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_ANL-5255^

CHEMISTRY—SEPARATION PROCESSES FOR PLUTONIUM AND URANIUM

UNITED STATES A T O M I C ENERGY C O M M I S S I O N

PURIFICATION OF NUCLEAR FUELS BY MELTMG IN REFRACTORY OXn)E CRUCIBLES, l i te r im Repor t

By H. M. Feder N. R. Chellew M, Ader

Price $ &J^ Avai lable from the

Of f ice of Technical Services

Department of Commerce

Washington 25, D. C.

March 15, 1954

Argonne National Laboratory LemoEt, Elinois

Technical Information Service Extension, Oak Ridge, Tenn.

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency Thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document.

\ildh 44<.:54

ANL™5255 Chemis t ry -Separa t ion P r o c e s s e s for Plutonium and Uranium

ARGONNE NATIONAL LABORATORY P . O. Box 299

Lemont , Illinois

INTERIM REPORT PURIFICATION OF NUCLEAR FUELS BY MELTING IN

REFRACTORY OXIDE CRUCIBLES

by

H. M. F e d e r , N. R. Chellew, M. Ader

CHEMICAL ENGINEERING DIVISION

15, 1954

CLASSIFlCATiOIJ CAIICELLED

l?oi? TfjTie /-Xkomie ckiieigv Comrnission

•J ns- c, 0

iZMet, BszlQfMhcQrmn B.rgncli ^ui^r

Operated by The Universi ty of Chicago under

Contrac t W -31 -109 -eng -3 8

TABLE OF CONTENTS

Page

ABSTRACT 4

I. SUMMARY 5

II. INTRODUCTION. 5

A. Review of E a r l i e r Work. 5 B . Thermodynamic Data 7 C. P r o p e r t i e s of Refractory Oxides Suitable for

Uranium Melting 9 D. Oxidation of Liquid Uranium by Solid Oxidants . . . . . . . 14 E . Mechanisms of Impuri ty Removal 18

III. EXPERIMENTAL RESULTS 23

A. Equipment and P r o c e d u r e s . . . . . . . . . . . . . . . . . . . . 23 B . Analytical Data 29 C. Discuss ion and In t e rp r e t a t i on . . . . . . . . . . . . . . . . . . 36 D. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

IV. APPLICATION TO NUCLEAR FUEL PROCESSING. . . . . . . . . 48

V. ACKNOWLEDGEMENTS 48

INTERIM REPORT PURIFICATION OF NUCLEAR FUELS BY MELTING IN

REFRACTORY OXIDE CRUCIBLES

by

H. M. F e d e r , N. R. Chellew, M. Ader

ABSTRACT

Redis t r ibut ion of fission e lements and plutonium between m e t a l and metalloid phases occu r s during the melt ing of p i l e - i r r ad i a t ed uran ium. This r e p o r t d i s cus ses the use and p rope r t i e s of re f rac to ry oxide c ruc ib les and p r e s e n t s the exper imenta l data obtained in an investigation into this phenom­enon.

The cruc ib le m a t e r i a l s acting as solid oxidants effect cons iderable concentra t ion of ce r t a in fission e lements by incorporat ing them into an oxide slag layer . In addition, impuri ty concentrat ion is effected by crys ta l l iza t ion of u ran ium monocarb ide , -n i t r ide and -oxide solid solutions and volat i le impur i t i e s a r e los t by diffusion. Photomicrographs and x - r a y data w e r e used to c h a r a c t e r i z e and identify the slag and inclusion l a y e r s . Theore t ica l con ­s idera t ions of the thermodynamic s tabi l i t ies of oxides and of the kinetics of s lag formation a r e co r re l a t ed with observa t ions on the sur face oxidation of liquid u ran ium by the re f rac to ry oxides .

The data thus far obtained on melt ing uran ium a t 1200^0 in an hel ium a tmosphere show that : (l) plutonium, r a r e ea r th s , s t ron t ium, cesii im, t e l ­lu r ium, z i rconium and niobium a r e concentrated to varying extents in the slag layer , whe reas rutheniuin is not; (z) a l l the r ad io -e l emen t s a r e removed from the ingot in te r io r to soine extent, although this r emova l is sma l l in the ca se of plutonium, ruthenium, niobium and molybdenum; (3) the remova l of r ad io -e l emen t s is independent of the use of thor ia , u ran ia , magnes ia or alumina as c ruc ib le m a t e r i a l s ; (4) the tendency for loss by diffusion, in o r d e r of decreas ing tendency, is ces ium > s t ront ium > r a r e ea r ths > te l lu r ium, niobiiim, z i rconium, plutonium and ruthenium; (5) significant amounts of r ad io -e l emen t s diffuse into the cruc ib le m a t e r i a l s , whe reas negligible amounts diffuse to the furnace a t m o s p h e r e and wa l l s . The r emova l of f i s ­sion e lements is a lso found to be affected by in te r re la ted factors such a s t ime a t t e m p e r a t u r e , s tar t ing concentrat ion, charge s ize and ave rage min imum diffusion d is tance .

The separa t ion of oxide s lag from, u ran ium me ta l can be made c h e m ­ical ly, a s by acid etching, or physical ly, as by pouring. The application of oxide slagging as a purif icat ion p r o c e s s for r e a c t o r fuels, pa r t i cu la r ly the enriched c o r e s of fast neutron pi les such a s the proposed Power Breede r Reac to r , is cons idered .

5

I. SUMMARY

This r e p o r t p r e sen t s the r e s u l t s of a par t ia l ly completed inves t iga­tion of the phenomena occur r ing during the melt ing of i r r ad i a t ed urani iun in r e f rac to ry oxide c ruc ib l e s . It is shown that under favorable c i r cums tances ce r t a in f ission product e lements a r e separa ted to a cons iderab le extent. Some of the separa t ions achieved have been cor re la ted by theore t ica l con ­s ide ra t ions .

Application of this p r o c e s s to r eac to r technology is cons idered . Its u se in connection with the enriched c o r e of a fast neutron pi le appears to be pa r t i cu la r ly a t t r ac t ive .

II. INTRODUCTION

A. Review of E a r l i e r Work

The idea of removing f iss ion products f rom i r r ad ia t ed uran ium without converting the m e t a l f rom its meta l l i c s ta te is a l m o s t as old as the Meta l lurg ica l P r o j e c t itself. La te in 1942, the group a t Ames under Dr. Spedding invest igated the diffusion of volat i le fission e lements away from uran ium maintained at elevated t e m p e r a t u r e . 1 It was observed that cyc lo t ron-bombarded u ran ium kept mol ten a t 1800°C.for 2 hr in vacuo in a bery l l ia c ruc ib le lost the r a r e g a s e s , iodine, ba r ium and s t ron t ium quan­ti tat ively and c e r i u m to the extent of 94%. At lower t e inpe ra tu re s in graphi te c ruc ib les l e s s quanti tat ive but s t i l l cons iderab le r emova l s w e r e obtained. In the course of these la t te r expe r imen t s , moreove r , a ve ry significant d i s ­covery was noted, namely , that the sur face sca le formed between the meta l and graphi te on being removed by filing showed a s t rong concentra t ion of ce r t a in f ission e l emen t s . The r e s u l t s of ana lyses a r e given in Table I.

The conclusion drawn from these and s i m i l a r exper iments was that " m o s t of the fission e lements o ther than molybdenumand te l lu r ium^ and the volat i le r a r e gases and iodine w e r e concentra ted in a ve ry s m a l l volume of sca le and slag between the u ran ium and graphi te s u r f a c e s . " However, the methods t r ied removed only a s m a l l pe rcen tage of the plutonium and n e p ­tunium. P r e s u m a b l y , these invest igat ions w e r e not intensively pursued beyond this point because the p r i m a r y in t e re s t a t that t ime res ided in r e ­covery of the t r a n s u r a n i c e l emen t s .

^Spedding, F . H., Johns, I. B . et al ,^MUC-NS-3068.

Niobium and ruthenium act iv i t ies w e r e not followed.

m s e e s o « e e e e e « e e « e s e so « e e e « e e « a e e e e e e e s 9 e e » «9« 9 o e » e e » a

9 ®ee e s e e e e a e o s am a s e e e e

/ :

Table I

CONCENTRATION OF ACTIVITIES IN THE_REACTION LAYER BETWEEN THE METAL AND GRAPHITE ' "

(Da-£a f rom MUC-NS-306S)

d / m / g sca le d / m / g or ig ina l

E lement 1200''C., 1-3/4 hours 1400°C., 2 hours

14.9

14.3

2.32

0.67

12,8

6.2

15.4

0.88

Ba 3 3 8

S r 3.25

T e 5.93

Mo 0.<»0

Z r fe.l2

Ce 7.30

L a , Y , F r 13 .30

Np

By 1945 su f f i c i en t t h e r m o d y n a m i c d a t a on u r a n i u m c o m p o u n d s a t h igh t e m p e r a t u r e s w e r e a v a i l a b l e to p e r m i t B r e w e r ^ to c o n s i d e r the t h e o r e t i c a l f e a s i b i l i t y of h i g h t e m p e r a t u r e p r o c e s s e s w h i c h "would k e e p u r a n i u m in t h e s a m e s t a t e a s i t i s u s e d in t h e p i l e . " F r o m t h e r m o d y n a m i c e q u i l i b r i u m c o n s i d e r a t i o n s the fol lowing r e s u l t s w e r e r e a s o n e d to be suf­f i c i en t ly p r o b a b l e to w a r r a n t f u r t h e r i n v e s t i g a t i o n :

m 1. Maintenance of u ran ium a t a high t e m p e r a t u r e would r e ­

move the volat i le f ission products- Xe, Ba, Sr, Cs , 1, Rb, Kr, Br , Sn, Cd, and Sb.

2. The addition of carbon to the molten u ran ium would cause the r emova l of z i rcon ium and niobium and poss ibly some r a r e e a r t h s a s a light ca rb ide scum. The plutonium would r emain with the u ran ium.

3. Addition of ni t rogen would be l e s s effective than addition of carbon .

^Brewer , L . , UCRL-314

7

4. Addition of oxygen a s the gas or in the form of solid u ran ium tr ioxide would probably r emove a l l the r a r e ea r th me ta l s including y t t r i um and possibly a lso plutonium in an oxide layer , which would sepa ra t e as a floating scum or on the walls of the conta iner .

5. The use of u ran ium sulfides or hal ides would produce e s ­sent ia l ly the s a m e r e s u l t s a s u ran ium t r ioxide except that r e m o v a l of plutonium would be m o r e effective.

6. A combination of s teps would r e su l t in the separa t ion of plutonium and a l l of the major f ission products except molybdenum and ruthenium.

The speculat ions of Brewer w e r e not put to extensive e x p e r i ­menta l tes t . Considera t ion of the poss ib i l i t ies inherent in such high t e m ­p e r a t u r e p r o c e s s e s was prac t ica l ly neglected until late in 1952. The reawakened i n t e r e s t s t e m s mainly f rom a growing rea l iza t ion of the need for g r e a t e r economy in fuel r ep roces s ing methods .

The p r e s e n t r epo r t will be confined to r e su l t s obtained by oxide slag format ion. It is ve ry na tu ra l to consider oxide slagging a s one of the mos t des i r ab le a t tacks on the p rob lem. The technique of slagging off the oxide of a m o r e e lec t roposi t ive e lement - e i ther as a solid oxide d ro s s or as a mol ten s i l ica te - in o r d e r to leave behind the nobler e lement in purified form is older than meta l lu rgy as a sc ience itself. The remova l of s i l icon and manganese from i ron, of i ron f rom copper , of i ron , copper and tin from lead, of var ious impur i t i es from tin, of lead from s i lve r a r e examples of this technique as p resen t ly applied in i ts var ious forms on a technological s ca l e . Occasionally these indus t r ia l purif icat ion p r o c e s s e s a r e a lso enhanced by the s imultaneous volat i l izat ion of an undes i red element , e.g. zinc from lead, and this fea ture a lso plays a ro l e in the p r e s e n t work.

B. Thermodynamic Data

It wil l be useful to review some re levant therm.odynamic data before proceeding to a d iscuss ion of the theory of the effects encountered and the exper imenta l r e s u l t s . In Table II a r e l isted the f ree energ ies of format ion of the oxides of the chief e lements of i n t e re s t over a useful t e m ­p e r a t u r e r ange . The values a r e f rom G l a s s n e r ' s r e c e n t compilation.^ The p rec i s ion of the data is not s tated in this r e f e r ence . It m.ay va ry considerably , depending on the adequacy of the heat capaci ty data at the higher t e m p e r a t u r e s .

The v e r t i c a l o rde r in Table II is that of dec reas ing stabil i ty of the oxides a t ISOO 'K, a t e m p e r a t u r e nea r that a t which the p r e s e n t e x p e r i ­men ta l work was done. F o r e lements with m o r e than one oxide the re is l is ted the oxide cons idered mos t likely to be encountered in this work.

