bwr spent-fuel measurements with the ion-1/fork detector
TRANSCRIPT
LA-10758-MS
UC-15Issued: August 1986
LA—10758-MS
DE87 000801
BWR Spent-Fuel Measurementswith the ION-1/Fork Detector
and a Calorimeter
Phillip M. RinardGerald E. Bosler
Los Alamos National LaboratoryLos Alamos, New Mexico 87545
DISTRIBUTION OF THIS DOCUMENT IS UNLIMITED
CONTENTS
ABSTRACT 1
I. INTRODUCTION 2
A. Context of the Measurements 2
B. Battelle Pacific Northwest Laboratory's
Objectives 2
C. Role oE GE-MO 3
D. Los Alamos Involvement 3
E. Chronology of Los Alamos A c t i v i t i e s 5
II. ION-1/FORK DETECTOR 5
A. Fork Detector Head 5
1. General Characteristics 6
2. Neutron Detectors 7
3. Gamma Detectors 8
B. ION-1 Electronics Unit 9
1. General Description 9
2. Pulse Channel Lower-Level
Discriminator Setting 10
3. Current Channel Amplifier Gain Ranges . . . 10
4. Calculated Uncertainties 10
c. installation at GE-MO 11
III. ION-1/FORK PRELIMINARY MEASUREMENTS 11
A. Preliminary Response Measurements 11
1. Neutron Measurements 11
2. Gamma-Ray Measurements 13
B. Background Values 13
C. Potential Sources oE Interference 13
CONTENTS (cont)
D. Assembly Positioning Within the Fork 14
1. Vertical Positioning 14
2. Horizontal Positioning 15
3. Axial Rotational Positioning 16
E. Neutron Count Rates at Different LLD Settings . 16
F. Neutron Count Rates from Cadmium-Wrapped
and Bare Fission Chambers 17
i
IV. ION-1/FORK MEASUREMENTS ON BWR FUEL ASSEMBLIES . . 19
A. Cooper BWR Assemblies 19
B. Data Summary Tables 19
C. Profile Measurements 29
1. Reproducibility 29
2. Gamma-Ray Cooling with Time 30
3. Neutron Count Rate Changes
with Cooling Time 30
4. Profiles and Areas for Similar Assemblies . 31
5. Effects of Tie Plates 33
D. Consistency Check of the Declared Exposures
and Cooling Times 36
1. Declared Exposure and Neutron Count Rate . 36
2. cooling Time and Gamma-Ray Response . . . . 41
V. CORRELATION OF ION-1/FORK AND CALORIMETER
MEASUREMEfcSTS 43
A. GE-MO Calorimeter 43
B. Gamma-Ray Heating Fraction 43
C. Correlation of the ION-1/Fork
and Calorimeter Data 44
1. Calorimeter and ION-1/Fork Measurements
Contrasted 44
vx
CONTENTS (cont)
2. Value of the Profile Information 44
3. Correlating the Data 45
VI. NUCLEAR SAFEGUARDS IMPLICATIONS 47
VII. SUMMARY AND CONCLUSIONS 49
ACKNOWLEDGMENTS 50
REFERENCES 50
vii
BWR SPENT-FUEL MEASUREMENTS WITH THE ION-1/FORK DETECTORAND A CALORIMETER
by
P h i l l i p M. Rinard and G e r a l d E. B o s l e r
ABSTRACT
Gamma-ray and neutron measurements were made on about 50irradiated boiling-water reactor (BWR) fuel assemblies usingthe Los Alamos National Laboratory ION-1/fork detector. Theassemblies were placed in a dry storage cask (DOE's REA-2023)at the General Electric Morris Operation (GE-MO) as part ofa program to evaluate the cask performance. Battelle PacificNorthwest Laboratory (PNL) conducted the program.
PNL compared axial radiation profiles developed fromION-1/fork measurements with calculated profiles to interpretthe temperature distributions within the cask. The gamma-rayprofiles correlated with heat-emission rates measured with acalorimeter, which suggests that the ION-1/fork detectorcould be used to determine heat-emission rates before fuelassemblies are placed in cask storage; the ION-1/fork detec-tor is much faster than the more direct calorimeter. Inaddition, the radiation profiles from the ION-1/fork detectorcan prevent cask loadings with undesirable heat sourcedistributions.
The detector also provides safeguards information byverifying the declared exposures and cooling times. Thegenuineness of the assemblies is thus confirmed just beforethe filling and sealing of a cask.
The ION-1/fork detector was permanently installed in theGE-MO fuel storage pond for 1 year without any breakdowns orsignificant maintenance required. Data were gathered for 9months and analyzed using techniques developed during pre-vious measurement campaigns. A few anomalies were found ingenerally satisfactory results. The detector's ease of use,reliability, and reproducibility were excellent.
I. INTRODUCTION
ft. Context o£ the Measurements
As public utility power plants spent-fuel ponds approach their capacities,
alternative .nethods of storing the fuel assemblies are being examined. One at-
tractive technique is to store the assemblies in iron casks outside the plants.
The casks must have walls sufficiently thick to provide radiation shielding but
still transport enough of the decay heat to the environment to avoid thermal
damage to the assemblies. The measurements described here were made as par*-
of a characterization test to study the thermal transport properties of the
DOE's REA-2023 cask.
Before being placed in the storage cask, the fuel assemblies' heat-emis-
sion rates were measured in a calorimeter, and their gamma-ray and neutron
emissions were measured with the Los Alamos National Laboratory ION-1/fork de-
tector. This report describes the measurement activities and the results from
the ION-1/fork detector, and correlates them with the calorimeter data. The
storage cask and its properties will not be discussed here.
B. Battelle Pacific Northwest Laboratory's Objectives
Pacific Northwest Laboratory (PNL) conducted a program to characterize the
thermal and shielding performance of a REA-2023 spent-fuel storage cask for
the Department of Energy's Commercial Spent Fuel Management Program. Figure 1
is a photograph of this cask. Part
of the performance test consisted of
characterizing the fuel before putting
it in the cask. The fuel was charac-
terized by calorimetry to determine
the decay heat magnitude, and radia-
tion scans to establish the decay heat
and radiation profiles in the cask.
The 0RIGEN2 code was used to predict
decay heat magnitudes before calorim-
etry of the boiling-water reactorFig. 1. The Department of Energy's
(BWR) fuel to help in guiding t*st REA-2023 spent-fuel storage cask on a
plans. After calorimetry was com- railroad carriage at the GE-MO site.Instrumentation wires are the irregu-
pleted, an evaluation of the code was lar line down the side of the cask.
made by comparing precalorimetry predictions with measured decay heat data.
This evaluation was sponsored by the Electric Power Research Institute
(EPRI). In a similar manner, predicted decay heat profiles based on core-
averaged axial burnups were compared with measured radiation profiles. The Los
Alamos National Laboratory ION-1/fork detector was used to measure the radia-
tion profiles.
C. Role of GE-MO
The fuel handling and measurements were conducted at GE-MO. GE-MO built
the calorimeter for spent-fuel assemblies and conducted in-basin sipping (to
check for leaking assemblies) and visual inspections with film and video
cameras.
The Cooper Power Station (Brownville, Nebraska) shipped 54 BWR assemblies
to GE-MO. The assemblies were removed from shipping casks, then measured with
the GE-MO calorimeter and the Los Alamos ION-1/fork detector. Fifty-two assem-
blies were then loaded into the REA-2023 cask. Repeat measurements with these
two instruments were made after the assemblies were removed from the cask.
D. Los Alamos Involvement
The neutron and gamma-ray emission measurements were valuable in several
ways.
(1) To calculate temperatures throughout the fuel and the cask, PNL needed
a heat-source term for each assembly in the cask. The source term is
a function of the axial position along each assembly. One of PNL's
objectives was to see how accurately the ORIGEN2 calculations could
produce such functions, given the irradiation history of the assem-
blies. The GE-MO calorimeter could not check the axial distribution
of the heat emission, but the ION-1/fork detector could scan along the
axis and monitor the neutron and gamma-ray emissions. The heat pro-
duction is almost entirely caused by gamma-ray and beta-ray emissions
from fission product decays, so a correlation between the two can be
expected. The calculated source profiles of gamma-ray and neutron
emissions could thus be compared with those measured with the ION-1/
fork detector system. Any unusual temperatures recorded within assem-
blies or around the cask could also be compared with the measured
profiles to find the cause of the anomaly. The profiles measured
with the ION-1/fork detector are presented in Sec. IV.C.
(2) The calorimeter directly measures the total heat production rate from
the assemblies (a correction is made for gamma rays that escape the
calorimeter) but requires about 5 h per assembly. If the ION-1/fork
detector results can be correlated with the calorimeter data, it is
possible to estimate an assembly's heat-production rate in about
6 min.
Beta particles are a major source of heat not measured by the ION-1/
fork detector. However, if the ratio of gamma heating to beta heating
is constant, it is sufficient to measure only the gamma rays. The BWR
assemblies used at GE-MO have generally similar irradiation histories,
so the gamma-ray emission rate could be proportional to the heat-
production rate. This topic is discussed in more detail in Sec. V.B.
(3) If casks become an accepted method of storing spent fuel, it could be
advantageous to quickly characterize the fuel assemblies as they are
loaded into the casks. We wished to demonstrate that the ION-1/fork
detector can quickly identify assemblies with skewed heat-source pro-
files and other anomalies, thereby preventing improper loading of
casks.
(4) The ION-1/fork detector system was developed for nuclear safeguards
applications; the GE-MO measurements offered an opportunity to apply
safeguards analyses and show how the ION-1/fork measurements could be
used for this application. The detector can assure fuel managers and
safeguards inspectors that the assemblies being placed into storage
have radiation characteristics consistent with the utility operator's
declarations, and thus an implied amount of fissile material. Occa-
sional errors in declared values have been found in the past.
(5) The PNL study at GE-MO gave Los Alamos an opportunity to measure the
same set of assemblies more than once with the ION-1/fork detector
over a 9-month period. The information gained is useful in further
characterizing the detector and refining the data analysis techniques
discussed in Sec. IV.D. Furthermore, GE-MO technicians used the de-
tector over an extended period of time in an industrial environment,
which was a good test of the detector's durability and ease of use.
E. Chronology of Los Alamos activities
After some preliminary studies with the ION-i/fork detector at Los Alamos,
four visits were made to GE-MO to install and remove the detector and to assist
with the data gathering.
The detector was installed on May 23, 1984. The Cooper fuel was not yet
present so a pressurized water reactor (PWR) assembly was used as a reference
assembly to establish neutron and gamma-ray readings that could be used to
check the stability of the detector with time.
The first measurements on the Cooper fuel were made on August 24-25, 1984,
as the fuel was received. After training a technician to use the ION-1/fork
detector on the first few assemblies, the GE-MO personnel continued with the
measurements alone.
The cask was loaded in stages, so the fuel was remeasured from October
1984 through November 1984. The sensitivities of the ION-1/fork detector to
measurement parameters were studied at this time to help determine the proper
procedures during the routine measurements.
During the final Los Alamos visit, some of the fuel was remeasured. The
detector was then removed from the receiving basin on May 23, 1985, and re-
turned to Los Alamos.
This report does not necessarily follow the chronology of events; measure-
ments are described in a manner that will most easily lead to an understanding
of their significance.
II. ION-1/FORK DETECTOR
A. Fork Detector Head
The fork detector used at GE-MO is the product of a 5-year design effort
to provide the International Atomic Energy Agency (IAEA) with a transportable
detector that can quickly verify the contents of spent-fuel ponds. The result-
ing design has been used at many domestic and foreign power plants since 1982.
1. General Characteristics. The fork detector head is a U-shaped piece
o£ polyethylene (Figs. 2 and 3). Each of the two cylindrical tines contains
two fission chambers and one ionization chamber. One of the fission chambers
in each tine is surrounded by polyethylene, which in turn is surrounded by a
sheet of cadmium. This fission chamber is most responsive to epithermal neu-
trons; the unwrapped fission chamber is most responsive to thermal neutrons.4
Measurements at GE-MO in 1981 on all four sides of assemblies led to
the conclusion that detectors on two opposite sides gave as much information
as detectors on four sides. This conclusion was retested and verified (see Sec.
III.D.3).
The two tines join to a back piece of polyethylene and steel that is at-
tached to a steel pipe ascending to the surface of the basin. The pipe is the
means of positioning the fork and also houses the electronic cables. The fork
and pipe are water tight; the ionization chamber response will quickly and
clearly indicate any leakage in the fork. After 365 days of continuous sub-
mersion no leakage took place.
