BEHAVIOR OF TRIBUTYL PHOSPHATE IN A-LINE PROCESSES

H. D. Harmon, M. L. Hyder, B. T i f f a n y , L. W . Gray, and P. A. S o l t y s

Approved by

M. L. Hyder, Research Manager Separat ions Chemistry D i v i s i o n

P u b l i c a t i o n Date: August 1976

sponrod by the United Stater Government. Neither the United Stater nor the United Statu Energy Research and Dcrelopmnt Administration. nor any of Ulcu cmployccs, "0. any O f lhci mntrrctor.. rubcontneton. 01 their crnplayees. makes m y wnmnty, cxpreu or impbed. or asurnel any legal liability or responsibility for the acculacy, cornpletcnev. or urfulnca of any information. a p p ~ a t ~ , p r o d ~ t or Q ~ O - S disclosed, or reprc~.%t~ that 11% use would not infnngc pnvatcly o w e d right%

E. I . DU PONT DE NEMOURS A N D C O M P A N Y

SAVANNAH RIVER LABORATORY

AIKEN, SOllTH CAROLINA 29801

PREPARED FOR THE U. S. ENERGY RESEARCH AND DEVELOPMENT ADMINISTRATION UNDER CONTRACT AT107-21-1

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.

ABSTRACT

The chemical and phys ica l p r o p e r t i e s of uranyl n i t r a t e - t r i b u t y l phosphate adduct (UO2) ( N 0 3 ) 2(TBP) 2 were s tud ied t o d e f i n e optimum, s a f e opera t ing condi t ions f o r d e n i t r a t i o n of uranyl n i t r a t e (UN) s o l u t i o n s containing low concent ra t ions of adduct.

The d i s t r i b u t i o n of TBP between aqueous UN s o l u t i o n s and organic phases (TBP pure o r d i l u t e d i n n-paraf f in) was measured.

S p e c i f i c g r a v i t y measurements confirmed publ ished d a t a f o r aqueous UN s o l u t i o n s , b u t d i sagreed with l i t e r a t u r e da t a f o r 100% TBP. I n t e r s e c t i o n of t h e UN s p e c i f i c g r a v i t y curve and t h e 100% TBP da t a of t h i s work ind ica t ed t h a t phase invers ion cannot occur when t h e aqueous phase conta ins 2330 g U / 1 .

Thermal decomposition of adduct occurs i n one gradual weight l o s s s t e p below 1 7 O o C and i n two success ive s t e p s above 170°C. Rate cons t an t s f o r t h e f i r s t r e a c t i o n were ca l cu la t ed f o r 130 t o 210°C. The major flammable decomposition product was 1-butene; inorganic gases formed were N 2 , NO, N 2 0 , C O Y and co2.

Adduct decomposition during d e n i t r a t i o n of UN was charac- t e r i z e d by foaming and by gas evolu t ion (most ly nonflammable) a t 135 t o 185°C.

Maximum flammable gas evolu t ion and p o t e n t i a l s e l f - h e a t i n g by TBP ox ida t ion were c a l c u l a t e d .

CONTENTS

In t roduct ion 5

Experimental 5

TBP Di s t r ibu t ion Measurements 5 S p e c i f i c Gravi ty Measurements 6 Thermogravimetric--Mass Spec t r a l Analyses 6 Gas Chromatographic Analyses 6 Den i t r a t ion Tes ts 7 Mater ia l s 7

TBP D i s t r i b u t i o n S tudies 8

S p e c i f i c Gravity of TBP and Uranyl N i t r a t e Solu t ions 11

Thermal Decomposition of Adduct 15

Thermogr avime t ri c Anal ys e s Rate Constant Calcu la t ions f o r First Adduct Reaction 1 7 Analysis of Gaseous Decomposition Products

15

19

Den i t r a t ion S tud ie s 2 2

E f f e c t of Heatup Rate on Foaming Ef fec t of Adduct Concentration 24 E f f e c t of Antifoam 24 Analysis of Gaseous Decomposition Products

2 2

26

Calcu la t ion of Maximum Flammable Gas Evolution during Deni t ra t ion 29

E f fec t of Self-Heat ing on t h e Adduct Decomposition Rate 32

Appendix - Computer Program f o r Deni t ra tor Off-Gas Calcula t ions 35

References -77

BEHAVIOR OF TRIBUTYL PHOSPHATE I N A-LINE PROCESSES

INTRODUCTION

On February 1 2 , 1975, an uncont ro l led , exothermic r e a c t i o n occurred i n t h e Savannah River P lan t (SRP) f a c i l i t y f o r UO3 pro- duc t ion . This f a c i l i t y (A-Line) r ece ives d i l u t e uranyl n i t r a t e (UN) s o l u t i o n ( ~ 9 0 g U / 1 ) from t h e Purex so lvent e x t r a c t i o n process , concent ra tes t h e s o l u t i o n by two evaporat ion s t e p s , and converts t h e concentrated s o l u t i o n (Q1200 g U/1) t o U O 3 by thermal d e n i t r a t i o n . The excess ive r e a c t i o n occurred when >30 g a l of t r i b u t y l phosphate (TBP) i n t h e form of UO2 ( N 0 3 ) 2 (TBP) 2 (adduct) was a c c i d e n t a l l y charged t o a d e n i t r a t o r ; t h e adduct decomposed forming flammable gases which escaped i n t o t h e d e n i t r a t o r room and subsequent ly i g n i t e d .

Small amounts of en t r a ined o r d i sso lved TBP e n t e r A-Line process s t reams, and a l l of t h e TBP cannot be removed from t h e uranyl n i t r a t e s o l u t i o n s with present equipment. Thus, t h e d e n i t r a t o r s must be operated t o slowly decompose small amounts of TBP under con t ro l l ed condi t ions . d e n i t r a t o r condi t ions , thermal decomposition of adduct, d e n i t r a t i o n of uranyl n i t r a t e with adduct p re sen t , and gas evolu t ion during adduct decomposition were s tud ied ; some phys ica l p r o p e r t i e s of t h e TBP-uranyl n i t r a t e system were a l s o determined. maximum flammable gas evolu t ion and p o t e n t i a l hea t r e l e a s e s during adduct decomposition were ca l cu la t ed .

To de f ine t h e optimum

In add i t ion ,

EXPERIMENTAL

TBP D i s t r i b u t i o n Measurements

The d i s t r i b u t i o n of TNP i n t o UN s o l u t i o n s was determined by contac t ing 20 m l of aqueous UN solut ior ls (50 t o 400 g U/1) with 2 m l of l o o % , 90%, and 30% TBP (n-paraf f in d i l u e n t ) . The n - p a r a f f i n d i l u e n t c o n s i s t s of a mixture of C 1 3 - c l 4 hydrocarbons with an average molecular weight of 191. The phases were gent ly a g i t a t e d i n a shaker ba th a t t h e chosen temperature (25 t o 65OC) f o r 23 t o 64 h r and were allowed t o sepa ra t e f o r 16 t o 64 h r . This extended procedure was followed i n o rde r t o : equi l ibr ium without vigorous a g i t a t i o n and poss ib l e entrainment , and 2 ) achieve complete phase sepa ra t ion without removing t h e v i a l s from t h e cons tan t temperature ba th f o r c e n t r i f u g a t i o n .

