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LEGAL NOTICE

Thisreportwas preparedas an accountofGovernment sponsoredwork. NeithertheUnitedStates,northe

Commission,noranypersonactingon behalfoftheCommission:

A. Makesanywarrantyorrepresentation, expressed

or implied,withrespectotheaccuracy,completeness,or

usefulnessoftheinformationcontainedinthisreport,or

thattheuseofanyinformation, apparatus,method,or process disclosedinthisreportmay notinfringeprivately

ownedrights;or

B. Assumes any liabilities withrespecttotheuse

of,or fordamagesresultingfrom theuseofanyinformation,apparatus,method,or processdisclosedinthisreport.

I

.1 I

.

As usedintheabove,“personactingonbehalfof the

Commission”includesany employeeor contractorofthe

Commission,oremployeeofsuchcontractor,totheextent

thatsuch employeeor contractoroftheCommission,or

employeeof such contractorprepares,disseminates,or

providesaccessto,any informationpursuantto hisemploymentorcontractwiththeCommission,orhisemployment withsuchcontractor.

-.

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LAMS-2441

REACTORS--POWER

TID-4500(15thEd.)

LOS ALAMOS SCIENTIFIC LABORATORY

OF THE UNIVERSITYOF CALIFORNIA LOS ALAMOS NEW MEXICO

REPORT WRITTEN: June27,1960

REPORT DISTRIBUTED:September13,1960

LARGE SCALE PREPARATION OF HIGH PURITY

PLUTONIUM METAL BY ELECTROREFINING

(PreliminaryReport)

by

L. J. Mullins

J.A. Leary

C. W. Bjorklund

—

ContractW-’74O5-ENG.36 withtheU. S.AtomicEnergyCommission

All LAMS reports are informal documents, usually prepared for a specfal purpose and prlmsrfly prepared for use wfthfn the Laboratory rather than for

general distribution. This report has not been edfted, reviewed, or veriffed

for accuracy. All LAMS reports express the views of the authors as of the

time they were written and do net necessarily reflect the opinfons of the Los

Alamos Scientific. Laboratory or the final opinion of the authors on the subject.

1
7-

ABSTRACT

Plutonium metal produced by the bomb reduction method has been

electrorefined successftillyon the 100 - 300 g. scale. The purified

product was collected continuously from the cathode as a liquid metal

of greater than 99.98 percent purity- In addition, plutonium - 10

atomic percent (2.sl+weight percent) iron alloy also has been electrorefined to produce a product containing less than 0.02 weiEht percent

iron. The results indicate that plutonium of exceptionally hi~h purity

could be produced by using the proper materials of construction for the

elecixrorefiningcell. A tungsten cathode has been sho~.mto be superior

to tantalum. Using a tungsten cathode, the major metallic impurity

detected in elec+aorefined product was 28 parts aluminum per million

parts plutonium, when alumina was used as the ceramic cell construction

material.

Collecting the product as a liquid at the cathode provides a means

for operating the electrorefining cell continuously. A continuous cell

design to be used in future experiments also is discussed.
TABLE OF CONTENTS

,

Abstract. . .

Introduction.

Experimental.

Discussion of

References. .

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LIST OF FIGURES

Batch Electrorefining Cell. . . . . . . . . . . . . “.

Tentative Continuous Electrorefining Cell . . . . . .

LIST OF TABLES

Summary of Experimental — Conditions for

refining Experiments.

Analyses of Plutonium

Analyses of Plutonium

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Plutonium Electro-

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INTRODUCTION ‘

‘ The electrochemical preparation of plutonium

ported in 191!Lby Kolodney of this Laboratory.(1)

amounts of

the method

success of

metal were produced by electrolysis of

metal was first reA1.thou@ milligram

plutonium(III) chloride,

was never applied to large scale operation because of the

the bomb reduction method.(2) At the present time essentially

all plutonium metal is produced by this latter metlnod.

As distinguished from electrolysis of plutonium salts, electrorefining of metal that has been produced by bomb reduction has the

following important applications:

a.

b.

c.

Production of high-purity @utonium metal for (1) metallurgical

B_kudies,and (2) a primary plutonium analytical standard.

To provide a pyrometallurgical method for reprocessing

plutonium reactor fuel.