Fig. 2. Fork detector in a disassembled state. On the left is thepolyethylene casing appropriate for BWR fuel assemblies. Two cad-mium-wrapped polyethylene cylinders fit into the casing. Each cylin-der has a hole and a notch for two fission chambers plus a hole foran ionization chamber; one fission chamber is inside the cadmium andpolyethylene, the other chamber is outside. Small L-shaped clampshold the cylinders in position. The cables for the chambers passthrough a pipe welded onto a steel backplate (shown on the right sideof the photograph). The cables connect to a feed-through flange.Long cables continue to the surface of the storage pond through addi-tional pipes not shown here. Rubber gaskets between mating piecesmaintained a water-tight condition inside the fork and pipes for theyear in which the detector was in the receiving basin at GE-MO.
Fig. 3. An assembled fork detector is shown adjacent to an ION-1electronics unit. An Epson HX-20 computer rests on top oE the ION-1.The ION-1 provides power for the fork detector's fission and ioniza-tion chambers and receives the signals from the detectors. The HX-20computer is used to log the data on a paper tape and can do some on-line analysis of the data.
The detector head is supported by some convenient structure on a bridge
or side of the basin. For IAEA purposes, the support allows an inspector to
maneuver the fork around an assembly. At GE-MO the detector was attached to a
support from an earlier detector used in the basin and rested against the basin
wall; the fuel was brought to the detector. Figure 4 shows the white polyeth-
ylene fork with a Cooper assembly in a measurement position between the tines;
a basket of other assemblies is to the right of the fork. Figure 5 is a sketch
of the items in the basin.
The fork at GE-MO had additional polyethylene sleeves on each tine, reduc-
ing the gap between the tines to about 0.5 in. greater than an assembly's
width. The reduced gap limited an assembly's positioning within the fork. Sec-
tion III.D.2 provides more details.
2. Neutron Detectors. The purpose of two sets of fission chambers is to
allow an IAEA inspector to determine the concentration of boron (a neutron ab-
sorber) in the basin water. The boron concentration can be inferred from the
Fig. 4. This photograph was takenthrough the water at the GE-MO basin.The white fork is partially obscuredby a Cooper assembly being measuredbetween the fork's tines. A basketwith other assemblies is to the rightof the fork.
ratio of the neutron count rates from the cadmium-wrapped and bare fission
chambers.
The boron concentration must be known to compare neutron data from dif-
ferent measurement campaigns at the same storage site or to compare data from
different sites.
There is no boron in the water at GE-MO, but this is still an important
case to study. The ratio of count rates can be measured at different assembly
exposures to determine the effect of exposure (see Sec. III.F.}.
3. Gamma Detectors. The ionization chambers respond to the gross gamma-
ray flux by measuring the ion current induced by the gamma rays. Although the
ion current produced in the chambers is affected by the flux and energy distri-
bution of the gamma rays, the current provides no clue about the nature of the
8
distribution. In almost all cases,
however, ionlzatlon chamber response
is primarily caused by the gamma rays
from Cs and Cs, with minor con-
tributions from a few other fission
products; after several years of cool-137
ing, the gamma rays from Cs domi-
nate.
B. ION-1 Electronics Unit
1. General Description. Refer-
ence 7 describes the ION-1 (Fig. 3)
and its operation, so this report dis-
cusses only a few pertinent features.
The ION-1 was developed at Los Alamos
specifically for spent-fuel applica-
tions by the IAEA, through funding by
the United states Program for Techni-
cal Assistance to IAEA Safeguards
(POTAS). Its high-voltage power sup-
plies, pulse counting, and current in-
put channels are general in purpose.
The fission and ionization cham-
bers in the fork detector head are
Fig. 5. Sketch of the approximate po-sitions of the items in the GE-MO re-ceiving basin. The water between thefork and the other objects preventedradiations from assemblies in thecask, basket, and calorimeter from af-fecting ION-1/fork measurements. Thefork rested against a wall of thebasin and fuel was brought to it froma basket or the cask.
biaseu with about 750 and 100 V,
respectively. The electrical signals from the fork detector are displayed to
the operator.
The ION-1 is battery operated to avoid the hazard of a main electrical
supply on a steel bridge above a water basin and to provide electrical isola-
tion from noise on main power lines. Battery operation also permits operation
of the unit in areas where main power is not available. The unit can contin-
uously operate for 1 day if the batteries are fully charged. If necessary, the
ION-1 can be run on a battery charger.
A microprocessor controls the ION-1 operations. A program in read-only
memory prompts the user through the operation of the ION-1 and performs some
data analyses such as background subtractions and count rate calculations. A
liquid crystal display and a keypad (Fig. 3) enable easy operation. An RS-232
output from the ION-1 enables printout of the data collected. At GE-MO an
Epson HX-20 (also shown in Fig. 3) was used for this purpose.
2. Pulse Channel Lower-Level Discriminator Setting. The ION-1 pulse
channel for neutron counting has a lower-level discriminator (LLD) that passes
only pulses with a voltage higher than that corresponding to the LLD setting.
This function eliminates the low-voltage pulses associated with alpha decays
inside the fission chambers and other noise sources.
Generally, the lowest LLD setting above the noise does not eliminate many
neutron pulses. Finding this ideal LLD value requires equipment not always
available in the field, so an LLD setting is needed that is certain to be well
above the noise. In effect, this reduces the detector's efficiency while en-
suring that neutrons are the only source of the pulses being counted. On the
scale of the ION-1, an LLL» of 30 to 40 is considered satisfactory. Data were
taken at GE-MO at both these settings.
3. Current Channel Amplifier Gain Ranges. The current channel measures
the electrical current generated in the ionization chambers as gamma rays pass
through. Eight amplification ranges are built into the ION-1, providing a— 12 —8
range in current measurements from 10 A to 10 A; the ION-1 automat-
ically selects the most appropriate range. However, the user may manually se-
lect a particular range.
In automatic operation the range is continually changed to best match the
current being measured; no operator action is needed. During early measure-
ments, the ION-1 unit used at GE-MO occasionally took about a minute to make
large range changes, instead of the normal fraction of a second. Some incor-
rect data values were obtained as a result. The ION-1 was repaired and the
measurements were made again.
4. Calculated Uncertainties. Among other information, the ION-1 displays
the neutron count rate and its uncertainty, which is the square root of the net
counts divided by the count time.
The uncertainty for the gamma-ray value is not so simple. The ION-1
gamma-ray reading is proportional to the ionization chambers' current, which in
10
turn depends on the gamma-ray flux. This relative number is an average of 16
consecutive readings (performed in about 0.5 ms). The uncertainty assigned to
it is either the equivalent value of half the least-significant bit in the
analog-to-digital converter or the standard deviation of the 16 readings,
whichever is larger.
C. Installation at GE-MO
£ne fork detector was held about 30 ft under water at the end of a steel
pipe. The upper end of the pipe was attached to the basin wall above the water
line. The fork rested against the wall, and lead weights added to the fork's
exterior ensured that it stayed against the wall.
For IAEA inspections, operations are simplified by attaching the fork pipe
to a movable bridge and manipulating the fork around an assembly that is only
partially removed from its storage rack. At GE-MO, however, it was simpler to
move the fuel rather than the fork.
Electrical cables ran through the pipe to a pulse channel preamplifier box
at the top of the pipe. Power for the preamplifier was supplied by the ION-1.
The ionization cables were also connected to the box, but these signals were
simply passed through without any change. Additional neutron and ionization
chamber signal cables ian from the preamplifier box to the ION-1.
III. ION-1/FORK PRELIMINARY MEASUREMENT
A. Preliminary Response Measurements
Although the ION-1/fork could not be absolutely calibrated at Los Alamos
without a spent-fuel assembly similar to the Cooper fuel, some responses could
be measured with locally available standard sources for future reference.
Should the equipment be changed, these same sources could provide a normaliza-
tion of the new results to the old.
1. Neutron Measurements. The fission chambers had matched sensitivities.
Differences in response to the same neutron source between any two chambers
were less than 2%. The pair of cadmium-wrapped chambers differed by about 1%,
as did the pair of bare chambers. This matching simplifies the analysis of the
11
fork data and reduces the sensitivity of the neutron data to different hori-
zontal positions of an assembly within the fork (see Sec. III.D.2).
A 252cf source (called CR-9 at Los Alamos) was centered between the
fork tines, which were under water. This source had an emission rate of
2.9 x 10 n/s on the day of the measurements.
The curves in Fig. 6 show the count rates from the cadmium-wrapped and
bare fission chambers as functions of the LLD setting. The cadmium-wrapped
detectors give the lower count rates in this case because the water between the
D = Bare Chamberso = Cadmium-Covered Chambers
35 40
LLD Setting45 50
Fig. 6. These curves show the effect of the lower-level discriminator(LLD) setting of the ION-1. The LLD eliminated low-voltage pulses fromalpha decays in the fission chambers from the counting circuitry. Forthe routine GE-MO measurements, an LLD of 40 was used.
The fork detector head was placed under water with a 2^2cf neutronsource centered between the tines. The bare chambers are outside thecadmium sheet and are most responsive to thermal neutrons; because of thewater between the 252cf source and the tines, the neutrons reach thetines well moderated and produce a large count rate. The cadmium-coveredchambers are sensitive to the epithermal neutrons and thus produce alower count rate for this geometry.
12
source and the fission chambers moderates the neutrons and the cadmium prevents
many of them from reaching the fission chambers. When an assembly is inside
the fork, the cadmium-wrapped detectors can give a higher count rate than the
bare detectors because the water is displaced by the fuel and most of the
moderation is caused by the polyethylene between the cadmium and the fission
chamber.
The count rates of both the cadmium-wrapped and bare fission chambers were
reduced about 40% by changing the LLD from 30 to 40.
2. Gamma-Ray Measurements. An intense Co source is available at Los
Alamos with which to calibrate the ionization chamber response. Dose rates up
to 1400 R/h were produced in the chambers.
The two ionization chambers selected had matched responses; over a range
of 20 to 1350 R/h, they differed on the average by only 0.1%. In air and out-
side the fork, each ionization chamber produced an ION-1 relative number re-
sponse of one while receiving 62.6 R/h. After the chambers were placed in the
fork and partially shielded by the polyethylene, the dose rate in air (at the
chamber's location) required to get an ION-1 response of one from a single
chamber increased to about 69.8 R/h.
B. Background Values
Background values were insignificant after the fork was installed in the
basin at GE-MO; neutron and gamma-ray backgrounds were taken repeatedly during
the measurements. Backgrounds could be caused by natural environmental
sources, contamination in the basin water, and fuel assemblies stored in an
adjoining basin,
The neutron background count rate was less than one per second (including
zero on many occasions) with an LLD of 30; at an LLD of 40, the rate was almost
always zero. The gamma-ray background responses were much less than 0.01,
which is insignificant compared with the 10 to 400 responses (relative units)
from the fuel assemblies.
C. Potential Sources of Interference
Other potential sources of interference that could be somewhat controlled
were identified and shown to be insignificant.
13
Although the ION-1 and Epson HX-20 can operate on batteries for many
hours, it can be convenient to run them from battery chargers. The chargers
may introduce noise into the ION-1, however, depending on the condition of the
supply line and the radiative electrical interference in the vicinity of the
equipment.
A comparison of responses on batteries with responses on the main supply
showed that the battery chargers had no effect on the data. The measurements
were made with a crane holding an assembly stationary in the fork and while
the crane was moving. Crane movement caused no discernible electrical inter-
ference.
Assemblies in the shipping cask, the storage rask, or basin storage bas-
kets were a few feet from the fork during the measurements (Fig. 5). With a
full shipping cask nearby, the readings were still at the background levels; a
partially removed assembly was detected by the ION-l/fork, however, as it was
lifted beyond the shielding of the cask. Data were taken as a basin storage
basket was filled with nine assemblies; no change in the background was seen.
The shielding by the water and the cask's wall were sufficient to prevent in-
terference with the fork measurements from nearby assemblies.
D. Assembly Positioning Within the Fork
1. Vertical Positioning.
a. Controls. Data were to be taken at predetermined, reproducible axial
positions of each assembly. A steel tape measure was attached along the fuel-
handling grapple; by sighting across the flat-topped rail of the bridge, the
tape markings could be read very accurately. The bridge was positioned a frac-
tion of an inch from the grapple to prevent parallax, or a card was placed
across the rail so that it even touched the tape.
