NATIONAL BUREAU OF STANDARDS REPORT

10 812

DETAILED ANALYSES OF MEASUREMENTS

IN THE

INTEGRATED SAFEGUARDS EXPERIMENT

This paper is based on work performed under

United States Atomic Energy Commission

Contract No. AT(49-2)-l 165

U.S DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
NATIONAL BUREAU OF STANDARDS

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT

4314429 April 1972

NBS REPORT

10 812

DETAILED ANAI YSFS OF MFASIIRFMFNIS

IN THE

INTEGRATED SAFEGUARDS EXPERIMENT

C. N. Smith

F. J. Perella

Technical Analysis Division

National Bureau of Standards

This paper is based on work performed under

United States Atomic Energy Commission

Contract No.. AT (49 — 2)— 1 165

IMPORTANT NOTICE NATIONAL BUREAU OF STAND

for use within the Government. Befc and review. For this reason, the pul whole or in part, is not authorized Bureau of Standards, Washington, D

the Report has been specifically prep

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

^counting documents intended

ected to additional evaluation

ing of this Report, either in

fice of the Director, National

5 Government agency for which

s for its own use.

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

REPORT ON THE

DETAILED ANALYSES OF MEASUREMENTS

IN THE

INTEGRATED SAFEGUARDS EXPERIMENT

Prepared by

C. N. Smith

Physicist

F. J. Perella

Gerieral Engineer

Reviewed by:

Walter G. Leight

Richard T. Penn, Jr

George Suzuki

Approved by:

W. Edward Cushen, Chief

Technical Analysis Division
,
CONTENTS

page

Preface 1

Introduction 3

Feed Material 6

Campaign 1 - Make-up and Treatment 6

Campaign 2 - Make-up and Treatment 8

Feed Results 10

Summary on Feed 11

Product Material 12

Discussion on Campaign 1 12

Discussion on Campaign 2 15

Product Results 17

Summary on Product 17

Additional Comments 17

Scrap and Measured Discards 20

Discussion on Campaign 1 20

Discussion on Campaign 2 25

Summary on Scrap and Waste 26

Summary 27

Feed Material - PUO2 27

Product Material - Sintered Mixed Oxide 27

Scrap and Measured Discards 27

Overall Balance 28

References 29

1
$9
PREFACE

An Integrated Safeguards Experiment (ISE) conducted

within a nuclear fuels manufacturing plant is, in a broad

sense, the tracing of fissile material through every stream

in a process or processes under production conditions in

an attempt to uncover those factors which contribute to the

imbalance (specifically the material unaccounted for (MUF)

when a material balance for such plant is periodically

calculated. The ISE, discussed in this paper, had as its

primary objective the evaluation of the usefulness to

Safeguards of material balance accounting based on all

measurements being completely quantitative. This was

accomplished by the utilization of non-destructive testing

techniques (NDT) to measure difficult to measure materials.

Generally, the fissile material content of these hard-tomeasure materials was previously determined by either an

educated guess or by a "by- difference" conclusion.

The ISE, from which material for this paper was drawn,

will be reported in detail in a report to be issued by the

USAEC. In conducting the experiment, however, many problems

were encountered which required detailed effort not anticipated in the planning of the project. These details are

considered important enough to be reported separately in

an effort to emphasize their significance. The intent of

this paper, therefore, is to acquaint those interested

- 1 -
-

I
in possibly conducting similar integrated tests of some

of the details and problems associated with experimental

determination of plutonium content of the major flows of

a mixed-oxide fabrication process.

- 2 -

INTRODUCTION

In January 1968, the U.S. Atomic Energy Commission

(AEC) , Office of Safeguards and Materials Management

established a Safeguards System Studies program which has

as a primary objective the study and analysis of the various

nuclear fuel manufacturing processes, for the purpose of

of developing a basis upon which criteria for acceptable

limits on material unaccounted for (MUF) , normal operating

losses (measured discards) , shipper-receiver (S/R) differences and unmeasured special nuclear material (SNM) inventory

could be established. Necessary information was to be compiled from both historical and current plant files and from

it develop analytical models which could be used to evaluate

plant data leading to the establishment of criteria for

acceptable limits for MUF, measured discards, S/R differences

and other critical factors. Visits to licensee plants soon

established the fact that historical data was lacking in

quality and depth and therefore not applicable to the

establishment of criteria. Also, current data was not

applicable since much of it was based on questionable

measurement data.