To provide a pyrometallurgical method for recovering plutonium

from alloys (and possibly compounds) generated as scrap from

various research programs. At the present time this type of

scrap is dissolved and converted to metal by rather expensive

methods.

Because of the electropositive natuxe of plutonium, electrorefining has been limited to molten salt electrolytes. Excellent purification of plutonium-iron alloy that contained macro amounts of typical

fission product elements has been reported.(3)

elements during electrorefining was predictable

JL

The behavior of impurity

from thermodynamic
. .

-.

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✎

considerations. The sma12.scale preparation of very pure plutonium

metal also has been reported recently.(4)

In this ayplication$ solid

plutonium was collected from a fused salt electrolyte on a tantalum

cathode. A massive rod of plutonium served as the anode. After a

suitable amount of cathode deposit had formed, the cathode was withdrawn from the cell and the deposited plutonium was collected by

melting in a different nmlten salt container.

In general it canbe assum?d that collection of solid plutoniumat

the cathode wild.result in a product that is more pure than if liquid

plutonium is collected. This is because the liquid product wi~ react

with the ce~ materials to a much greater extent. However, there are

several practical advantages to collecting the product as a liquid.

For example, the product can be cast directly into the desired shape

in the electrorefining cell. Moreover> a liquid cathode deposit can

be adapted to continuous celILoperation more easily than a solid deposit.

The advantages of continuous operation are obvious when cell set-up time

and criticality limitations on batch size are considered.

The experiments discussed in this report were directed toward

demonstrating the following:

a. The purification of plutonlum-iron a~oy and collection of

plutonium in a molten state.

b. The preparation and collection of molten plutoniumof 99.98

percent purity, using production grade metal as the anode.
.

.-

--

?

The procedure

bei~ able to

retision.

and cell design were selected from the viewpoint of

convert to a continuous

These experiments indicated that

process with a minimum of

plutonium metal of greater than

99.98 percent

collected (or

alloy is used

purity can be produced on the hundred gram scale-and

cast) as a coalesced product even when plutonium-iron

as the starting metal.

EXPERIMENTAL

Preparation of Electrol@e: A chloride electrolyte consisting of 10

weight percent plutonium(III) chloride, 50.4 weight percent _potassium

chloride and 39.6 weight percent sodium chloride was used in all the

experiments. A sodium chloride-potassium chloride cylinder was prepared by melting and casting equimolar mounts of A.R.

under vacuum. Plutonium(III) chloride was preparedby

propylene reaction(5) followed by vacuum distillation.

grade materials

the hexachloro12reparation of Anode Feeds: The plutonium metal was prepared by the bonib

reduction of plutonium fluoride.(a) The metal was then vacuum cast

into a cylindrical shape. In the case of the plutonium-iron alloy the

plutonium was alloyed with iron prior to casting.(6)

Procedure: The electrorefining equipment is shown schematically in

Fig. 1. The cell consisted of an outside compartment (2-5/8 in. O.D.

by 4 in. high) which contained the molten salt electrolyte and a concen.

tric inner anode compartment (1-1/2 in. O.D. by 1-3/4 in. high). Both

compartments were made of higlil-yvitrified alumina} and were cementd

6
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together. A 2-1/2 in. O.D. by 2 in. long by 0.010 in. metal tube was

immersed in the electrolyte above the anode compartment to act as the

cathode. A tantalum stirrer served as the conductor to the impure

plutonium in the anode compartment and provided agitation to the molten

plutonium and to the electrolyte. The entire assembly was contained in

a 3 in. O.D. stainless steel tube mounted in a commercial tube furnace.

During operation, plutonium was oxidized at the anode, entered the

molten salt electrolyte, and was reduced back to metal at the cathode

surface. Because the cell was operated above the melting point of

plutonium, the dense cathode deposit drained continuously down into the

annular space around the inner anode compartment during operation.