G l a s s n e r , A., ANL-5107

1 8

T a b l e II

F R E E E N E R G Y O F F O R M A T I O N O F OXIDES, K I L O C A L O R I E S P E R G R A M - A T O M O F O X Y G E N

-AFf^

Compound

ThOg

CaO

LagOg

B e O

CcgOa

P r z O j

MgO

AI2O3

S r O

UO2

ZrOa

LigO

B a O

PuOg

B2O3

SiO^

NbO

CO

HgO

M 0 O 2

TeO^

CS2O

RUO2

lOOO^K.

125.5

131

123.3

123.3

120.3

120

119

112

116

109

108

112

111

100

81.3

82 .5

76

47 .9

4 6 . 0

4 6 . 5

15.8

35.1

6,0

1500°K.

115.0

114

112

111.6

107

106,7

103

102

102

99

97

96.1

95

95

73

72

66

58.4

39 .3

38

4 .7

3.6

-2 .7

2 0 0 0 ° !

104.5

99 .3

100.3

99 .5

94

94.3

78.9

93

80.4

88 .5

86 .5

66,0

80

85

65,7

61

57

68 ,5

32 .3

30

- 7 . 3

-15 .7

-10

9 " I

It may be noticed that Table II contains information which pe rmi t s the se lect ion of poss ible r e f rac to ry oxides for the melt ing of u ran ium ( M . P , = 1406°K,). Thus , the re la t ive s tabi l i t ies indicate, and exper imenta l r e su l t s confirm, the poss ib le utility of thor ia , ca lc ia , bery l l i a , magnes ia , a lumina, u ran ia and z i rconia . L ikewise , the unsuitabil i ty of r e f r ac to r i e s containing la rge amounts of bora tes and s i l i ca tes is indicated by the table and confirmed by exper iment .

C. P r o p e r t i e s of Refrac tory Oxides Suitable for Uranium Melting

Whereas the suggest ion of Brewer regard ing oxide slagging was couched in t e r m s of addition of the oxygen ei ther as gas or as uran ium tr ioxide it was recognized at the outse t of this investigation that the r e ­act ion of liquid u ran ium with a r e f r ac to ry oxide container was likely to give the s a m e net r e su l t . The chemica l and technological p rope r t i e s of these refractories^'*^ and p r io r exper ience with them in u ran ium mel t ing" a r e the re fore of cons iderab le in te res t . These a r e examined in the following p a r a g r a p h s .

^ * Thor ia - This is the highest melt ing and mos t iner t of the re f rac to ry oxides . It has a low vapor p r e s s u r e and is s tab le in oxidizing a tmosphe re s and in contact with carbon up to 2200*0. It is a lso repor ted ly s table in contact with acidic and bas ic s l ags . Because of i ts high fusion point it is difficult to f i re to a dense m a s s of high pur i ty . Two pe r cent z i rconia is frequently incorporated in o rde r to aid the firing of w a r e . The porosi ty of h igh-f i red crucib les is quite low. Crucibles may be p repa red by e i ther d r y - p r e s s i n g or s l ip-cas t ing to apparent densi t ies of 9.5 - 9.7. P u r e thor ia c ruc ib les a r e ve ry suscept ib le to rup tu re from mechanica l or t h e r m a l shock because of the difficulty of s in ter ing . At the Argonne National Labora to ry , exper ience with thor ia c ruc ib les for u ran ium melt ing indicates that thei r r e u s e for a second or third me l t is attended with g r e a t difficulty because of b r eakage . It has been repor t ed that liquid u r an ium does not wet thor ia or xmdergo vis ib le reac t ion with it up to 1500°C. However, these r e p o r t s a r e based on shor t t ime contacts involving induction mel t ing. With longer contact t i m e s , as in the c u r r e n t work, definite sur face reac t ion and apparen t wetting w e r e observed . The pickup of thor ium by the mel t has not been m e a s u r e d .

Thor ia c ruc ib les a r e not commerc ia l ly avai lable but may be obtained by spec ia l a r r angemen t . Their cos t is high.

^Norton, F . H., Re f rac to r i e s , McGraw-Hi l l Book Company, 3rd . Edition, 1949, pp. 304-324

6Schwartz, M. A., Repor t on Crucibles for Melting Uranium, NEPA - 674

"^Schwartz, M, A., White, G. D. and Cur t i s , C. E , , Crucible Handbook, ORNL-1354

10

2. Calcia - Calcia has a high but at ta inable fusion point. Both the raw m a t e r i a l and the fired c ruc ib les a r e hygroscopic and m u s t be con­stantly protected f rom a i r . Above 1750°C-lime may not be heated unshielded from graphi te . Crucib les may be formed by tamping, jolting or d r y - p r e s s i n g . The las t method gives the mos t uniform, dense bodies , but these s t i l l have a 10% poros i ty . The wetting of l ime c ruc ib les by liquid u ran ium is repor ted to be a function of pa r t i c l e s i ze ; e ros ion of calc ia l iners by liquid uran ium has been frequently observed . At l600°C.the reac t ion between calc ia and u ran ium becomes rap id . Calcium, being vola t i le , is not introduced into the u ran ium.

Tamped or jolted l ime or dolomite (CaO + MgO) l iners a r e commonly used in the bomb reduct ion method of ixianufacturing biscui t u r a ­nium. Such l iners a r e not genera l ly r eused . L ime cruc ib les have also been used successful ly as molds in vacuum cas t ing .

L ime of g r ea t pur i ty may be obtained cheaply, but the re a r e no c o m m e r c i a l sou rces of fabricated c ruc ib l e s ,

3- Beryl l ia - Beryl l ia is one of the fnost s table r e f r a c t o r i e s . It may be used up to t e m p e r a t u r e s c lose to its melt ing point, 251 O^C, in oxidizing, reducing and neu t ra l a tonospheres . It i s , however^ at tacked by water vapor a t high t e m p e r a t u r e s . F i r e d beryl l ia is white , ve ry hard , and may have a poros i ty as low as 1% . The bulk density ranges f rom 2.7 to 2.9. T h e r m a l conductivity is high, and hea t - shock r e s i s t a n c e is unusually good. These p r o p e r t i e s make beryl l ia pa r t i cu la r ly sui table for induction heating. Crucibles of bery l l i a a r e made by e i ther d ry -p re s s ing or s l ip -cas t ing . Beryl l ia has been used to a s m a l l extent for melt ing u ran ium. It has been repor ted that quanti t ies of bery l l ium l a rge r than allowable in r eac to r g r a d e fuel e lements a r e picked up by the u ran ium.

Beryl l ia c ruc ib les a r e available commerc ia l ly . The heal th hazard connected with the i r handling may not be neglected, and ce r ta in specia l m e a s u r e s involving housekeeping and monitor ing a r e r equ i red ; but it should be pointed out that the common precaut ions taken in this labora tory in handling radioact ively contaminated objects wil l genera l ly a lso suffice to prevent t rouble in handling beryl l ia c r u c i b l e s . "

4. Magnesia - E lec t r i ca l ly fused magnes ia makes an excel lent r e f rac to ry for high t e m p e r a t u r e work . The vapor p r e s s u r e of magnes ia is higher than that of the previously mentioned oxides, and it may not be used in vacuum above 2000°C. The reac t ion with carbon to give magnes ium vapor and carbon monoxide p roceeds rapidly a t elevated t e m p e r a t u r e s . Magnesia is sens i t ive to any type of reducing conditions and r e q u i r e s a s t rongly ox id iz ­ing a tmosphe re above 1700*C. High pur i ty magnes ia w a r e contains 1 or 2%

'Steindler, M,, The Safe Handling of BeO Cruc ib les , Memo To F i l e , Dec. 22, 1953

11

of s i l ica which is helpful in lowering the firing t e m p e r a t u r e . Dry -p re s s ing o r s l ip-cas t ing (in absolute alcohol) methods may be used for the p repara t ion of dense , white c ruc ib l e s . With the la t ter method apparen t poros i t i e s of 0.5 to 8.5% may be expected, depending on firing t e m p e r a t u r e in the range 1990°C. to 1850°C. The high t h e r m a l expansion of magnes ia makes it r a the r sensi t ive to t h e r m a l shock, but the m a t e r i a l is mechanical ly s t rong .

High g r a d e magnes ia w a r e has been one of the pr inc ipa l c ruc ib le m a t e r i a l s used in the me ta l lu rgy of u ran ium. Surface react ion between the me l t and c ruc ib le is slow, and li t t le magnes ium is introduced because of its volat i l i ty.

A spec t rochemica l ana lys i s of r eac to r g rade u ran ium kept for 2 hr at 1200°C in the p r e s e n t equipment (see Section I I I A ) gave the r e ­sul ts indicated in Table III, p . 13.

5. Alumina - This r e f r ac to ry ( M . P . 2050®C) is ve ry widely used in mel t ing pure m e t a l s . The cheaper grades a r e clay-bonded, less r e f r ac to ry , and have poros i t i e s ranging from 35 to 50%. However, they have the advantages of usabil i ty up to iSSS^C-and of good t h e r m a l shock r e s i s t a n c e . Recrys ta l l i zed alumina of ve ry high puri ty is re la t ive ly easy to vitrify and w a r e may be formed into very hard , nonporous (0.2%), t r ans lucen t bodies with excellent mechan ica l and e l ec t r i ca l p r o p e r t i e s . Such c ruc ib les have good r e s i s t a n c e to acid and basic a t tack and a r e near ly iner t under varying furnace condit ions. Inorganic sa l t s high in a lka l ies , ha l ides , phosphates o r s i l i c ides may be fused in a lumina without apprec iab le con ­taminat ion of the me l t . Ware may be formed by d r y - p r e s s i n g , s l ip-cas t ing o r even by actual melt ing and cas t ing .

The r e s i s t a n c e of a lumina to liquid u ran ium has apparent ly not been fully invest igated. In this labora tory it has been observed that the obvious c r i t e r i a of at tack, i .e . , d iscolora t ion, su r face roughening, wetting, a r e less apparen t with alumina than with thor ia , u ran ia , magnes ia or z i rconia , Spec t rochemica l ana lys is of r e a c t o r g rade u ran ium kept for 4 h r a t 1200°C. i n t h e p r e s e n t equipment (see sect ion I I I A ) gave the r e su l t s shown in Table III, page 13.

^- Urania - Urania has only recent ly become avai lable for r e f r ac to ry c ruc ib les .9 .4 0 As such it p o s s e s s e s the evident advantage for u ran ium mel t ing of not introducing additional foreign e l emen t s . The m e l t ­ing point of u ran ia , 2875°C., is second only to that of thor ia among the r e ­f rac tory oxides . Urania w a r e may be formed by d r y - p r e s s i n g o r s l i p -cas t ing .

9corwin , R, E . , Eyer ly , G. B. , J. Am- Ce ram. Soc, 36_, 137(1953); ANL-4855

Ofiyerly, G, B , , Lamber t son , W. A,, Kraft, R, G., Corwin. R, E . , ANL-5038

12

followed by firing in a purified hydrogen a tmosphere a t 1750*C. A m o l y b -denuim. r e s i s t a n c e furnace is used in o rde r to e l iminate carbon contamination. D r y - p r e s s e d and fired urania r eaches a density about two- th i rds of theore t ica l densi ty. Its color va r i e s from ve ry dark brown to black, and its composit ion is very c lose to UO2,00" Considerable exper ience has been obtained in the use of u ran ia for the mel t ing of high puri ty uranium.^-^ The reac t ion of u ran ium with uran ia leads to the formation of uran ium monoxide. However, this r e ac t i on l^ has been observed to proceed a t a m e a s u r a b l e r a t e only above 2000*'C., and the re is no evidence that it occu r s to any apprec iab le extent at t e m p e r a t u r e s not far above the melt ing point of u ran ium.

7. Zi rconia - E lec t r i ca l ly fused z i rconia may be formed into mechanical ly s t rong ce ramic f o r m s . Because z i rconia undergoes a r e v e r s i b l e t rans i t ion at about 1000°C,with a m a r k e d volume change, the pure m a t e r i a l cannot be used alone. The addition of l ime (5 - 8%) to form a solid solution r a i s e s the t rans i t ion t e m p e r a t u r e ; the '"stabilized" m a t e r i a l r e s i s t s the effect of rapid t e m p e r a t u r e changes . Zi rconia is chemical ly s table in acid fusions and it is not readi ly reduced except by carbon a t 1500*^0,in a vacuum or at ISOO^Cin an iner t a tmosphe re . Zi rconia becomes an e l ec t r i ca l conductor above l600°C. Ware having a porosi ty of 0.7 to 5% may be formed by s l i p -cast ing.

