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PURIFICATION OF pLUTONIUM FUE&S

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LEGAL NOTICE

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LOS ALAMOS SCIENTIFICOF THE UNIVERSITY OF CALIFORNIA LOS

LAMs-2 518CHEMISTRY( TID-4500, 16th Ed. )

LABORATORYALAMOS NEW MEXICO

REPORT WIUTTEN. November 1960 .

REPORT DISTRIBUTED: May 16, 1961

.

PURIFICATIONOF PLUTONIUMFUELS

BY MERCURY PROCESSING

(Experimental Survey)

by

D. F. Bowersox and J. A, Leary

Contract W-7405-ENG. 36 with the U. S. Atomic Energy Commission

All LAMS reports are informal dcmments, usually prepared for a speoial pur-pose and prfmarily prepared for use wttldn the Laboratory rather than forgeneral dletribution. TM report baa net been edited, reviewed, or verifiedfor acouraoy. AU LAMS reports express tie views of the authora aa of thetfme they were written ad do net neceemrily reflect the oplnlone of the LoeAlamos Scientific Laboratory or the ffnal opinion of the authors on the subjeot.

— ._-_-r

.

fu3sTRAcr

The solubilities of selected fission product elements in mercury

indicate that the puril?ication of plutoniun fuels bymercuqy processing .

is chemically feasible. Such a process was e.xperimentdly carried out

on a ten gram plutonium scale with ssmples of two sinmilated fuels. If

rare earthproductswere used ss di.luentsin fuel,mercuryprocessing

resultedin satisfactorypurification.If not, a combinationwith

halideslaggingwas shownto be satisfactory.Yieldsof 80.96~of

totalplutoni.wn were obtained in these smaJJ_-scaJ.e experiments. Iron,

cobalt, cerium, lanthanum, niobium) ruthenium, zirconium} end mo~bdenmn

were sll remuved to satisfactory levels. Plutotiumwas obtained as a

xneixild.ic button by heating a mercury-plutonium solutionto 750°Cfor

two hoursin a vacuum.

AcKN~as

We are tidebtedtoW. J. Maremanfor helpfuldiscussionsand advice

on all phasesof thiswork, ad to the AnalyticalChemistryGroupunder

C. F. Metz for chemical.analyses.

2

TABLEOF CONTENTS

Psge

Abstract...,..... .

Acknowledgements.. . . . .

Introduction.. . . . . . .

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✎

Volubilityof SelectedElements

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☛

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s.

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✎

✎

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✌

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✎

in Meroury.

Purificationof PlutoniumFuel Alloys . . .

Processingof

Processingof

plutonium-iron

plutonium-ironrecrystallization.. . . . .

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a

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.

aJ.loyby recrystallization

● ✎✌✎✎☛☛ ✎☛☛

Wocessing of plutonium-cerium-cobalkalloybyrecrystall.izationo... . . . . .. O.....

Materialsof

References.

Construction. . . . . . . . ..6...

.* ****m 9.***** ● “ege”

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*

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*

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XL

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15

3

I

INTROIXK?ITON

The studyof mer~ as a liquidmetsl solventis

programbeing conductedto obtaindata relativeto the

1spentplutoniumfuels.

one phase of the

Pymprocessingof

2>3 ~Recrystallizationfrommercuryhas previouslybeen proposed

a high temperaturereprocessingmethodfor spent

a processthe fuel is dissolvedin mercuryat an

snd filtered. The rare gas fissionproductsend

productswouldbe separatedin this step. After

and filteredto removesolublefissionproducts,

uranium fuels. In such

elevatedtemperature

insolublefission

the filtrateis cooled

the residueOf urenhm

tetremercuridewouldbe deccnnposedto recoverthe uranium.

A similarprocessfor plutoniumfuelswould a~ear to be feasible

on the basis of the volubilityof plutoniumin mercuryas a functionof

temperature.4

In this studythe solubilitiesof selectedfission

productelementsin mercurywere measuredto furtherestablishsuch

feasibility.Basedon thesesoltiili~ measurements}severalprocesses

for separatingfissionproductelementstromplutoniumwere eveJ.uated

experimentally,

4

SOIJ%KIIJITY

The solubilitiesof

tantslumin mercurywere

OF SELECTEDIIrmrmls IN MERUJ’RY

iron,zirconium,niobium,molybdenumand

detezmdnedby hmersing weighedcoupons,each

approximately0.5 g., into200 ml.

measuringthe couponweight. Thus

the smountof elementdissolved.

of boiling

the weight

mercuryma periodically

losswould correspondto

The solubilitiesof ruthenium,cerium,snd lsnthanumwere determined

individuallyby the methodused for the plutonium-mercuryvolubility

4study. Awei@ed qmtity of the desiredelementwas equilibrated

with 90 ml. of redistilledmercuryin sn inertatmospherefor 24 hours

at 350°C, The mixturewas adjustedto a selectedtemperature,sna

sampleswere

hours. Each

element.5,6

Results

draw througha coarsePyrexfrit at intervslsof 5 to 90

ssmplewas cooled,weighed,and ansdyzedfor the appropriate

obtainedh theseexperimentssre summsxized in Table1.

