UNC LASSI FI ED

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UMCLASSI H E D

NAA-SR-1057. .

Subject Category: CHEMISTRY

L UNITED S T A T E S ATOMIC ENERGY COMMISSION

1:

THE EVAPORATION OF PLUTONIUM FROM SMALL PIECES OF URANIUM REACTOR FUEL

BY I

Daniel Cubicciotti 1 ) 2 ’

., . . . - . . . . . r . . . . . .

October 15, 1954.

North American Aviation, Inc. Downey, California . , - .

Technical I n f o r m a t i o n Service, Oak Ridgo, Tennessee

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ate ~e~lee~ified: Decesiber 12,1955.t

+ I

This report was prepared asa scientific account of Govem- ment-sponsored work. Neither the United States, nor the Com- mission, nor any person acting on behalf of the Commission makes any warranty or representation, express or implied, with respect to the accuracy, completeness, or usefulness of the in- formation contained i n this report, or that the use of any infor- mation, apparatus, method, or process disclosed in this report may not infringe privatelyowned rights. The Commission assumes no liability with respect to the use of,or from damages resulting from the use of, any information, apparatus, method, or process disclosed in this report.

This report has been reproduced d i r e c t l y f r o m the best available copy.

Issuance of this document does not consti tute authri ty f o r declassi f icat ion of c lass i f ied mater la l of the s a w or s imi lar content and title by the 88me authors.

Pr in ted in USA, Pr ice 20 cerate. Avai lab le from the Office of Technical Services, DepartmSnt of Cornmeme, Wash- '

lngton 25, D. C.

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.. . .. C. . .

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N U - SR- 1 05 7

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THE EVAPORATION OF PLUTONIUM FROM SMALL PIECES OF URANIUM REACTOR FUEL

PREPARED BY:

DANIEL CUBlCClOlTl

s P. 0. B O X 3 0 9

OCTC

CQNTRACT AT- 1 1 - 1 -GEN-8

D O W N E Y , C A L I F O R N I A

ER 15, 1954

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f

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I. 11.

IV .

' I/

/I TABLE 1,OF CONTENTS

I

Abstrac t . . . . . . Introduction. . . . . . . . Experimental 'I . . . . . / I * *

- 1 . *

*'i *

* ' I * - A. Plutonium Data . . . I / . .

Conclusions. . . . . . I/ . .

A. Materials . . . . . .I; . . . B. Gloved Boxes . . C. Method

II -11

. . . . !I Resul ts and D i s c u s s i o n .

I B. Fission Product Data . . . jj (I i/

Re fer enc e s . . . . . . . .

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Page No.

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16 16 18

ACKNOWLEDGMENT

The course of this work was expedited by severa l people to whom'the

author is grateful. Mr. R. Koontz assis ted in the development of safe handling

techniques. Mr. R. Owen took charge of the transfer and disposal of the active

material . Mr. A. Epp aided in the procurement of the spent fuel. Mrs. N.

McCarty performed the radiochemical analyses.

The cutting and breaking of the X-10 slug into usable pieces was performed

by personnel of the Operations Division of the Oak Ridge National Laboratory

to whom the author is indebted. r ABSTRACT

The ra te of evaporation of plutonium from small pieces of uranium con-

taining initially about 0. 01 per cent plutonium has been measured a t 1600" and

1680" C.

based on Raoult's Law.

as expected f rom their relative vapor pressures .

The resul ts show that the ra te of evaporation follows the equations

The evaporation of fission products w a s approximately c <

6

.

1. INTRODUCTION

The possibility of separating P u from spent U fuels by direct evaporation

In order a t high tempera tures has been the subject of some discussion.1’ 2’ 3 9

to make any intelligent estimate of the feasibility of such a process , i t is necessary to know the ra tes of the evaporation and the degree of completeness

that can be attained in practice. The present study was made t o determine the

experimental r a t e s for comparison with theoretical values using fuel that

simulated actual reac tor material .

In a previous study5 i t was found that the r a t e s of evaporation of t racer

Pu agreed with values calculated on the assumption of ideal solution behavior

at 1600’ C and above. However, at large values of the fraction of P u evaporated,

the uncertainities in the experimental values were large, and some question

has been ra i sed a s to whether or not the experimental ra te fell markedly below

the theoretical value beyond 90 per cent Pu removed. 6 The present experiments

were more accura te because of the higher concentrations of P u .

that the evaporation ra te follows the theoietical values closely to at l eas t 99 per

cent Pu removed.