As a result of the findings of this early industry

survey the AEC decided to conduct Integrated Safeguards

Experiments (ISE) within licensee plants which were producing

nuclear fuel materials of major critical interest from a

need-to-safeguard viewpoint.

- 3 -
'I

’

%
The Integrated Safeguards Experiment was conducted

at the General Electric Company Plutonium Laboratory,

Vallecitos Nuclear Center near Pleasanton, California.

This laboratory contains a fabrication process where plutonium dioxide and uranium dioxide are physically mixed to

produce mixed oxide master blends of a given enrichment

(percent of plutonium in the mixed oxide) ; the material

is then prepressed, granulated, pressed, sintered, and

acceptable pellets loaded into fuel clad. The ISE consisted

of two campaigns of mixed oxide material: one utilized 90

percent fissile plutonium and the other 80 percent. Each

campaign consisted of two different enrichments, with each

enrichment made up of one or more master blends. The higher

of the two enrichments within a given campaign was fabricated

into annular pellets, while the material from the lower

enrichment was formed into solid pellets. The measurements associated with the major flows of the fabrication

process are analyzed for the two jobs (campaigns) which

were run as part of the experiment. The major flows

considered for this paper are the plutonium dioxide feed,

the sintered mixed oxide product, and the scrap and measured

discards (waste) materials. For each of these flows the

details of each campaign are discussed; results are presented

for the various plutonium analysis techniques which were

applied. In each section, the procedures developed for

determining the uncertainties and for combining the random

_4_

and systematic errors to obtain a total limit of error are

discussed or referenced.

In addition, this paper contains a few comments and

observations on the subject of plutonium concentration uncertainties in the propagation of errors; specifically,

it deals with the coefficient of variation (CV) and limit of

error (LE) values for the various blends of product.

- 5 -

FEED MATERIAL

Feed Material for each campaign is discussed separately

in order to identify the difference in handling procedures.

Campaign 1 - Make-up and Treatment

The makeup of the feed material used in Campaign 1 was

rather complex. The plutonium dioxide used in this first

campaign was obtained in 1969. Six cans of PuC^ were used;

namely, cans designated as A, B, C, E, F, and G. Cans E, F

and G were unopened, full cans. On the other hand, some of

the contents of cans A, B and C had been used for other

work in 1969. It was assumed that the atmosphere in the 3 unopened cans remained the same as when sealed by the shipper.

According to information from the shipper, (ARCHO) , the

relative humidity (RH) of the loading box atmosphere was

about 4 percent. Another assumption was that the 3 open

cans (A, B and C) had picked up moisture during their use

in 1969, since the RH of the GE plutonium fabrication laboratory is normally in the 30-60 percent range. Equilibration

test data on plutonium dioxide powder, indicates a sharp

rise in the powder weight within the first few hours when

"very dry" powder is exposed to a 50% RH atmosphere. It

was therefore assumed that the moisture content of the unopened cans was different than that for the opened cans of

Campaign 1 feed material. This was confirmed by equilibration

tests performed later. These equilibration experiments

indicated that plutonium concentration in PuC>2 can change by

- 6 -

as much as 1 percent depending upon temperature, humidity,

particle size and surface area. For Campaign 1, samples

were taken from cans B, C, E and G, for wet chemistry

analysis of the plutonium concentration. It was generally

agreed that any PuC>2 samples sent to the plutonium analytical

laboratory would reach the equilibrium plateau before they

were analyzed. Therefore, any "as received" plutonium concentration values were assumed to be stable insofar as

the analyzing environment was concerned. Before the samples

were destructively analyzed for plutonium content, the sample

were "dried" at a selected temperature to drive off moisture.