Although the a t tack by liquid uran ium on s tabi l ized zirconia is not profound, it p roceeds to an appreciably g r e a t e r degree than with the previously l isted r e f r ac to r i e s , as might be expected from the re la t ive s t a ­bi l i t ies of the oxides . Table III, p . 13, gives the r e su l t s of spec t rochemica l ana lyses of r eac to r g rade u ran ium kept molten at approximately 1200°C for 4.5 hr in the equipment descr ibed below (see sect ion IIIA),

^- Others - Li t t le is known about the other sufficiently s table re f rac to ry oxide c ruc ib le m a t e r i a l s . Some poss ibi l i t ies include: the other alkal ine ea r th oxides , the r a r e ea r ths oxides, the spinels having the genera l formula MIIAI2O4, the z i rcona tes Mz^^ZrO^ or MF^ZTO^, and the re f rac to ry porce la ins composed of mix tu res of t h r ee oxides from the group ThOa-BeO-AljOj-MgO. The r e a d e r is r e f e r r e d to Nor ton ' s comipilation^ for further d i scuss ion . An interes t ing and rela t ively unexplored field (except in connection with u ran ium production) is the use of r e f r ac to ry oxide l iners for c ruc ib les of other m a t e r i a l s . Des i rab le combinations of chemica l and mechanica l p rope r t i e s might be m o r e readi ly achieved by this technique.

^^Blumenthal , B . , ANL-5019, ANL-5124

l^Baenz iger , N. C. and Rundle, R. E. , CC-1984

/ .J Table III

S P E C T R O C H E M I C A L ANALYSES OF URANIUM MELTED IN MAGNESIA, ALUMINA, AND ZIRCONIA CRUCIBLES

Ma te r i a l : Reac tor g rade Uranium Equipment and P r o c e d u r e : See Section IIIA, p . 23 Conditions: MgO - 2 hr at 1200*^0; flowing helium a tmosphe re , 110 c c / m i n .

AI2O3 - 4 hr a t 1200®C; flowing h e l i u m a t m o s p h e r e , 110 cc/i:nin. ZrO^ - 4 . 5 hr a t 1241 -1151°C; flowing hel ium a tmosphere ,

110 c c / m i n .

Composition of Uranium After Melting, p a r t s per mil l ion^

E lement

Ag A l A s B B e B i Ca Co C r Cu F e K L i Mg M n Mo Na Ni P P b Sb Si Sn T i Z n Z r

Magnesia Run 15

< 1 10

<10 0,4

< 0.5 < 1 < 2 0 < 5

5 3

40 <20

< 1 1 5

<20 < 2

15 < 5 0

2 < 1

30 < 5 <50 <50

- -

Alumina Run 16

< 1 40

< 1 0 < 0.1 < 0.5 < 1 <20 < 5

3 3

40 <20 < 1

I 5

<20 < 2

15 <50 < 1 < 1

40 < 5 <50 <50

- -

Zirconia Run 19B

< 1 < <

< < < <

< <

< <

< < <

< < <

5 10

0 .5 0.5 1

20 5 3 2

30 20

1 2 6

20 2 7

50 1 1

50 5

50 50

<400

Typical Remel ted Biscut Metal^

1 - 2 5 - 2 0 <10 < 0.1 < 0.2 < 1 < 2 0 < 5 1 - 5 2 . - 5

30 - 50 <10 < 1 2 - 1 0 2 - 1 0 <20 < 2 5 - 3 0 <20 1 - 2 < 2

30 - 50 < 5 <50 <20 <ioc

^The symbol (<) r e p r e s e n t s the lower l imit of detection in the samples analyzed.

"Data f rom B, Blumenthal , ANL Metal lurgy Division

CFrom The Reac tor Handbook, RH-3 , Apr i l , 1953, p . 434

14

D. Oxidation of Liquid Uran ium by Solid Oxidants

The mechan i sm and r a t e of the oxidation of meta l l i c u ran ium by a var ie ty of r eagen t s (air , dry oxygen, wate r , s t eam, e lec t rons a t an anode) have been studied a t t e m p e r a t u r e s up to 850°C. The r e su l t s a r e ins t ruct ive , but they a r e not c l ea r ly applicable to the p rob lem under study, namely , the oxidation of liquid u ran ium by solid oxidants . To dea l with the la t ter p r o b ­lem, the uranium-oxygen sy s t em at high t empe ra tu r e should f i r s t be reviewed.-^ •' 'I '*

1. Solubility of Oxygen in Uranium - The solubility of oxygen in liquid u ran ium is very low. Values of 0.046, 0.05 and 0.2 a tomic % have been repor ted^^ a t 1133X, IZZTC and 1727°C, respec t ive ly . Even these sma l l values may be higher than the t r u e solubility va lues . Analyses varying from 5 - 2 5 ppm, of oxygen (0.0075 - 0.027 atom %) have been obtained^^ on well- l iquated purified me ta l .

2. Uranium Monoxide - Uranium monoxide, a g ray m e t a l l i c -looking substance is the solid phase in equi lbr ium with oxygen-sa tura ted liquid u ran ium. Uranium monoxide may be formed by d i r ec t union of the e lements a t low p r e s s u r e s of oxygen (<10 mm) and t e m p e r a t u r e s above 800°C,^° The reac t ion ceases after the formation of a sur face layer . The reac t ion to form the monoxide from uran ium and u ran ium dioxide p roceeds a t a mieasurable r a t e only above 2000°C. Even at 2400^0 this reac t ion is far from complete , and the pure substance has not yet been obtained in bulk. Ordinary , i .e . , not highly purified, u r an ium contains carbon, oxygen and ni t rogen in excess of their solubility jus t above the melting point. On m e l t ­ing such uran ium, even in the absence of a l l other r eac t an t s , a g r ay surface forms containing these impur i t i e s .

Uranium monoxide is a face centered cubic (rock salt) s t r u c t u r e with a la t t ice p a r a m e t e r (ag = 4.92A) differing only sl ightly f rom uran ium monocarb ide (a^ = 4.96A) and uran ium mononi t r ide (a^ = 4.95A). It is very likely that these i somorphous substances form a complete s e r i e s of solid solut ions, U(C,N,0), and that the sur face coating r e f e r r ed to above is this solid solution.

^^Katz, J, J. and Rabinowitch, E. , The Chemis t ry of Uranium.), P a r t I, McGraw-Hi l l Book Co., 1951

14seaborg, G, T, and Katz, J. J. , The Actinide E lemen t s , McGraw-Hil l Book Co., 1954

l ^Cleaves , H. E . , Cron, M. M., and Sterl ing, J. T . , CT-2618

1 W i l s o n , A. and Rundle, R., CN-1495

/ : :

15

3 . Uranium Dioxide - The next higher we l l - cha rac t e r i zed oxide of u ran ium is the dioxide. This phase v a r i e s in color from da rk brown to glossy black. The solid has a face centered cubic (fluorite) s t r u c t u r e . A second high t e m p e r a t u r e form, p>, is a l so known. The range of solid so lu ­tions with oxygen extends^"^ from UO^ oo *o UO2.33, the lat t ice p a r a m e t e r diminishing l inear ly with increas ing oxygen content f rom a0 = 5.458A for UOj.oo- Evidence agains t formulating this substance a s Uj-xOz is d i s ­cussed by Katz and Rabinowitch. f

Urania is an e l ec t r i ca l semi-conduc tor . The inc rease in conductivity with increas ing oxygen content, the posit ive Hall coefficient, and the magnet ic and light t r ansmi t t ing properties*of its solid solutions in thor ia a l l give evidence that a ce r t a in fraction of the u ran ium atoms in uran ia , approximately 10""^, is miss ing . E l ec t r i c a l neutral i ty in u ran ia is maintained by the resonance of u ran ium ions between the +4 and higher valence s t a t e s . The lat t ice vacancies become increas ingly mobile a t higher t e m p e r a t u r e s . The oxide ions in excess of the s to ich iomet r ic composit ion occupy lat t ice vacanc ies ; they a r e , p resumably , a lso mobile at high t e m p e r a t u r e s in a c ­cordance with Tammann ' s ru l e .

The excess oxygen in UO2+X ^^ not readi ly removed. Thus , the oxygen p r e s s u r e above UO2.20 is only 22 mic rons at 1160'*C and further decomposi t ion leading to UO .oo r e q u i r e s t e m p e r a t u r e s much higher than 1160''C.

An exper imenta l study of the r a t e of sur face oxidation of liquid u ran ium by solid oxidants , such as the r e f rac to ry oxides , has been s t a r t ed . F igu re 1 shows a photomicrographic sect ion through the contact l a y e r s . The 30 m i c r o n contact layer has been examined by X - r a y d i f f rac­tion. Two face-cen te red cubic la t t ices were identified with a^ p a r a m e t e r s of 5.471 ± 0.002A and 4.952 ± O.OOIA, respec t ive ly . The f i r s t s t ruc tu re has been identified as U02.oo(30 t 5%); the second was s t ronge r and was tentatively identified a s U(C,N,O)(70 t 5%).

It appea r s that for equal contact t imes at constant t e m p e r a ­tu re the oxidation by magnes ia and alumina has proceeded at equal r a t e s . The lack of undercutt ing with thor ia , magnes ia and alumina shows that oxidation p roceeds inward f rom the sur face . These facts may be tentat ively explained by the following hypothesis concerning the format ion of u ran ia . At the or iginal in ter face (Figure 2) oxide ions a r e detached from the lat t ice of the solid oxidant and become attached to the uran ia la t t ice .

1 7 A single observa t ion that it a lso extends down to a composit ion UOj^-jj may be re jec ted in the light of subsequent fai lures to r epea t this observa t ion .

s 9 e s « e « 8 9 e a e e e e f l e » « < 9 9 e s s e e » « s « e » » « » a » e 9 A 9 « 9 e a 9 0 9 9 9 0 9 9

16

Figure 1

PHOTOMICROGRAPH OF URANIUM INGOT: VERTICAL SECTION AT CRUCIBLE (MgO) WALL

Test Conditions: 2 hr at 1200*'C; flowing helium atmosphere

Phofogrophic scale: 1 cm = 10 microns

Oxide Loyer

' A

>..4

'"Si

1 •*

Uronium Metal

9 9 9 9 9 9 9 99 99 9 a e » « e«

9 0 e 9 » 9 9 9 S 9 9 9 9 9 9 9 9 a <S 9 0 9 9 9 « > 9 9 9

.' I,. ',' J.f t I . . * ..'II I I.

e

17

Original Interface

Growing Interface

Solid Oxidant

M ^ + 0~

UO2 M o l t e n l a y e r U r a n i u m

0= ^

Figure 2

The local high concentra t ion oxide ions and meta l a tom vacancies , thus c rea ted , mig ra t e under the influence of the concentra t ion gradients to the growing in ter face , where u ran ium a toms may be incorpora ted into the la t t ice . Designating the vacancies by the sym.bol [v] , r ep re sen t ing a deficit of 4 e l e c ­t r o n s , the p r o c e s s may be wr i t ten schemat ica l ly a s follows:

A, Net r eac t ion of growing in t e r l ace :

U + Q + 20= - UO2

B. Net reac t ion at original in ter face :

2M^O - ™ M + 20= + [ 2

It may be noted that the r a t e of oxide l aye r growth i s thus supposed to be de te rmined by the r a t e of diffusion of vacanc ies or of oxide ions through the la t t ice (whichever i s the slowest) and i s thus cha rac t e r i s t i c of the u ran ia r a t h e r than of the solid oxidant.-^^ Secondly, it may be noted that the meta l a toms , M, formed at the or iginal in ter face a r e supposed to diffuse away in all d i rec t ions , and the react ion, the re fo re , does not a t ta in equi l ibr ium until a sufficient concentra t ion of such a t o m s i s built up at the growing in te r face . This point i s of pa r t i cu l a r impor tance in the phenomena under d i scuss ion . If the meta l a toms , M, were l ibera ted at the growing

^°A parabol ic r a t e law for oxidation i s thus impl ied . Too few observa­t ions have been made to provide evidence of the r a t e law.

9 9 9 9 a e a o 9 0 9 9 9 0 9 0 9 9 9 a 9 9 9 9 9 9 9 6 O S 9 9

18

interface and r ema ined dissolved in the liquid u ran ium, the reac t ion with, say, thor ia would cea se after ve ry l i t t le oxidation because the equi l ibr ium constant for the reac t ion:

Th02(s) + U(l) = Th(in liq. U) + U02(s)

is unfavorably s m a l l , i .e . , about 10~* at 1500'^K, Indirect evidence of dif­fusion of me ta l a t o m s , M, through the wal ls of the c ruc ib les used is p r o ­vided by the following observa t ions :

1. The crucible m a t e r i a l was always discolored to a ce r t a in depth;

2. The quantity of a luminum picked up by molten u ran ium after contact with the alumina is far l e s s than equivalent to the quantity of u ran ium oxidized.