They show

II. EXPERIMENTAL

The experimental method was essentially the same as that used in the 5 t r ace r study; however, the techniques were complicated by the higher levels

of P u and fission product activities used.

A. Materials

The samples used in the study were pieces o f a n X-10 fuel slug obtained

from Oak Ridge. The slug was cut into s l ices about 1/8-inch thick and then

broken into pieces of about 3 grams. The irradiation history of the slug w a s

unknown; however, i t was known to have been discharged from the reactor in

October, 1951. Plutonium analyses on several of the pieces gave the resul ts

shown in Table I.

received a total integrated flux of about 3. 8 by 1019 neutrons per cm . The average value of 94.5 p g Pu/g U indicates that the slug

2

7

TABLE I

PLUTONIUM ANALYSES OF UNTREATED SAMPLES

Micrograms P u per Gram U

95.4

92

95. 5

91.5

, 96. 8 different .analyses on same sample :r2j. Aver age : 94. 5

The radiation from 1 g ram of sample at a distance of 1 centimeter was .

found to be about 1 roentgen per hour of gamma and about 100 t imes that 'level

f rom beta..,. Because of these levels of activity i t was necessary to handle the'

samples sc that the hands were a r e least 6 inches away a t all times.

B. Gloved Boxes

All the work with the sample and undiluted solutions made from the

One contained a sample was performed in two "Berkeley" gloved boxes.

vacuum line and all the apparatus necessary to handle the sample pr ior to,

during and immediately after heating.

analysis of and dilution of the solutions made from the treated samples.

The other box was equipped for P u

These boxes were sealed and lined with plastic so that no activity could

leak out as dust o r liquid in-case of a spill.

in them by connecting the exhaust of the boxes to the main exhaust sys tem of

the building through a C W S filter. Although the interior of the boxes became

highly contaminated, periodic s m e a r s of the outsides showed no contamination.

The gloved box system, though somewhat cumbersome in use, served as a

positive control for the activity and contaminated ar t ic les , which might other-

wise have been spread about the laboratory.

A negative pressure was maintained

8

..

b

B .

P

a

Figures 1 and 2 a r e photographs of the inter iors of the boxes. The /

vacuum box was mounted on a movable dolly which housed a high vacuum pump-

ing system and gauge.

supported a sca le r for the alpha counter.

C. Method

The analytical box was mounted on a dolly which also

' In a typical run a piece of active uranium in a closed container was

delivered into the box, cleaned in nitric acid, dried with acetone and weighed.

A layer of the surface of the sample was dissolved in nitric acid for a control. The remainder was dr ied with acetone and reweighed. The sample was then

put in a CeS crucible which was placed on a tantalum plus zirconia stand and

enveloped by a silica. jacket with tantalum radiation shield liner.

was lowered into a s i l ica tes t tube which was then evacuated.

diagram of this arrangement is shown in Fig. 3.

This assembly

A schematic

After the system had been evacuated overnight to a good vacuum, the

crucible and contents were heated ' to temperature by induction heating. The

induction heating system was a 6 kilowatt Ajax-Northrup converter and coil.

The temperature was measured with a Leeds and Northrup optical pyrometer.

To co r rec t the readings of the pyrometer to t rue temperature an absorption

correction was applied for th:e windows and pr i sm through which the light passed

and an emissivity correction for the surface of the uranium measured.

emissivity of the uranium surface was assumed to be the same as that measured

in the t r a c e r result^,^ namely 0 .82 .

equivalent to an emissivity of 0 .67 .

corrected by applying an over-all emissivity correction of 0. 55.

pera tures thus calculated were probably within 30" of the t rue temperature.