The zero point of the measurements had the lowest point on the assembly
in the center of the fork tines. To find this position, an assembly was low-
ered beside the fork and moved horizontally. When the assembly just grazed a
tine, the zero point was chosen 2-3/8 in. lower (half the diameter of the
tine). An underwater television camera assisted in this process.
The bridge was deflected slightly by a person's weight. The data were
taken with one person on the bridge, so the deflection was practically
14
constant. A second person on the bridge caused an additional deflection of
only 1/16 in.
Given this positioning and measurement process, errors in the vertical
positioning were certainly less than 1/8 in. and possibly less than 1/16 in.
The zero point was determined on two occasions about 6 weeks apart; the two
points differed by less than 1/32 in.
b. Effects of Errors. To quantify the effects of any errors in the ver-
tical positioning, data were taken near the middle of assembly CZ331 at the
117.3-in. height. Data were then taken at the 116.3- and 118.3-in. heights
with no significant change in responses. The slopes of the neutron and gamma-
ray axial profiles were not large at this position, but with the confidence in
the ability to position assemblies accurately, further checks were not made.
2. Horizontal Positioning. The gap between the fork tines was only
0.5 in. wider than an assembly. Still, the crane operators had no difficulty
inserting an assembly into the fork; they thought that the 0.5-in. gap could
have been half as large without hindering them greatly.
All measurements were made with an assembly contacting the back of the
fork. The operator on the bridge could easily see when this contact was made.
To raise or lower the assembly, the crane first pulled the assembly a few
inches away from the fork's back, keeping the assembly within the tines. This
prevented catching a projection (such as a tie plate) on the back and possibly
damaging the fork or the assembly.
With the help of skillful operators, assembly CZ331 at the 77-in. height
was moved from contact with one tine to contact with the other tine in steps
of about 0.125 in. The five neutron readings had an average of 107.4 counts/s
with a standard deviation of 2.0 counts/s; the counting statistics uncertainty
in a single measurement was 3.3 counts/s, so the neutron count rate was in-
dependent of the horizontal position. The fission chambers had been selected
because they are matched in sensitivity; had there been a large difference in
sensitivities, there also could have been a horizontal position dependence.
The five gamma-ray responses on the ION-1 during this movement averaged
161.9 with a standard deviation of 0.5; the uncertainty for a single measure-
ment was displayed as 0.4, again indicating that with matched ionization cham-
bers the horizontal position within the tines was not an important parameter.
15
For consistency, the operators centered the assemblies as much as possible
without spending more than a few seconds to do so.
3. Axial Rotational Positioning. The detectors inside the fork tines are
most sensitive to the radiation from the adjacent portions of an assembly.
It had already been demonstrated that it was not necessary to gather radiation4
from all four sides of PWR assemblies, but it seemed prudent to check this
conclusion for the Cooper BWR assemblies.
Assemblies CZ331 and CZ259 were studied because they have quite different
irradiation histories. The axial neutron and gamma-ray profiles of CZ331 have
two maxima after irradiation for two cycles, reaching 21.332 GWd/tU before dis-
charge on fcpril 1, 1978. Assembly CZ259 has a larger exposure of 26.466 GWd/tU
after irradiation for five cycles and a later discharge date of April 21, 1981;
its axial profile is rather smooth.
Axial profiles of these assemblies were measured in a normal orientation
(lifting bail in a particular orientation relative to the fork) and then after
a 90° rotation (bringing the other two sides adjacent to the tines). For each
of six vertical positions, a ratio of the normal and rotated responses was
computed.
For neutrons from CZ331, these ratios averaged 0.965 with a standard de-
viation of 0.097; this is consistent with an average of 1. For gamma rays from
CZ331, the average ratio was 1.0012 with a standard deviation of 0.0080; this
again is consistent with an average ratio of 1.
From assembly CZ259, the ratios were 1.006 ± 0.085 for neutrons and
1.0067 ± 0.0057 for gamma rays. These ratios are also essentially 1.
From these limited data, there is no indication that the choice of assem-
bly sides placed adjacent to the tines has any effect on the data. Neverthe-
less, the normal orientation was always selected.
E. Neutron Count Rates at Different LLD Settings
Host of the data were taken with an ION-1 LLD setting of 40, a conserva-
tively high setting designed to ensure that low-voltage noise (possibly related
to the gamma-ray intensity in the fission chambers) would not introduce spur-
ious neutron counts. Some of the earliest data were taken with an LLD of 30,
however, so the effect of this change was studied.
16
Axial profiles of assembly CZ331 were taken with each LLD setting. A
ratio of the neutron count rate with LLD = 40 to the count rate with LLD = 30
was calculated at each of the nine axial positions where high count rates were
found. The average ratio was 0.896 with a standard deviation of 0.031, showing
that the LLD = 40 reduced the count rate by about 10%. (The gamma-ray response
is not affected by the LLD setting and its . vai ge ratio for these two scans
was 0.980 with a standard deviation of: 0.055, which is consistent with a ratio
of 1.)
The default IID setting on the ION-1 was 30. If data were accidentally
taken at- rhis value instead of 40, the neutron count rate could simply be mul-
*.it'iied by 0.896 to calculate the effect of using LLD = 40. This never became
necessary.
F. Neutron Count Rates from Cadmium-Wrapped and Bare Fission Chambers
The ION-1 used had only one pulse channel input, so data frqrn both sets
of fission chambers could not be collected at the same time. The two cadmium-
wrapped fission chambers shared the same cable to the preamplifier, while the
bare fission chambers shared a second cable. The set of fission! chambers to
use was selected by connecting the appropriate cable to the input, of the pre-
amplifier.
For the IAEA application in determining the water's boron concentration,
data would be taken with both sets of fission chambers only once. The rest of
the data would then be collected with only one of the sets of fission chambers.
For use at GE-MO, the cadmium-wrapped fission chambers were used, with the
bare chambers available as an emergency backup. To prepare for such an emer-
gency, data were taken on assembly CZ259 with an LLD of 40 using both sets of
fission chambers. By using several axial positions, we estimated the effect of
exposure on the ratio of the cadmium-wrapped count rates to the bare count
rates. We calculated the exposure at an axial position from the declared av-
erage exposure and the radiation profile shape. Figure 7 shows the data ob-
tained by this process.
For exposures between 25 and 35 GWd/tU, the average of six ratios was
0.844 with a standard deviation of 0.016. A seventh ratio at about 15 GWd/tU
was 0.803 with a counting statistics uncertainty of 0.021; it is not clear if
this is a real drop in the ratio.
17
0.85-
oa:CD
o 0.80-
0.7510 15 20 25 30
Exposure GWd/tU35 40
Fig. 7. The ratio of count rates from the cadmium-coveredand the bare fission chambers in the fork can be used toestimate the boron concentration in the water. At GE-MO,there is no boron in the water, so data were taken to studythe variation of this ratio with fuel exposure. The datashown here are from different axial locations along the sameassembly. The exposures at the locations are estimated fromthe gamma-ray profile and the declared average exposure. Theerror bars are l-o uncertainties because of counting sta-tistics only. The solid horizontal line is the average ofall seven ratios; the dashed line is the average of the sixratios with exposures between 25 and 35 GWd/tU. These datasuggest that the ratio of neutron count rates may be inde-pendent of exposure, although more data with longer counttimes are needed.
Had a problem developed with the cadmium-wrapped detectors, it would have
been possible to use the bare detectors to estimate the results from the cad-
mium-wrapped detectors. The need never arose for this adjustment.
18
IV. ION-1/FORK MEASUREMENTS ON BWR FUEL ASSEMBLIES
A. Cooper BWR Assemblies
Each Cooper assembly is marked with an identifier beginning with CZ, which
could easily be read through the water in the GE-MO pond. Table I gives the
exposure of each assembly, its irradiation cycle history and discharge date.
Figure 8 shows the measurement points selected by PNL. More details on this
fuel are in Ref. 1.
B. Data Summary Tables
Tables II-V display the ION-1/fork measurement data. Tables II and III
are the gamma-ray responses, with Table III containing results for some closely
spaced axial locations near a tie plate of a couple of assemblies. Tables IV
and V provide the same information for the neutron count rates.
The tables show an assembly's identifier, the date and time of the meas-
urement, the ION-l's LLD setting (in the neutron tables only), the count time
used by the ION-1 (not very pertinent in the case of the gamma-ray responses),
and the data at the axial locations selected for that date. The very bottom
of an assembly is at 0.0 in.; the fuel region is from 7.6 in. to 153.6 in.
Gamma-ray data that were clearly erroneous because of the sluggish gain
range changes during the October-November 1984 campaign (see Sec. II.B.3) are
not included in Table II.
Before the May 1985 measurements, the ION-1 wrs slightly modified. Sur-
prisingly, we quickly noticed that the neutron count rates were nearly half
the previous values. To verify that both fission chambers were functioning
properly, we placed an assembly on the outside of one tine and then the other;
similar count rates were obtained. The source of the differences was in the
ION-1, so the new results were normalized to those of the October-November 1984
campaign with a multiplier of 1.990. The neutron data in Tables IV and V from
the May 1985 measurements have already been multiplied by 1.990. The gamma-ray
measurements were not affected.
A very small number of anomalies remain (such as tne identical gamma-ray
readings for CZ222 at 21.5 and 41.6 in. on November 5, 1984) that are not ex-
plained but also have no significant impact on the overall analysis that fol-
lows in this report.
19
Assembly
CZ102CZ147CZ148CZ182CZ195CZ205CZ209CZ211CZ222CZ225CZ239CZ246CZ259CZ264CZ277CZ286CZ296CZ302CZ308CZ311CZ315CZ318CZ331CZ337CZ342CZ346CZ348CZ351CZ355CZ357CZ369CZ370CZ372CZ379CZ398CZ415CZ416CZ429CZ430CZ433CZ460CZ466CZ468CZ472CZ473CZ498CZ508CZ515CZ526CZ528CZ531CZ536CZ542CZ545
Form 30Exposure(GWd/tU)
11.66726.70926.31026.82426.39225.34425.38326.67926.69225.79627.24627.36326.46626.49626.47827.14126.38826.59425.81527.39226.88126.56821.33226.72027.06628.04827.48125.75325.41927.14026.57626.J4225.84825.92527.47825.86327.46127.64126.82525.97726.51226.07726.75725.95726.51926.48226.35725.73727.59625.71526.69926.58926.69126.668
COOPER
TABLE I
FUEL IRRADIATION DATA
Irradiation History 1IIOOII6/01/82
X
XX
XXXX
X
XXXX
XXXXXXXX
XX
XXX
XXXXXXX
X
X
XX
IIIIIO4/21/81
XX
X
X
XXX
X
:i=in, o=out)IOOIIO4/21/81
X
XX
X
X
X
X
X
and Discharqe DateIOOOOO IIOOOO4/01/78 9/18/77
X
X
20
ft' 176.2
j ! r 153.6 (ac t i ve r e g i o n )
\" ^ - 1 5 1 . 6
N137.5
117.3
Fig. 8. This scale drawing of a97.1 cooper BWR assembly shows the axial
^ 94.5 __ _ measurement locations (in inches from"*— 89.5 the bottom). The cluster of loca-
""87.0 „ ,. tions near the 87-in. height were** 82.0 *-- used t o studY the effects of a tie
__ _ •*— 79.5 plate on the radiation profiles. The^ fuel is in the active region between
the 1.6- and 153.6-in. heights.
-61.8
-51.7
-41.6
-31.5
7.6 (ac t i ve r e g i o n )
21
hoTABLE II
ION-1/FORK OAMMA-RAY RESPONSES TO COOPHH BUR FUEL
1234
678910
i±
id1415161718192021222324
25262728293031323334353637383940
414243444546
Assem.