In the ca se of oxidation by z i rconia a somewhat different s i tuat ion o c c u r s , because the equi l ibr ium constant for the reac t ion:

Zr02(s) + U(l) = Zr( in liq. U) + UOgCs)

is favorable , i .e . , about 5 a t 1500°K. Direc t a t tack by liquid u ran ium on the z i rconia sur face might the re fore be expected to occur at r a t e s competi t ive with the preceding p r o c e s s . That such is possibly the c a s e is indicated (l) by the undercutt ing of the s ides of a z i rconia crucible by mol ten uranium; (2) by the enhanced thickness of the reac t ion layer - about I6O m i c r o n s -in 4,7 hr a t approximate ly 1200°C; and (s) by photomicrographs (Figure 3) that show points of d i r ec t a t tack.

An additional phenomenon which takes place during the melt ing of a l l but the highest puri ty u ran ium is the tendency of excess oxygen, carbon and ni t rogen to form a sur face layer . The tendency of this m a t e r i a l to float is respons ib le for the formation of a liquation layer which can be readi ly identified in F igure 4. The depth of this layer is about 300 m i c r o n s . The volume fract ion of inclusions in the u ran ium m a t r i x is of the o rde r of 5 to 10%. The p r e s e n c e of a s m a l l amount of the s a m e inclusion m a t e r i a l in the contact layer has a l ready been noted.

E . Mechan i sms of Impuri ty Remoyal

A number of mechan i sms may account for the r emova l of var ious impur i t i e s .

1. If the proposed m e c h a n i s m of oxidation by the cruc ib le is c o r r e c t , the p r o c e s s has the following c h a r a c t e r i s t i c s :

19

I •

Figure 3

PHOTOMICROGRAPH OF URANIUM INGOT: VERTICAL SECTION AT ZIRCONIA CRUCIBLE WALL

Test Conditions: 4.7 hr at 1151 - 1233^C; flowing helium atmosphere, 110 cc/min.

M0gnificofion: 100X

Ur0niym--——•» ««••—Bokelite Cost

4 "

Figure 4

PHOTOMICROGRAPH OF URANIUM INGOT: VERTICAL SECTION

AT TOP OF INGOT

Test Conditions: MgO crucible; 2 hr at 1200®C; flowing helium atmosphere^ 110 cc/min

Photographic scale: 1 cm = 70 microns

m^ H%

Inclusion Layer

9 0

e

»«

9

9 9

« 9

9

9

e e

* ,

t.l—.

Casio!ite Mounting

Crucible Contact Layer

Uranium Metal o

:^i 21

a. It p roceeds p r i m a r i l y a t the uran ia - u r an ium interface,

b . It proceeds m o s t rapidly at the beginning and subsequently t ape r s off to a ve ry slow r a t e .

c. Thermodynainic equi l ibr ium is not es tabl ished because of the r emova l of reac t ion products by diffusion. With r ega rd to i n c o r p o r a ­tion into the u ran ia lat t ice, the fate of an imipurity a tom, M, original ly p r e s ­ent in the molten urani iun and f ree to r e a c t " will depend on the re la t ive r a t e s of reac t ions (l) and (z):

(1) U(l) + 0 + 20= - U02(s)

(2) M(in liq. U) + Q + nO= - MOn(solid solution in UOg)

If reac t ion (2) is much m o r e rapid than ( l ) , the impur i ty will be highly concentra ted in the e a r l i e s t u ran ia to be formed and will be l e s s and less concentra ted toward the growing interface because of its depletion in the mel t . If reac t ion (z) has about the s ame r a t e a s reac t ion ( l ) , no con­cent ra t ion in the s lag will occur , while if react ion (2) is much slower or does not proceed at a l l the slag layer wil l actually be depleted in the i m ­puri ty .

The determinat ion of such re la t ive r a t e s m u s t be done e x p e r i ­mental ly . However, it is not unreasonable to a s s u m e that they will be roughly co r r e l a t ed with the thermodynamic s tabi l i t ies of the oxides given in Table H, page 8. F o r each individual type of impuri ty a tom other factors may influence the specific r a t e . Some of these factors a r e :

a. s i ze of the ion with r e s p e c t to the s i ze of the vacancy;

b . cha rge of the ion and poss ib le resonance stabil izat ion by in teract ion with the surrounding u ran ium ions;

c . polar izabi l i ty of the ion.

The fission product e lements molybdenum, te l lu r ium, ce s ium and ruthenium a l m o s t cer ta in ly wil l not be removed by this mechan i sm.

2. Another sou rce of impuri ty r emova l is the migra t ion of U(C,N,0) toward the su r f aces . Because of the fine s t a t e of subdivision of the inclusions and the intimacy of contact with the raelt , it may be expected that any tendency of f ission product e lements to concent ra te in them wil l be very marked ly felt. Quali tat ively, the f ission product removal by this mechan i sm will be the s a m e a s by incorporat ion in the u ran ia la t t ice , except for the poss ib le ro le played by carb ide and ni t r ide formation. The carb ides of niobium and z i rconium a r e m o r e s table than u ran ium ca rb ide .

19impurity a toms tied up in the monoxide - monocarbide - mononitr ide inclusions a r e not h e r e cons idered .

I 22

3, Another sou rce of f ission product r emova l is loss by dif­fusion. The extent of this loss in each individual case wil l be dependent on t e m p e r a t u r e , p r e s s u r e , s ta te of combination, diffusion coefficient and t ime .

a. Xenon and Krypton - These iner t e lements will diffuse out rapidly above the melting point of u ran ium, r e g a r d l e s s of the use of vacuum or iner t a t m o s p h e r e .

'^' Iodine - The v a p o r - p r e s s u r e of u ran ium t r i - iod ide is sufficiently l a rge a t elevated t e m p e r a t u r e s (est imated 280 m m of m e r c u r y a t 1200°C) to cause i ts volat i l izat ion into a vacuum.

c. Cesium - The vapor p r e s s u r e of ces ium a t 1200®C is about 19 a tm. Ces ium does not fo rm a s table oxide, carb ide or n i t r ide a t this t e m p e r a t u r e , and i ts solubili ty in u ran ium is probably ve ry smal l . Even |n an ine r t a tmosphere and a t low concentrat ions dissolved ces ium should diffuse away from the m e t a l fair ly rapidly. It should be r e m a r k e d that diffusion into porous boundary l aye r s and cruc ib le m a t e r i a l s wil l take place s imul taneously with diffusion into the a tmosphe re .

^' Stront ium - This e lement , if uncombined with oxygen, may volat i l ize readi ly into a vacutim (vapor p r e s s u r e = 200 m m of m e r c u r y ) . The diffusion constant of s t ron t ium ions through oxide la t t ices at 1200*^C has not been m e a s u r e d ,

e. R a r e Ea r th s - The s a m e r e m a r k s apply a s for s t ron t ium. The vapor p r e s s u r e s a r e much lower, being in the range 10~* to 10""^ m m of m.ercury a t 1200°C.

f. Te l lu r ium - The situation for t e l lu r ium is s imi l a r to that for s t ron t ium, except that the t e l lu r ium may form s table u ran ium te l lu r ides which, In analogy to the sulfide and se lenide , wil l be non-volat i le . Te l lu r ium itself, has a vapor p r e s s u r e of 1.9 a tm, a t 1200°C,

g. Others - No o ther f iss ion e lement likely to be p resen t in significant concentra t ion in this work is apprec iably volat i le . The dif­fusion constants of the corresponding cat ions through oxide la t t ices a r e not known.

23

lU. EXPERIMENTAL RESULTS

A„ Equipment and P r o c e d u r e s

1. Equipment

The high t e m p e r a t u r e s tudies re la t ing to redis t r ibut ion of f ission products between me ta l and metal loid phases were conducted in a porce la in tube heated by a Globar r e s i s t a n c e furnace. P rov i s ions were made for blanketing the tube with argon. Additional auxi l iary s y s t e m s were provided to degas the tube plus contents and to p e r m i t a purified hel ium a t ­mosphe re during slag formation and liquation expe r imen t s . The units were ins ta l led in a venti lated hood and the furnace was surrounded with 3 in. of s tee l shielding.

F igu re 5s p . 24, shows the exper imenta l furnace and the a c ­c e s s o r y sys tem requi red for purging a i r from the system., blanketing the porce la in tube with argon, and cooling a neoprene vacuum sealing gasket . The furnace tube was an unglazed McDanel porce la in tube of 2 -5 /8 in. inside d i ame te r and l / 4 in. wall th ickness . Cruc ib les were supported in the tube on porce la in cy l inders in such a way that the melt would be approximate ly in the cen te r of the furnace heating zone. The 4 -e l emen t Globar furnace was insulated with 4 in, of f i rebr ick and made tight enough to contain an iner t a t ­m o s p h e r e by welding a l / S in, s t ee l ca se around the outer sur face and c a p ­ping the ends . Melt t e m p e r a t u r e s (ca, 1200°C) were attained in approximate ly I h r with a 2-3 kw input. T e m p e r a t u r e was regulated with a Minneapol i s -Honeywell P y r - O - V a n e con t ro l l e r in conjunction with a p la t inum/p la t inum-rhodium thermocouple that touched the outside of the porcelain, tube in the cen te r of the furnace heating a r e a . Heating t e s t s w e r e made on the furnace to de t e rmine the re la t ionship of t e m p e r a t u r e indicated by the ex te rna l thermocouple and one located inside the furnace tube in. a well dr i l led in a I -kg urania c ruc ib le . When the furnace cont ro l was set at 1300®C and then at 1200*'C the lag between in te rna l and ex te rna l the rmocouples was about 10 min . After the furnace had reached control t empera tures the t e m p e r a t u r e differential was smal l , reaching 4°C at equilbrium.. It i s felt that charge t e m p e r a t u r e s indicated in th is r e p o r t a r e c o r r e c t to ± 15°C,

Auxil iary s y s t e m s connected to the furnace tube, which include a he l ium purif icat ion t r a in and a m e t a l vacuum system., a r e shown s c h e m a t i ­cally in F igu re 6, p . 25. P e r f o r m a n c e of the me ta l vacuum sys t em used for charge and c ruc ib le degass ing p r i o r to melt ing in purified he l ium has been sa t i s fac tory . The m e a s u r e d leakage r a t e into the evacuated sys tem of about 15 l i t e r s capaci ty is 12 m i c r o l i t e r s per hour . Minimum equi l ibr ium non-condensable gas p r e s s u r e s of 1,5 x 10""* m m of m e r c u r y at room tempera ture^ and of l e s s than 10" ' m m with the furnace at ISOOT. , have been obtained. Although the above equi l ibr ium p r e s s u r e s a r e sa t i s fac tory for degass ing of furnace components , the u l t imate vacuum obtainable in the furnace tube is

9 999 a 9 » oe 99 e S09 e s e e ee o e e s 9 9 9 9 e e e e » 9 e t t e e « « 9 »»« 9 » ® o 0 9 9 9

9 9 e o o s e e e e oe «» » » o e e o ®e

; 4^

Figure 5

HIGH TEMPERATURE MELTING FURNACE WITH ARGON

COOLING AND BLANKETING SYSTEM

Argon Cooling Flowmeter Gas Inlet

Vacuum or Helium

Woter Cooling

Heat Exchanger

Key

A Sight Glass

B Top Flonge

C Heod

D Gasket (Argon Cooled)

E Porcelain Tube

F Shroud

G Sealing Pan

H Supporting Baffle

1 Roots-Connersville Gos Pump

J Crucible

K Crucible Support

L Globor Heating Element

M Tantalum Poil

N Refractory Brick

^ Pressure Gauge

® Volve

> « e 1

Figure 6

EXPERJMENTAL FURNACE AUXILIARY SYSTEM

ffiw Meter I Vent

dnr —\ t -—-^^-^ ^ Copper Oxide | | I Uranium

Furnace ~ ~ Furnace Copper C®pper Oxfdi Furnace Furnace

Anhydrone Ascarlte ^©Id Trop

HELIUM PURIFICATION TRAIN

Helium Exhaust

Mercury "^"P Seal

- ^ Exhaust

Mtchonlca Forepump

Cold I

Trap Cold Cathode Oil Diffusion Gouge

Cold Trap

METAL VACUUM SYSTEM

Vent

t i_i Globar Furnace

26

l imited by tabing d iamete r t r a p s , bends and mechanica l and oil diffusion pump s i zes With this l imited vacuum sys t em uranium me l t s with clean sur faces were not formed., Sat isfactory me l t s have been obtained with the use of a flow of hel ium purified i r the g l a s s t r a in shown in F igure 6. T e s t s a r e coEtemplated to de te rmine the necess i ty of the complex 6-component purification sys tem. F i g u r e 7^ p . 27, i s a photo of the u ran ium melt ing furnace and includes the a«ixiliary sys t em used in gas purification,, The s tee l shielding wall normal ly surrounding the box-l ike furnace has been removed to obtain a view of the furnace a s sembly