1) reach

- >-

TBP concent ra t ions i n t h e UN s o l u t i o n s were determined by both phosphate and i n f r a r e d (IR) ana lyses . For the phosphate method, TBP was oxidized t o P O k 3 - by hea t ing i n a HNO~-H~SO~-HZO~ media u n t i l SO3 fumes were observed. The concent ra t ion was then determined by a molybdenum b lue co lo r ime t r i c method.' For t h e I R method, a 10-ml a l i q u o t of UN s o l u t i o n containing d isso lved TBP was s t r i p p e d with t h r e e % 3 - m l volumes of C C l 4 , and t h e combined C C 1 4 s t r i p was d i l u t e d t o 10 m l i n a volumetr ic f l a s k . The TBP concent ra t ion was determined by measuring t h e absorbance of t he C C 1 4 s o l u t i o n a t 2876 cm-l (C-H band) and by use of a s u i t a b l e c a l i b r a t i o n curve. Extreme care was taken i n p i p e t t i n g t o avoid contaminating UN samples with undissolved TBP s o l u t i o n , e s p e c i a l l y wi th 30% and 90% TBP,because n-paraf f in i n t e r f e r e s by absorp t ion i n t h e same IR region.

Specific Gravity Measurements

For s p e c i f i c g r a v i t y measurements, 100% and 90% TBP (n- p a r a f f i n d i l u e n t ) s o l u t i o n s were contacted twice with aqueous UN s o l u t i o n s a t aqueous-to-organic volume r a t i o s of 2.5 a t 25°C. Equ i l ib ra t ed aqueous s o l u t i o n s were analyzed f o r U and "03, and s p e c i f i c g r a v i t i e s of t h e organic p h a s e s and s e v e r a l aqueous s o l u t i o n s were determined us ing 5- o r 10-ml volumetr ic f l a s k s . The f l a s k s were c a l i b r a t e d t o k0.002 m l a t 25OC with t r i p l y d i s t i l l e d water. Volume c o r r e c t i o n s f o r 45OC and 65°C were c a l c u l a t e d assuming t h e cub ica l c o e f f i c i e n t of expansion o f b o r o s i l i c a t e g l a s s t o be 0 .000025"C-1.

Thermogravimetric-Mass Spectral Analyses

For thermogravimetric-mass s p e c t r a l analyses (TGA-MS) a modified Model RH e lec t roba lance (Cahn Instrument Co., Paramount, CA) was used with both helium and 80% He - 20% 0 2 atmosphere. The evolved gases were f e d t o a Model MS-10 mass spectrograph (AEI S c i e n t i f i c Apparatus Corp., Elmhurst, IL) .

Gas Chromatographic Analyses

Gas chromatographic ana lyses were made with a Hewlett- Packard Model 5756B gas chromatograph equipped with thermal conduc t iv i ty and flame i o n i z a t i o n d e t e c t o r s , and a Finnigan Model 1015C quadrupole mass spec t rometer (QMS) f i t t e d with a g l a s s j e t s e p a r a t o r f o r sample enrichment i n t h e gas stream. The helium flow r a t e was 100 cc/min; approximately 45 cc/min i s suppl ied t o each d e t e c t o r , and 10 cc/min i s suppl ied t o the QMS.

- 6 -

Inorganic and lower molecular weight organic gases (methane through butane) were separa ted with,a 6 - f t glass column. The column was packed with 30/60-mesh SA molecular s i e v e which was he ld a t 24°C with dry i c e f o r f i v e minutes and then heated a t 40"C/min t o 300°C.

The p o l a r organic compounds (organic a c i d s , a l coho l s , aldehydes, ketones, and n i t r a t e s ) were separa ted on a 6 - f t g l a s s column packed with 10% Ca~~bowm*-20M t e r e p h t h a l i c ac id on 100/ 1 2 0 mesh high-performance Chron W. The column was heated from 50 t o 180°C a t 10"C/min.

Osc i l lographic s t r i p cha r t recordings of mass spec t r a were i n t e r p r e t e d manually by comparison with s tandard mass s p e c t r a l compilat ions. The concent ra t ions of organic ac ids were t o o low f o r d e f i n i t e mass s p e c t r a l i d e n t i f i c a t i o n . Mass s p e c t r a l d a t a agreed with re ference s p e c t r a f o r a l l o the r observed compounds.

D e n i t r a t i o n T e s t s

Deni t ra t ion experiments ( a c t u a l l y a combined hydrate evap- o r a t i o n and d e n i t r a t i o n ) were conducted with 250 m l of i n i t i a l UN s o l u t i o n (400 g U / 1 ) i n 500-ml s t a i n l e s s s t e e l beakers; t he beakers were equipped with thermocouples t o measure t h e tempera- t u r e of t h e bulk UN s o l u t i o n and t h e beaker su r face . The beakers were i n s u l a t e d with asbes tos t o f a c i l i t a t e temperature c o n t r o l . In most t e s t s , t h e hea t ing r a t e was %2"C/min during adduct de- composition. S t i r r i n g r a t e s were 100 rpm except i n t e s t s using SRP feed s o l u t i o n s . For t h e s e s o l u t i o n s , t h e s t i r r i n g r a t e was decreased t o 18 rpm f o r b e t t e r r ep resen ta t ion o f SRP opera t ion .

M a t e r i a1 s

U 0 2 ( N 0 3 ) 2 (TBP) 2 was prepared both by repeated e q u i l i b r a t i o n of TBP with 400 g U / 1 s o l u t i o n s and by contac t of TBP with seve ra l f r e s h q u a n t i t i e s of s o l i d uranyl n i t r a t e hexahydrate (UNH) ( u n t i l r e l eased water of hydrat ion was no longer observed, and t h e maximum s p e c i f i c g r a v i t y was obta ined) . Analyses of adduct samples a r e shown i n Table 1. The a n a l y t i c a l r e s u l t s and l i t e r - a t u r e d a t a 4 i n d i c a t e t h a t t he adduct prepared by contac t ing aqueous so lu t ions probably contained 0 . 2 t o 0 . 3 w t % ex t r ac t ed water .

* Registered tradename of Carbide and Carbon Chemical Co.

TABLE 1

Elemental Analyses of Adduct Used in The rmog ra v i met ri c An a 1 y s e s

Composition, u t % Element Calculated Smple Aa Sample Bb

U 25.69 25.19 25.90

P 6.68 6.48 6.61

a . Prepared by repea ted ly contac t ing aqueous 400 g U / 1 s o l u t i o n with TBP.

b . Prepared by contac t ing s o l i d U" and TBP.

TBP, n -pa ra f f in , and Antifoam B emulsion (Dow-Corning) were obta ined from t h e Savannah River P lan t . A l l o the r chemicals used were r e a g e n t g r a d e .

TBP DISTRIBUTION STUDIES

The equi l ibr ium TBP conten t of UN s o l u t i o n s was measured t o determine t h e maximum q u a n t i t y of TBP which could e n t e r A-Line process streams by t h i s mechanism. The s o l u b i l i t y o r d i s t r i b u t i o n * of TBP i n UN s o l u t i o n s decreased as uranium concent ra t ion increased (Figures 1 and 2 ) . Thus, p a r t of t h e TBP d i s so lved i n t h e d i l u t e UN s o l u t i o n (90 t o 100 g U/1) from so lvent e x t r a c t i o n w i l l slowly s e p a r a t e as a second adduct phase a f t e r t h e UN s o l u t i o n i s concen- t r a t e d t o Q400 g U / 1 i n A-Line.

TBP concent ra t ion decreases with inc reas ing n - p a r a f f i n d i l u e n t concent ra t ion (Figure 2 ) , p a r t i c u l a r l y a t (200 g U / 1 , because TBP has a lower a c t i v i t y i n t h e d i l u t e phase and, t he re - f o r e , i s a t equi l ibr ium with a lower concent ra t ion of aqueous TBP. A s i m i l a r e f f e c t of d i l u e n t concent ra t ion was observed i n ORNL s t u d i e s .