CZ102
CZ147
CZ148
CZ182
CZ195
CZ205
CZ209
CZ211
CZ222LOW
CZ225
CZ239
CZ246
CZ259
CZ264
CZ277
CZ286
CZ296
CZ302
8/25/8411/05/848/25/8411/03/848/25/8411/29/849/01/8411/07/845/22/858/25/8410/29/848/25/8411/29/848/25/848/25/84U/07/848/25/8411/03/849/01/8411/05/845/23/858/25/8411/03/849/01/84
9/01/849/01/849/01/B49/01/8410/30/849/01/8410/30/848/25/848/25/8411/29/848/25/8411/05/849/01/8411/07/848/25/8411/05/848/25/8411/03/848/25/845/22/855/22/855/22/85
Time
7:1223:0318:5512:568:298:55
11:0517:5321:529:0613:595:459:2611:3711:3915:2720:5515:155:5610:571:17
14:479:531:28
1:331:341:411:4711:205:3018:483:173:2012:503:3719:339:0013:347:47
23:4513:459:162:3518:2918:3018:31
CountTime
101010101010
oooooooo
oooooooooo
10101010101010101010101010101010101010101010
_L£
16.1
114.6
111.2
115.4105.3
111.3
60.0
107.6
106.8
113.2102.9
110.4
118.7
109.5
111.4
102.9
90.9
13.5
147.7
140.7
140.9
21.5
52.351.0216.3208.1
196.2241.2230.6205.6
205.6232.5217.5
199.3213.7206.8
246.2216.9
224.3
256.2259.4248.7
205.6
208.1216.2208.7
228.1215.0208.7
168.1
31.5
283.8
261.2
263.7
Axial41.6
70.0
274.3
257.5318.1293.7262.5
265.6298.8280.0
250.6281.2270.0
246.2278.1
280.0
331.8
320.6
264.4
265.6276.9266.2
292.5
271.2
232.5
Heiqht (Inches from the
51.7 "" ~ — "
74.4
297.5
287.5
285.0
308.8
270.0
270.6
295.0
335.6
303. a
364.4
343.8
288.1
278.8
280.0
310.0
293.1
283.8
61.8
73.6
288.1
275.6
307.5272.5
273.7320.0292.5
263.1300.6288.1
312.5290.6
295.6
348.7
334.3
269.4
270.6280.0269.3
302.5
288.7
246.2
77.0
75.7
310.0
300.6
327.5
288.1
322.5
285.6
306.9
351.2
314.4
374.4
375.0375.0375.0370.0
359.4
288.1
281.9
279.4
328.8
307.5
282.5
bottom)
97.1
71.9
293.1
276.9
318.7281.8
268.1327.5304.4
272.5305.0290.6
328.1291.2
297.5
349.3
331.2
261.9
265.6270.6260.0
308.7
292.5
258.1
248.1246.8
117.3
63.562.4285.0270.6275.6257.5313.1300.6267.5250.0240.6313.1291.2269.4
256.2280.0268.1315.0330.6267.5292.5278.1338.8
323.1313.12-29.32;2.5
236.2
251.9242.5243.7234.3296.3281.8280.6268.7295.0250.6
137.5
38.538.2201.3190.6193.1185.0217.5209.3188.1166.9161.2220.6205.6186.9
178.7198.7190.6214.3302.5184.4201.3191.2230.0
222.5208.8200.016B.81 CO O1OO . D158.1169.4163.1164.4158.7206.3191.2198.1189.3210.6185.0
151.
90.
87
9386
7210195
849288
20586
91
100
90
74
767774
86
90
88
8888
.1
.2
.4
.5
.7
.1
.3
.8
.3
.9
.6
.4
.2
.7
.4
.6
.4
.04
.7
.5
.9
.3
. 1
.1
1fiQ *\± U 7 • L>
23.0
23.0*J1 QZi .O21.219.9
12.122.820.9
21.3
22.622.194.620.7
22.415.9
15.123.322.2
13.4
12.413.913.3
21.1
26.5
0.0
Table II (cont)
474849505152535455565758596061626364656667686970717273747576777879808182838485868788899091929394
Assem.
CZ308
CZ311
CZ315
CZ318
CZ331
CZ337
CZ342
CZ346
CZ348
CZ351
CZ355
CZ357
CZ369
CZ370
CZ372
CZ379
CZ398
CZ415
CZ416
CZ429
Date
9/01/0410/30/849/01/8411/07/845/23/858/28/8411/29/848/28/8411/30/848/25/8410/29/8411/02/8411/28/8411/30/845/22/855/23/855/23/859/01/8410/30/848/28/8411/30/849/01/8411/07/849/01/8410/30/848/28/8411/30/845/22/855/22/859/01/8411/07/849/01/8411/30/849/01/8411/03/848/28/8411/07/848/28/8411/07/849/01/8411/03/849/01/8411/07/848/28/8411/07/849/01/8410/30/848/25/84
Time
5:0917:457:2111:102:3011:4014:3311:106:575:0411:4011:0314:4723:5016:403:029:433:5517:1510:3210:398:3012:553:3016:4314:4013:2022:4122:509:3314:5011:2311:0312:3213:2812:0719:4017:193:2412:1411:297:4311:4615:021:343:1415:0811:16
CountTine(s)
101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010
7
99
114105
89
108
848383798079
125
81.128,124.
122.
114.107.107.
106.
106.
76.
95.
110.
125.
91.
120.
.6
.5
.9
.0
.1
.4
.4
.0
.0
.4
.2
.7
.1
.1
.8
.6
.3
855
3
2
4
7
9
9
5
1
13.5
143.1
173.7
169.4
164.4
136.7
21
191
240213
224210197
134132132123123124263252
210260250251.242,
219.
198.199.192.
233.
220.
193.
195.
200.
242.210.202.
216.
.5
.2
.6
.1
.4
.6
.5
.9
.3
.3
.7
.4
.1
.1
.5
.6
.0
.0
.2
.5
,4
,144
1
6
1
0
6
505
2
31
254
315,
315.
306.
263.
.5
.4
.0
.6
2
1
Axial41
246
305271
290269251
162162160159152152152330319
268335322322,315
272.
241.
246.
295.
293.
268.
263.
253.
306.286.276.
276.
.6
.8
.0
.9
.6
.4
.9
.5
.5
.0
.4
.5
.5
.5
.0
.3
.1
.6
.5
.5
.0
.5
.5
2
6
1
1
1
1
B32
8
Helqht51
266
323
320
280
172
339
296
346
339
296
265.
326.
315.
283.
291.
269.
335.
300.
300.
366.
.9
.1
.6
.0
.5
.4
.1
.9
.4
.9
.0
.2
,6
6
9
3
6
0
0
3
(inches61
264
310275
301288270
165164162161153154155341328
281351336345329,
278,
253.
260.
305.
307.
282.
285.
262.
323.306.293.
295.
.8
.3
.6
.0
.2
.1
.6
.0
.3
.5
.2
.7
.4
.0
.9
.1
.2
.9
.8
.0
.3
.7
.7
.6
6
5
5
0
5
797
0
from the77
286
326
331
299
166
349
310
357
350.
308.
283.
331.
328.
300.
310.
277.
346.
315.
320.
369.
.0
.2
.9
.3
.4
.9
.4
.0
.5
.0
.8
,1
8
7
0
6
5
2
0
0
4
bottom)97
277
340279
309303283
165163161160153153155349335
291355341348333
295,268,268,
271.
311.
315.
290.
292.
268.
335.316.304.
310.
.1
.5
.6
.4
.4
.1
.1
.0
.7
.2
.6
.7
.7
.6
.4
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.9
.6
.2
.1
.7
.0
.1
.1
,8
.2
0
6
5
1
693
0
117
272263316305270313291295276173168166163168155156158330316310286351335,321.308.307.283,
259.266.254.324.301.315.301.285.273.299.287.278.267.346.329.305.294.312.297.
354.
.3
.5
.1
.9
.0
.6
.1
.2
.6
.2
.8
.1
.8
.7
.7
.6
.2
.1
.0
.8
.0
.2
.2
.6
.9
.7
.5
.7
.3,2.9.32080745759303554
137.5
190.0185.0221.9212.5193.1218.1203.1210.0198.1132.9128.5127.4126.2125.6120.1122.4123.4228.1220.0224.4208.7271.2260.0220.0211.2213.1196.9
183.7184.4176.2227.5211.2221.8213.7200.0193.1221.9213.1219.3207.5250.6238.7218.8212.5223.7211.8
244.4
151.6
85.9
97.888.6
88.996.691.5
67.366.366.165.863.363.865.5100.898.1
94.7120.9117.494.892.2
91.9
86.9
80.1
95.0
100.3
88.7
98.6
99.8
107.8104.2101.5
97.3
169.5
19.313.721.521.420.722.121.216.917.0
19.318.918.718.617.718.118.120.620.122.921.914.715.212.612.421.220.2
20.318.217.925.321.425.224.012.512.613.413.917.917.222.422.815.315.022.321.4
Table II (cont)
9596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140
Assem.
CZ430
CZ433
CZ460
CZ466
CZ468
CZ472
CZ473
CZ498
CZ508
CZ515
CZ526
CZ528
CZ531
CZ536
CZ542
CZ545
Date
11/07/849/01/8410/30/848/28/8411/08/848/28/8411/30/848/28/8411/30/848/28/8411/30/845/22/855/22/855/22/858/28/8411/30/848/28/8411/30/848/25/8411/03/845/22/855/22/858/28/8411/30/848/28/8411/08/848/25/8411/03/8411/03/8411/03/845/23/855/23/858/25/8411/03/849/01/849/01/8410/30/845/22/855/22/855/22/858/28/8411/07/848/28/8411/30/848/28/8411/30/84
Time
92921114131311161523232315151521191419191311:19:1:15:11:11:11:00:00:19:13:2:2:7:21:20:21:18:1:12:12:16:21:
:22:58:3l:54:07:23:52:28:24:39:00:05:24:13:56:20:30:20:47:50:2l:22:08:40:43:402005172243442655384110055200560034405855
CountTime(s)
10101010101010101010101010101010101010101010101010101010101010
101010101010180180101010101010
7
127
105973
117
112
113
105
115
97
9583
88.
91.
97.97.
58.
68.58.
53.
115.
111.
.6
.1
.1
.8
.6
.3
.5
.3
.4
.4
.8
.6
.7
.4
.2
62
6
60
9
9
a
13
127
171.
140.140.139.
.5
3
113
21
265
248202201
2252
192
230208208208
231
194
246213
215.
196.268.
222.228.220.
200.
243.213.
191.
205.
210.
.5
.6
.7
.5
.2
.0
.5
.5
.6
.7
.7
.7
.2
.4
.2
.7
.6
98
,576
6
77
2
6
6
31
253
321.
271.272.269.272.
266.
_5
.8
3
9545
2
Axial41
337
317275266
278
242
297271271271
297
245
313276
271.
267.338.324.
286.
307.274.
263.
263.
262.
.6
.5
.5
.6
.9
.1
.5
.5
.9
.2
.2
.5
.0
.7
.2
.2
,5.1.3
9
53
7
7
5
Helqht51
338
288
302
325
321
273
340
299.
291.
348.
295.
295.2B4.324.
263.
292.
289.
.7
.8
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.4
.9
8
0
634
7
5
4
{Inches61
349
335291282
280
259
301
275
300
262
323285
280
280.358.324.
298.
320.277.
285.
280.
270.
.8
.3
.0
.3
.5
.6
.4
.2
.0
.0
.5
.1
.6
.6
.0
.1
.3
7
05
6
0
6
from the77
341
296
309
285
322
325
292
345
310.
301,
365.
302.
305.295.331.
305.
315.
288.
.0
.9
.9
.4
.6
.5
.6
.5
.0
.0
,3
.0
5
062
6
6
1
bottom)97
357
328299289
290
295
301
273
296
278
328288
293
288.361.336.
302.
286.
321.282.
298.
301.
275.
.5
.1
.4
.4
.6
.0
.9
.1
.2
.7
.7
.1
.7
.1
.3
.2
.5
.2
85
7
2
6
117
336321308288277301279286266301280
255
305280290271328310272
306.281.288,273.368.348.
303.
302.
331.
322.281.281.281.299.288.316.291.275.255.
.3
.2
.9
.7
.8
.5
.9
.4
.3
.2
.9
.6
.6
.0
.6
.6
.9
.1
.0
.5
.3
.9
.1
.7
.1
.1
7
5
2
5888419200
137
234223213202197210193208193205188
176
?1519a209193225212193192215,198.200191,275,346
236.
222.
249.249.243.216.216.216.214.207.218.201.190.171.
.5
.3
.1
.1
.5
.5
.6
.7
.1
.7
.0
.1
.2
.0
.7
.6
.7
.6
.5
.1
.5
.0
.7
.0
.9
.6
.8
,2
,5
.4
.47,222451269
151
104
929290
90
89
83
79
88
89
9591
95,
92.130.263.
117.
116.106.
98.
90.
82.
.3
.5
.2
.1
.3
.5
.6
.5
.0
.2
.75
.1
.6
.9
.7
,5
22
7
0
8
169.5
1313132121131313121110
11
12112120
1313
14141314.
16,
25.
16.
16.16.
26.25.23.23.13.11.