The solubilitiesof zirconium,iron,niobium,and molybdenumat 25°C

7>8 plutonium,UUltlUUllRIl)were in agreementwith thosereportedat 25°C.

and ceriumsM. a~ar to be temperature-dependentin solubil.ity,snd

thesesolubilitiesare sXL of the samemagnitude. Althoughruthenium

apparentlydissolvedin mercuy at 350° C, it ditt not pass througha

coarsel&rexfrit at either350°Cor 30°C. Therefore,sincethe

“volubility”is consideredhere to be the quantitythat passesthrough

sucha frit in mercury,rutheniumwoulabe by definitioninsoltile.

5

Table1

THE SOllJBILITIESOF SELECTEDI!ImMmTsIN MERCURY

.

Volubility,Temperature,‘c grams solutelitermercuryElement

23? 350 <0.001

Nb 350 <0.001

Mo 350 <0.001

Fe 350 0.002

Ta

I?u

350 c 0.001

1:325

2.6520.085.7

Ru

La

20250

<0.002<0.002

20150250

2.8722.937.0

Ce 20150250

1.3119.874.5

Theseresults

maybe possibleby

indicatedthat goodpurificationof plutoniumfuel

mercuryprocessingprovidedthere are no insurmountable

difficultiesencounteredin dissolutionor in coprecipitation.App~ently

the rare earthsare sufficientlysolubleat 20°C,while the otherelements

are relativelyinsolubleat 350”C.

PURD’ICATIONOF PIUTONIUMllUELALLOYS

Thesesurveyexperimentswere conductedwith plutonium-fissium

allxly. This alloywas prepzmedby ccnneltingzirconium,niobium,

molybdenum,ruthenium,lanthanum, end ceriumin a masterfuel slloy(90

atompercentplutoniwn-10atompercentiron),folluwedby quench-casting

to preventsegregation.9 The masterslloywas representativeof the

LAMPRE-Ifuel. Typicslfissionproductelementswere addedin amounts

that correspondto 10 percentburnupof the plutonium. Only six fission

productelementswere addedbecauseof limitationsin alJx@ng ad

awilysesfor the otherfissionproducts. However,the elementsthat

were added,togetherwith easilyremovablevolatilefissionproducts,

representthe majorityof the impuritiesthatwill.be presentin

irradiatedliquidfuel.

Threeprocessingmethodswere tried. Althoughvolubilitydata

obtainedwith individualelementshad indicatedthat goodpurification

couldbe achievedby simplerecrystallization,experimentswith fissium

alloyshowedthat rareearthelementscoprecipitatedwith plutonium.

Thereforea secondmethodusingha3ideslaggingconibinedwith recrystaU.i-

zationfrommercurywas evaluated. The thirdmethodwas used to process

plutonium-cerium-cobeltslloy,sincethis liqtidmetd.has been propose?.

as a fuelfor futuremoltenplutoniwnreactors.

Processingof Plutonium-IronAlloyby Recrystallization

The flowsheetfor theseexperimentsis sham in Fig. 1. A 10 g.

rod of fissiumalloywas contactedwithmercuryat >25°C for 7 hours in

7

Pu-Fe Alloy Fuel

*

Hg DissolutionStorage P

325°C ● Volatile Fission ProductsL

W“’’’i’Loss)

●I

RecrystallizePuHgx at 25°C

FiltrateSoluble

Filter at 25°C b FissionProducts

+ Pu Lossr

Solid Phase(PuHgx Product)

To Puand Hg (_Recycled

Recovery Hg)

Condense Vacuum DecompositionHg and 4 750°C at 30 ~Recycle Pressure

●Purified Pu

Product

To Reactor

Fig. 1, Flowsheetfor processingrecrystallization.

of plutonium-iron

8

SJ.loyfuelby

a ~ex vessel filled with argon. Afterdissolutionof the plutonium,

the mercurysolutionwas passedthrougha coarsePyrexfilterdisk at

325°Cto removeelementsthatwere not solublein hot mercury. The

filtratewas then cooledto 25°C

intennetdld.icccmpound(probably

coarsefritteddisk. This solid

to recrystallizea plutonitzn+nercwy

Pu&), thenfilteredagainthrougha

phasewas heatedin vacuumto *750°c

in orderto recuverthe metalproductas a coa3escedingot.