Resul t s o f t he IR method of a n a l y s i s were c o n s i s t e n t l y h igher than those o f t h e phosphate method (Figures 1 and 2 ) . To i n v e s t i - ga t e t h i s d i f f e r e n c e , TBP d i s t r i b u t i o n i n t o water was measured by both methods and compared i n Table 2 t o r e s u l t s from an independent method5 ( 3 2 P count ing) . Because t h e 3 2 P r e s u l t s a r e about midway between the phosphate and IR r e s u l t s , t h i s comparison gives no b a s i s f o r determining which method i s more accura te . However, t h e

*The term " s o l u b i l i t y " a p p l i e s only f o r 100% TBP; with excess TBP o r with d i l u e n t p re sen t , TBP i s d i s t r i b u t e d between t h e organic and aqueous phase a t equi l ibr ium.

- 8-

f a i r agreement between a l l t h r e e methods i n d i c a t e s t h a t t h e phosphate and I R methods a r e accura te wi th in a f a c t o r of 2 . A-Line process a p p l i c a t i o n s , t h e I R r e s u l t s a r e most p e r t i n e n t because a similar method i s used by SRP l a b o r a t o r i e s t o analyze A-Line s o l u t i o n s .

For

I I I 1 .;300h c a, u c

200 0

90% TBP -

-

- a m

rn 3 0 a,

rn 3 0 a, 3

200 300 400 B 00 100

Equilibrium Uranium Concentration, q b

FIGURE 1. Distribution of TBP (in n-paraffin) into Aqueous Uranyl Nitrate Solutions at 25°C (Analyzed by Phosphate Method)

Equilibrium Uranium Concentration, g / l

FIGURE 2. Distribution o f TBP (in n-paraffin) into Aqueous Uranyl Nitrate Solutions at 25°C (Analyzed by Infrared Method)

- 9-

TABLE 2

Distribution o f TBP in Water at 25°C

TBP Concentration, mg/Z TBP, voZ Xa Methodb I R Methodb 32P Method

30 19 8 305 23SC

90 314 420 39 Off

100 336 466 410

a. Diluent i s n -pa ra f f in i n p re sen t work; ORNL used Amsco 123-15, a similar kerosene-type d i l u e n t .

b. Phosphate r e s u l t s a r e t h e average of t h r e e de t e r - minat ions; t h e I R r e s u l t s a r e one measurement.

Obtained by g raph ica l i n t e r p o l a t i o n of ORNL d a t a i n Reference 5.

c.

The e f f e c t of temperature on TBP d i s t r i b u t i o n could n o t be i n t e r p r e t e d wi th c e r t a i n t y because of i r r e g u l a r i t - i e s i n t h e d a t a . The d i f f e r e n c e between t h e I R r e s u l t s and t h e phosphate r e s u l t s i nc reased wi th inc reas ing temperature and TBP concent ra t ion . This r e l a t i o n s h i p suggested a chemical e f f e c t r a t h e r than ana ly t - i c a l d i f f i c u l t i e s . I n add i t ion , as t h e temperature was increased from 25 t o 45"C, TBP d i s t r i b u t i o n decreased, e s p e c i a l l y a t lower uranium concen t r a t ions (Figure 3 ) . A decrease i n TBP d i s t r i b u t i o n was a l s o observed by Kennedy and Grimley6 f o r 16 t o 22°C. ever, t h e 55 and 65°C experiments of t h e p re sen t work exh ib i t ed a r e v e r s e i n t h i s t r e n d with t h e 65°C d a t a (confirmed by d u p l i c a t e runs) showing t h e h ighes t r e s u l t s of any experiment i n t h e 200 t o 4 0 0 g U / 1 range. This unexpected temperature e f f e c t a l s o suggested some chemical phemmenon.

How-

I n v e s t i g a t i o n i n d i c a t e d t h a t TBP hydro lys i s was t h e cause of t h e s e i r r e g u l a r i t i e s . h r before t h e samples were analyzed. us ing publ i shed r a t e c o n s t a n t s 7 for TBP i n 0.25M UN-0.05M HN03 i n d i c a t e d 0.08% hydro lys i s occurred a f t e r 80 hr a t 25°C and 7.7% hydro lys i s a f t e r 80 h r a t 65°C. Thus, enough hydro lys i s could have occurred a t t h e h i g h e r temperatures t o a f f e c t t h e d i s t r i b u t i o n measurements. fo l lowing e q u i l i b r a t i o n t imes of 6 t o 64 hours showed t h a t any change i n aqueous TBP concent ra t ion due t o hydro lys i s was less than experimental e r r o r .

Some d i s t r i b u t i o n experiments l a s t e d %SO TBP hydro lys is was c a l c u l a t e d

However, measurement of TBP d i s t r i b u t i o n a t 25OC

- 10-

300

250

QY

E

\ Is,

200 c 0 . _ t

P - c W v 150 C 0 0 a I- m cn 100 3 0 W 3 0- a

50

e

- -i 0

0 I O 0 200 30 0 400 Equilibrium Uranium Concentration, g/d

S o l u t i o n s as a F u n c t i o n o f Temperature. 35 and 55°C were n o t shown because o f o v e r l a p . (Analyzed b y Phosphate Method)

FIGURE 3. D i s t r i b u t i o n o f TBP i n t o Aqueous Uranyl N i t r a t e Data a t

SPECIFIC G R A V I T Y OF TBP AND URANYL NITRATE SOLUTIONS

S p e c i f i c g r a v i t y d a t a f o r UN s o l u t i o n s and f o r TBP i n equi l ibr ium with UN s o l u t i o n s a r e important t o A-Line opera t ions t o allow choice of opera t ing condi t ions which w i l l prevent phase invers ions (heavy organic l a y e r ) , and t o design a coa lescer u n i t f o r poss ib l e use i n removing en t ra ined organic m a t e r i a l .

-11-

The r e s u l t s ob ta ined agree well with l i t e r a t u r e d a t a 4 (Figure 4) except f o r 100% TBP. based on one high r e s u l t a t 500 g U / 1 i n t h e aqueous phase. In t h e p re sen t work, repea ted contac t of TBP with f r e s h q u a n t i t i e s of c r y s t a l l i n e U" yie lded a maximum s p e c i f i c g rav i ty of 1.467. The high l i t e r a t u r e va lue i s t h e r e f o r e ques t ionable . I n t e r s e c t i o n of t h e UN s p e c i f i c g r a v i t y curve and t h e 100% TBP d a t a of t h e p re sen t work ind ica t ed t h a t phase invers ion cannot occur when the aqueous phase conta ins >330 g U/1.