.8
.2
.1
.6
.0
.1
.1
.8
.8
.0
.7
.7
.2
.0
.2
.7
.0
.8
.0
.3
.4
.2
.9
,5
7
08
188002
TABLE III
ION-1/FORK GAMMA-RAY RESPONSES TO COOPER BUR FUEL(Tie Plate Vicinity)
Axial Height (Inches from the bottom)Assent. Date Time (s) 79.5 82.0 84.5 8T.0 89.5 92.0 94.5
1 CZ205 8/25/84 5:48 10 322.5 325.0 319.4 319.4 321.3 325.6 326.92 CZ526 8/25/84 15:28 10 359.4 356.3 350.6 353.1 351.3 361.9 358.83 5/23/85 00:43 10 301.9 300.6 296.9 291.2 295.0 298.1 300.6
25
TABLE IV
ION-1/FORK NEUTRON COUNT RATES (counts/s) FROM COOPER BWR FUEL('Normalized by a multiplier of 1.990)
123456189101112131415161718192021222324252627282930313233343536313839404142434445
Assent.
CZ102
CZ141
CZ148
CZ182
*CZ195
CZ205
CZ209
CZ211
CZ222
*
CZ225
CZ239
CZ246
CZ259
CZ264
CZ211
CZ286
CZ296
CZ302
*
Date
8/25/8411/05/848/25/8411/03/84B/25/8411/29/849/01/B411/01/845/22/858/25/8410/2<»/848/25/8411/29/848/25/848/25/84
11/07/848/25/8411/03/849/01/8411/05/845/23/85B/25/8411/03/849/01/849/01/849/01/849/01/849/01/8410/30/849/01/8410/30/848/25/848/25/8411/29/848/25/8411/05/859/01/8411/01/848/25/8411/05/848/25/8411/03/848/25/8411/05/845/22/85
Time
1:1223:0418:5512:518:298:5511:0511:5321:509:0614:005:459:2611:3111:3915:3020:5515:165:5610:511:15
14:419:551:281:331:341:411:4111:205:3018:493:113:2012:503:3118:339:0013:331:41
23:4513:459:152:3511:3118:29
LLD
404040404040404040404040404040404040404040404040404040404040404040 '404040404040404040404040
CountTime(s)
101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010
FC
CdCdCdCdCdCdCdCdCdCdCdCdCdCdcdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCd
CUCdCdCdCdCdCdCdCdCdCd
1
0
4
3
55
465
333
66.
0.
1.
8.
5.
4.5.4.
0.
0.
0.3.
.6
.2
.3
.0
.1
.4
.9
.6
.6
.8
.3
.4
.1
.2
.0
,5
.0
2
152
0
0
54
13.5
32.5
20.8
22.6
21
54101062609390901461881516
13,11,10,111109,94.92.95.112.
111.114.114.19.
69.14.13.69.66.101.103.66.65.62.51.53.
.5
.0
.0
.4
.2
.8
.9
.1
.1
.3
.6
.3
.1
.6
.1
.1
.1
.4
.5
.4
.9
.1
.1
.6
,6
e,34
913656311005
Axial Height (inches from31.5
150.4
119.8
121.8
41.6
14.5
150.0
124.0
190.3185.1
152.1119.8169.1
150.3141.3152.1
109.4214.9
191.2
231.6
235.1
151.2
150.3136.5141.6
213.0
140.4
164.4159.0
51.1
14.4
162.3
150.4
209.1
166.3
192.8
110.9115.2
163.8
248.2
211.1
259.4
262.1
166.9
163.5
149.6
216.5
164.3
200.0
61.8
11.6
161.3
144.8
194.0204.0
151.0198.5183.3
110.6113.9184.4
225.4243.0
205.9
260.1
269.3
165.0
150.8148.4143.1
220.5
162.4
196.4204.4
the bottom)11.0
16.4
181.0
164.1
212.5
164.1
214.2
191.3
188.8
251.1
190.0
263.9282.8212.8215.0261.4
212.9
161.1
151.0
145.6
238.1
114.4
191.6
91.1
19.9
115.0
164.2
246.2232.2
142.0232.0214.6
182.3191.1180.5
241.9239.2
202.0
251.1
251.0
139.1
146.4131.0121.3
223.9
115.0
243.0255.9
111.3
12.414.5151.8144.3136.6125.9204.1208.1191.8112.2101.2201.1201.9151.1
149.4148.9141.5190.8233.5185.1165.1164.0214.2
196.4181.4186.5111.9
103.3111.3109.195.595.9111.9165.4145.5143.9216.1245.1249.1
131.5
3.92.159.555.048.250.511.112.266.138.334.183.;15.255.1
49.158.351.369.8193.062.356.459.568.3
65.066.159.431.131.531.831.631.029.131.860.155.156.251.8109.2102.9110.8
151.6
0.4
4.1
2.1
4.86.0
2.26.35.2
3.54.13.3
63.64.6
5.2
5.2
5.2
2.3
3.53.11.3
3.1
4.0
3.910.3
169.5
0.0
0.0
0.10.00.00.0
0.00.10.0
0.0
0.00.14.20.0
0.00.0
0.00.00.0
0.0
0.00.00.0
0.0
0.0
0.00.0
TABLE IV ( c o n t )
464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293
ftsseia.
*
CZ30B
CZ311
*
CZ315
CZ318
CZ331
ft
*
ft
CZ337
CZ342
CZ346
CZ348
CZ351
**
CZ355
CZ357
CZ369
CZ370
CZ372
CZ379
CZ398
CZ415
CZ416
Date
5/22/855/22/859/01/8410/30/849/01/8411/07/845/23/858/28/8411/29/848/28/8411/30/848/25/8410/29/8411/02/8411/28/B411/30/845/22/855/23/855/23/859/01/8410/30/848/28/8411/30/849/01/8411/07/849/01/8410/30/848/28/8411/30/845/22/855/22/859/01/8411/07/849/01/8411/30/849/01/8411/03/848/28/8411/07/848/28/8411/07/849/01/8411/03/849/01/8411/07/848/28/8411/07/849/01/84
Time
18:3018:315:0917:457:2111:112:3011:4014:3311:106:575:0411:4011:0514:5023:5216:403:029:433:5517:1510:3210:408:3012:553:3016:4514:4013:2022:4122:499:3314:5511:2311:0512:3213:2812:0119:4011:193:2512:1411:291:4311:4615:021:361:14
LLD
404040404040404040404040404040404040404040404040404040404030404040404040404040404040404040404040
CountTlae(s)
101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010
PC
CdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdcdcdcdCd
1
4
64
453
0123,312.7,5.
4.6.6.6.5.
5.4.5.
4.
4.
0.
3.
4.
5.
4.3.3.
i&
.8
.6
.6
.4
.4
.8
.1
.6
.5
.6
.2
.6
.0
.9
.5
.8,3.16,7
834
5
9
0
4
2
2
997
13.5
24
40
33
33.
(LLD)
23.
.9
.7
.1
.8
3
21
62621091059895857163390403841332844.
118.112.86.71.
104.102.109.104.100.92.
85.10.65.104.101.13.19.68.68.62.62.15.69.
101.93.66.65.82.
.5
.9
.9
.3
.5
.5
.4
.1
.8
.3
.4
.0
.3
.9
.2
.4
.9
.2
.6
.2
.4
.2
.514.946
627580831471879253
31
134
189
190
192
131,
Axial Height (inches from.5
.2
.3
.5
.2
.9
41.6
141.3
223.5220.3
181.9151.6152.0
69.481.687.384.383.487.789.0215.3220.9
169.5222.4226.0228.4236.2
181.2
183.7
152.2
216.6
175.6
178.1
170.9
155.9
200.0183.4187.3
51.7
162.5
232.6
218.1
186.0
107.4
232.9
190.9
248.7
255.8
194.1
171.5
240.9
196.2
198.6
214.8
171.9
228.5
206.8
198.0
61.8
163.1
223.1222.1
219.8207.1184.9
100.297.9100.8101.4100.599.9104.7243.8229.8
191.8249.7242.6274.8260.5
182.1
188.7
173.5
222.4
204.0
207.3
214.9
164.1
235.7217.5219.6
the bottom)77.0
187.4
230.4
246.0
216.6
102.3
249.4
213.0
256.4
275.8
202.9
181.9
230.1
227.9
231.7
235.5
175.0
249.6
237.0
250.9
97.1
177.1
239.5238.2
246.4247.7232.1
114.9112.8115.8116.4115.8105.7122.4249.8253.7
226.7:.JS.6264.5286.4284.5
232.6186.8228.7
186.8
250.1
256.5
238.5
248.9
183.7
260. B272.4210.2
111.3
166.6153.1246.2229.1226.9226.1214.8226.2221.2144.0125.6134.0132.6127.1126.8130.7130.1227.4215.7228.9221.0284.2271.3241.2223.8217.8207.2
(LLD)203.2158.1156.3254.1250.6236.3231.2220.2218.4267.4251.7192.2197.8273.8262.3256.1254.1263.3
137.5
62.358.792.093.489.986.471.189.281.166.1
61.159.864.861.363.377.869.585.278.8102.2100.1160.1149.185.580.880.374.1
84.649.557.499.595.394.589.788.691.6127.4122.8106.297.6121.4111.4114.2110.6108.2
151.6
8.6
9.6
4.6
6.25.0
5.08.16.5
4.33.14.04.95.04.06.64.44.9
1.310.911.51.11.4
6.7
6.0
3.7
6.5
6.6
7.1
8.1
9.0
9.47.68.3
169.5
0.10.10.00.00.00.00.10.10.0
0.00.0
0.10.00.00.00.00.10.00.00.00.00.00.00.00.00.0
0.00.10.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
ho00
TABLE IV ( c o n t )
94959697989910010110210310410510610710810911011111211311411511611711811912012112212312412512612712812913013113213313413513613713d139140141
Asseta,
CZ429
CZ430
CZ433
CZ460
CZ466
CZ468
**A
CZ472
CZ473
CZ498
*
CZ508
CZ515
CZ526
*A
A
*
CZ528
CZ531
A
*
*
CZ536
CZ542
CZ545
Date
10/30/84fa/25/84
11/07/849/01/8410/30/848/28/8411/08/848/28/84
11/30/848/28/8411/30/848/28/8411/30/845/22/855/22/855/22/858/28/8411/30/848/28/8411/30/848/25/84
11/03/845/22/855/22/858/28/84
11/30/848/28/8411/08/848/25/8411/03/845/23/855/23/855/23/855/23/858/25/8411/03/849/01/849/01/8410/30/845/22/855/22/855/22/858/28/8411/07/848/28/8411/30/848/28/8411/30/84
Time
15:0811:169:232:589:30
21:541:08
14:2313:5013:2811:2416:3915:0023:2423:0523:1315:5615:2115:3021:2319:4714:5219:2119:2213:0811:4019:431:40
15:2011:0500:4300:4400:1700:2219:2613:552:382:417:15
21:0520:5020:5518:561:02
12:3412:4016:5821:55
LLD
404040404040404040404040404040404040404040404040404040404040404040404040404040404040404040404040
CountTlae(s)
101010101010101010101010101018018010101010101010101010101010101010180180101010101010180180101010101010
FC
CdCdCdCdcdCdCdCdCdcdCdCdCdCdCdBrCdCdCdcdCdCdCdCdCdCdCdCdcdCdCdCdCdBrCdCdCdCdCdCdCdBrCdCdCdCdCdCd
7
3
8
843
4
4
53
6
4,
55,
5.
3.7.0.4.5.
3.
5.4.
3.
4.
6.
.6
.9
.1
.0
.1
.5
.6
.6
.3
.4
.8
.6
.8
.8
.4
8
042
9
30
8
7
1
13
19
30.
35.
28.35.
Ji
.6
1
8
76
21
80134123114116676710410471691011009499
118,105,103,62.69.111.113.102.
90.86.76.69.
116.5.
99.
100.118.66.71.102.
110.94.
62.64.81.80.87.91.
Ji.7.2.7.1.6.6.1.0.3.3.3.3.4.7.1.2.5.2.8,7.64,9
6145417
36046
07
10709
2
31
140
190.
178.189.181.216.
Axial Helqht (Inches from
.3
6
9155
41.6
180.3
245.6
241.3184.7182.3
205.8
150.2
224.4225.5215.7256.9
208.5
141.3
231.3220.3
177.0
184.1231.2227.9230.8
173.4
209.7205.8
175.2
170.1
180.6
51
281
247
206
215
162
222
226
165
240
198
216
246.
•?27,
205.
223.