The

The absorption by the window' system was Therefore, the pyrometer readings were

The tem-

When the heating period was completed, the system was allowed to cool

and then disassembled. The C%S crucible, containing the residual uranium,

was inverted in a carbon crucible and replaced in the vacuum system. The crucible was then reheated so that the uranium either melted out or a t l eas t

pulled away from the CeS facilitating i ts removal.

in dilute acetic acid to remove- any CeS and dissolved in nitric -hydrochloric

acid.

chloric acid and then etched with hydrofluoric acid; however, i t was never

The uranium was cleaned 9

The tantalum radiation shield and sil ica par t s were washed with hydro-

..

d-

d 0 c

m

.rl

3

a P) E 5 5 k 0

k

.,-I

W 0

-E Ki k

M

0

0

U

if M

.rl

6(

c

10

a 0 9

V

h

11

"0" RING GASKET

WATER-COOLED "HEAD"

- SILICA TEST TUBE

SILICA ENVELOPE

CeS CRUCIBLE

I ZrOZ PLATE

Fig . 3 . Schematic Diagram. of Evaporation Cell

12

I

1

possible to recover all the activity that had distilled.

diffused into the fused sil ica during the heating.

Presumably some of i t - 1 .

I .

The solutions made from the control, the uranium residue and the

washings of the container were then t ransferred to the analytical. gloved box.

Analyses for plutonium were made on them by a lanthanum fluoride method

with only one precipitation. A few mill i l i ters of each of the solutions were

t ransferred to clean volumetric flasks and removed f rom the glovedabox for

bench top fission product analyses.

fuel mater ia l the only fission products that could be determined by radio-

chemical analysis were Ce, total r a r e ear ths , Sr, Cs, 'Ru and Te. .The. . 7 analyses were made by the methods suggested by Coryell and Sugarman;

Because of the long cooling period'of the

911. RESULTS AND DISCUSSION' . r

A. Plutonium Data

The resu l t s of the plutonium evaporations a r e given in,-Table 11.

f i r s t five columns give the experimental conditions and the next two give the

observed distribution of the plutonium.

per cent removal based upon the per cent plutonium left in the metal;

recovery of the distillate was not sufficiently quantitative to allow comparisons

based on it.

The I

The eighth column l is ts the measured 4

The.

The data a r e shown in Fig. 4 plotted a s logarithm of fraction of plutonium

left v s the paramete c A , 1. e . , the a r e a of sample per unit weight multiplied

by the t ime of heating.

Raoult's Law and ideal kinetic theory evaporation from the surface.8 The

c rosses a r e experimental points at 1680" C and the c i rc les a r e those a t 1600" C.

a t . - W

The dotted lines were calculated on the basis of

/

Figure 4 show:j that the resul ts a t each temperature fall within a region I

of 25" spread. That is, the experimental data fall inside a band of width

equivalent to 25" centered on the f u l l l ines of Fig. 4.

in the temperature determinations were at least 25", the data may ?e said to

agree within experimental e r r o r except for the point at the lowest .per cent

plutonium.

lie at about 1585" arid 1665" C rather than 1600" and 1680" a s measured. This

Since the error-s expected

The curves drawn through the averages of the experimental points 8 .

I

13

c c

*

Corrected Temperature

"C

1.680

1680

1600

1600

1600

'Y TABLE I1

PLUTONIUM EVAPORATION UNDER VARYING CONDITIONS

Surface A r e a )f Evaporation

cm2 _ .

1.4

2.3

1.7'

" 2.1

1.1

Veight of samples

g

3.60

3. 30

3.79

5. 63

2.74

rime of Evaporation sec

8400

2460

1 4,400

9900

1800

a t W

3800

1700

6500

3700

74 0

'$0 PU Found

In Residue

1. 4

9. 1

3. 4

10

77

In Sublimate

53

36

55

7

% P u Evaporated

Measured

98. 6 -

90. 9

96.6

90

23

C alc ula ted

99

89

97

86

33

,

1.

3 Q

LL 0

3

z I- 0

a t Fig. 4. Fract ion of P u Left in Sample as a Function - W

-

1 5 -

. . _ .

discrepancy is minor.

per cent plutonium evaporated taken from the solid lines of Fig. 4.

In the ninth column of Table I1 a r e l isted values of thei

The.agreement, then, of the measured values with those calculated f rom

Raoult's Law indicates that the ra te of evaporation may justifiably be calculated

as proposed in Ref. 8. minations a t 1500" C did not follow the expected curves.

evaporations below 1600" C it is not possible to assume the Raoult's Law ra te

without fur ther justification; however, the ra te pf evaporation below 1600" C

is so low that such temperatures will probably not be of commercial interest.