2. Pr_oc ed ure

a. Melting

The p rocedures followed in the slag format ion and liquation s tudies using the appara tus shown in F i g u r e s 5-7, were a s follows ( l ) c ruc ib les w e r e degassed at a min imum t e m p e r a t u r e of 1000°C and permi t ted to cool m ei ther pa.rified he l i am a tmosphere or vacuum, (z) the charge was Si^rface cleaned with n i t r i c acid and dr ied; (3) the charge after t r ans fe r to the melt c ruc ib le was degassed in vacuum at 600°C to a p r e s s u r e of approximately 10~* m m oi m e r c u r y , (4) purified hel ium at a p r e s s u r e of approximate ly 1,1 a tm absolute was introduced to the sys tem; sparging at 100 - 150 c c / m i n was begun and the t e m p e r a t u r e inc reased to 1200*C for a p rede te rmined t ime , (s) the e lec t r i ca l power was shut off, and the furnace tube and contents were allowed to cool overnight in an hel ium a tmosphe re . Approximately 24 h r were requi red for the t e m p e r a ­tu r e to d rop to 100°C Uranium mel t s were removed from the furnace at t e m p e r a t u r e s of 150°C or lower

Varia t ion of the above p rocedure was made in Run 12A (Table XII, p . 34) m *vhich bot iom-pouring with s toppe r - rod and cast ing of meta l were c a r r i e d out with c ruc ib l e s a r r anged a s shown in F igu re 8, p . 28. The me ta l was heated to 1200°C for 3 - l / 2 hr and then to 1250°C for 40 min, at which t ime the stopper rod was r a i sed and the molten m e t a l was cas t in a secondary tantalum cruc ib le . By the use of th is technique, approximately 2 % of the liquated meta l w^s re ta ined in the p r i m a r y c ruc ib le a s a skull ,

b . Ingot P r e p a r a t i o n for Radiochemical_Analysis

Ni t r ic acid dissolut ion was used to obtain analyt ical s amples for de te rmina t ion of fission product and plutonium concentra t ions in the slag or skin sect ions and in the ingot i n t e r i o r s . The weight pe r cent r emova l of uranium from the ingot was determir.ed by in te rmi t ten t spot checks of the acid uranium concentra t ions Rate of dissolut ion was roughly controlled by acid t e m p e r a t u r e and corcen t ra t ion . Separa te r emova l of the top ingot skin (approximately SOOn-LicTO-- inclusion depth) or bot tom and side skin (approximately 30 mic ron slag depth) was accomplished by painting the

I 1

Figure 7

VIEW OF URANIUM MELTING FURNACE

» e 9 » 9 BOS

III

- J

— I«

Flgyre 8

BOTTOM-POyR STOPPER-ROD CRUCIBLE AND MOLD ARRANGEMENT

(Equipment Used In Run 12A)

Thorio Crucible

Thorla Funnel

Tonfolum Mold »•»

Molybdenum Wire to Lift Meehonism

Thorlo Stopper-Rod

— Alondum Crucible Support

surface to be protected with a benzene solution of Apiezon W" vacuum wax. Skinning of the selected a r e a was then c a r r i e d out with dilute n i t r i c acid (4 N to 8 N ) heated to a maximum t e m p e r a t u r e of 65°C (20°C below the wax melt ing point). Where no a t tempt was made to differentiate between top, side and bot tom sur faces the ingot was dissolved to a point where clean meta l , i„e.5 free from da rk oxide was obtained. After the skinning operat ion the remaining meta l was dissolved in boiling 13 N n i t r i c acid under reflux. F ina l acid concentra t ions oi both skin and in te r io r analyt ical s amples were about 6 N to 8 N.

Skinning of the cas t ingot was not employed when the s topper - rod type crucible was used since the g r e a t e r port ion of the slag or skin layer was re ta ined in the crucible during the pouring operat ion. Ana­lyt ical s amples for de termining fission product concentra t ions were obtained by dissolving the re ta ined slag and the cas t ingot separa te ly .

B, Analyt ical Data

Tables IV -XIV contain data re levant to the observed dis t r ibut ion of uranium, plutonium and fission e lements in each of the runs 3m.ade in r e ­f rac tory oxide c ruc ib l e s . The p r o c e d u r e s were a s desc r ibed in the p r e c e d ­ing sect ion. The t e r m "skin'"' i s used in these t ab les r a t h e r than ' s lag" because the deep etching p rocedure cannot be control led with sufficient d e l i ­cacy to prevent undercutt ing the surface and dissolving sonae of the in ter ior meta l . However, it i s not probable thai any of the conclusions of this inves t i ­gation would be ma te r i a l ly a l t e red by a m o r e p r e c i s e separa t ion . The chemica l and rad iochemica l ana lyses were performed by the analyt ical se rv ice section of th is Division using standard methods . R a r e ea r ths , ce r ium, strontiums rutheniuirij, ces ium and te l lu r ium, we r e counted a s beta ac t iv i t ies using a G.M, tube. Z i rcon ium and niobium g a m m a s were counted through a lead abso rbe r using a scinti l lat ion counter which was adjusted to d i sc r imina te against photons of l e s s than 0.1 Mev, energy. Molybdenum was de termined by a newly developed co lo r ime t r i c method.^^ Uranium was de termined ei ther by weighing d i rec t ly a s meta l or by the acetone- thiocyanate co lo r ime t r i c Miethod. Plutonium was followed by means of s tandard lanthanum fluoride c a r r i e r technique and counting in an alpha propor t iona l counter .

The m a t e r i a l employed throughout th is work was Oak Ridge i r r ad ia ted uran ium slugs which had been previously decanned, sl iced and cleaned of adhering bonding m a t e r i a l . F o r purposes of compar i son untreated s l i ces w e r e dissolved a s near ly a s poss ib le at the s ame t ime a s t r ea ted s l i ce s . In the cour se of examination of these cont ro l s l i ces it was de termined that t he re was essent ia l ly no longitudinal var ia t ion in activity along the slug. In o rde r to i n c r e a s e the p rec i s ion of rad iochemica l ana lyses of the cont ro ls , the fission product ac t iv i t ies were plotted v e r s u s the decay t i m e s (semi™ logar i thmic paper) and bes t l ines fitted to the data. In miost c a s e s the s lopes

Crouthamelj C, E, and Johnson, C. E. , ANL-5224,

Table IV

DISTRIBUTKW OF MATERIAL AFTER MELTING

Run 2A

Crucible: Funnel-shaped urania crucible. Ingot sectioned vertically into 3 sections and each section individually skinned

Slice: 7 g/t, 70.5 g, 265 days cooled. 4 hr at 1200''C

Percentage of Starting Material

e 9 e e » s

« e e s «

0 0 9 0 9 e

9

e 9

e 9 9 « e

e e 9

9 e « 9 9

9 9 9

9 e

O 9 B 9 9

9 « 99e f f

Section

Top sections skin Top section, int. Middle section, skin Middle section, int. Bottom section, skin Bottom section, int. Unaccounted

Uranium

4.1 SS.O 0.8

21.9 2.1 IS.7 0.4

Plutonium

6.0 49.6 1.7

20.2 2.4 14.3 5.8

Rare Earths

69.9 0.5 11.0 0. 1 4.2 0.4 13.9

Ce

59.S 0.2 10.7 0.05 4.7 0.05

24.8

Sr

86.3 0.9 4.2 0.1 0.3

o.os 8.1

Ru

3.0 38.2 0.4 20.9 1.6 15.5 20.4

Cs

41.8 1.7 3.6 0.6 0.3 0.4 51.6

Te

83.3 5.4 5.4 1.5 l.O 1.0 2.4

Nb

12.5 49.5 1.6

21.3 1.8 14.7 ...

Zr

67,1 21.0 5.4 8.6 1.2 8.1 ...

Total

/3

63.8 6.4 8.5 4.0 3.3 1.7

12.3

Total y

28.0 43.4 2.7 16.9 1,8

12.2 ...

Table V

DISTOIBUTICM OF MATERIAL AFTER MELTING

Run 5A

Crucible: Thoria. Ingot skinned 3 times in succession

Slice: 7 g/t, 78.4 g, 298 days cooled. 4 hr at 1200''C

Section

Outer skin Middle skin Inner skin Interior Unaccounted

JJ ranium

0.7 0.7 2.9

95.5 0.2

Plutonium

2.1 1.2 2.4

87.3 7,0

Rare Earths

43,8 26.7 16.7 l.l

11.7

Ce

45.7 25,1 16.S 1.3

11.4

Sr

61.4 26,0 7.2 0. I

5.3

Ru

O.S

0.6 2.8

91.1

S.l

Cs

21.3

14.7

6.7 3.4

53.9

Te

25.5

19.7

6.0 19.4 29.5

Nb

4.8 2.7 2.7

74.9 14.9

Zr

38.6 17.4 10.2 27.4 6.3

Total /3

40.5 22,0 12,9 9.5 15, 1

Total

7

13.6 6,5 4,7

47.4 27.8

o

J7 Table VI

DISTRIBUTION OF MATERIAL AFTER MELTING

Run 6A

Crucible: Magnesia. Ingot skinned 3 times in succession

Slice: 7 g/t, 51.8 g, 306 days cooled. 4 hr at 1200''C

Percentage of Starting Material

Unaccounted 0.3

Sect ion

Outer skin Middle skin Inner skin Interior

Uranium

1.2 1. 1 1.9 95.5

PI utoni

3.7 1.8 1.7

88.0

um Rare

Earths

44.7 23. 3 11.9 1.7

Ce

46.6 26. 1 12.6 1.9

Sr

74.9 17.6 6.4 1.6

Ru

0.4 0.6 1.6

8S. 1

Cs

24.5 11.9 5.6 2.7

Te

47.0 10.0 3.6

39.8

Nb

5.9 2.7 2.7

74.3

Zr

41.8 IS.5 8.9 24.7

Total

/

44.1 20,5 10.3 9.9

Total 7

19.4 7.7 4.9

64.8

4.9 18.3 12.8 12,3 55.2 14.5 IS.2 3.2

Crucible;

Slice:

Table VII

DISTOIBUTION OF MATERIAL AFTER MELTING

Run 7A

Urania. Skinned once

7 g/t, 30.6 gs 314 days cooled. 30 min at 1200'C

Percentage of Starting Material

Secti on

Skin Interior Unaccounted

Uranium

2.8 97.2 0,0

Plutonium

7.2 96.6 ...

Rare Earths

73.4 10.3 16.3

Ce

80.6 11.8 7,6

Sr

85.7 10.6 3.7

Ru

2.2 80.6 17.2

Cs

56,4 12,9 30.7

Te

77.1 16.2 6.7

Nb

16,0 81,0 3.0

Zr

55.9 34.8 9.3

Total

^

69,3 18,2 12.6

Total

y

27.9 67.4 4.8

Table VIII

DISTRIBUTIOM OF MATERIAL AFTER MELTING

Run 8A

Crucible: Alumina. Very thin disc ingot.

Slice: 7 g/tj 45.2 gs 321 days cooled.

Skinned 3 times in succession

4 hr at 1200''C

Percentage of Starting Material

Oft as e

«

• eee»

«90

s

9 e

a

9999

e 9 e

8 e»e

9 9 9

esse

9«o

Sec

Outer

Middl

Inner

Inter

t ion

skin

e skin

skin

ior Unaccounted

U

Sect ion

Outer

Middle

Inner

Interi

skin

ski skin

or Unaccounte

ran

1 I 3

93 0

-

n

d

lum

5 6 1 8 0

U

PI

Cruci Slice

ranium

0.9

1.0 3.2

95.2 ...

utonium

1.6 1.5 2,8

83.4 10.7

Rare Earths

35.0 10.8 0.0 1,8

52.4

DISTRIBUTION

ble: Magnesia. Sk : 7 g/t

Plutonium

l.l 0.9 2.8

82.8 12.4

, 91.4 g

Sr-

92.6 0.8 0.0 0,3 6.3

Table

Ru

13.9

IS.O

3. I

86.3 ...