According to GE, plutonium concentration values obtained

under "dried" conditions were supposed to represent the

dry received plutonium dioxide. It was interesting to note

that the average value of the 3 sub-samples taken from a

composite sample was 87.27% Pu for a "dried" condition when

the drying temperature was in the 200-300°C range. The

average value for these same 3 sub-samples was 88.09% for

a "dried" condition when the drying temperature was in

the 700-800°C range. It is clear that the meaning of the

word "dried" depends on conditions, and that it must be

defined by a specific temperature range which will condition

the sample in such a way that it may be considered representa

tive of the feed. Since the drying process used by the plant

to produce feed that was representative of the total lot

could not be supported quantitatively, the results from

- 7 -

chemical assay were not considered usable in measured

material balance calculations.

The nondestructive technique of replacement calorimetry

was used for the measurement of plutonium content of the PuC>2 feed material. All cans of material used in Campaign 1 were

measured at least once. The limit of error (LE) associated

with the feed gPu value was due mainly to the uncertainty

associated with the contained Pu 238 and Am 241. The GE

Plutonium Laboratory did not have adequate analytical

capability for measurement of Am 241; therefore, the

vendor's value (corrected for growth) and uncertainty

had to be used in the calculation of the grams plutonium

as determined by calorimetry. The LE associated with the

gPu in the feed material was 4% for Campaign 1. (For details

on the procedure for calculating the total LE associated

with calorimetrically determined values, see reference 1).

Campaign 2 - Make-up and Treatment

The PuC>2 feed material was first calorimetrically

determined which revealed an error in the vendor's isotopic

values, then equilibrated, sampled and analyzed coulometrically

reweighed, calorimetrically determined again and finally introduced to the clean process line for fabrication purposes. The

80% fissile plutonium dioxide was contained in three cans.

The contents of each can and the accompanying composite

sample were equilibrated for several days. This equilibration

process consisted of allowing the material to pick up moisture

- 8 -

from the glove box system until there was no additional weight

change. This was accomplished by transferring the contents

of the PuO^ cans to flat pans permitting a greater surface

of the oxide to be exposed to the glove box atmosphere.

The change in weight averaged about 0.5 percent; this value

representing a minimum since there was a lapse of time

between the opening of the shipping containers and the

transferring to the large tared equilibrating pans.

Relative humidity (RH) gauges indicated that the atmosphere in the analytical laboratory was in approximately the

same range as that of the fabrication* laboratory. Thus,

this equilibration process eliminated or, at least, minimized a variable which Campaign 1 feed material was

subjected to suggesting questionable results, and allowed

for a meaningful value and LE to be obtained for Campaign 2

feed material by an accurate chemical analysis method.

After equilibration, eight samples were withdrawn for

Pu analysis using the coulometry technique: 2 from each

of the three cans as well as from the composite. The

average of the 8 plutonium concentration values was used

for the feed concentration value for the purposes of the

material balance. The distribution of values was also

used to calculate the limit of error associated with the

mean concentration value. No additional uncertainty (e.g.,

due to moisture difference between fabrication and analytical

laboratories) except for that due to weighing, was included

9 -
' * 

d
in the computation of the feed material LE value using

chemical assay information. (See reference 1 for LE

formulation details.)

The three cans of equilibrated PuC^ material were removed from the fabrication line and each measured twice

by calorimetry. The uncertainty of the calorimetry measurements

was due to the uncertainty associated with the Pu 238 and Am 241

abundance determinations. As with Campaign 1, the vendor's

value for Am 241, corrected for buildup, had to be used since

the plant did not have that capability on a routine basis.

The LE associated with the gPu value in the feed material was

^8% for Campaign 2. This is twice as great as that in

Campaign 1 and it reflects the percentage increase in the

heat contribution from Pu 238 and Am 241 for 80% fissile

plutonium.

Feed Results

Technique Campaign 1

Chemical Assay NA

Calorimetry 4919. ± 197. gPu

Campaign 2

2425.1 ± 5.8 gPu

2429. ± 190. gPu

- 10 -

Summary on Feed

1. The moisture problem which obscured true Campaign 1

feed values was solved in Campaign 2 by equilibrating the

PuC>2 feed. Therefore an improvement over Campaign 1 was

made and good chemical assay data was obtained for Campaign 2

feed

2. No improvement was made on calorimetry. In fact,

the percent LE was a factor of two larger for Campaign 2

than for 1 because the percent heat contribution from Pu 238

and Am 241 isotopic abundance was higher for the 80% fissile

material

3. There was remarkably good agreement between the

chemical assay and calorimetry results for Campaign 2 feed.