187.
181.
195.
.7
.7
.6
.3
.6
.9
.6
.1
.3
.7
.9
.9
.9
.9
1
,2
3
.5
6
61
209
287
246206212
196
173
202213
210
173
">24217
197.
212.251,218.239.
209.
227.202.
209.
187.
206.
.8
.2
.6
.0
.8
.3
.5
.6
.6
.1
.6
.8
.9
.5
.5
.5
.2,7,4
9
44
8
6
0
the bottom)77.0
2B7.2
242.4
216.8
207.7
202.2
216.6
215.0
211.3
235.2
214.3
241.3
252.9
245.0
218.3
229.3
231.6
224.2
199.2
97.1
253.4
295.1
265.2235.9236.5
215.1
203.4
203.2212.5
210.2
226.2
244.7238.6
222.6
260.6266.6238.5272.6
247.2
240.4243.4
263.1
242.4
214.5
117.3
245.3257.7251.0232.1233.7234.7236.5200.7188.5202.2198.8200.6180.6196.8
202.4183.7216.9217.6223.2217.0210.9
222.9207.4244.9242.8300.8267.1291.5
248.7249.22C1.0
261.7254.7252.9296.9258.2253.1229.9227.4184.3164.9
137.5
94.3
101.193.785.880.298.793.173.070.786.082.770.659.565.3
79.575.3
85.5884.776.375.275.072.486.576.892.895.0
157.7296.4164.4
116.3117.5132.7136.2136.0135.3133.5153.8107.9112.288.578.261.057.9
151.6
7.4
8.9
6.76.08.1
6.4
6.5
3.54.0
5.3
5.2
5.06.8
5.8
5.912.4
154.811.5
8.7
9.811.9
8.0
4.3
3.6
169.5
0.1
Ci.O
0.00.00.00.00.10.00.00.00.00.00.0
0.00.00.20.1
0.10.0
0.20.00.00.0
0.00.0
0.00.0
0.20.0
0.00.00.00.00.00.0
TABLE V
1 CZ2052 CZ5263 *
ION-1/FORK NEUTRON COUNT RATES (counts/s) FROM COOPER BUR FUEL(Tie Plate Vicinity)
(•Normalized by a multiplier of 1.990)
8/25/848/25/845/23/85
Time
5:4815:2300:43
LLD
404040
CountTime
101010
reCdCdCd
Axial Height (Inches from the bottom)79.5
210.2262.8250.5
82.0214.7249.9243.2
84.5
223.9245.9251.9
87.0213.7247.4225.3
89.5
221.9242.4245.6
92.0 94.5
224.2 223.6257.3 267.4248.9 259.7
C. Profile Measurements
1. Reproducibilitv. The data in Tables II and IV show the good repro-
ducibility of the gamma-ray and neutron count rate results, taking into account
the decreasing activities with cooling time. For a given assembly, some data
were taken only minutes apart, while other data were taken months apart.
For simplicity, uncertainties in the data values are not indicated in the
tables. They can be stated in general, however, and applied to any data in the
tables. In the neutron tables, the standard deviation in a count rate is the
square root of the quotient of the count rate and the count time. The gamma-
ray uncertainties produced by the ION-1 follow a step function as the gamma-ray
response increases, but a useful approximation is that the uncertainties are
0.16% of the response values.
No correction for cooling time has been applied to any of the data in
these tables (except implicitly in the normalization of the neutron count rates
for the Hay 1985 campaign), and the small decreases in the activities with time
are apparent in the tables.
The reproducibility of the ION-1/fork data is most easily seen for assem-
bly CZ331. This assembly had been cooling for 3 years longer than the others
and thus the decay rate for CZ331 was the smallest of the Cooper assemblies at
GE-MO. Whereas CZ331 was not used in the storage cask because of its lower
heat output, it was well suited as a reference assembly to check the operation
of the ION-1/fork detector. Although some decay is still evident in its data,
the decay rates for neutron and gamma-ray emissions are much lower than those
of the other assemblies.
29
2. Gamma-Ray Cooling with Time. The gamma-ray cooling can be illustrated
with assembly CZ182, which has one of the shorter cooling times. In Table II,
the gamma results can be seen to decrease by about 4% from September 1 to
November 7, 1984; they drop another 11% from November 7, 1984, to May 5, 1985;
between the September 1, 1984, and May 5, 1985, dates, there is an overall drop
of about 15%. If we assume that only Cs and Cs produce the gamma-ray re-
sponse, then these percent drops indicate that 35% of the response comes from
Cs and the rest from Cs. This mixture is in agreement with an average ofT O T £\
39% Cs previously calculated for three other BWR assemblies.
To find the best expression for the rate of decrease in the gamma-ray re-
sponses with cooling time, we examined the data from each assembly in Table II,
ignoring the axial positions smaller than 21.5 in. and greater than 151.6 in.;
they were less precise than at other locations. At each of the other locations
for a given assembly, we calculated the ratio of a later response to an earlier
response. These ratios were generally very similar for all the locations on
each assembly, and an average ratio was calculated. Each assembly thus had one
to three sets of cooling times and responses relative to the earliest response.
Figure 9 is a plot of these relative responses, with an exponential curve
that is the least-square fit to the data points. The "decay constant" for this
curve is 0.000577 ± 0.000022 per day.
3. Neutron Count Rate Changes with Cooling Time. The neutron data for
CZ182 in Table IV can also be examined for cooling time effects, although the
statistical fluctuations from only 10-s count times limit the precision. From
September 1, 1984, to November 7, 1984, the count rate decreases about 7%. As-244 242
suming that only Cm and Cm are important contributors of neutrons (as can
be expected from Ref. 8), this drop is consistent with 93% of the neutrons com-244
ing from Cm; 98% is calculated from the data in Ref. 8. Further compari-
sons with the May 1985 data are not possible because these data were normalized
after the ION-1 modification mentioned in Sec. IV.B.
The good reproducibility is still apparent in all these data, allowing for
the statistical fluctuations that must be expected with only 10-s count times.
This short count time was used because good gamma-ray data could be obtained
while minimizing the total time spent on all the assemblies. In previous
spent-fuel examinations, count times of 30 to 60 s have been entirely satisfac-
tory to gather good neutron data, as well as good gamma-ray data.
30
0.8050 100
Cooling150
Time200
(days)250 300
Fig. 9. The decline in the gamma-ray emissions from the Cooper assemblies.The cooling times are relative to the first measurements made with the ION-1/fork detector in August or September 1984. Although the curve fitted to thedata points may appear to be a straight line, it actually is an exponentialwith a "decay constant" of 0.000577 ± 0.000022 per day. The gamma-ray measure-ments would thus be half those shown here after about 3.3 years.
4. Profiles and Areas for Similar Assemblies. Table I shows that many
of the assemblies had exposures between 25 and 28 GWd/tU and were discharged
on the same date. Similar assemblies have similar data (see Tables Til and
IV). This can be seen by comparing individual numbers in the tables, or by
plotting the profiles in Fig. 10(a)-(e) and computing the areas under the pro-
files.
The profiles can be categorized according to the number and location of
extrema. Each of the basic types is shown by one of the profiles in Fig.
10(a)-(e). Just specifying the exposure and cooling time is not sufficient to
predict the shape of the profile; the proximity to poisons during irradiation
is quite important. Assemblies with the same gamma-ray profile may have dif-
ferent neutron profiles, and vice versa.
31
CZ225 n/03/84 CZ351 11/30/84
(a )20 40 80 80 100 120 U0 160Distance Above Base (inches)
c
IsoT
(d)0 20 40 80 SO 100 120 MO 160
Distance Above Base (inches)
CZ246 10/30/84
(b)0 20 40 tO 80 100 120 140 180
Distance Above Base (Inches)
CZ468 11/30/84
cT3oO
73
( e )
0 20 40 SO 60 100 120 140 160Distance Above Base (Inches)
(c)
oI A -
O
o-
o
ga-
l l -
ION
-11
ISO
100
oirt"
CZ264
I
1
11/05/84
— ^ \
\ A\
20 40 SO 80 100 120 140Distance Above Base (inches)
160
Fig. 10(a)-(e). The measuredgamma-ray and neutron profilesfor various assemblies. Theupper curves are the gamma-rayprofiles; the lower curves arethe neutron counts/s profiles.The curves through the pointsare spline fits that merely con-nect the curves in a smooth man-ner; there is no physical argu-ment for the shape of the curvebetween the data points asidefrom continuity. These profilesillustrate the types of profilesseen for the Cooper assemblies.
32
The curves drawn through the data points in Fig. 10(a)-(e) are simply
spline fits that have no physical justification. However, the areas under the
spline curves approximate the areas under the true profiles. After fitting
spline curves to only five data points, we Eound that additional data points
tended to lie very near the spline curves; Fig. 11 is an example of such a
process for CZ526. The areas under the spline curves for five and nine data
points differ by only 0.3%. Table VI presents the profile areas for the gamma-
ray responses; the calorimetry data in that table will be discussed in Sec.
V.B.
5. Effects of Tie Plates. The tie plate at the 87.0-in. location was
used to study the effects of a tie plate on the gamma-ray and neutron emis-
sions. The seven measurement locations shown in Fig. 8 near 87.0 in. were
2.5 in. apart and led to the data in Tables II and IV.
400-
o
a:
or
350-
300-
250
200-
o 150-
5 100-
50-
9 Points
5 Points
25 50
Axial75Loca ti on
100(in.)
125 150
Fig. 11. Gamma-ray profiles for assembly CZ526 were formed from fiveand nine data points to determine the effects of using only five points.The nine-point profile shows that the spline fit to five points canslightly deviate from the true profile. The areas under the two pro-files, however, differ by only 0.3%. Using the smaller number of datapoints reduces the measurement effort without introducing an importantloss in accuracy.
33
TABLE VI
GAMMA-RAY PROFTLE AREAS, CALORIMETER POWERS, COOLING TIMES(Gamma-Ray Profile Areas Corrected to Calorimeter Measurement Dates)
Data from the September-December 1984 MeasurementsFork Positions from 7.6 to 151.6 in.
Fork Data
Assembly
CZ147CZ148CZ182CZ195CZ205
CZ209CZ211CZ222CZ225CZ239CZ246
CZ259
Cooling Time(Days)
1 2921 318890
1 287912
8901 292388886882882
1 318
CZ264CZ277CZ286CZ296CZ302CZ308CZ311CZ315CZ318CZ331
CZ337
11
11
2222
294296889292294882890912913403407433435882
Gamma-RayProfile Area
33 43132 50737 17431 04234 447
313338344037373130313034333331373532
301861602932042930864147226271772531356119249793137203
Calorimeter DataCooling Time Pc
(Days) (
1 2931 281849
1 287846856860861874876881885888918924934
1 0771 092880
1 259887854882885888
1 2871 3391 2811 285919
1 2921 282884878920920
331.8
296.0
262.7278.4256.7285.6269.7356.9328.0277.6
38 636 884 347.7
34
TABLE VI (cont)
Assembly
C2342CZ346CZ348CZ351CZ355CZ357CZ369CZ370CZ372CZ379CZ398CZ415CZ416CZ429CZ430CZ433CZ460CZ466CZ468CZ472CZ473CZ498CZ508CZ515
CZ526CZ528CZ531CZ536CZ542CZ545
ForkCooling Time
(Days)
913890882913890913886
1 2961 296886890
1 296882890882
1 297913913913913913886
1 2781 297
8861 292881
1 296913913
DataGamma-RayProfile Area
33 52140 49438 07633 22430 92035 95536 30733 54434 40231 83339 03035 44635 18341 20038 22133 86233 57633 07234 71836 31631 42437 99134 82633 59533 01842 44633 75238 07334 23932 62131 483
CalorimeterCooling Time
(Days)
919879883922880921877
1 2561 254886879
1 254883878882
1 253922850924848923876922
1 2531 283853
1 283882
1 255921924
DataPower(W)
280.1388.7342.8313.8290.5320.3347.7288.1288.7287.4372.0289.3319.8385.6353.3287.4313.5302.1325.3325.0293.2359.4310.0294.0296.039S.3297.6347.2295.2311.9295.2
Figure 12 plots the radiation responses Eor CZ526; the plots for CZ205 are
very similar. A well-defined dip in the gamma-ray responses is certainly due
to shielding by the tie plate.
A smaller dip in the neutron count rates is still about three times the
uncertainty in a sing]3 count rate and thus is also likely to be real. The tie
plate apparently scatters some neutrons away from its neighborhood and the fork
detector.