The s t e e p s lope of t h e l i t e r a t u r e d a t a 4 i s

1.8

1.7

I .6

A c

5 1.5

c3 E

0 . _ Lc ._ " 1.4 W a v,

1.3

1.2

0 100% T B P , Present Wor A 90% TBP, Present Work

UN, Present Work

0 100% T B P , Reference 4 W UN, Reference 4 All measurements a t 25°C

d I 1.1 ~

Aqueous U r a n i u m Concent ra t ion , g / P

FIGURE 4. S p e c i f i c Gravit,v of TBP and Uranyl N i t r a t e Solut ions

- 12-

The e f f e c t of temperature on s p e c i f i c g r a v i t y of UN and TBP s o l u t i o n s was a l s o determined. S p e c i f i c g r a v i t i e s of UN s o l u t i o n s (Table 3) decreased only a few percent as t h e temperature increased from 25 t o 65°C. S imi la r decreases were observed f o r TBP s o l u t i o n s i n equi l ibr ium with UN s o l u t i o n s (Table 4 ) . TBP s p e c i f i c g r a v i t y decreased due t o l e s s uranium e x t r a c t i o n a t h igher temperatures and thermal expansion e f f e c t s . The e f f e c t of thermal expansion a lone i s shown i n Table 5; i n t h i s case, s p e c i f i c g r a v i t y of t h e TBP s o l u t i o n i n equi l ibr ium with 373 g U / 1 was measured a t 25, 45, and 65°C without add i t iona l e q u i l i b r a t i o n with t h e aqueous phase. Based on t h e observed changes between d a t a i n Table 5 and d a t a i n Table 4 , thermal expansion was t h e major cause o f t h e observed s p e c i f i c g r a v i t y changes. Because s p e c i f i c g r a v i t y of TBP and UN s o l u t i o n s decreased with increas ing temperature by approximately t h e same percent , opera t ing condi t ions t h a t prevent phase invers ion a t 25°C w i l l a l s o apply a t h igher temperatures .

\

TABLE 3

E f f e c t o f Temperature on t h e S p e c i f i c G r a v i t y o f Uranyl N i t r a t e Sol u t i ons

U Concen- Temperature, UN S p e c i f i c t ra t ion , g/Z *C Gravi ty

Spec i f ic Gravity Difference from 2S°C, %

38.9 25

45

65

1.066

1.059

1.048

-

-0.66

-1.69

1 9 7 . 5

387.6

25 1 . 2 6 7

45 1.257

65 1 . 2 4 7

-

-0 .79

-1.58

25

45

65

1.536

1.521

1.506

-

-0.98

-1 .95

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TABLE 4

E f f e c t o f Temperature on t h e S p e c i f i c G r a v i t y o f TBP Contacted w i t h Uranyl N i t r a t e So lu t i ons

Original Equi Zibr-iwn TBI' Specific (iravi t y TBP Concen- Aqueous / I , Aqueous U, Temperature, Specific Difference from tration, uol X g / 1 g/1a "C &-avity 25"C, %

100 350 340.0 25 1.441

322.0 45 1.431 -0 .69

332.6 65 1.404 -2 .57

100 400 382.0 25 1.441

379.4 45 1.433 -0 .56

382 .3 65 1.408 -2.29

90 350 329.5 25 1.379

337.9 45 1.357 -1 .60

339.8 65 1.346 -2.39

90 400 379.1 25 1.382

380.2 45 1.364 -1 .30

388.0 65 1.352 -2.17

a . Ilecreased uranium e x t r a c t i o n a t h i g h e r tempera tures should be r e f l e c t e d by i n c r e a s i n g e q u i l i b r i u m aqueous uranium c o n c e n t r a t i o n s . This e f f e c t i s not observed €or t h e 100% TBP d a t a probably because of v a r i a t i o n s i n t h e uranium c o n c e n t r a t i o n of t h e nominal 350 g U / 1 and 400 g U / 1 s o l u t i o n s .

TABLE 5

E f f e c t o f Thermal Expansion on t h e S p e c i f i c G r a v i t y o f TBP Equi 1 i b r a t e d w i t h Urany l N i t r a t e S o l u t i o n

S p e c i f i c Gravity Temperature, S p e c i f i c Dif ference from Oca Gravity 25'C, %

25 1.446

45 1.427 -1.31

65 1.410 -2 * 49

a. Equilibrium uranium concentration was 373 g U / 1 at 2 5 O C . The TBP solution was heated to 45°C and 65OC €or specific gravity measurements without additional equilibration with the aqueous uranyl nitrate solution.

THERMAL DECOMPOSITION OF ADDUCT

Thermogravimetric Analyses

Thermogravimetric analyses (TGA) of adduct showed weight l o s s i n two success ive r eac t ions at '>170°C, and only a s i n g l e gradual weight l o s s a t lower temperatures (Figure 5 ) . l o s s a t lower temperatures and t h e weight l o s s from t h e f i r s t r e a c t i o n a t >170°C correspond c lose ly t o the formation of anhydrous UN and phospKoric ac id . decomposition of organic molecules could provide t h e hydrogen needed t o form phosphoric ac id . )

The weight

(The presence of en t ra ined water o r t h e

Weight loss c a l c u l a t i o n s f o r t h e second r e a c t i o n suggest formation of one o r more of t h e fol lowing combinations of products ( i n o rde r of decreasing agreement with experimental r e s u l t s ) :

e Uranyl phosphate and pyrophosphoric ac id

0 Uranyl phosphate and phosphoric ac id

e U 0 3 and pyrophosphoric ac id

e UO3 and phosphoric ac id

- 15-

I I I I

, I 0.8

I 7 8 9 I O

0.3 1 0 I 2 3 4 5 6

Ti me, hours

F IGURE 5. Thermogravimetric Analysis o f Adduct

In some cases , t h e second r e a c t i o n of adduct appeared t o fol low zero-order k i n e t i c s during p a r t of t h e r e a c t i o n . d e n i t r a t i o n of uranyl n i t r a t e fol lows zero-order k i n e t i c s ' and weight l o s s c a l c u l a t i o n s ind ica t ed U03 formation, t h e second adduct r e a c t i o n was thought t o involve d e n i t r a t i o n of U N . How- eve r , T G A s of UNH d i d no t resemble adduct TGA curves during t h e second adduct r e a c t i o n . gases showed t h a t organic products a r e formed during both t h e f i r s t and second adduct r e a c t i o n s . occur r ing during t h e second adduct r e a c t i o n , bu t o the r r e a c t i o n s are occurr ing s imultaneously.

Because

A l s o , mass s p e c t r a l analyses of evolved

Den i t r a t ion of UN may be

Residues were obta ined from hea t ing of adduct t o 130, 170, and 210°C; t h e s e r e s idues were examined t o determine t h e r e a c t i o n s occurr ing on hea t ing adduct. t h e r e s idues contained mostly uranium and phosphate. A s expected, t h e q u a n t i t y of r e s i d u a l organic m a t e r i a l decreased with increas ing temperature . U3(PO4)4 and UP207 i n t h e 13OoC r e s i d u e ; t h e 170°C and 210°C r e s idues were amorphous and could no t be i d e n t i f i e d . i n t h e r e s idues may not be t h e products of t h e primary adduct decomposition r e a c t i o n because of a d d i t i o n a l r e a c t i o n s occurr ing wi th in t h e r e s idue .

Chemical analyses ind ica t ed t h a t

X-ray d i f f r a c t i o n analyses showed some evidence of

Products

- I h -

Rate Constant C a l c u l a t i o n s f o r F i r s t Adduct Reac t ion

The weight l o s s (weight of v o l a t i l e r e a c t i o n products . evolved) of adduct samples with t ime were measured t o determine decomposition r a t e cons tan ts f o r t h e f i r s t adduct r e a c t i o n . * The weight of adduct a t any in te rmedia te time during t h e f i r s t r e a c t i o n minus t h e f i n a l weight a t t h e completion of t h a t r e a c t i o n r ep resen t s t h e weight of v o l a t i l e component (decomposition products) remaining i n t h e sample. p ropor t iona l t o the amount of adduct no t decomposed. A similar approach was used by Nicholsg i n a previous s tudy , i n which t h e volume of gas r e l eased was assumed t o be propor t iona l t o t h e ex ten t of r e a c t i o n . shown i n Equation 1

The quan t i ty was assumed t o be

The d a t a followed f i r s t - o r d e r k i n e t i c s a s

0 ) t + log c 1 -k

( 2.303 log c = t

where C t i s t h e concent ra t ion of adduct a t time t , k l i s t h e f i r s t - o r d e r r a t e cons tan t , t i s t h e t ime, and Co i s t h e i n i t i a l concent ra t ion of adduct. P l o t s of log (weight of v o l a t i l e com- ponent) versus time were l i n e a r (Figure 6 ) , and r a t e cons tan ts were ca l cu la t ed by l eas t - squa res ca l cu la t ions of t h e s lopes of t hese l i n e a r p l o t s . The r a t e cons tan t r e s u l t s a r e compared t o those of Nichols ' workg with U02 ( N 0 3 ) z-HN03-TBP adduct i n Figure 7 .