IX

Cs

44.3 0.7 0.0 1.3

S3.6

Te

85.0 0.9 0.2 7.3 6.7

OF MATERIAL AFTER MELTING

Run 9A

inned 3

, 330 d

Percentage Rare

Earths

46.7 8.0 3.9

20.2 21.2

St

31.1

27.2

27.2

16.8 ...

times m succession ays cooled.

of St

Ru

0,6 0,9 3.2

94. 1 1. 1

arting

Cs

24.2 19.0 15.0 18.8 23.0

30 min

Materi

Te

28.3 24.3 21.6 17.3 8.5

at

al

Nl

14 6 S

74 .-

Nb Zi

23.6 57 1.7 1 2.3 0

69.9 12 2.6 28

I200''C

3 Zr

0 29.2 1 9.8 7 14.0 8 42.5

4. 1

Total

/3

2 41,8 4 2.5 4 0.2 2 9.1 8 46.4

Total Total /3 7

45.4 15.2 10.5 6,8 6.0 5.4

25,1 47.1 13,0 25.6

Total,

7

31.6 1.4 1.8

54.3 11.0

Table X

DISTRIBUTICW OF MATERIAL AFTER MELTING

Run IDA

Crucible: Thoria. Top of ingot skinned separately from sides and bottom Slice: 7 g/t, 63.8 g, 336 days cooled, 11 hr at 1200°C

Percentage of Starting Material

Sect ion

Top skin Bottom outside Interior Unaccounted

skin

Uranium

3.3 0.9 95.5 0,3

Plutonium

3.7 1.9

83.3 11.1

Rare Earths

42,3 30.6 1.3

25.8

Sr

60.6 27.3 1.3 10.9

Ru

3.3 5.7

102.6 ...

Cs

36.9 16.3 0.9

45.9

Te«

7. 1 9.0 9.3 74.7

Nb

9.7 11.7 78,7 ...

Zr

30,2 50.2 16.2 3.4

Total

ft

43.6 30,1 8.4 17.9

Total 7

16.8 16.7 49.5 17.0

These values considered doubtful because of inadequate analysis of control.

Table XI

DISTRIBUTION OF MATERIAL AFTER MELTING

Run llA

Crucible: Thoria. Top of ingot skinned 2 times. Bottom and sides skinned once. Crucible leached with acid.

Slice: 7 g/t, 218.5 g, 372 days cooled. 4 hr at nOO^C

Percentage of Starting Material

Section

Bottom and side skin Outer top skin Inner top skin Crucible leaching Interior Unaccounted

Uranium

0.6 0.8 1.0 0.01 97.8 . . -

Pi utonium

1.0 1.3 1.1 0,5

99.1 ...

Rare Earths

27.3 25.1 19.0 3.0 11.7 13.9

Sr

41.8 27.4 8.1 8.1 6.4 8.2

Ru

0.3 0.7 1.0 0.0

109,0 ...

Cs

15.3 17.2 8.2

41.8 5.6 11.9

Te

33.7 36.8 2.3 8.7 7.5 U.O

Nb

4.7 4.1 2.4 0.03 86,2 2.6

Zr

26.1 24.7 13,3 0.2

32.1 3.6

Total

26.7 26.1 18.3 4.3 19.2 5.4

Total

7

13.3 12.1 7.3 4.4 61.7 1.2

UJ

Table XII

DISTRIBUTKW OF MATERIAL AFTER MELTING

Run 12A

Crucible: Bottom-pour with stopper-rod thoria crucible. Ingot cast in tantalum pail

Slice: 42 g/t, 263.3 g, 298 days cooled. 4 hr at 1200''C

Percentage of Starting Material

s » a e

99 9

9 9

9 9

9 9 9 «

e » e

9 9 9

999

Section

Skull Ingot Unaccounte d

Uranium

2.0 97.6 0.4

Plutonium

2.0 88.4 9.6

Rare Earths

64.0 3.1 32.9

Sr

42.1 0.2 57.7

Ru

1.6 85.2 13.2

Cs

6.0 0.1 93.9

Te

72.5 14.5 13.0

Nb Zr

9.2 38.3 9.3* 39.7

81.5* 22.0

Total

50.9 9.3

39.8

Total 7

18.3 21.7 60.0

•Questionable Value

Crucible;

Slice:

Table XIII

DISTRIBUTIW OF MATERIAL AFTER MELTING

Run ISA

Lime-stabilized zirconia. Ingot skinned once

42 g/t, 68.0 g, 323 days cooled. 4.5 hr at 1241 - ilSl^C

Percentage of Starting Material

Section

Skin Interior Unaccounte •d

Uranium

3.2 96.7 0. 1

Plutonium

3.4 67.0 29.6

Rare Earths

58.4 0.8

40.8

Sr

46,7 0. 1

53.2

Ru

1.7 61.7 36.6

Cs

7.2 O.S

92.3

Te

33.1 32.5 34.4

Nb

5.4 68.2 26.4

Zr

33.8 34.4 31.8

Total ft

50.2 6.8

43.0

Total

7

15.2 42.4 42.4

Table XIV

DISTRIBUTION OF MATERIAL AFTER MELTING

Runs 16A - 17A - 18A

Crucible: Alumina. Reused twice. Each ingot skinned once

Slice: 16A - 42 g/t, 80.3 g, 325 days cooled. 4 hr at 1200°C 17A - 42 g/t, 83.9 g, 326 days cooled. 4 hr at 1200°C 18A - 42 g/t, 61.8 g, 338 days cooled. 4 hr at 1200^C

Percentage of Starting Materia!

Rare Total Total Section Uranium Plutoniuii Earths Sr Ru Cs Te Nb Zr ^ 7

(First Use)

Skin Interior Unaccounted

4.0 96.1 ...

4.6 73.0 22.4

37.8 0.3

61.9

53.0 0.1 46.9

2.6 71,9 25.5

5. 8 0. 1

94.1

26.2 7.2 34.1 31.8 75.4 46.1 42.0 17.4 19.8

(Second Use)

Skin Interior Unaccounted

4 95 0

8 0 2

36.2 6.7 57.1

14.2 47.3 38.5

5.2 78.6 35.1 3.6 8.7 83.7 12,9 61,6 71.7 27.2 89.0 2.1 0.05 87.4 0.06 6.5 99.1 37.1 9.0 53.3 5.8 19.3 64.8 9.0 91.2 9.8 — - 1.3 19.3 19.5

(Third Use)

Skin Interior Unaccounted

4.1 95.7 0.2

4.7 75.9 19.4

64.7 1.0

34.3

36.3 0.2 63,5

3.1 91.7 5.2

6.1 0.07 93.8

51.6 21.1 27.3

6.0 63.2 30.8

36.0 40.2 23.8

57.3 7.0 35.7

16.9 44.3 38.8

36

of the bes t l ines coincided with the known hal f - l ives . The rad iochemica l ana lyses of the t r ea t ed m a t e r i a l s could then be compared with interpolated values for the cont ro ls in o rde r to el iminate the var ia t ion due to decay t ime between ana lyses . Separa te c e r i u m ana lyses w e r e discontinued after Run 7A since total r a r e ear th activity was found to be due a lmos t ent i re ly to c e r i um - 144 in the slugs p rocessed (about 260 - 350 days cooling).

The accuracy ar_d prec is ion of these r e s u l t s i s not easy to a s ­s e s s . The accepted p rec i s ion of ana lyses (relat ive per cent) f rom the se rv ice l abora to ry a r e : uraniums t 2%; plutonium, 1 5%; total beta and gamma ac t i v i ­t i e s , t 5%; individual fissior- e lements , ± 20%. Actually the confidence l imi ts of these p rec i s ions have not been determinedj and it would not be surpr i s ing if 95 % confidence levels w e r e m o r e than twice these valueso The accuracy of the rou t i r e determiinations of individual r ad io -e l emen t s tends to de t e r io r a t e badly if the counting ra t e is low or if separa t ion f rom much l a r g e r amounts of other ac t iv i t ies i s r equ i r ed . In such c a s e s var ia t ions f rom run to run of fac tors of 2 for a pa r t i cu la r activi ty at low leve ls have not been a s sumed to be significant. Finally^ s ince the ent ry marked '^unaccounted* i s obtained by difference from 100 %, only major va r ia t ions or consis tent t r ends will be a s ­sumed to have significance in the following d i scuss ions , A dash has been used to indicate that the analyzed m a t e r i a l s total m o r e than 100 % of the s tar t ing m a t e r i a l . These exces se s range from 1 to 18 %o

C, Discussion and In terpre ta t ion

In Tables IV - XIV each entry under a r ad io -e l emen t which signifi­cantly and consis tent ly differs from the corresponding entry under u ran ium indicates a concentrat ion or r emova l of that r ad io -e l emen t f rom the given location. In r ega rd to red is t r ibu t ion of plutonium and fission products :

1„ Except for ru thenium every r ad io -e l emen t repor ted in Tables IV - XIV i s concentra ted to a g r e a t e r or l e s s e r extent in the slag. This i s demons t ra ted m o r e c l ea r ly by Table XV, The l a rge var ia t ion from run to run of the slag layer concentrat ion of some r ad io -e l emen t s will be shown, la ter to be due to the in teract ion of severa l va r i ab l e s ,

2, Every r ad io -e l emen t repor ted in Tables IV - XIV i s removed f rom the in te r io r of the ingot to a g r e a t e r or l e s s e r extent. This i s demon­s t ra ted m o r e c l ea r ly by Table XVI„ The effect of the chief va r i ab l e s on the concentra t ion of res idua l ac t iv i t ies will be d i scussed in the following p a r a ­graphs e

ao Crucible Mate r i a l - In runs 2 -5-6-8A the single i m ­por tant va r i ab le changed was the cruc ib le m a t e r i a l . With the poss ible e x ­ception of t e l lu r ium the res idua l ac t iv i t ies do not change by la rge amounts from run to run„ It may be concluded that urania , thoria,, magnes ia and alumina do not br ing about r ad io -e l emen t r emova l by specia l mechan i sms pecul iar to the

e o

9 e

99

«» e

»« e

a 1

9 9

9 > 9 «

9

« OS

e e

e 9

99

99 9

O 9 9 &

99 a

999 9

e » a

s e e

9 9 t

«»«

a

9 9

»«

S7 Table XV

RADIO-ELEMENT CONCENTRATICM FACTORS* IN SUG LAYERS

Description Pu Rare Earths Sr Cs Te Nb ZT Ru

Run

Run

Run

Run

Run

Run

Run

Run

Run

Run

Run

Run

Run

2A,

SA,

eAs

7A

8A,

9A,

lOA,

llA,

12A,

ISA

16A

17A

18A

top

outer

outer

outer

outer

bottom and side

bottom and side

skull

1.6

2.8

3. 1

2.8

1.0

1,3

2.1

1.9

1.0

1.0

1.1

1,1

1.1

18

59

38

38

23

54

33

49

32

18

9.4

16

16

22

83

63

33

60

34

30

75

21

14

13

7.3

8.9

11

29

21

22

29

28

18

27

3.

2.

I.

1

1.

0

2

4

8

5

22

34

40

30

55

33

9.8«

60

36

10

6.5

17

12

3.2

6.4

4.9

6.1

15

16

13

8.4

4.6

1.7

1.8

2.7

1,5

17

52

35

21

37

34

55

47

19

10

8.4

13

8.8

0.77

0.61

0.32

0.83

0.91

0.73

0.62

0.54

0.80

0.53

0.63

0.75

0.75

^Defined as cpm/miilimole uranium in slag T com/mi 1limole uranium in control.

''The skin showing maximum concentration of activities has been chosen where more than one skinning

was performed.

'^Questionable value.

Table XVI

RESIDUAL ACTIVITIES IN THE INGOT INTERIOR

Percent of Original Concentration®

e e 9 s e e

e « « « 9

9 « S « 9 «

e

9 9

9 9 ® 9 9 9 9 9

9 9 9 9 e 0 9 e

9 9

e 9 9 9 9

e 9 a 9 9 e

Run

2A

SA .

6A

8A

7A

9A

lOA

ISA

16A

17A^

ISA**

llA

12A«

Crucible

UO,

ThOj

MgO

Al,03

UO^

MgO

ThOj

ZrO,

AI.O3

AlA Al,03

ThOj

ThOj

Hr at 1200°C

4

4

4

4

O.S

0.5

11

4.5

4

4

4

4

4

g/t'' Level

7

7

7

7

7

7

7

42

42

42

42

7

42

Charge,

g

70.5

78.4

51.8

45.2

30.6

91.4

63.8

68.0

80.3

83.9

61.8

218.5

263.2

Pu

90

92

92

92

99

87

87

69

76

94

79

102

91

Rare Earths

0, 9

1.2

1.8

1.9

11

21

1.4

0.9

0.4

2.3

1.0

12

3.2

Sr

1.7

0. 1

1.7

0.3

11

18

1.3

0. I

0.1

0.1

0.2

6,5

0.2

Cs

3.0

3.6

2.9

1.4

13

20

0,9

O.S

0.1

O.l

O.l

5.7

0.1

Te

9.7

20

42

8.1

17

18

9.7*

34

33

6.9

22

7.7

15

Nb

90

78

78

77

83

79

82

71

78

105

66

88

9.5

Zr

38

29

26

13

36

45

17

36

48

39

42

33

* 41

Ru

71

95

89

95

83

99

108

64

75

92

96

111

87

^Defined as 100 cpm/miilimole uranium in ingot -r cpm/miilimole uranium in control.

The concentration of radio-elements is roughly oroportional to the plutonium content which is given in

ppm in the starting material.