For both gamma-rays and neutrons, the tie plate has small, localized ef-
fects on the radiation transport.
35
400
350-
300-
o 250 HQ.ina; 200-|
Z 150 HO
~ 100-
50-
Gamma—Rays
Neutron cps
20 40 60 80 100 120A x i a l L o c a t i o n ( i n . )
140
Fig. 12. Detailed axial profiles for assembly CZ526. Of par-ticular interest are the effects of the tie plate at the87-in. location. Apparently, the plate scatters neutrons awayfrom the detector while gamma-ray absorption causes oniy asmall dip in the detector's gamma-ray response.
D. Consistency Check of the Declared Exposures and Cooling Times
The data can be examined for internal consistency through techniques pre-4 9
viously used with the ION-1/fork detector. ' If consistency is found among
the assemblies already measured, the curves developed can be used for near-
real-time checking of assemblies measured at some future time.
1. Declared Exposure and Neutron Count Rate.
a. Curium-244 Decay-Corrected Relations. A power-law relationship has4
been applied between the declared exposure and the measured neutron count
rate. The general form is
(corr. n counts/s) = (a) E(S)
(1)
where (corr. n counts/s) is the measured neutron count rate corrected for the244
Cm decay back to the discharge date, E is the exposure, and a and B are
36
parameters obtained by a curve-fitting procedure. This assumes that the242
cooling time is sufficiently long so that the Cm has decayed to insignif-244 242
icance compared to Cm. The half-life of Cm is only 163 days and for a242
PWR assembly freshly discharged with 26 GWd/tU exposure, Cm contributesabout half as many neutrons per second as does Cm. This fraction rapidly
242
decreases with time; after 2 or 3 years, the Cm can be ignored as a signifi-
cant neutron emitter.
For PWR assembles with fairly flat axial profiles, the corrected neutron
count rates can be calculated from measurements at the midpoint of the assem-
blies. However, the Cooper BWR assemblies had uneven profiles, so the area
under the neutron profile was used as the neutron count rate in Eq. (1).
There will always be scatter about this curve because of count rate and
declared-exposure fluctuations, but the trend is generally agreeable. Allow-
ance must generally be made for about a 5% uncertainty in the operator-declared11
exposures.
The relationship in Eq. (1) was examined for the Cooper assemblies. It
seems that the neutron count rate, after an exposure of more than 20 GWd/tU and
a cooling time of 3 years, is almost entirely caused by the spontaneous fis-244
sioning of the Cm isotope. To account for the assemblies' different cool-
ing times, we applied a correction factor to each count rate; this recovers the244
count rate that would have been measured from cm emissions alone immedi-
ately after the fuel was discharged. The correction is simply an exponential244
factor whose argument is the product of the decay constant of Cm and the
cooling time.
The data and the fitted power law function are shown in Fig. 13. The
range of exposures is quite small. The least-square fit choice of beta is
3.55, which is similar to values found at other BWR facilities.
However, it is obvious from Fig. 13 that some data points trend across the
fitted curve rather than along it. The assemblies responsible for this trend
have longer cooling times (they are marked by plus signs and crosses in Fig.
13). If Eq. (1) is applied to only those assemblies that have the most common
operating history (marked by circles in Fig. 13), than the curve of Fig. 14 is
produced. The value of beta is now 4.18 and the points in this subset lie
along the curve very nicely.
The corrected neutron count rates were used with the fitted curves to in-
terpolate exposures. Even when using all the assemblies (Fig. 13), the average37
350-
300-
g 250
g. 200o
o 150
I 100
50-
00
100110110011111110
(a)
10 15 20Exposure GWd/tU
25 30
350
300-
50-
100110110011111110
20(b)
22 24—I—26
i—28 30
Exposure GWd/tU
Fig. 13. The neutron count rates from the Cooper assemblies (inte-grated along the assemblies' axes) are plotted against the declaredexposures. Figure 13(b) is a magnification of the region containingthe data points. Three operating histories are shown: 1 indicateswhen the assembly was in the core during that cycle; 0 indicates whenthe assembly was out of the core. The fitted curve is a power func-tion. Assemblies with the same operating history tend to clusterseparately from other assemblies, implying that exposure alone is notsufficient to characterize assembly neutron emission rate.
38
350
(a)10 15 20
Exposure GWd/tU30
350
20(b)
22Exposure GWd/tU
Fig. 14. These assemblies with the same operating history demon-strate that the neutron data can be correlated to the exposurethrough a power-law relation. Without data from other assemblies,the power-law relationship is clear.
39
difference in absolute value between the interpolated and declared exposures
is only 0.87 GWd/tU; on a percentage basis, the average absolute difference is
3.3%. When using only the short-cooling-time assemblies (Fig. 14), the average
absolute difference between the interpolated and declared exposures is 0.40
GWd/tU, or 1.5%. This is a very good result considering that the probable un-11
certainty in the operator's declared exposures is about 5%.
The apparent effect of operating history seen in Fig. 13 needs further
discussion. From calculational studies on a PWR assembly, we know some
parameters can affect the neutron source strength. Differences in the initial235
U enrichment can easily produce the spread seen in Fig. 13; however, it
appears that all the enrichments of these Cooper assemblies were 2.5%. Varia-
tions in the UO densities are not likely to affect neutron emission rates
as greatly as needed to understand Fig. 13. The effect on neutron production
by variations in the reactor's power level is also slight over the 160- to
240-W/cm range; for the exposures and cooling times of the Cooper assemblies,242
the power level can not explain Fig. 13 either. The production of Cm is
very sensitive to power history; this is an important subject of continual
study in spent-fuel measurements, and is discussed in detail in the following
section.
b. Curium-242 Decay Corrected Relations. The only parameter that dis-
tinguishes one group of assemblies from another in Fig. 13 is operating his-
tory, which is known to affect the relative amounts o£ the important neutron242 244
emitters Cm and Cm. If an assembly is given a continuous irradiation up242
to a certain exposure, a certain amount of Cm will be produced. However, if241 241
the irradiation had been interrupted, Pu would have decayed into Am dur-242
ing the interruption, which would have led to the formation of additional Cm241
from the Am after irradiation was restarted. Thus when other factors are
equal, an assembly with an interrupted irradiation history will have an en-242
hanced amount of Cm.
However, there are two problems with applying this argument to the Cooper
assemblies. Firstly, all the cooling times are about 2.5 years or more. If
other parameters of the assemblies are equal (for example, initial enrichment),242
as they seem to be, the Cm after this much cooling time should be insig-
nificant regardless of the operating history. Secondly, if the operating his-
tory argument did apply, it would not explain why the points marked by plus
40
signs in Fig. 13 are above those marked with circles. These two sets of points
represent assemblies that both cooled for two cycles and then were irradiated
for two more cycles; the assemblies shown as circles have a shorter cooling
time and thus should fall above the plus signs, not below them.
To examine the Cm effect in a more quantitative way, a code was used
to calculate the fraction of neutrons emitted by isotopes of uranium, pluto-
nium, americium, and curium. The operating history is part of the input to
this code and histories of eight Cooper assemblies are presented in Ref. 3;
this includes two of the assemblies shown by plus signs in Fig. 13 and one
shown by an cross.
For those five assemblies with the shorter cooling times (circles in Fig.244
13), the code calculated that 95% of the neutrons came from Cm; for the
three assemblies with the longer cooling times (pluses and crosses in Fig. 13),
the fraction was 98.5%. These are all very near 100%, as expected for cooling
times of 2.5 years and more.
Although it seems that operating history affects the measured count rate,
the exact mechanism by which it does so is poorly understood at this time. A
few anomalies were also seen in ION-1/fork data from Three-Mile Island assem-
blies. Even though some assemblies had the same exposure, cycle pattern,
and cooling time, neutron count rates could still differ. A possible cause
discussed in Ref. 13 is the local neutron spectrum each assembly experiences,
which itself depends on the proximity of control materials. The neutron spec-
trum could affect the amounts of the curium isotopes generated, and hence the
neutron emission rates.
2. Cooling Time and Gamma-Ray Response. A second power-law relationship
exists between the gamma-ray response divided by the exposure and the cooling
time9:
g/E = a T , (2)
where g is the gamma-ray response, T is the cooling time, and E is the expo-
sure; the parameters a and b are found by a curve-fitting procedure.10 For
41
cooling times less than a year, a great deal of scatter has been found about
such a curve, but with the longer cooling times of the Cooper assemblies there
is no such problem.
The data and fitted curve are shown in Fig. 15. With essentially only two
cooling times, the data separate into two collections of points. The fitted
value of b is 0.04202, with T in days and E in GWd/tU, which is similar to
values from other fuel examinations.
No inconsistencies are seen among the gamma-ray and cooling time data.
However, because there are only two cooling times and neither is short, little
significance can be attached to the fitted curve. The data points form clus-
ters as expected.
0
O
X
C
oG.(/)Q)
O
EEoo
500 1500
Cooling (days)
Fig. 15. A power-law relation between gamma-ray response data di-vided by the exposures and the cooling time. With essentially onlytwo coding times, the curve is not very informative. However, theclustering of the data points indicates no inconsistencies among theoperator-declared parameters (exposures and cooling times) and themeasured data.
42
V. CORRELATION OF ION-1/FORK AND CALORIMETER MEASUREMENTS
A. GE-MO Calorimeter
Reference 14 describes the GE-MO calorimeter for BWR and PWR assemblies
in detail. Only its basic features will be noted here. An assembly is en-
closed inside a water-filled tube that is well insulated thermally from the
pool water. The water in the tube can be stationary and its temperature moni-
tored with time, or the rate of water circulation can be found that maintains
a fixed temperature differential across the calorimeter's length. Some gamma-
ray monitors are built into the calorimeter to estimate the gamma-ray flux es-
caping the calorimeter. A correction for the lost gamma-ray heating can thus
be made to the measured heat rate for this loss; the correction for Cooper
fuels was about 10%.
The calorimeter was used in 1982 with an excellent reproducibility fluc-
tuation of about 2% at 300 W (Ref. 14). However, the standard deviation of
repeated measurements on assembly CZ205 was 4%, or 14 W out of about 350 W
(Ref. 1). The calorimetry data for the Cooper fuel placed in the REA-2023 cask
are given in Table VI.
B. Gamma-Ray Heating Fraction
Before attempting to correlate the gamma-ray data with the calorimetry
results, the variations resulting from different gamma-ray heating fractions
from the assemblies must be analyzed. If the fraction of the heating caused
by gamma rays is constant, or nearly so, the gamma-ray responses from the
ION-1/fork detector will also be proportional to the heat-emission rate from
the assemblies.
Calculated gamma-ray fractions for these Cooper assemblies were not read-
ily available and not pursued because our estimates of the differences among
fractions were less than the variations in the calorimeter data. The rest of
this section justifies this decision.
We based our estimates of the sensitivity of the gamma-ray fraction to
differences in exposures and cooling times on thy calculated fractions for some
other BWR assemblies given in Ref. 15. These calculations show that for cool-
ing times in the range of 2 to 3 years, the gamma-ray fraction changes by less
than 2% for an exposure difference of 1 GWd/tU. The Cooper assemblies had
these cooling times and exposures of 25.3-26.6 GWd/tU, a range of 1.3 GWd/tU.
43
Variations in the gamma-ray fraction due to different exposures are thus taken
to be 2% or less.
Furthermore, from the information in Ref. 15 for exposures between 18 and
36 GWd/tU. the gamma-ray fraction changes by only about 1% as the cooling time
increases by 20 days (a time greater than nearly all the differences between
the lON-1/fork and calorimeter measurement dates). This deduction of a low
sensitivity of the gamma-ray fraction to cooling time is further supported by
two gamma-ray fractions extracted from the 0RIGEN2 calculations by PNL for
CZ342; the initial Eraction of 38.1% increased to only 38.8% after about 90
days of additional cooling, a time much greater than any needed for correcting
Cooper fuel data.
These arguments convinced us that the differences in the gamma-ray heating
fractions among the cooper assemblies were insignificant.
C. Correlation of the ION-1/Fork and Calorimeter Data
1. Calorimeter and ION-1/fork Measurements Contrasted. A calorimeter can
give an accurate measure of the heat-emission rate from an assembly. This in-
formation is important for the safe loading of a dry storage cask such as the
REA-2023.
However, a calorimeter has two drawbacks: (1) The time required to meas-
ure one assembly is long (about 5 h at GE-MO), and (2) no information is ob-
tained about the axial distribution of the heat emission.