The v a r i a t i o n of r a t e cons tan ts with temperature can be represented by t h e Arrhenius equat ion (Equation 2)

where k i s t h e r a t e cons tan t , E i s t h e a c t i v a t i o n energy, R i s t h e gas cons tan t (1.99 cal/moleaoK) , T i s t h e absolu te temperature, and C i s a cons tan t of i n t e g r a t i o n . Least-squares ca l cu la t ions of t h e s lope and y - in t e rcep t of t h e Arrhenius equat ion were made us ing t h e ra te cons tan ts measured i n helium, those measured i n s imulated a i r , and t h e combined d a t a . The r e s u l t s a r e compared t o Arrhenius parameters f o r prev ious ly r epor t ed r a t e cons tan tsg i n Table 6. The helium atmosphere d a t a and t h e simulated a i r da t a a r e s i g n i f i c a n t l y d i f f e r e n t , bu t reasons f o r f a s t e r adduct decom- p o s i t i o n i n heli-am than i n s imulated a i r ( i f a r e a l e f f ec t ) are not known. Thus, Arrhenius parameters f o r t h e combined d a t a were used t o c a l c u l a t e r a t e cons tan ts f o r d e n i t r i i t s r s a f e t y c a l c u l a t i o n s presented i n l a t e r s e c t i o n s o f t h i s r e p o r t .

* The second adduct r e a c t i o n d id not follow simple k i n e t i c s . Because t h e f i r s t adduct decomposition s t e p was t h e f a s t e s t r e a c t i o n , r a t e cons tan ts based on t h e f i r s t r eac t ion w i l l be used i n s a f e t y c a l c u l a t i o n s presented l a t e r .

0.3 I

0.2

0. I CI,

+- c W c 0 n

5 0 W

0

- .- c - 3

0.0 I

100 I I I I I '

Arrhenius Equation Parameters for Combined Data:

FIGURE 6. Thermal

First Reaction i n econipos i t i on o f Adduct

Time, hours

FIGURE 7. Adduct Decomposition 0

' C 0

c Rate Constants a s Function ul

of Temperature 0 aJ f

B

Activation Energy = 26.1 kcol/mole Intercept = 12.81

Slope = -5704 -\ -

- 0 80% He - 20% \ 0,

A 100% He

Nichols' Datag A <

\ 0'012.0 2.1 2.2 2.3 2.4 2.5

1 0 0 0 / O K I I I I

Temperature, "C 220 200 180 160 140 120

- 18-

TABLE 6

Least-Squares Fi t o f Arrhenius Equation t o Adduct Decomposition Rate Constants

Ea, Basis Slope Intercept kea Z/mo Ze

Present helium data -6603 14.85 30.3

Present 89% helium - -5158 11.59 23.6 20% oxygen data

Present combined -5704 12.81 26.1 helium and 80% helium - 20% oxygen data Reference 9' -6070 13.96 27.8

a. For TBP equilibrated with 1.5M UN - 3.OM "03.

A n a l y s i s o f Gaseous Decomposi t ion Products

Samples of pure adduct and organic ma te r i a l (>95% adduct) from A-Line tanks were thermally decomposed i n a i r under non- isothermal condi t ions . Evolved gases were co l l ec t ed by water displacement and were .analyzed by gas chromatography ( G C ) . The resul ts (Table 7) ind ica ted t h a t t h e major flammable product was butene o r butyne, bu t p o s i t i v e i d e n t i f i c a t i o n by GC alone was not poss ib l e . Analyses of t h e gases with an MS-10 mass spectrom- e t e r a l s o suggested unsa tura ted CL, compounds; t hese analyses could not be confirmed because t h e observed s p e c t r a were a composite of parent peaks and fragmentation p a t t e r n s of a l l t h e gaseous products (Table 8 ) .

The bu ty l compound was i d e n t i f i e d by i n t e r f a c i n g a quadruple mass spectrometer (QMS) with t h e gas chromatograph t o allow ana lys i s of each gas a s it ex i t ed t h e column. The organic gases (Table 9 ) were i d e n t i f i e d by t h e i r f ragmentat ion p a t t e r n and by comparison t o s tandard mass s p e c t r a l compilations. The major flammable componeiit was i d e n t i f i e d as 1-butene. Both 1-butene and t rans-2-butene iiere suggested by t h e butene mass s p e c t r a , but mass peak r a t i o s suggest 1-butene is a b e t t e r choice . c e n t r a t i o n s of o the r organic compounds ind ica t ed by MS-10 mass s p e c t r a l analyses (Table 8) were too low f o r de t ec t ion by t h e GC-QMS technique.

Con-

- 19-

TABLE 7

A n a l y s i s o f Gases Evolved by Thermal Decomposit ion o f Adduct

Concentration of Gas EvoZved, V O Z % a A-Line

Gas Adduct Duplicate SampZes of Pure Adduct

0 2 0.06 0 .07

N 2 21 .5 24.9

NO 3 2 . 1 2 8 . 2

N20 8 . 9 1 1 . 7

co 4 .9 9 . 3

con 1 7 . 8 21 .7

1 -Bu tene 1 7 . 8 (20) 20.9 (11)

O t h e r Hydro- c a r b o n s 0 .2 0 . 4

T o t a l 1 0 3 . 3 117.2

0.0s

19.2

1 4 . 1

9 . 3

5 . 4

15.8

40 .0 (24)

0 . 4

1 0 4 . 3

a . A l l r e s u l t s e x c e p t t h o s e i n p a r e n t h e s e s were o b t a i n e d w i t h a SA Molecu la r S i e v e column. The l a t t e r v a l u e s f o r b u t e n e ( o b t a i n e d w i t h a 10% Carhmm 20M - t e r e p h t h a l i c a c i d column) are more r e l i a b l e .

- 20-

a . A l l products except b u t y r i c ac id were observed f o r each sample r ega rd le s s of t h e temperature o r atmosphere.

b . P = parent peak o r molecular ion .

e. Also i d e n t i f i e d by gas chromatography.

d . For s t r a i g h t chain monocarboxylic a c i d s , t h e parent peak i s normally very f a i n t , and t h e peak a t 60 i s c h a r a c t e r i s t i c of such compounds (Reference l o ) .

- 2 1 -

TABLE 9

Gas Chromatographi c-Quadruple Mass Spect ra l Analysis o f Gases Evolved by Thermal Decomposition of Adduct

Gas

0 2

N 2

NO

N20

co co 2 ethene

propene 1 -butene

Total

Concentration, voz %

0.06 21.6

29.7

1 1 . 4

16.7 31.3 0.06

0.10

1 2 . 2

123. la

a. Indicates ana ly t ica l uncertainty.