^First re-use of crucible from 16A.

Second re-use of crucible from 16A.

^Bottom-pour stopper-rod run.

Questionable value.

39

r e f r ac to ry oxide.. This i s ii good ag reemec t with expectation inasmuch a s the mel t i s cor tamed in aa envelope of -uranium oxides soon after it i s formed ar.d the sou rce oi the oxidizing agent i s then immate r i aL This i s fa r ther con­f i rmed by T-^ns 16 - 17 - 18A !•, which removal of ac t iv i t ies does not change significaatly although the i.rard"jm is i r i t ia l ly exposed to different surfaces iri 16A a s against 17A ar.d ISA,

The or»e r ' j i made ir, a zircorj.a c ruc ib le (Run 15A) is a l so in ag reement except foi rutherdsmi^ This i s m o r e c lea r ly demons t ra ted by the appropr ia te e c t i i e s in Table XIII which shows that 37 % of the ruthenium is utacco' jcted tor,. This may i rd ica te a poss ib le connect iot with the fact that z i i coa i a i s rapidly ar.d d i rect ly at tacked by the melt„

b T ime at T e m p e r a t a r e - If the p r o c e s s e s involved in r e ­moval a r e not ve ry rapid t ime will be ar* impoi tan t va r i ab le . Examining Table XVI, d i rec t compai i son immedia te ly r e v e a l s that r a r e earthp ces iuin and s t ront ium removal a l t e r 1/2 hr i s l e s s complete than, after 4 h r . On the other hand a l te r 11 hr (Run I O A ) remova l i s not significantly different than, after 4 h r . An obvious exception *o th is i s ces ium which im the 11-hr ruR is removed to a slightly g rea te r degree a s might be expected for con-tiE'tting evaporation from the mel t . One cor.cludes that under the given e x ­per imenta l cofiditioas the slagging p r o c e s s tor the other r ad io -e l emen t s i s near ly complete at some t ime between l / z and 4 h i ,

Co Original Concentrat ion of Activity - Compar ison of RaES 1 6 - 1 7 - 1 8 A with Rur_s 2 - 5 - 6 - 8 - IOA ir. Table XVI r evea l s that ces ium, cer ta in ly and stror. t iam, possibly, a r e sigrif icantly be t t e r removed a s activity level iacreasesa Moieove i their r emova l i s not iato the slag layer a s exami ­nation of Table XV will show» A poss ib le explanatioa for th is i s given below in sect ion 3.

do Charge Size - The weight ol the charge melted should have no signiiicaiice i& itself except a s it af iects the geomet ry of the e x p e r i ­ment , i,e„ the exter.t of sur faces exposed to the aicmosphere or the crucible or the d is tance a pa i t i c l e mus t diffuse to r each a boimdary. Let it be assumed that the la t te r t ac tor i s the sigmiilcact oiie« For coaver.ience it will be m e a s ­ured by the ave rage t h i c k t e s s of the ingot measured a c r o s s i t s s a r r o w e s t dimeosion, i<.e„ the average miniimim diffusion d i s tance . The r ad io -e l emen t s which will be subsequently shown to be mos t susceptible to loss by diffusion, a r e ces ium, s t ron t ium a t d the r a r e e a r t h s . In Table XVII the r e s idua l ac t iv i t ies of these elemerits a r e shown as a function of the ave rage ingot th ick­ness., othei va r i ab l e s beisg kept constant . IiispectiOE ol th is table r e v e a l s that, with the exception oi the eEtr ies marked by a s t e i i s k s , the t rend is well marked , ir .creasing i tgot th ickness pa ra l l e l i sg increasirLg activi ty retention^ At tempts to apply the s ame coi re la t ion to other r ad io -e l emen t s mee t with l e s s s u c c e s s . Likewise atfempi<s to c o r r e l a t e the retent ions of ces ium, s t ron t ium and r a r e e a r t h s t4Si»tg a s va r i ab l e s weight, total surface a r ea , c ruc ib le contact a r ea ©r +op Surface a r e a were l e s s successful .

lL,i

Table XVII

RESIDUAL ACTIVITIES IN THE INGOT INTERIOR AS A FUNCTION

Average Thickness of Ingot, In.

0.20

0.25

0.48

0.53

0.96

0.18

0.63

O F

Hr at IZOO' C

4

4

4

4

4

0.5

0.5

DIFFUSION DISTANCE

g/ t Level

7

7

7

7

7

7

7

Run

8A

2A

5A

6A

l l A

7A

9A

P e r Cent of Original Concentrat ion

C s

1.4

3.0

3.6

2.9*

5.7

13

20

S r

0.3

1.7

0.1*

1.7

6.5

11

25

R a r e E a r t h s

1.9*

0.9

UZ

1.8

12

11

22

Ce

as,

0.4

1.4

1.9

-

IZ

-

*See text , page 39.

- ^ /

3, After me l t i t g , the r ad io -e l emen t s p r e sen t in the s tar t ing m a t e r i a l mus t be r ecoverab le in the slag layers^ the ingot interior^ the crucibles or the furnace a tmosphere and wal l s . The en t r i e s marked "un­accounted' ' in Tables IV-XIV a r e , therefore^ m e a s u r e s of the ac t iv i t ies diffused to the crucible or to the furnace a tmosphe re .

The p e r c e r t a g e s under d iscuss ion a r e tabulated in Table XVIIL

Because the en t r i e s in Table XVIII a r e de termined i n ­d i rec t ly from the summat ion of the analyzed fractionSs the i r accuracy is inde te rmina te , A rough es t imate may be obtained by the following cons ide r ­ation. If the analyzed f ract ions const i tute only 10% of the s tar t ing m a t e r i a l and if the p rec i s ion of i ts ana lys i s i s ± 20% (relative)^ then the activity lost by diffusion will be 90% of the s tar t ing m a t e r i a l , and the p rec i s ion of the value will be t 2 % (absolute), e tc . By this a rgument , the en t r i e s a r e e s t i -inated to have absolute p rec i s ions a s follows:

Activity Lost , % Abs. P rec i s ion , %*

10 20 30 40 50 60 70 80 90

''"Divide by 4 for plutonium.

18 16 14 12 10

8 6 4 2

Inspection of Table XVIII with the foregoing r e m a r k s in mind leads to the observat ion of a definite t rend toward g r e a t e r diffusional l o s se s of the r ad io -e l emen t s a s thei r concentra t ion in the s tar t ing m a t e r i a l i s aug­mented. On re -examin ing Table XV (Run 12A-18A v s . 2A-11A) it miay be seen that s imultaneous with thei r g r e a t e r diffusional l o s s e s the r ad io -e l emen t s b e ­come re la t ive ly l e s s co rxen t ra ted in the slag l a y e r s . The phenomenon i s not s trongly t ime dependent. As a tentat ive explanation it may be suggested that the diffusing a toms may occupy a l imited number of s i tes (^traps'*) in the boundary l aye r s , and that passage of the diffusing a toms through the boundary l aye r s i s consequently r e t a rded until these s i t e s s t a r t to fill up. The number of s i t e s avai lable to each kind of diffusing a tom may be different, depending on a tomic or ionic rad ius or other fac to r s , A very rough es t ima te of the concentra t ion of c e s i u m '' 'traps* in the slag may be made if they a r e a s sumed to have been filled in these exper imen t s . F o r the runs at 7 g / t level the ave rage fraction of the total ces ium found in the slag was 45 ± 5%. The fission

^i2 Table XVIII

ACTIVITIES LOST BY DlFFUSIONa

Percentage of Starting Mater ia l^

Run No.

7A

9A

8A

2A

5A

6A

11A=

IDA

12A

16A

17A

18A

15A

g / t Level

7

7

7

7

7

7

7

7

42

42

42

42

42

Hr at IZOCC

0.5

0.5

4

4

4

4

4

11

4

4

4

4

4 .5

Cs

31

23

54

52

54

55

57

46

94

94

91

94

92

Sr

4 _

6

8

5

-

16

11

58

47

65

64

53

Rare Ear ths

16

21

52

14

12

18

18

26

33

62

19

34

41

P u

-

12

11

6

7

5

-

11

10

23

7

19

30

Te

7

9

7

2

30

-

21

75d

13

42

10

27

35

Nb

3

-

3

-

15

15

6

-

82d

17

_

31

26

Zr

q

4

29

..

fa »

15

3

22

20

l

24

32

Ru

17

1

-

20

5

12

_

-

13

26

9

5

37

^Determined by difference. Dashed entr ies indicate sum of analyzed fractions exceeds 100 %.

"Values rounded to nea res t per cent.

^Crucible leachings included in these values .

"Questionable value.

yield of ces ium is about 6%, arid the total yield of ces ium will be about 12% (33 y. C s " " + 2.1 X 10*" y. Cs''^ ), The slag weight ave rages roughly 3 % of the s tar t ing weight of the uraraum. Accordingly

Conc&nfafon of ccjimri * trap = « g ; = 1 3 * 10"" weigfct fraclion

At the 42 g / t level the average fraction found in the slag is 7 ± 1 % and a s imi l a r calculation yields a ' t rap concent ia t ion ol 1 2 x 10"^. The ca l cu ­lated order of magnitude 10 • i s a quite reasonable value for the fraction of la t t ice imperfect ions in arania capable of accomodating the la rge a toms of ces ium, ^^ If these notions a r e r ea l i s t i c o r e Vtrill expect that a t inuch higher s ta r t ing co tcen t ra t ions of ces ium i ts r emova l by diffusion will be v e r y near ly quantitative Similar calculatior.s foi other r ad io -e l emen t s indicate that the t rapping s i tes available to them were Kot completely filled in these exper imen t s . This i s not too surpiisir^g whet one cons ide r s the per t inent iordc or atomic rad i i . Exper iments at higher levels will be i^eeded for tes t ing this explanation.

In any ca se the data thus ta r obtained give a qualitative indication oi the diffusional t e rdenc ies of the r ad io -e l emen t s . These a r e , in o rde r of decreas ing tendency ces ium ^ s t ion t ium > r a r e ea r t h s > te l lur ium, niobium, z i rconium plutoniam la then ium.

Mention sho-.ld be made of some aromalous ly high diflusion lo s ses for which no explanation is offered. These a r e : r a r e ea r th s in runs 8A and 16A using new alumina c ruc ib les , and niobium in the bo t tom-pour s topper - rod run 12A.

4. The fate of the e lements lost by diifusion has been subjected to p r e l im ina ry investigatior.. In run 1 lA the c ruc ib le in te r ior was acid leached after the run to effect ext ract ion ot some of the subs tances diffused into i ts sur face . L e s s than 0.01% of the s tar t ing u ran ium was thus extracted; but of the r ad io -e l emen t s lost bv diffusion 70 % of the ces ium 50% of the s t ront ium, 42% of the t e l lu r ium and 16% of the r a r e ea r th s were recovereds along with negligible quanti t ies of platonium ruthenium, iiiobium and z i rconium. To what extent these r e c o v e r i e s fell shor t of 100% due to the inability of the leaching to ex t rac t i s not k town. One concl-s ioaj however, can be f i rmly stated, namely: u rder the given exper imenta l conditions (l200°C , he l ium a tmosphere ) significant f rac t ions of the r ad io -e l emen t s diffuse into the c r u ­cible wal ls .

The l a rge exposed surface arid the poros i ty of the c ruc ib le m a t e r i a l s make th is observat ion readi ly usderstai idable . That the phenomenon i s quite genera l in these exper iments i s further verif ied by the constant o b ­servat ion (by survey me te r ) of inter se be t a -gamma activi ty levels near the c ruc ib les aftei the i rgot has been removed .

'The imperfect ion of the lat t ice may va ry f rom place to place depend­ing on i t s inode of formation.

44

/

On the c iher hand the l a ige l o s se s of r ad io -e l emen t s which have been observed by o thers a s a r e su l t of volat i l izat ion at higher t e m p e r a -t a r e s and lower p r e s s u i e s a r e r o t observed in these exper iments . Surveys of the larr .ace walls ar^d exit gas t i a p s aftei completion of a run show only slight radioact ive contaminatioi . By ase of a cold l inger suspended over the c ruc ib le during a run, the p re sence of deposited ces ium pl.»s some other ac t iv i t ies could be picked 'up by gamma ray scinti l lat ion spec t rome t ry . The quanti t ies were inadequate io i rad iochemica l ana lys i s , so the following e x ­pedient was r e s o r t e d to . After 7 runs at the 7 g / t Jevel arid 16 inactive runs the porce la in furnace tube was d i sassembled and thoroughly decontaminated with hot n i t r i c acid. The solution was concentrated and s i l ica removed by fuming with hydro- l luor ic - su l fu r ic acid. Thir ty m i l l i g r a m s of uran ium were r ecovered in this solutiOR, The r e s j l t s of the rad iochemica l ana lys i s a r e shown in Table XIX and a r e compared with typical ana lyses of s tar t ing m a ­t e r i a l s and s lags i r o m the s ame r a r s . At f i r s t glance it may seem that compar ison of the deposit and the s tar t ing m a t e r i a l indicates a strong e n -r i c h m e ' ^ oi the former in a r. imber of r a d i o - e l e m e n t s . C lose r considerat ion of the physical si taatior however indicates that compar ison is m o r e proper ly made with the surface l aye r s throagh which the m a t e i i a l must diffuse. On th is b a s i s it i s evident that or ly ces ium i s definitely volat i l ized. The p r e s e n c e of the non-volat i le elemer.ts a r a u u m zirco-^ium -s-iobi^m and ruthenium in the deposit must be acc0 4.K.ted tor by a slight dusting up of the surface coating of the ingot (This m a t e i i a l has been observed to dast readi ly . ) That they a r e l e s s cor^centrated than in the slag i s due to dusting of the surface coating of inactive ingots . Tel lur ium ir combination with u ian ium mus t be reckoned a s non-volat i le . The data fox the remainirjg e lements does not es tabl ish the i r volati l i ty or non-volat i l i ty unequivocally.