The ION-1/fork detector requires only about 6 n>in to generate a profile
of the gamma-ray (and neutron) emissions of an assembly (from which the calo-
rimeter value can be inferred, as discussed in Sec. V.C.3).
2. Value of the Profile Information. Knowledge of the axial distribu-
tion can prevent creating an unexpectedly "hot" spot inside the cask. An as-
sembly with an unusually high heat-emission rate at some location would be de-
tected, and a collection of assemblies that would lead to an unacceptable com-
bination could be avoided. The heat-emission profile calculated with ORIGEN2
in Ref. 3 was virtually a mirror image of the measured gamma-ray profile; the
two profiles have a single maximum at opposite ends of the assembly. This
emphasizes the value of measuring the profile directly.
44
3. correlating the Data. For the Cooper assemblies, we expected that the
areas under the gamma-ray profiles were directly proportional to the calorim-
eter power data (see Sec. V.B). Because most of the assemblies were measured
by the two instruments on different days, some adjustment might be needed be-
cause of the cooling discussed in Sec. IV.c.2.
a. Correlation Without a Cooling Time Difference Adjustment. For most
of the assemblies, the time between ION-1/fork and calorimeter measurements was
less than 30 days, so the cooling corrections are generally small. We first
correlated these two sets of data, ignoring the time differences. The most
complete sets of data are from the October-November 1984 period during which
each assembly was measured in the calorimeter before loading into the storage
cask. The ION-1/fork profiles collected during this time were from eight
points that were nearly equally spaced along the length of the assemblies.
The calorimetric heat power P was assumed to be a simple linear function
of the ION-1/fork gamma-ray profile area A:
P = s A . (3)
The slope s was determined by a least-square fit of the data in Table VI
and has the value 0.009061 + 0.000063 W. Figure 16 is a plot of the data
points and the fitted curve. The error bars on P are all ±14 W. The uncer-
tainties for the profile areas are all under 1% and are not drawn on the ?lot.
Of the 52 data points, 27% are more than one standard deviation from the
fitted line, which indicates that the ±14 W uncertainty is indeed about one
standard deviation; the same can be said for the fact that 4% of the data
points are more than two standard deviations from the line. The average abso-
lute value of the residuals between the data points and the curve is 12.8 W or
4.2%. In general, the fit to the data is as good as the stated uncertainty in
the calorimeter data would allow.
b. Correlation With a Cooling Time Difference Adjustment. Typically, we
measured assemblies with the ION-1/fork detector and the calorimeter
45
400-
OQ_
0)
a>E
ooo
(a)
5000 10000 15000 20000 25000 30000 35000 40000 45000Fork Gamma-Ray Area
420
o
u0}
OQ.
V
lOri
me
oo
370
320
270
220
o HIM 0 4/21/81
x 100IIO 4/21/81
& II00II 6/01/82
28000 30000 32000 34000 36000 38000 40000 42000 44000(b) Fork Gamma—Ray Area
Fig. 16. A simple correlation between the calorimeter and ION-1/forkgamma-ray data. (a) A straight line through the origin. (b) A mag-nified view of the region containing the data points, which showstftere may be a slight dependence on the operating history. 1 indi-cates when the assembly was in the core for a cycle; 0 indicates whenthe assembly was out of the core during that cycle. A discharge datefollows a cycle description. No correction has been made for differ-ent ION-1/fork and calorimeter measuring dates, which introduces asmall error in the correlation.
46
on different days. The exponential decay discussed in Sec. IV.C.2 was used to
correct for the efEect of time on the assemblies' cooling.
The largest time difference between the two measurements was 44 days (as-
semblies CZ433 and CZ515). The correction factor in this case is about 2.5%.
Many other assemblies had time differences of less than a week, and their cor-
rection factors were less than 0.5%.
Figure 17 shows Eq. (?) fitted using these small corrections. The slope
is now 0.008961 ± 0.000062 W, which hardly differs from the slope without the
cooling time correction. The statistics of the fit are virtually the same as
in Sec. V.C.2.a.
Apparently the uncertainties stated for the calorimeter data are quite
accurate and the much smaller corrections for cooling time differences have no
important effect.
VI. NUCLEAR SAFEGUARDS IMPLICATIONS
Before fuel is loaded into dry storage casks and thereby removed from view
for an extended period of time, there should be a guarantee that special nu-
clear material has not been removed from the fuel. After the casks are loaded,
a seal can then be attached to the cask to guarantee that the contents remain
intact. The ION-1/fork system can verify the characteristics of spent-fuel as-
semblies just before chey are placed in a dry storage cask. The measurements
at GE-MO gave us an opportunity to test the ION-1/fork under conditions similar
to those one might find in a storage basin where fuel is being moved into dry
storage casks.
For best results, the fork detector should be installed in a fixed loca-
tion (probably on a wall) and the fuel should be moved to the detector before
it is placed in the cask. In this manner, the detector could be located in a
low-radiation background area and a consistent measurement geometry could be
maintained. For PWR fuel, a single measurement at one axial position could
suffice for the verification. BWR fuel may require measurements at two or
three axial positions to be sufficiently characterized. The fork at GE-MO re-
mained in the pool for about 1 year without any problems, demonstrating that
the equipment can be left in the pool at a facility for an extended period of
time.
47
400-VI
15000 20000 25000 30000 35000 40000 45000Fork Gamma-Ray Area
420
370-
oQ_
l _Q>
Dri
me
lC
ah
320
270
(b)
220
o IIIII0 4/21/81
x 100110 4/21/81
A 110011 6/01/82
28000 30000 32000 34000 36000 38000 40000 42000 44000Fork Gamma-Ray Area
Fig. 17. The same data used In Fig. 16 are shown here after adjustingthe ION-1/fork data for cooling between the dates on which measurementswere made with the ION-1/fork and the calorimeter. The largest differ-ence in dates, 44 days, generated a 2.5% correction. Most of the cor-rections were less than 0.5%. The straight-line fits in Figs. 16 and17 show that these differences in measurement dates have no significanteffect on the linear correlation between the ION-1/fork and the calo-rimeter data.
48
This final check before storage could be done quickly and easily with the
type of equipment used at GE-MO.
VII. SUMMARY AND CONCLUSIONS
The study o£ the Cooper BWR assemblies with the Los Alamos ION-1/fork
detector was useful in five ways.
Profiles of gamma-ray and neutron emission along the lengths of the assem-
blies showed that there are a variety of profile types. Some profiles were
smooth and regular, whereas others had peaks at various positions, presumably
because of the proximity of control blades. This profile information was
available to assist in the calculated heat emissions and could be correlated
with temperature measurements made within assemblies and around the cask.
The fraction of the heating caused by gamma rays appears to be very nearly
the same for all the Cooper assemblies. This justifies correlating the ION-1/
fork detector's gamma-ray data with the heat-emission rates measured by the
calorimeter. The correlation was linear, with a spread about the curve nearly
equal to the 4% uncertainty in the calorimeter data alone; the precision of the
ION-1/fork gamma-ray data is estimated to be better than 1%.
These results suggest that an ION-1/fork detector could be used to quickly
monitor fuel assemblies during routine cask loadings. Assemblies could be se-
lected on the basis of their gamma-ray profiles to produce an even heat distri-
bution within the cask. Undesirable loadings with highly skewed heat distribu-
tions or dangerously high total heat emissions could be prevented.
From international and domestic nuclear safeguards standpoints, the veri-
fication of the operator's declared exposures and cooling times is an important
step just before sealing the assemblies in a cask for long-term storage. The
ION-1/fork detector can quickly determine that genuine fuel assemblies are be-
ing loaded.
The data were analyzed with what have become standard procedures for nu-
clear safeguards applications for the ION-1/fork detector. The analyses gen-
erally agreed with results from measurements at other facilities, but some neu-
tron count rates were inexplicably inconsistent. These anomalies seem to be
related to operating history, possibly depending on the proximity of control
materials in the core. High neutron count rates have been found before, but
49
242could be explained by unusually high amounts of Cm; this explanation fails
here. The unusually low count rates are a new feature (at least in nonrecon-
stituted fuel). The continued study of these data can aid in understanding the
spent-fuel emissions and the future applications of the ION-1/fork detector.
The fork was continually under water for exactly a year without any prob-
lem. The ION-1 prototype electronics unit also performed well, although some
modifications to it part way through the measurements forced the normalization
of some of the neutron count rates. This unit was developed at Los Alamos, but
commercial units are now available (the GRAND-1 from Davidson Co., 19 Bernhard
Road, North Haven, CT 06473). The GE-MO personnel who used the ION-1/fork de-
tector remarked on its ease of use.
ACKNOWLEDGMENTS
Mikal McKinnon of PNL and James Doman of GE-MO invited Los Alamos to par-
ticipate in this cask chracterization project; we welcomed the opportunity and
appreciate the offer.
The bulk of the measurements were made by several technicians under the
supervision of James Doman. The work was done with care and attention to
details.
The electronics support of Jim Halbig and Jim Caine and the mechanical
design by Ray Holbrooks, all of Los Alamos National Laboratory, were invalu-
able.
REFERENCES
1. M. A. McKinnon, J. W. Doman, J. E. Tanner, R. J. Guenther, J. M. Creer,and C. E. King, "BUR Spent Fuel Storage Cask Performance Test," PacificNorthwest Laboratory report PNL-5777, Vol. I (February 1986).
2. A. G. Croff, "A User's Manual for the ORIGEN2 Computer Code," Oak RidgeNational Laboratory report ORNL/TM-7175 (July 1980).
3. M. A. McKinnon, J. W. Doman, C. M. Heeb, and J. M. Creer, "Decay HeatMeasurements and Predictions of BWR Spent Fuel," Electric Power ResearchInstitute report NP-4269 (1985).
50
4. J. R. Phillips, G. E. Bosler, J. K. Halbig, S. F. Klosterbuer, and H. O.Menlove, "Nondestructive Verification With Minimal Movement of IrradiatedLiqht-Water Reactor Fuel Assemblies," Los Alamos National Laboratory re-port LA-9438-MS (ISPO-172) (October 1982).
5. P. M. Rinard, "Neutron Measurements in Borated Water for PWR Fuel Inspec-tions," Los Alamos National Laboratory report LA-10068-MS (ISPO-223) (July1984).
6. P. M. Rinard, "Gamma Doses from Irradiated Assemblies Under Water," LosAlamos Scientific Laboratory report LA-7914-MS (July 1979), with new fig-ures addendum.
1. J. K. Halbig and J. C. Caine, "ION-1 Technical Manual," Los Alamos Na-tional Laboratory report LA-10433-M (ISPO-240) (July 1985).
8. G. E. Bosler, J. R. Phillips, W. B. Wilson, R. J. LaBauve, and T. R. Eng-land, "Production of Actinide Isotopes in Simulated PWR Fuel and TheirInfluence on Inherent Neutron Emission," Los Alamos National Laboratoryreport LA-9343 (July 1982).
9. P. M. Rinard, "A Spent-Fuel Cooling Curve for Safeguard Applications ofGross-Gamma Measurements," Los Alamos National Laboratory report LA-9757-HS (ISPO-195) (April 1983).
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11. C. C. Thomas, D. D. Cobb, and C. A. Ostenak, "Spent-Fuel Composition: AComparison of Predicted and Measured Data," Los Alamos National Laboratoryreport LA-8764-MS (March 1981).
12. S. Rohar, V. Petenyi, P. Liptak, and L. Krajci, "The Fuel Burn-up Deter-mination by Combined Passive Neutron and Gamma-Spectrometrie ND-Measure-ments," Nuclear Power Plant Research Institute progress report to the IAEAon Research Contract No. 2639/Rl/Rb (March 1985).
13. G. E. Bosler, H. 0. Menlove, J. K. Halbig, N. Nicholson, L. Cowder, P.Ikonomou, J. D. Luoma, W. S. Wilkerson, H. Arvanitakis, and R. Tropasso,"Physical Inventory Verification Exercise at a Light-Water Reactor Facil-ity," Los Alamos National Laboratory report LA-10695-MS (April 1986).
14. B. F. Judson, H. R. Strickler, and J. W. Doman, "In-Plant Test Measure-ments for Spent Fuel Storage at Morris Operation," Vol. 3, General Elec-tric Company report NEDG-24922-3 (February 1982).
15. W. B. Wilson, T. R. England, and R. J. LaBauve, "Gamma Fraction of TotalDecay Power of Discharged BWR Fuel," Los Alamos National Laboratory memoT-2-M-1486 to G. E. Bosler (April 26, 1984).
51