DENITRATION STUDIES

During d e n i t r a t i o n of UN s o l u t i o n s , adduct present decom- poses when t h e b o i l i n g temperature o f t h e s o l u t i o n i s increased s u f f i c i e n t l y by evapora t ion . The decomposition i s cha rac t e r i zed by foaming and evolu t ion o f brown NO,-containing gases (Figure 8 ) . The s t u d i e s descr ibed below were conducted t o determine t h e effect of va r ious process parameters on adduct decomposition and t o b e t t e r understand t h e decomposition r e a c t i o n .

E f f e c t o f Heatup Rate on Foaming

Deni t r a t ions of UN conta in ing i n i t i a l l y 0 . 2 vo l % adduct were conducted t o determine t h e e f f e c t of heatup r a t e on foaming behavior and on t h e i n i t i a t i o n temperature of foaming. Although t h e d a t a were somewhat s c a t t e r e d (Figure 9 ) , t h e i n i t i a t i o n temperature (10 t o 15°C) increased s l i g h t l y when t h e heatup r a t e was increased by a f a c t o r of 10. Measurements of i n i t i a t i o n temperature were d i f f i c u l t t o reproduce; s e v e r i t y of foaming va r i ed and apparent ly was not r e l a t e d t o heatuy, r a t e . The heatup r a t e s s tud ied were h ighe r than those an t i c ipb red i n SRP ( 0 . 5 t o l.O"C/min) because of problems with s o l i d i f i c a t i o n of UN a t low

- 2 2 -

heatup r a t e s i n l abora to ry - sca l e equipment. SRP tes ts have shown t h a t s o l i d i f i c a t i o n i s no t a problem i n p l a n t equipment a t heatup rates of 0 .5 t o 1°C/min.

3 170 I I I I I I I I I v) c L - m 160-

.- P I

- Heating Rate, "C/min

FIGURE 9. Effect of Heatup Rate on I n i t i a t i o n Temperature of Foaming

-23-

E f f e c t o f Adduct C o n c e n t r a t i o n

Tes t d e n i t r a t i o n s were conducted with reagent-grade UN s o l u t i o n s conta in ing d i f f e r e n t amounts of adduct (Table 10) t o determine t h e temperature a t which adduct decomposition began and t o def ine t h e e f f e c t of adduct concent ra t ion on foaming. In add i t ion , d e n i t r a t i o n s of a c t u a l SRP s o l u t i o n s were conducted t o determine t h e expected foaming behavior during resumption of A-Line processing (Table 11) .

With both s y n t h e t i c and SRP s o l u t i o n s , no foaming was observed a t temperatures (<130°C) corresponding t o t h e SRP evaporat ion s t e p s . However, i n t h e temperature range (1.130 t o 2 0 O O C ) corresponding t o t h e d e n i t r a t i o n s t e p , foaming was s i g n i f i c a n t with t h e reagent-grade UN s o l u t i o n s even a t 0 .04 vol % adduct . Contents foamed out of t h e conta iner i n experiments conta in ing 0.5 t o 1.0 vo l % adduct. SRP s o l u t i o n s t h a t had been f i l t e r e d and processed through a coa lescer u n i t t o remove most organic m a t e r i a l foamed very l i t t l e , i f a t a l l (Table 11) . In a l l cases , adduct decomposition was complete before d e n i t r a t i o n of UN began a t an observable r a t e .

These t e s t s i nd ica t ed t h a t adduct concent ra t ions must be

Recent SRP ope ra t ing experience i n d i c a t e s t h a t <0 .1 maintained as low as p o s s i b l e ( c e r t a i n l y <0.5 vol %) t o con t ro l foaming. v o l % adduct i n hydra t e evapora tor feed can be c o n s i s t e n t l y achieved, and t h a t antifoam add i t ions a r e requi red i n only 1.10% of t h e d e n i t r a t i o n s . The e f f e c t of d i f f e r e n t amounts of a n t i - foam i s d iscussed i n t h e fol lowing s e c t i o n .

E f f e c t o f An t i f oam

Deni t r a t ion tes ts were conducted wi th SRP UN s o l u t i o n s t o determine t h e number and volume of antifoam add i t ions r equ i r ed f o r foaming c o n t r o l . A s shown i n Table 11, 4 t o 6 antifoam add i t ions of 25 p1 (equiva len t t o t h e 75 m l recommended f o r use on p l a n t s c a l e ) had l i t t l e o r no e f f e c t on t h e maximum foam he ight during d e n i t r a t i o n t e s t s wi th s o l u t i o n s conta in ing 0 . 1 t o 0 . 2 v o l % adduct. Much l a r g e r volumes of antifoam (100 t o 200 111) were r equ i r ed t o s i g n i f i c a n t l y reduce t h e l e v e l of foaming; no volume t e s t e d completely e l imina ted foaming. Foam momentarily receded a f t e r each antifoam a d d i t i o n , bu t qu ick ly recovered. Thus, t h e t iming of t h e add i t ions i s important , and i n t h e s e t e s t s , t h e antifoam add i t ions were separa ted by approximately equal time i n t e r v a l s . For SRP s o l u t i o n s conta in ing 0 . 1 t o 0 . 2 vo l % adduct, t h e s e r e s u l t s i n d i c a t e t h a t 4 t o 6 add i t ions of 1.500 m l of a n t i - foam w i l l b e r equ i r ed during d e n i t r a t i o n t o s i g n i f i c a n t l y reduce foaming. With s o l u t i o n s conta in ing lower adduct concent ra t ions (0.02 t o 0.08 vol %) , recent SRP experience has shown t h a t one or two antifoam add i t ions o f 50 t o 75 m l reduce foaming s i g n i f i - cant 1 y .

- 24-

TABLE 10

Den i t ra t i on of Uranyl N i t r a t e w i t h Varying Amounts o f Adduct Prescnt

Temperature, O C

Return o f

0

0.04

0.10

0.20

0.50

0.50

0.75

1.00

None

134

146

152

154

143

143

140

Adduct, Onset of Onset of color les i V O Z % Foaming Brown Fwneaa Fumed

150

167

156

152

153

146

150

150

160

186

180

>170

174

174

a. The fumes con ta in ing NO2 r e s u l t from t h e de- composition of adduct r a t h e r than from d e n i t r a t i o n of uranyl n i t r a t e .

b. The c o l o r l e s s fumes were evolved u n t i l Q200°C was reached, and d e n i t r a t i o n o f u ranyl n i t r a t e reached an observable ra te .

TABLE 11

C h a r a c t e r i z a t i o n o f Foaming D u r i n g D e n i t r a t i o n o f SRP U r a n y l N i t r a t e S o l u t i o n s

A n t i f o m Addit ions Temperature M a x i m a Organic VoZume of Range of r"0m

Description of Solu t ion Content, vo l % b Number Each, !.il Foaming, O C .Lieight, in.'

E-1-3 So lu t ion n . a . , 0.010 0 0 145-165 5/8 6 25 160-175 5/8 6 100 148-184 3/8

S-1-8 So lu t ion with 0.18, 0 .11 @ 0 152-178 2 - 1 / 4 organic m a t e r i a l added 4 25 150-186 1-7/8

1 100 155-183 1-7/8 4 100 146-180 1-1/4 4 200 148-180 3/4

0 5-1-8 So lu t ion processed 0.03, 0 .008 0 0 through a coa le sce r u n i t

S-1-9 So lu t ion processed 0.04, 0.008 0 0 140-166 <1/8 through a coa le sce r u n i t

C-1-1 So lu t ion processed 0.03, 0.006 0 0 0 through a c o a l e s c e r u n i t

a. Tank E-1-3 con ta ins d i l u t e uranyl n i t r a t e s o l u t i o n (90 t o 100 g !.i/l); Tanks S-1-8, S-1-9, and

b.

c. The depth of t he s o l u t i o n was % l / Z i n . when foaming began; t he ind ica t ed form he igh t was measured

C - 1 - 1 con ta in s o l u t i o n concentrated t o %400 g p / l .