- 11 -
?T

' ,< " '

.
PRODUCT MATERIAL

Discussion on Campaign 1

There were two master blends of material made up for

each of the two enrichments. The two master blends for a

given enrichment were supposed to be the same. For the

first enrichment, master blends M0094 and M0095 appeared

to be statistically different according to the F test* on

the product plutonium concentration variances. Because of

this, the grams of M0094 mixed oxide and the M0094 plutonium

concentration data were kept and treated separate from the

M0095 information. Details are presented below. The master

blends of the second enrichment, M0096 and M0098, were not

statistically different, and therefore probably came from

the same material sources. Thus, for the second enrichment,

all the information was pooled together.

For the M0094 material, the total grams plutonium was

calculated by multiplying the average M0094 plutonium concentration value by the total grams of M0094 mixed oxide that

were loaded into the rods. The percentage LE associated with

the M0094 grams plutonium value was obtained by adding together

the LE values (in percentages) for the average plutonium

* The F statistic is the ratio of the variances of the

two samples. The F test provides the probability that

the two samples came from normal distributions with the

same variance.

- 12 -

concentration and for the total weight of mixed oxide* The

same procedure was followed for M0095. To obtain the LE

on the total grams plutonium in the first enrichment,

the LE values for M0094 and M0095, in absolute units, were

propagated in the usual manner. The usual error propagation

technique was again used to combine the two enrichment LE

values to obtain the Campaign 1 total product LE. The

usual propagation of error technique is applied in all situations except where the total grams of mixed oxide value is

multiplied by the average Pu concentration value. The treatment of errors in this case requires a systematic procedure

because a collection of values is being multiplied by a

constant.

* See references 1 and 2 for discussion of the philosophy

of this procedure.

- 13 -
L , f ' '• ' • I; * • *• ~ • • • . • I ' j O: - , “i 

: ' J :
The following tables give information about the

Campaign 1 Product as determined by chemical assay.

Product Average Pu Concentration and LE

Enrichment n* Average Pu concentration LE

1 M0094 13 0.03548 . 00020

MO 095 12 0.03536 .00035

2 M0096 , 98 26 0.03427 .00011

Product Grams of Mixed Oxide

Enrichment Grams of Mixed Oxide LE

1 M0094 26323.2 0.8

MOO 9 5 28993.3 0.7

2 M0096 , 98 61249.0 0.9

n* - Number of Production Samples.

- 14 -
* -
Product gPu and LE

Enrichment Grams Plutonium LE

1 1959.1 11.5

MOO 9 4 933.9 5.3

MOO 9 5 1025.2 10.2

2 2099.0 6.8

1+2 4058.1 13.4

The fuel rods were gamma scanned twice; once using a

Nal detector and later using a GeLi detector. Unfortunately,

the analyses of the gamma scanning data were not completed

in time to be used in this report. The same explanation

applies to the 20 rods of Campaign 2.

Discussion on Campaign 2

The product consisted of two sets of fuel rods. One

set of 10 rods contained solid pellets; the other set of

10 rods contained annular pellets whose plutonium concentration was slightly higher than that for the solid pellets.

Samples were withdrawn for purposes of plutonium concentration determination from the boats of sintered mixed

oxide pellets in accordance with the fuel fabrication

contract, one sample every fourth boat. Approximately

15 plutonium concentration determinations were made for each

of the two enrichments. Since pellets within a given enrichment were supposed to come from the same population (master

blend) an average plutonium concentration value was determined

and used in determining the plutonium content of the sintered

mixed oxide product. The distribution of values was also

used to calculate the limit of error associated with the

- 15 -
a

’

• .

.
average Pu concentration value for the enrichment. This

LE value, converted to a percentage, was added to the percentage weighing LE to obtain the percentage LE on the product

on an enrichment basis. To obtain the product LE for the

campaign, the absolute LE values for each enrichment were

combined using the usual error propagation techniques.

The following tables give information about the Campaign 2

Product as determined by chemical assay.