It should be noted he re that in the t r a c e r study,deter-

Therefore, for

B. Fission Product Data

The pe r cent f ission products remaining in the residual uranium after the

distillations a r e given in Table 111. significance only because of possible c r o s s contamination of activit ies during

The resul ts there a r e probably of qualitative

analysis. In general , the resul ts a r e as expected. The vapor p re s su res of

some fission products a r e given in Table IV.

would expect that cesium would show the least residual percentage tellurium,

strontium, cer ium, then the r a r e ear ths , and all of these should be l e s s than

plutonium.

e r r o r o r because the tellurium tends to form a compound with uranium.

cer ium values should be smaller than the r a r e ear ths but a r e not. The

F r o m these vapor p re s su res one

In fact, the Te values a r e too large possibly because of analytical

The

ruthenium values a r e reasonable and, in fact, should probably all be 100 per

cent.

IV, CONCLUSIONS

The ra te of evaporation of plutonium f rom uranium has been found to

follow the equation calculated f rom Raoult's, Law.

that the calculated equation is applicable to the distillation for as much as

99 p e r cent plutonium removed.

in general as expected.

The present experiments show

The evaporation of d e fission products was I

16

TABLE 111 I

FISSION PRODUCT EVAPORATION RESULTS I

. Temperature ' O C

1680

1680

1600 - '

1600

1600

-- a t -- W --

3 800

1700

6500 . 3700 74 0 --

I

70 Activity Found in Residue

77

Rare Earth:

1

S r C s Te Ru i

0.2 5 100 0.2 2 100

0.1 3 75 0.3 3 90

. *

- TABLE IV

VAPOR P.RESSURE OF SOME FISSION PRODUCT ELEMENTS AT 1680" C

Element I

C s

Te

Sr Ba

. C e

La Pr

P u t Y U

Z r

Ru

Nb 1. i

I

Vapor Pressure* Atm. -

\

90' 60

4 . F . 1

- 3 ~ 3 x 10

6 x

3 x . 1 ~ - 4

1

2

2 IO-' 10'lO

8 x

1 10-l1 I

*Data extrapolated from data of Ref. 9. t F r o m Ref. 10.

17

1.

2.

3 .

4.

5.

6.

7.

8.

9.

10.

REFERENCES

J. E. Vivian, t lPrinciples of Vacuum Distillation of Metal Mixtures, It LRL-88, March 1954,

E. L. Anderson, e t al. , "The Thermodynamics of Pyrochemical Processing, LRL-107, March 1954.

Chalk River Pro jec t (Canada), "Progress Report, October 1 -December 3 1, 1952; Chemical and Engineering Division, reports.

E. E. Motta, e t al. , "Separations Chemistry P rogres s Report July- September, 1953, !' NAA-SR-844, April 1, 1954.

E. E. Motta, e t al., "Separations Chemistry P rogres s Report October- December, 1953, NU-SR-943, June 1, 1954. D. Cubicciotti, "The Volatilization of T race r Plutonium from Molten Uranium Metal, I t NAA-SR-242, May 22, 1954. Chalk River Project (Canada), P rogres s Report, April-June, 1953, 'I

C. D. Coryell and N. Sugarman, eds . , Radiochemical Studies: The Fiss ion Products, National Nuclear Energy Series , Vol. IV-9, Book 3 (McGraw Hill Book Co., New York, 1951).

W. A. Rosser , f tTheoretical Rate of Volatization of P u f rom a Dilute Solution of P u in U Metal, I t NAA-SR-218, February 24, 1953.

L. Brewer, "Paper 3. the Elements, National Nuclear Energy Series , Vol. IV-19B (McGraw Hill Book Co. , New York, 1950).

L. Brewer et al. , "The Thermodynamic Propert ies and Equilibria at High Temperatures of the Compouqds of Plutonium, October, 10, 1947.

PR-C-E-16 and ea r l i e r PR-C-E

PR-C -E - 18.

The Thermodynamic and Physical Proper t ies of in Chemical and Metallurgy of Miscellaneous Materials,

BC-88,

18 OPO 071087

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