The f i r s t value was determined by SRP; t h e second value uas measured at SRL using t h e phosphate method; n . a . i n d i c a t e s no t analyzed.

from t h e s u r f a c e o f t h e uranyl n i t r a t e s o l u t i o n t o t h e highest point t ha t foam reached.

Analysis o f Gaseous Decomposition Products

Gas chromatographic (GC) analyses were conducted of gases emit ted from d e n i t r a t i o n s of UN during adduct decomposition. samples were obtained by t h e fol lowing methods:

Gas

8 Water displacement (Table 1 2 )

e Quenching a d e n i t r a t i o n during foaming a t %150°C and s e a l i n g t h e v e s s e l (Table 13)

e Withdrawing samples with a s y r i n g e f r o m t h e gases above a d e n i t r a t i o n a t va r ious temperatures (Tables 14 and 15)

The major inorganic gases observed were N2, N20, NO, C o n , and CO. it was produced e i t h e r d i r e c t l y during adduct decomposition o r i n d i r e c t l y by r e a c t i o n of NO with a i r . GC a n a l y s i s probably because of r e a c t i o n with water during c o l l e c t i o n o r r e a c t i o n w i t h water on t h e G C column. NO2 d id not r e a c t completely with water during c o l l e c t i o n because gases c o l - l e c t e d by water displacement (Table 1 2 ) were analyzed soon a f t e r c o l l e c t i o n , and t h e brownish c o l o r of NO2 was d e f i n i t e l y observed i n t h e sample i n j e c t e d i n t o t h e G C . The t o t a l concent ra t ion o f inorganic gases roughly equaled 100% with an est imated unce r t a in ty of 210%. Thus, 10% i s considered as an upper l i m i t on t h e NO2 concen t r a t ion .

NO2 was observed v i s u a l l y , bu t no t with GC a n a l y s i s ;

NO2 was not de t ec t ed by

As shown i n Table 15, t h e concent ra t ion of flammable compounds i n t h e evolved gases was very low (<1 vo l %). Analyses of t h e samples withdrawn from d e n i t r a t i o n r e a c t i o n s a t var ious temperatures (Tables 14 and 15) showed t h a t t h e concent ra t ions of both organic and inorganic decomposition gases decreased a t 160 t o 180°C. decrease i n d i c a t e s t h a t most of t h e adduct had decomposed and c o r r e l a t e s wi th t h e observed ces sa t ion of foaming.

This

The adduct probably decomposes during d e n i t r a t i o n of UN i n t h e fol lowing s t e p s : 1) decomposition of adduct t o form f r e e TBP and TBP degradat ion products such a s b u t y l n i t r a t e and b u t y r i c a c i d , and 2 ) ox ida t ion of most TBP and TBP degradat ion products t o CO and CO2. The oxida t ion s t e p i s b e n e f i c i a l t o d e n i t r a t o r s a f e t y i n one r e spec t because t h e d e n i t r a t o r of f -gas i s l e s s flammable. However, as d iscussed i n a fol lowing s e c t i o n , t h e oxida t ion r e - l ea ses hea t which could a c c e l e r a t e t h e decomposition r e a c t i o n .

- 26-

TABLE 12

A n a l y s i s o f Deni t r a t i o n Off-Gas C o l l e c t e d Over Watera ( 5 i M o l e c u l a r S ieve Column)

Concentration i n O f f - G a s “ I ~

f o r Uuplicate Samples Compound Sample 1 Sample 2

0 2

N 2

NO N20

co COP ethane

propane

0 . 7

52.8

25.3

10 .6

- 2.5

8 . 1

4 PPm

5 PPm

0.7

57.0

20.8

10 .7

3.9

7 . 1

4 PPm -

a. Denitrat ion reac t ion mixture contained i n i t i a l l y 1 vol % adduct.

TABLE 13

A n a l y s i s o f Gases Obta ined by Quenching A D e n i t r a t i o n D e n i t r a t i o n R e a c t i o n a t 156°C and S e a l i n g t h e Vessela (5A M o l e c u l a r S ieve Column)

Concentration of Off-Gas, voZ % Compound l 0 O 0 C b 150 OCb

02 5.3 4.6

N2 58.3 56.6

NOc 0 0

N20 22.7 25.4

co 2.9 0 . 7

CO2 10.8 12.7

a. Deni t ra t ion r eac t ion mixture contained i n i t i a l l y 1 vol % adduct.

b . Reaction mixture was reheated t o the ind ica ted temperatures before sampling gas.

a f t e r co l l ec t ion . undetectable NO2 during t h i s waiting per iod.

c. Gas mixture was not analyzed u n t i l severa l hours NO may have been converted t o

TABLE 14

A n 2 l y s i s o f Deni t r a t i o n Off-Gas a t Va r ious Temperatures (5A M o l e c u l a r S i e v e Column)

Compound

0 2

N2

NO

N 2 0

co co 2

ethane

Concentration i n Off-Gas, voZ %a 146'C 160°C 278OC

0 . 7 16.0 17 .9

50.6 82.0 81.5

9.8 t r a c e t r a c e

18.9 2.8

1.5 0

18.3 1 . 7

0 . 4

0

0.2 t r a c e - -

99.8 102.5 100 .0

a. Gas samples were withdrawn from the same d e n i t r a t i o n r e a c t i o n containing ( i n i t i a l l y ) 1 v o l % adduct when t h e r eac t ion reached t h e ind ica t ed temperatures.

TABLE 15

A n a l y s i s o f Organ ic Compounds i n Deni t r a t i o n Off-Gas a t V a r i o u s Temperatures (Carbourn- 20M T e r e p h t h a l i c A c i d Col umn)

Compounds Concentration of Gas, ppma 150°C 160 OC 170 OC

n-butyl n i t r a t e b - 400 60

b u t y r i c acidc 800 900 1000

t o t a l organic 2400 6000 2900

a . Gas samples were withdrawn from the same d e n i t r a t i o n r e a c t i o n containing l n i t i a l l y 1 vo l % adduct when t h e r eac t ion reached t h e ind ica t ed temperature.

I d e n t i f i e d by GC r e t e n t i o n data and QMS.

I d e n t i f i e d by GC r e t e n t i o n da ta only. b . c.

CALCULATION OF MAXIMUM FLAMMABLE GAS EVOLUTION DURING DENITRATION

With e x i s t i n g A-Line equipment, small q u a n t i t i e s of adduct cannot be prevented from reaching t h e d e n i t r a t o r s . Therefore , s a f e opera t ion of A-Line can be achieved only by opera t ing t h e d e n i t r a t o r s i n such a way t h a t any adduct present i s decomposed slowly, under con t ro l l ed condi t ions . The t h r e e b a s i c process parameters which must be con t ro l l ed f o r s a f e opera t ion a r e 1) quan t i ty of adduct p re sen t , 2) heatup r a t e , and 3 ) d i l u t i o n a i r t h a t e n t e r s t h e of f -gas flow. The quan t i ty of adduct p re sen t c o n t r o l s t h e volume of flammable gas t h a t can be produced; t h e heatup ra te c o n t r o l s t h e r a t e of adduct decomposition and, t he re - f o r e , t h e r a t e of flammable gas evolu t ion ; enough a i r must be added t o t h e off-gas flow t o d i l u t e t h e flammable gases below t h e lower l i m i t of f lammabil i ty . Flammability d a t a f o r s eve ra l p e r t i n e n t compounds a r e shown i n Table 16. Based on t h e lowest expected va lue , 1 .5 vol % flammable gas i s a s u i t a b l e va lue f o r process design purposes.