Product Average Pu Concentration and LE

Enrichment n* Average Pu Concentration LE

1 MOIOO 15 0.02584 . 000062

2 MO101 16 0.02388 .000143

Product Grams of Mixed Oxide

Enrichment Grams of Mixed Oxide LE

1 MOIOO 39260.5 o •

00

2 MO101 43424.8 00 o • Product gPu and LE

Enrichment Grams Plutonium LE

1 MOIOO 1014.5 2.5

2 MO101 1037.0 6.2

Campaign 2 2051.5 6.7

*n - Number of Production Samples.

- 16 -
.

' :

--

«
Product Results

Techniques Campaign 1 Campaign 2

Chemical Assay 4058.1 ± 13.4 gPu 2051.5 + 6.7 gPu

Nal Results not Available

GeLi Results not Available

Summary on Product

1. The % LE for each campaign was 0.33%.

2. More blending work was performed on Campaign 2

master blends than on Campaign 1 materials. One

conclusion may be that the plutonium heterogeneity

variance between pellets does not appear to be

one of the dominant variances.

3. There was a factor of ^ 1.7 difference between the

LE associated with gPu of enrichment 1 and 2 of

Campaign 1. For Campaign 2 the difference between

the two enrichments was a factor of ^ 2.5. In

one campaign the annular pellets had the larger

LE, in the other campaign it was the solid pellets.

Additional Comments

As indicated in the introduction of this paper, a few

observations and comments would be made on the uncertainty

of the product plutonium concentration values. The distribution of n production samples (sintered pellets) produced

the following coefficients of variation for the various

blends

- 17 -

Campaign Master Blend %CV n

1 MOO 9 4 0.93 13

M009 5 1.57 12

MOO 9 6 0.90 14

M0098 0.61 12

2 MOlOO 0.43 15

MO101 1.13 16

The above data may emphasize the importance of the

complete blending process. For example, we observed that

a longer blending time was performed on the fourth blend

of Campaign 1 (M0098) than on the first three blends.

The %CV for (M0098) blend is lower than any of the others,

which may be attributable to the longer blending time.

In Campaign 2, however, the preparation and blending

time for both blends involved (MO100 and MO101) , were

approximately the same and yet the difference between the

%CV of these blends is a factor of approximately 2.6.

Considering the similarity of preparation and blending time

of both blends, why should there be such a large difference

in the %CV? Possibly the non-homogeneity of the pellet

sample or the lack of complete dissolution before analysis

may be a logical conclusion. In the case of blend MOlOO

the GE-VNC analytical laboratory rejected the results

of five of the fifteen samples as unusable and requested

substitute samples from this blend. These were analyzed

and results recorded. This was not repeated for blend MO101

since the analyses were considered normal.

- 18 -
'
Although considerably more effort was put into the

blending preparation for Campaign 2 material than there was

for Campaign 1, pooled CV values and the total % LE values

indicated there was little difference between the results

of the two campaigns.

A nested design experiment was performed by GE-VNC using

samples from blend MOIOO which had a 0.43 %CV value. The

objective of this experiment was to evaluate the errors

between and within plutonium determinations when using

three different measurement techniques. This experiment

also was expected to elucidate and segregate the several

variance components, such as the analytical, dissolution,

Pu hetrogeneity , lot-to-lot and others. The results of

this experiment have not yet been reported; however, in

light of the non-consistent behavior of the process, it is

questionable whether results of such tests will be useful.

Such results may be meaningful only if many nested design

type experiments were conducted within the plant in order

for the process to be characterized under its various

conditions. Practical and economic considerations of this

approach, however, would probably preclude doing this. Even

if many sets of results were obtained, the usefulness of such

information would be questionable in the propagation of error

to obtain a meaningful LEMUF value. How would an inspector

or plant operator know which set of results to use in the

propagation? In plutonium fuel manufacturing plants where

- 19 -
.
the %CV values vary greatly between blends, the best type

of information to use for LEMUF calculations is the distribution of current values. This will probably require more

samples than are normally taken, but it provides a means

for obtaining a meaningful LEMUF value which, after all, is

the judge of the MUF value.

- 20 -

SCRAP AND MEASURED DISCARDS

Discussion on Campaign 1

The measured discards (waste) and scrap materials resulting from the fabrication of mixed oxide pellets for

Campaign 1 were measured for plutonium content by passive

neutron coincidence counting. This method detects neutrons

from the spontaneous fission of isotopes such as Pu238,

Pu 240 and Pu 242. The standards used for calibration

purposes were fabricated from existing mixed oxide materials.