Analysesof the fissiumslloyand finalprciluct=e shownin Tdble

2. Calculationsbased on individualsolubilitiesshownin Table1 had

indicatedthat sll impuritiesin the plu%onitnn should basre been below

the limits of detectability, i.e., < 0.01 percent. A comparisonof the

lanthsnumand ceriumimpuritiesactuallypresentin the plutoniumproduct

with predictedvaluesindicatesthat a lage fractionof the ram earth

fissionproductswill coprecipitatewith pltioniumin the recrystsX1.ization

step. ‘lhe.refarea simpledissolutionrecrystallizationprocessis

inadequatefor a high degreeof purificationfrom rare esrths. Plutonium

yieldsvariedfrom 80-967$of the totalPu present. Higheryields shmihl

be attainablein

Element

Pu

Fe

Zr

ml

lb

Ru

La

Ce

lsrgerscd.eprocessing.

Table 2

FURD?ICATION OF P.WKMUM-IRON FISSIUMALU3Y BYREXRYSMLLIZATION FRcM MERCURY

Concentration of’ Element, v/oNssium A.llo~ Final Product

91.3 98,32.37 O.oa0.6? 0.019O.oh N.D.

0,75 0.00+390.97 N.D,

1,59 1.060.74 0.53

, 9

Processingof l?lutonium-Iron Alloy by sls&ging and RecqystsJ.lization

Removalof rare earthelementsfrommoltenplutoniumalloyby

halideslsggingat 6000C has been demonstratedpreviously.10Therefore,

a slaggingstepwas incorporatedintothe dissolutionstep of the flow-

sheetshownin Fig. 1 in cm attemptto convertthe rare earthsti the

mercuxysolutionto insohiblerare earthchlorides. Althougha solid

reactiveslagcouldbe used;previousexperiencehad indicatedthat a

liquidslagphasewas preferdble. The slag selectedwas the 70 wt. per-

centrUbidiumchloride-30wt. percentlithiumchloride(soliduspoint

310°C) as the unreactivesolventsystem.

The reactiveslagcomponent,ferrouschlofide,was added to the slag

phase to a concentration of 110 percentof that calculatedto oxidizeall

rare earthelementspresent. This excessis equivalentto <0.7 w/o of

the plutoniumpresent. Rare earthswere removedfromthe mercmy

solutionaccordingto the reaction

-1- 3FeC~ ~ Z?L&& -1- ye

(in Hg sol’n) (in RbC1-KClsol’n) (in RbC1-KClsol’n) (solid)

The flowsheetof Fig. 1 was furthermodifiedby conductingthe high

temperaturefiltrationat 300”C to freezethe slag and preventit frcm

passingthroughthe filterwith the plutonium-mercurysolution.

Resultsof the coxibinedslagging-recrystallizationmethodsare

shuwnin Table3. The decontaminationfactor(D.F.)is deftied as the

weightof an impurity,per grsm of plutonimn,in the fissiumalloy

10

Element

Pu

Fe

Zr

Mo

Ru

La

Ce

Table3

PURIFICATIONOF PIZJTONIUM-IRONFISSIUMALLOYBYCOMBINEDSIAGGING-RECRYSTAIJJIZATIONPROCESS

(38 g, salt phase,9.3 g. f’issium alloy, 100 ml. IQ)

Concentrationof Element,w/oFissiumAlloy PlutoniumProduct D. l?.

91.3 99.?

2.54 N.D. > 25M

0.77 N.D. > 770

0.89 0.008 120

1,30 N.D. > 1300

2.13 0.11. 21

1.02 0.08 14

dividedby the weightof the impurityper grsm of plutoniumin the

finalproduct. Theseresultsindicatethat adeqpateremovalof fission

product elements, including mz’q esz%hs, can be achieved by this combined

slagging-rec~stalli zation procedure.

Processingof Plutonium-Cerium-CobaltAlloyby Recrystallization

The plutonium-cerivm-cobsltternarysystemhas been proposedfor

liquid-fueledpowerreactors.U. In this systemthe compositionof

cobaltcan be fixedat approximatelyU-25 atcmpercent,whilethe

concentrationof plutoniumcan be variedover a wide rangewithout

seriouslyalteringthe soliduspoint of the system.

IL

Thus ceriumis present in this type of fuel

eX1.eying constituent. For a power reactor fuel,

probably will exceed the plutonium concentration

in gross emountsas an

the ceriumconcentration

(on an atombasis).