D. Summary

The separa t ion of r ad io -e l emen t s from uranium by the p r o c e s s of melt ing in r e f rac to ry oxide c ruc ib les and subsequent chemica l or mechan i ­cal r emova l of slag has been investigated ir_ a p i e l i m i n a r y fashion. The knowledge gained to date may be sumrnai ized by cOT»sidering the individual e l emen t s .

1. Ces ium - The separa t ion of th is elemer.t i s ent i re ly a dif­fusional p r o c e s s involviK.g a tomic ces ium: cesiijm oxide i s unstable under the given exper imenta l copditions. Diffusion takes plaxe fii st to the envelope of slag, where the avai lable s i t es a r e lapidlv f iked, then to the crucible and the furnace a tmosphe re . The g i o s s r emova l of ces ium from the in te r io r Bietal i s favored by t ime short distar.ce, l a rge cor.ceTitiatior . and probably high t e m p e r a t a r e . The nea r ly quarititative remova l of th is e lement poses no specia l p rob lems except for minimizing the spread of contamination due to volati l i ty.

Table XIX

COMPARATIVE ANALYSIS OF ACTIVITIES DEPOSITED ' ON FURNACE WALLS

Specific Activity, lO''' c p m . / m i l l i m o l e u ran ium

Activity

C s

Sr

R a r e E a r t h s

Ce

T e

Z r

Nb

R u

P u

Total ^

Total 7

Deposit

Z9

1.05

100

97

0.079

3.3

4 .1

0.02

0.046

150

70

Typical Start ing Mater ia l

0,099

0.25

2.6

2 .0

0.0055

1.1

2.2

0.19

0.013

3.7

3.8

Typical Slag""

2.0

15

97

78

0,22

40

11

0.062

* 0.041

140

63

Run 6A

•^L

2 ' Stront ium - The separa t ion of s t ron t ium i s conditioned by 2 fac tors : (a) a s t rong tendency to oxidize so a s to become incorpora ted in the slag la t t ice , and (b) a modera te tendency of s t ront iuin ions to diffuse from the slag to the c ruc ib le . Near ly quantitat ive r emova l of s t ront ium by exaggerat ion of the favorable fac to r s may be expecteda

3. R a r e Ear ths - All the exper imenta l r e s u l t s show the b e ­havior of total r a r e e a r t h s and the r a r e ea r th c e r i u m to be s t r i c t ly pa ra l l e l . The va r i a t ions of behavior within the lanthanide s e r i e s may be expected to be smal l . The r e m a r k s pertaining to s t ront ium a l so apply to the r a r e ea r th elementSo

4a Te l lu r ium - The analyt ical data concerning t e l lu r ium a r e l e s s regu la r than those for the other e lements . If the i r r e g u l a r i t i e s a r e not due to analyt ical uncer ta in t ies caused by the low counting leve l s , other ex ­planat ions must be sought. One possibi l i ty i s that r emova l of t e l lu r ium takes place by m e c h a n i s m s not akin to those operat ing for the previously d i scussed e lements and hence is affected by different v a r i a b l e s . Two likely suggest ions have been proposed: (a) liquation of an in te rmeta l l i c compound (UTe?)s and (b) incorporat ion of t e l lu r ium as t e l lu r ium anions in the s lag. Diffusional loss of t e l lu r ium takes place to a mode ra t e extent.

5. Z i rconium - Zi rconium may be cha rac t e r i zed a s an e lement which is incorpora ted into the slag somewhat l e s s readi ly than s t ront ium or the r a r e ea r ths but s t i l l much m o r e than would be predic ted on the b a s i s of i t s oxide stabil i ty alone. To what extent th is is due to the fact that the f o r m a ­tion of z i ronium carb ide may play a ro le cannot be a sce r t a ined . Removal of z i rcon ium by diffusional l o s s t akes place to a smal l extent. In general^ the fac tors that favor the r emova l of ce s ium, s t ront ium, r a r e ea r th s and t e l lu r ium do not a l so enhance the r emova l of z i rconium to any marked extent. A m o r e c lean-cu t separa t ion of z i rconium from uranium by chemica l ine ta l lurg ica l m e a n s would s e e m to depend on the development of additional t rea tments^ e,g.j exaggerated liquation of added carbide^ volat i l izat ion of zirconiuixi fluoride^ or o the r s ,

6* Niobium - The r e m a r k s made with r e s p e c t to z i rcon ium apply with st i l l m o r e force to niobium. It will be of spec ia l i n t e re s t to a s ­ce r t a in whether or not the excel lent separa t ion of niobium encountered in the s toppe r - rod run can be duplicated and, if so^ to de t e rmine the causat ive fac to r s .

"^' P lutonium - Plutonium behaves in a fair ly pred ic tab le m a n ­n e r . It i s misc ib le with liquid u ran ium and fo rms an ideal solution the re in . ^ Extens ive , and probably nea r ly ideal , solid solutions occur among the oxides of the 2 e l ements , Plutonium i s l e s s readi ly oxidized than uraniumi, and i t s

Cubiciott i , D,, NAA-242.

47

re te r t ion in the melt i s near ly complete except for a sma l l fraction which i s lost by diffusion. At the exper imenta l t e m p e r a t u r e and p r e s s u r e used in these exper iments the loss by volati l ization is negl igible .

8. Ruthenium - Ruthenium is a'^ eas i ly reduced noble meta l , and i t s loss f rom the melt i s quite negligible by ei ther slagging or diffusion. The smal l amounts actually encountered in the slag layer can be ent i re ly accounted for by the me ta l inclusions found the re in . The one exceptional observat ion of ruthenium remova l in which a z i rconia crucible was employed r e q u i r e s further sc ra t iny .

9. M o l y b d e n a m - Not enough a n a l y s e s for t h i s e l e m e n t h a v e b e e n m a d e t o jus t i fy i t s i n c l u s i o n in t h e t a b u l a t i o n s . In 3 r u n s , a n a l y s e s of s t a r t i n g m a t e r i a l s and ingot i n t e i i o r s for m o l y b d e n u m c o n c e n t r a t i o n s w e r e m a d e . T h e r e s u l t s ol t h e s e a n a l y s e s a r e g iven in T a b l e XX, In e a c h c a s e , n o c h a n g e wi th in e x p e r i m e n t a l e r r o r c a n b e d e t e c t e d . A v e r y p r o b a b l e c o n c l u s i o n f r o m t h e s e e x p e r i m e n t s and f r o m t h e p o s i t i o n of m o l y b d e n u m in t h e p e r i o d i c t a b l e and in T a b l e II p a g e 8^ i s t h a t i t s b e h a v i o r i s c o m ­p l e t e l y a n a l o g o a s t o t h a t of r u t h e n i u m .

T a b l e XX

ANALYSIS O F M O L Y B D E N U M IN INGOT I N T E R I O R S AND S T A R T I N G M A T E R I A L

M a t e r i a l . ORNL i r r a d i a t e d s l u g s , 3 0 0 - 3 3 0 d a y s coo led C o n d i t i o n s . 4 h r a t 1200°C % f lowing h e l i u m a t m o s p h e r e ^ 110 c c / m i n .

Run

7A

12 A*

15A

C r u c i b l e

UO2

ThOz

ZrOz

g . / t . L e v e l

7

42

42

C h a r g e

g=

57 .9

263,2

68.0

M o l y b d e n u m C o n c e n t r a t i o n f i g . / g . U r a n i u m

Ingot I n t e r i o r S t a r t i n g M a t e r i a l

1.1 0.87

3 . . 3,^

3,- 3 •3

Bottom-pour s topper - rod run,

10. Total Beta and Gammia Act ivi t ies - The g r o s s ac t iv i t ies were followed in the exper imenta l work because they afJorded an excellent oppor­tunity for c ro s s - check ing the individual analyt ica l r e s u l t s . The m e a s u r e m e n t of these ac t iv i t ies has lit+le i n t r i r s i c i n t e r e s t un less the i r rad ia t ion and cooling of the me ta l has been specified. When the r emova l of a l l the individual f ission produc ts car. be p rede t e rmined by means of adequate exper imenta t ion the g r o s s r emova l of f ission activi ty will become calculable a s a function of i r rad ia t ion and cooling t ime .

48

IV. APPLICATION TO NUCLEAR FUEL PROCESSING

The na tu re of the chemica l meta l lu rg ica l manipulat ions under d i s ­cussion does not lead to the expectation that further development can achieve the kind of f ission product decontamination now requi red to make poss ib le non- remote handling oi the end product . This c i i cums tance s t rongly m i t i ­gates against the notion that these methods will find application in the c o m ­plete p ioces s ing of the luel ot any existing nuc lear r e a c t o r . More likely., the appropr ia te applicat ions of such new p r o c e s s e s will be found in connection with r e a c t o r s planned for the future, in which the remote handling and r e -fabrlcation fea tures can be made in tegra l with the csver-all des ign. Moreover , because the specific p r o c e s s investigated in th is r epor t i s one in which plutonium is not separa ted f rom uranium, it s e e m s likely that i t s application can be made most readi ly to a plutonium-enriched fuel. The Power Breede r Reac to r ( P B R ) i s one to which the p r o c e s s under development can be applied in a nea r ly ideal fashion. F i r s t , the PBR is in the planning stagCj and hence the concepts of r emote p rocess ing and refabr icat ion can be integrated in the plan. Second, the fuel m a t e r i a l p resen t ly planned is u ran ium enriched with 10% plutonium. Third , the expected daily turnover of the fuel is smal l and so is ideally saited to the smal l batch operat ions envisioned. Four th , the PBR opera te s in the fast neutron region where the nuc lear c r o s s - s e c t i o n s of the f ission e lements a r e monotonic functions of the a tomic number . Consequently, no specific e lement need be removed to ex t r eme l imi t s , and it i s n e c e s s a r y only to r emove a g r o s s fract ion of tota l f ission product m a s s ; the r emova l need be only to such a degree that the depress ion of reac t iv i ty by the r e m a i n ­der i s readi ly overcome . Fifths the burnup of a toms in the PBR core is planned to be so l a rge that the p i inc ip le pu rposes of r ep rocess ing a r e the el imination of radiat ion damage and the reconst i tu t ion of the nuclear components ; these functions a r e readi ly served by melt ing, alloying and r ecas t ing .

An in t e r im r e s e a r c h r epor t like the p re sen t one often tends to be wr i t ten with only the m o r e obvious goals in mind. It may well be that chemica l me ta l lu rg ica l p rocess ing of nuc lear fuels will in the future play a m o r e signifi­cant ro le than i s now visual ized even by i t s advocates ,

V. ACKNOWLEDGEMENTS

The au thors wish to acknowledge with gra t i tude help f rom many p e r s o n s who have contributed grea t ly to th is work: B. Blumenthalj for continuing con­sultation and the loan of equipment: J. H, Schraidt and H. Smith, for furnace design and drafting: D. C. Hampson and J, Jos t for a s s i s t a n c e in p rocu remen t

A chemica l me ta l lu rg ica l operat ion might find application a s a head ­end step in connection with existing p r o c e s s e s and r e a c t o r s . Such an operat ion would se rve to effect a bulk re inoval of fission products in concentrated forin and to reduce radiat ion damage in p r e sen t p r o c e s s e s such a s solvent ext ract ion.

and construction; D. P^ Krause and L. E. Ross, for conscientious efforts to meet a demanding schedule of radiochemical analyses; C. E. Crouthamel, for the development of new analytical methods for trace nnolybdenum and radiosamiarium and radioeuropium; D, S. Flikkema for optical and X-ray diffraction analyses; H, H, Chlswick, for photomicrographic examinations; J, Fa r i s , for spectrochemical analyses. The staff members of the Chemical Engineering Division are thanked for stimulating discussion and crit icism.