Element and isotopic content from previous analyses were

used. The standards were originally produced to meet the

needs of the Plant Instrumentation Program (PIP).* The

gPu limit of error (LE) values for several of the standards

are larger than one would normally use in materials balance

accounting. Another point to mention is that some of the

scrap packages were "hotter" than the largest standard used

in the calibration. In these cases the calibration curve

was linearly extrapolated. No additional uncertainty was

included to cover this procedure. The LE on the gPu in the

standards used for campaign calibration purposes ranged from

0.4% to 1.9% for scrap standards and for waste standards

was 3.2% or 3.5%. Most of this LE is due to the uncertainty

* This program, sponsored by the AEC, will, hopefully,

introduce non-destructive measuring techniques in the

routine handling of nuclear fuel thus providing more

effective and timely material control within the plant.

- 21 -

1 j JL . OCK'Vr IVOir,

LE CALCULATIONS USING DATA FROM NEUTRON

COINCIDENCE COUNTING

y

= aX + b general equation

X

i =

t>’i'bVa

x =

Ix

i

= (Z/i

- nb)/a

From calibration data:

a. - slope

b - intercept

cr 2 - slope variance

- intercept variance

cov (a,b) - covariance be

tween slope and intercept

y^

- net corrected coincidence counts of sample i.

- calculated g?u 240 eq. cf sample i.

X

2

a

2 (Zy - nb) a

2 2 Cov (Ey - nb, a)

+ • JL

(Ey - nb) 2 a

2 (Ey - nb) (a)

a? + n

2 o

2 a

2 2[cov(Ey, a) - n cov (b,a)]

EL_ + JL - - (Ey - nb) 2 a

: (Ey - nb) (a)

Ey - nb\

2 a

2 + n

2 o? a2 2n cov (a,b)

Ey b

+ _a ^ J

(Ey - nb) 2 a

2 (Ey - nb) (a)

If there was one calibration curve for the waste (measured discards) and J calibration periods for the scrap the limit of error

expressions would be:

hE (waste) =

LE (scrap) =

(waste)

?

- 22 -

associated with the plutonium concentration determination

for the standards.

From the counting data collected on the known standards

a calibration curve was fitted by using the least squares

technique. The y axis, or ordinate, represented the coincidence counts for a fixed time corrected for accidental

counts, dead time losses and background counts. The x axis,

or abscissa, represented the grams of plutonium 240 equivalent

in the standards. The weighting of calibration data had

no significant effect on the resulting calibration parameters.

From the least squares fit of the standards data the slope,

intercept, standard deviations of the slope and intercept,

and the covariance between the slope and intercept were

obtained. The standard deviation of the slope and intercept

represented the uncertainty associated with the standards

provided that all the standards did not come from the same

master blend. When the scrap and discarded materials were

coincidence counted, the count, Ey^, was obtained with

information for the counting variance. The following figure

shows the pertinent expressions used to obtain the grams of

plutonium 240 equivalent, X, and the associated variance,

o x* Note that the summation of the individual gPu 240

equivalent values, X^, takes place before the error propagation is applied. If this procedure is carried out in

reverse order, the covariance effects among the individual

counts would have to be accounted for. The X^ values for all

- 23 -

of the material counted within a given calibration period

were related through the use of the same calibration

parameters. In other words, the variances associated

with the individul values are not independent

and cannot be summed to obtain the variance on the total,

2 o x

. On the other hand, variances from different periods

based on independent calibrations can be summed together

in the usual manner since they are not related. The procedure followed in the ISE is shown at the bottom of Figure 1.

A point that should be emphasized concerns the gPu 240

equivalent of the standards. If the standards used to generate

a calibration curve all came from the same isotopic lot and

master blend, the abscissa may be biased. This systematic

error would not show up in the standard deviation of the

intercept and slope values. It would then be necessary to

account for this systematic error separately.