Rnploying a slagging stepin the fuel reprocessingcycleprobablywoul.d

be undesirable,owingto the factthat essentiallyall of this cerium

wouldbe extractedintothe slagphase. However,it seemslikelythat

removal.of soluble rare eez%hfissionproductsis not necessq for such

fuels. Becausetheiratomicfractionswill be low in comparisonto the

ceriumalreadypresent,they shouldnot

pointof the moltenfuel. Moreover,in

application,substitutionof rare earth

seriously increase the liquidus

the proposed fast reactor

fission product atcms for

ceriumin the moltenfuelwilJ not seriouslyalterthe neutroneconmqy

or energydistribution.

EinsX1.scaleexperimentswere conductedwith83 a/o plutonium-12a/o

cobslt-5a/o ceriumto determine

dissolutionand filtration.The

of plutoniumwith 3.53 g. cerium

crucible. This bi.ruzry all-oy was

the behaviorof the fuel during

aUoywas preparedly cmelting 100 g.

at 900°Cfor 30 tiutes in a tantalmn

then cooled,3.60 g. cobaltwere sdded,

and the systemheatedto 8000Cfor 15 minutes. A soliduspoint of -4200C

was observedby

1/8 in. andl/4

4 g. segmentof

325”C,followed

decomposition

thermalanalysis. The slloy was remeltedand cast into

in. diameterrodsby injectioninto quartztutes. A

theserodswas then dissolvedin 50 ml. of mercuryat

by filtrationandvacuumdecompositionat 900°C. This

productcontained90-95percentof the plutoniuminitially

12

addedto the dissolver.The chemicslcomposition of the finalproduct

was 96.9percentby wt. plutonium,2.9 percentcerium,and 0.2 percent

cobalt.

Experimentshave not been conductedtodeterminethe decontamination

of fissionproductelementsfromthis fuelbecausethe sclmslfuel

applicationis stillin doubt. However,the informationgainedto date

indicatesthat the simpleflowsheetshownin Fig. 2 wouldprovide

adequatepurification.

MMWKMGS OF CONSTRUCTION

~exwas usedas the containermaterialfor most of the experi-

ments in the temperaturerangeof 25-325”C. Duringvacuumdecomposition,

the mercuries were containedin eithertantalumor magnesiacrucibles

locatedwithina stainlesssteeltube. In aU. experimentssn inert

atmosphere(argonor helium)was used to preventoxidationof the

plutonium. The plutonium-cerium-cobaltsUoy dissolutionaud filtration

experimentswere conductedin Type 304 stainlesssteelequipment,

includingstainlesssteelfilterdisks. A“7 hour corrosiontest ind-

icated no weightlossby 5-g.couponsof Type 304 stainlesssteeland

tantslumtiterhmnersionat 3400Cin boilingmercurycontaining85 g.

plutoniumper liter,0.7 g. ceriumper liter,and 1.4 g. lanthanumper

liter. This correspondsto a corrosionrate of less than 0.010 in. per

yeax for the stainlesssteeland less than 0.005in. per year for

tantalum.

13

Fuel

vHg Dissolution

Storage -b 325°C ~ Volatile Fission Products

4

Filtration Insoluble Fission325°C Products Plus Pu Loss

HgVacuum

Condensation4 Decomposition

850°C, 30 p

Purified Pu-Ce Alloy

+To Reactor

Fig. 2. Flowsheetfor processingplutonhn-cerium-cobaltfuel.

14

REFERENCES

1. Leary,J. A., et sl., P/529USA, SecondU.N. GenevaConference,1959.

2. Dean,o. c.,Reprocessing

3. Morrison,B.

Messing,A. F., end Forsberg,H. C., “Useof MercuryinNUCl~ FUAS,” CF-60-2-3(1960).

H. snd Bknco, R. E., “TheHermexProcessfor MetalDecontamination,”C’F-56-1-151(1956).

4. Bowersox,D. F. andlkary, J. A., ~. Inorg.Nucl. Chem.} ~ 108-IJ.2)(1959)●

——

5. Smith,M. E., Los AlsmosScientificLaboratoryReportLA-1995,(1956).

6. Waterbury,G. R., privatecommum“cation.

7. Lyon,R, N. (cd.),LiquidMetalsHandbook,82-87 (1950)..—

8. Strachan,J. F., and Harris,N, L., ~. Inst.MetsJ-s,85, 17-24,(1956-7).

9. Lesly,J. A., “PyrmetallurgyExperiments on Plutonium-RichReactorFuels,”Los AlsmosScientificLaboratoryRepotiLA-2132,(1957).

10. NulMns, L. J., Lesry,J. A., andMarsman,W. J., Ind. snd~, Chem.,~, =7-230, (1960).

XL. Coffinberry,A. S,, U. S. Pat. 2901345,Plutonium-cerium-cobaltandplutonium-cerium-nickelaJJ.oys.

15