120 140
160 180 200 220 240

60
80 100 120 140 160 180 200 220 240
b. Run 10 with Specimen F in Oxygen

10
O
20
40
c. Run 7 with Specimen H
60 80 100 120 140 160 180
Irradiation Time, hr
200 220 240
AE -43294
FIGURE 6. FISSION-GAS-RELEASE FRACTIONS FROM SPECIMENS CLAD WITH
IRON-30 w/o CHROMIUM-1 w/o YTTRIUM AND WITH IRON-25 w/o
CHROMIUM-1 w/o YTTRIUM-4.67 w/o ALUMINUM
14
}
Since leakage from the specimen was suspected, a second identical specimen was
also irradiated at 2200 F. This specimen exhibited the same fractional-release behavior
as the first specimen, and, consequently, the test was discontinued.
Both of these tests were run with helium as the sweep gas. A third test was run
at 2200 F reusing the first specimen but with oxygen as the sweep gas to determine its
effect on fractional release of the fission gases (Run 10, Specimen F). The results of
this test appear in Figure 6b. Helium was used as the sweep gas for the first 8 hr and
then oxygen was introduced. While the readings showed a wide spread initially and
narrowing of the spread upon the introduction of oxygen, followed by a gradual increase
in release with continued exposure, there was little significant difference in the
results of the runs made in helium and in oxygen atmospheres.
Iron-Chromium-Yttrium-Aluminum-Clad Specimen
A single specimen clad with an iron-25 w/o chromium-1 w/o yttrium-4.67 w/o
aluminum alloy was irradiated at 2200 F (Run 7, Specimen H). Oxygen was used as the
carrier gas throughout the test, and in the latter part of the experiment the oxygen was
saturated with water vapor at room temperature by bubbling the oxygen through water.
The specimen was exposed in-pile for a total of 245 hr, the last 27 hr to the water vapor-
oxygen gas stream.
The results of this experiment are shown in Figure 6c. The release fraction in-
creased slightly initially and then leveled off. No change in release occurred with the
introduction of water vapor.
Iodine Release
Figure 7 shows a typical plot illustrating the continued release of xenon-133 and
xenon-135 after removal of the loop from the reactor. This continued release is a re-
sult of decay of iodine trapped or plated out in various parts of the loop, as can be seen
by the dependence of xenon production on the precursor iodine half-life. Extrapolation
of the continued xenon evolution rates back to the completion of irradiation in a series
of experiments indicated that from 25 to 75 per cent of the xenon release detected during
irradiation was a product of iodine decay. Thus, the indications are that iodine and
xenon release fractions are roughly equivalent.
The results of washing and scrubbing various components of the loop after irradi-
ation are summarized in Table 3. Recovery of iodine was generally incomplete as
indicated by the number of iodine atoms recovered compared with the number required
for the levels of xenon production by iodine decay after removal of the loop from the
neutron environment. However, it seems reasonable to assume that the percentage
recovery of each of the three iodine isotopes of interest is equivalent.
Table 3 gives the number of atoms present at the completion of in-pile irradiation.
These values were obtained by counting the number of atoms in the wash solutions ob-
tained and correcting these numbers for decay back to the time of retraction of the loop
out of the reactor flux field. These values were converted to equilibrium release rates
:
Apparent Release Fraction
10-4
103
Xe
135
Xe 133
X
*
15
1135 (half-life, 6.7 hr)-
133 (half-life, 20.8 hr)
X
O
X
|+
け
​O
10-5
O
10
20
30
40
Time after Irradiation, hr
AE-43294
FIGURE 7. APPARENT XENON RELEASE FRACTIONS AFTER IRRADIATION DUE TO
IODINE DECAY FOLLOWING RUN 7
i
16
by multiplying the number of atoms present by the decay constant. The values for re-
lease per fission were obtained by dividing the previous numbers by the fractional fission
yield of the individual isotopes. The resulting values are comparable in terms of re-
lease fractions and indicate that within experimental accuracy the fractional releases of
the three iodine isotopes are equivalent.
TABLE 3. IODINE-RECOVERY DATA
Iodine
Isotope
Run 6
Run 7
Run 8
..
Number of Iodine Atoms
131
1.11 x 1012
Present at End of
1.26 x 1013
133
1.07 x 1012
Irradiation
5.52 x 1012
135
1.21 x 1011
4.45 x 1014
2.66 x
1014
Equilibrium Release
131
1.1 x 105
Rate, atoms per sec
133
9.9 x 106
135
6
1.3 x 107
5.1 x
107
4.4 x 108
2.36 x
109
2.5 x 10
Comparable Release per
131
3.8 x 107
Fission, atoms per sec
133
1.5 x 108
4.5 x 108
7.8 x 108
135
4.2 x 10
07
1.53 x 108
3.63 x 108
DISCUSSION
The fractional releases of xenon-133 and xenon-135 and krypton-85m and
krypton-87 from the various clad samples are summarized in Table 4 except for those
runs where the specimens were believed to be defective. The consistent behavior of
iron-30 w/o chromium-1 w/o yttrium-clad specimens in Runs 3 and 4 suggests that these
specimens may release fission products at a fairly high rate by migrates through the
cladding.
On the basis of results of continued fission-gas monitoring for iodine decay to
xenon after removal of the specimen loop from the reactor flux, the release fractions
of iodine-133 and iodine-135 are of the same order of magnitude as their xenon daughter
products. The results of washing and scrubbing various loop components to collect
iodine further indicate that the release fractions of iodine-131, iodine-133, and iodine
iodine-135 are all roughly equivalent.
The program described was designed to provide proof tests of the capabilities for
fission-product retention of the various cladding materials. It is believed that the pro-
gram was successful but no conclusions concerning mechanisms of release can be drawn
from the data. Only in two experiments was any evidence of a time-dependent release
mechanism, such as diffusion, obtained, and in these experiments the data were too
limited for confirmation. A program aimed specifically at studying mechanisms of
release would be required for this purpose.
MK:AEB:FAR:RFD/dnm
!
17 and 18
TABLE 4. SUMMARY OF FRACTIONAL RELEASE DATA
Cladding
Composition, w/o
Run
Temperature,
F
Sweep
Cladding
Thickness,
Maximum Average(a)
Gas
mils
Release Fraction,
R/B
Niobium
1 ∞ ∞ ∞ ∞ a
1
2200
He
10
<8.7 x 10~7
8
2200
-6
He
13
<3.3 x 10
8
2500
He
13
<3.3
X 10-6
9
2500
He
13
<2.5 x 10-6(b)
9
3000
He
13
<3 x 10-6(b)
9
3200
He
13
<3 x 10-6(b)
Nb-29.6
2
2200, 2500
He
13
<8.5 x 10-7
Al-33.7 Ti
Fe-30 Cr-1 Y
3
2200
He
7-10
2 x 10-2(c)
4
2200
He
7-10
2 x 10-2
10
2200
He
7-10
10
10
2200
02
7-10
1.6 x 10-2
2.5 x 10
x 10-2
Fe-25
Cr-1
Y-4.67
Al
77
7
2200
02
7-10
7
2200
O2 with
7-10
1.6 x 10-3
1.6 x 10-3
H₂O
(a) Release fractions apply to all xenon and krypton isotopes measured, except where noted.
(b) Xenon-133 release appeared significantly higher, 10-5 at 3000 and 3200 F.
(c) Krypton-87 release appeared significantly lower, 1.5 x 10-3, than releases for remaining isotopes.