Prior to each experiment-the cell was outgassed at 700°C for 2 hr.

under vacuum. The general procedure for an experiment consisted of

loading the plutonium anode, the sodium chloride-potassium chloride

cylinder and the plutonium(III) chloride into the electrorefining cell,

heating the mixture to slightly above the melting point of plutonium(III)

chloride (767°C) and electrolyzing the mixture at a potential of 2 volts

at 700°C in a helium atmosphere. The molten anode and salt were stirred

continuously. At the conclusion of the electrorefining period} the

contents of the cell were permitted to freeze after withdrawing the anode

stirrer from the melt. The cell was broken apart and the plutonium

product was recovered as an annular metal casting. This casting was

sampled by cutting wedges from the ring~ The samples were pickled in

water and nitric acid prior to analysis. Samples for iron determinations

7
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=.

.

were

cell

were

also pickled in hydrochloric acid. Although the electrorefining

was operated under a dry helium atmosphere, all salts and metals

handled at room temperature in the glove box filled with room air

while loading and unloading the cell. The results indicate that an

inert atmosphere within the glove box is not necessary, even when the

experiments were conducted on humid days, provided that exposure of

matertals to the moist air was not excessive.

The conditions for each experiment are summarized in Table 1. All

runs were made in alumina cells containing 0.1 percent magnesia by

weight. In Run IVj the helium was purified by passing the gas through

a Drierite tower and a uranium chip furnace at 6000C. In Runs 1, II

and III the chip furnace was not used. Tantalum cathodes were used in

Runs I and II and tungsten cathodes were

Analyses of the anode feed material

given in Tables 2 and 3. Iron, tungstenj

used in Runs III and IV.

and the plutonium products are

and tantalum were determined

calorimetrically”, carbon and oxygen were determined by combustion

snalysis. All remaining elements were done spectrochemically. The

wide variations in tantalum analyses on duplicate samples necessitates

the recording of both values in Table 3. These variations are caused

by segregation of tantalum metal upon cooling and freezing of the

casting.

It is apparent from

DISCUSSION OF RESULTS

the results of Run IV that plutonium metal of

excellent purity can be produced from bomb reduction metal by this

electrorefining procedure. A comparison of the plutonium produced using

8
II

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9
Table 2

ANALYSES OF PLUTONIUM FEED MATERIAL

-.

Element

Li

Be

Na

Mg

Ca

Al

La

Si

Pb

Cu

Ni

Cr

B

Yin

Sn

Bi

co

Zn

f%

Fe

w

Ta

c

o~

Concentration of Element} parts per million

Run I

parts plutonium

Run II Runs III, IV

< O*2 < 0.2 < 0.2

< 0.2 < 0.2 < 0.2

< 10 < 10 < 10

30 15 80

< 5 20 25

20 90 25

< 10 < 10 < 10

< 100 20 35

< 20 <1 <1

20 7 2

< 100 50 35

< 100 10 10

< 10 < 0.5 < 0.5

< 20 15 5

< 20 <1 <1

< 20 <1 <1

< 5 <5 <5

<200 10 < 10

-- -- <1

2.54 X 104 60 80

-- -- < 20

< 50 280;490 < 50

80 140

90 135

10
.

Table 3

ANALYSES OF PLUTONIUM PRODUCTS

,.

=.

.

Li

Be

Na

%

Ca

Al

La

Si

I%

Cu

l!li

Cr

B

Mn

Sn

Bi

co

Zn

Ag

Fe

w

Ta

c

o=

*High

(see

Concentration of Elementj parts per million parts plutonium

Run I Run II Run III Run IV

c 0.2 < 0.2 < 0..2 < 0.2

< 0.2 < 0.2 < 0.2 < 0.2

< 10 < 10 < 10 < 10

30 ~5 <5 <5

<5 <5 10 15

35 20 250 28

< 10 < 10 < 10 < 10

< 10 < 10 < 10 < 10

<1 <1 <1 <2

1 <1 2 <2

< 10 < 10 < 10 < 10

< 10 <5 5 <5

.- -. <1 --

178 20 40 < 20

-- .- <20 I-2

270 600; 220 275; 400* < 35

60 35 -- 32

-- 25 -- 25

tantalum concentration was caused by tantalum th,ermowellfailure

Discussion of Results)

u.
. .

*.

.

a tungsten cathode (Runs 111> IV) with that produced using a tantalum

cathode (Runs 1, II) shows that tungsten is a superior cathode material.