Because the neutron equipment was not stable over the

three month period that the Campaign 1 waste and scrap material

was counted it was not possible to use just one calibration

curve. A study of the scrap standards calibration data showed

that the system drifted upward in a quasi step function fashion

resulting in four calibration periods for the three month

time interval. A weighted regression analysis (linear least

squares fit) was performed on scrap standards data for each

of the four periods. Coincidence counting statistics were

used as weights. Data analysis on the very weak waste

- 24 -
'

.
standards did not show any statistically significant trend.

Therefore all neutron coincidence measurements on waste

standards were used in one weighted regression.

- 25 -

Discussion on Campaign 2

Much of the above discussion on Campaign 1 applies to

Campaign 2. The counting times were the same - 10 min.

independent of whether the material was low level waste or

recoverable scrap. Some of the standards used for calibration purposes were the same ones used for calibration during

the measurement of Campaign 1 materials. In addition,

three other standards utilizing 80 percent fissile

plutonium were incorporated into the calibration curves.

The problem of neutron counting equipment instability

was present during the measurement of Campaign 2 waste

and scrap. Therefore, there were several calibration curves

and sets of parameters. The waste standards data and scrap

standards data were not regressed separately by GE-VNC

personnel within a given stable period as was done by NBS

personnel in Campaign 1. This made the calculations within

a given period simplier but caused complications when computing the LEMUF value because the waste and scrap values

were not independent.

The problem of counting scrap packages which contained

more plutonium than the standards was also present in

Campaign 2.

For Campaign 2 regressions, weighting was done by GE-VNC

on a mass-of-standard basis. An examination of the scrap

standards data for a given period showed that the resulting

intercept and slope values from least squares fits were

-26-

statistically the same when weighting was done by mass as

when done by coincidence counting statistics.

Summary on Scrap and Waste

1. Campaign 2 measurement results were not expected

to show improvement over those of Campaign 1 since

the data collecting and data reducing procedures

were the same for both campaigns.

2. On a percentage basis the scrap and waste uncertainties were larger for Campaign 2 because the

plutonium in the standards came from different

lots than was the plutonium used in Campaign 2.

This created the situation where the impact

of the isotopic abundance uncertainties as well

as the spontaneous fission ratios uncertainties

had to be evaluated and included in the limit of

error calculations.

- 27 -
.

- i
SUMMARY

Feed Material - PuC>2 The moisture problem which affected the plutonium

dioxide of Campaign 1 was eliminated in Campaign 2 by

equilibrating before sampling; this procedure permitted

a meaningful chemical assay value to be obtained.

More effort on Pu 238 and Am 241 abundance determinations is needed if calorimetry is to do the job that this

nondestructive technique is capable of performing for

materials balance accounting.

Product Material - Sintered Mixed Oxide

The product % LE value, obtained from chemical assay,

was the same for both campaigns, even though more blend

preparation work was performed on Campaign 2 material.

There was a factor of approximately two between

the % LE values of the two enrichments within each of the

campaigns

The variation in the % LE or %CV values between

enrichments implies that this non-consistent process

behavior will render nested design results useless for

purposes of error propagation in material balance accounting,

thus necessitating the requirement to obtain sufficient data

for determining limits of error for each job.

Scrap and Measured Discards

The neutron coincidence counting procedure for measuring

Campaign 2 materials was the same as that for Campaign 1.

- 28 -
!j 1 1 I

iif,

|

«
The percent uncertainty on a given scrap item was

higher in Campaign 2 because of the additional uncertainty

due to the isotopic abundance and spontaneous fission ratio

considerations. This additional complex uncertainty existed

because the plutonium in the standards came from different

lots than that used in Campaign 2.

Overall Balance

Campaign 2 was more successful on the whole than was

Campaign 1, mainly as a result of the improved quantification

of the feed material. The MUF and LEMUF values for Campaign 2

were in the 10 grams plutonium range as compared to a factor

of 10+ larger for Campaign 1.

- 29 -

REFERENCES

1. Smith, C. N., "Limit of Error Calculations Used in

Safeguards Experiment," Institute of Nuclear Materials

Management, June, 1971, Proceedings of Twelfth Annual

Meeting. NBS Report 10491.

2. Ku, H. H. , "Precision Measurement and Calibration - Statistical Concepts and Procedures, "NBS Special

Publication 300, Volume 1, February, 1969.

3. Natrella, M. G., "Experimental Statistics, "NBS Handbook

91, August, 1963.

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