The only detectable imparities in

Ca, 28 ppmAl, E ppmli, 32 ppm c

of tantalum in Run III was caused

sheath which resulted in the loss

the product from Run IV were 15 ppm

and 25 ppm 02. The high

by failure of a tantalum

of the end of the sheath

concentration

thermocouple

and the leakage

of air into the cell. Potentiometric determinations of the plutonium

concentration of the product from Runs I> 11> III dnd IV Gave results of

99.98, 100.02, 100.00 and 100.02 percent} respectively. It is interesting to note that remelting of the product from Run II in an alumina

crucible and holding the melt at 8000C for 2 hr. resulted in an increase

in aluminum contamination from 20 to 150 ppmo In an effort to reduce

the aluminum contamination in the product, calcia coated alumina

crucibles will be tested in future experiments. The greater thermodynamicstability of calcia should make it a superior container material

for plutonium metal.

Batch electrorefining will produce superior metal more economically

than the method now used to meet pure metal requirements. However,

present and forecast requirements indicate that sufficient high purity

plutonium will be required to justify development of continuous

operation. Therefore, the effort

to developing a continuous method

metal.

on this project is now being devoted

for electrorefining bonibreduction

1.2
.

The continuous ce~ design is shown schematically in Fig. 2. It

is essentially the same as the batch cell, except that the molten

plutonium product will be removed continuously by overflowing in the

center bottom of the cell. This lower portion of the cell also is

tapered to minimize liquid metal residence time and holdup. Impure

plutonium canbe added periodically to the anode through an inert

atmosphere air lock in the top of the ce~ lid.

Electrorefining of the @utonium iron alloy, Run 12 reduced the

iron concentration from 2.5h weight

Therefore plutonium-rich iron alloy

percent to 0.018 weight percent.

scrap probably can be recovered

direct~ by electrorefining. No additional experiments on the electrorefinin& of irradiated plutonium reactor fuels have been conducted.

Previous experiments(3) have indicated that vezy good purification can

be achie’~edif large scale ce13.operation is successful. Cel& designed

to electrorefine bomb reduction metal should also be applicable to reprocessing plutonium alloy scrap and irradiated fuel.

ACKNOWLEDGI!MENTS

The authors sre indebted to CMB-1 for conducting analytical work,

to CM%6 for fabricating the alumina crucible and to W. J. Maraman,

$-.

*

CM!3-11for frequent consultation and advice on this project.

13
-*

.1

. .

1. Kolodney, M.) “Woduction of Plutonium by Electrolysis)” Ias Alams

Scientific Laboratory Report M-148 (1944).

2. Baker, R. D., “Preparation of Plutonium Metal by the Bomb Methodj”

ks Alamos Scientific Laboratory Report LA-473 (1946).

3. Leary, J. A., ~ al., Second International Conference on Peaceful

Uses of Atomic Ene~~j Geneva (1958), ~ P/529, pp. 376-82.

4. Blumenthal; B., Brods@, M., “The Preparation of High Purity

Plutonium,” Conference International sur la Metallurgic du

Plutonium, Grenoble (1~60).

5* Christensen, E. L.} Mullins, L. J., “Preparation of An.hydrous

Plutonium Trichloride)” Los Alamos Scientific Laboratory Report

LA-I-431(1952).

6. Morgan, A. N., “The Preparation of Plutonium Alloys in the

Reduction process)” Ios Alamos Scientific Laboratory Report

LA-2231, (WC. 1957).

.
.

.

.
,. . r

To STIRRER AND ANODE LEAD

,Ta TUBE FOR INTRODUCING Pu ( CAN BE RAISED OR LOWERED) / e$ “ W CATHODE T—.MOLTEN SALT

—-

—-

A1203 CELL

=

Ill——. —

PLUTONIUM ANOD

E

‘ PLUTONIUM PRODUCT

k PLUTONIUM DRIP OVERFLOW TO

MULTIPLE CASTING UNITS

Fig.1 Batch Electrorefinin~ Cell.

15
4

.

la STIRRER AND ANO

II

Ta CATHODE

EN SALT

PLUTONIUM

DE

CYL

\ IMPURE PLUTONIUM ANODE

Fig. 2 Tentative Continuous Electrorefining Cell.

LEAD

,INDER

16