TABLE 16

Flammabil i ty o f Adduct Decomposition Products i n A i r a t Atmospheric Pressure

L i m i t o f M i n i m

Compound

n-butane

n-butyraldehyde

n -bu ty r i c ac id

n-butanol n-butyl n i t r a t e

1 -ni t robutane

ethane

propane

P l m a b i l i t y , vo l % Autoignition Lo#er Upper Temperature, O C

1 . 8 6

2 . 1

1 . 7 1.5"

< 2 0

3 .0

2 . 1

8 . 4 1

-

-

1 2 . 4

9 . 5

405

230

450-552

345

<190Q -

515

450

a. Estimated from values €or t h e appropriate methyl, e t h y l , propyl and pentyl compounds.

b . Data from References 11-15.

- 2 9 -

A computer program (see t h e Appendix) was developed t o c a l c u l a t e t h e maximum vo l % of flammable gas ( a s b u t y l compounds) a t any t ime during a d e n i t r a t i o n . These c a l c u l a t i o n s are based on decomposition r a t e cons t an t s f o r t h e f i r s t adduct r e a c t i o n , t h e q u a n t i t y of adduct p r e s e n t , formation of 3 moles of b u t y l compound p e r mole of TBP, t h e added a i r as expressed i n t h e o f f - gas flow r a t e , and t h e heatup r a t e (assumed t o remain cons t an t ) . The fol lowing ope ra t ing condi t ions were assumed i n t h e s e and succeeding d e n i t r a t o r s a f e t y c a l c u l a t i o n s :

o Each d e n i t r a t o r ba t ch con ta ins 2000 l b of uranium.

e Volume of each hydra te evaporator feed ba tch i s 600 g a l .

0 Adduct i s l imi t ed t o 0 . 2 v o l % o r 1 . 2 g a l (corresponds t o 3820 g TBP) -

Q S p e c i f i c g r a v i t y of adduct i s 1.467.

m Di lu t ion a i r e n t e r s t h e d e n i t r a t o r a t room temperature of 25°C and i s expanded t o a volume corresponding t o t h e of f -gas tempera ture .

e The of f -gas temperature i s assumed t o be 60°C l e s s than t h e po t conten ts temperature (based on A-Line t e s t s ) .

Off-gas ana lyses ind ica t ed t h a t adduct i s not converted completely t o flammable gases during d e n i t r a t i o n o r during thermal decomposition of pure adduct. Therefore , use of maximum t h e o r e t i c a l conversion of TBP t o b u t y l compounds (3 moles of b u t y l compound p e r mole of TBP) incorpora tes cons iderable con- serva t i sm i n t o t h e c a l c u l a t i o n s .

-

The r e s u l t s can be app l i ed t o i l l u s t r a t e t h e e f f e c t of t h e heatup r a t e on gas evolu t ion (Figure 10) . Lower heatup r a t e s are advantageous because t h e flammable gases a r e evolved over a longer time i n t e r v a l , and l e s s a i r p e r u n i t time i s requi red f o r d i l u t i o n . Also, l a r g e r q u a n t i t i e s of adduct can be decomposed s a f e l y f o r t h e same reason. Because gas evolu t ion i s d i r e c t l y p ropor t iona l t o t h e q u a n t i t y of adduct p re sen t (Figure 6 ) , a t O.S"C/min heatup r a t e and 100 cfm d i l u t i o n a i r flow, g r e a t e r than 3 g a l of adduct can b e decomposed s a f e l y . Conversely, a t 2'C/min heatup r a t e and 100 cfm d i l u t i o n a i r flow, t h e lower l i m i t of f lammabil i ty i s nea r ly reached wi th 1 g a l of adduct.

The peak concent ra t ions of b u t y l compounds i n t h e of f -gas were ca l cu la t ed f o r d i f f e r e n t heatup r a t e s and d i l u t i o n a i r f lows (Figure 11 ) . In t h e s e c a l c u l a t i o n s , t h e heatup r a t e has been assumed t o remain cons t an t . However, a s discussed i n t h e follow- ing s e c t i o n , exothermic r e a c t i o n s could hea t t h e melt and inc rease

2 .o I I 1

1.8 - L

1.6 - Flammable - __------_____-_----- s? - 9 Heating Rate, OC/min

Time, hours

FIGURE 10. Maximum C o n c e n t r a t i o n o f B u t y l Compounds i n D e n i t r a t o r Off-Gas

Assumptions

0 1 g a l adduct

0 100 cfm d i l u t i o n a i r a t 25°C (expanded t o 6OoC below tempera tu re o f p o t c o n t e n t s f o r d i 1 u t i on c a l c u l a t i on)

0 3 moles o f b u t y l compounds produced p e r mole o f TBP

-31-

EFFECT OF SELF-HEATING ON THE ADDUCT DECOMPOSITION RATE

Laboratory s t u d i e s have demonstrated t h a t a po r t ion of t h e TBP p resen t (as adduct) i n uranyl n i t r a t e s o l u t i o n s undergoing thermal d e n i t r a t i o n i s oxidized by n i t r a t e i n t h e condensed phase. balance of t h e system. t h e flammable organic gases o r i g i n a t i n g from thermal decomposition or chemical at tack on TBP wi th a l a r g e volume of nonflammable gaseous combustion products : CO2, CO, H 2 0 , and n i t rogen and i t s oxides . From the s t andpo in t of s a f e t y , t h e s e e f f e c t s a r e opposed. i t s rate of hea t ing and thereby a c c e l e r a t e s f u r t h e r TBP decom- p o s i t i o n . However, t h e un reac t ive gases generated decrease t h e q u a n t i t y of a i r f l o w through t h e d e n i t r a t i o n vesse l t h a t would be r equ i r ed t o d i l u t e t h e o rgan ic gases below t h e lower flammable limit. dominates.

This ox ida t ion i s exothermic and can a f f e c t t h e hea t Oxidat ion a l s o has t h e e f f e c t of d i l u t i n g

Addi t iona l h e a t added t o t h e d e n i t r a t i o n melt inc reases

These e f f e c t s were c a l c u l a t e d t o determine which p re -

FIGURE 11. Peak Concentration of Butyl Compounds i n Deni t ra tor Off-Gas per Gallon o f Adduct

Calculat ions assume t h a t : 1 ) d i lu t ion a i r enters a t 25°C and is expanded t o a volume corresponding t o 60°C bel ow the temperature of the pot conten ts , and 2) 3 moles o f butyl compounds a re produced per mole of TBP

The ex ten t of TBP oxida t ion under SRP condi t ions is unknown and probably i s a func t ion of po t geometry and s t i r r i n g condi t ions ; t hus , ex ten t of ox ida t ion cannot be determined from labora tory s t u d i e s . Laboratory s t u d i e s have not i n f a c t de t ec t ed any hea t r e l e a s e from oxida t ion . Therefore , t h e hea t and gas evolved f o r var ious degrees of oxidat ion were ca l cu la t ed (Table 17) . The c a l c u l a t i o n s assume t h a t t h e model condi t ions a r e those s t a t e d i n t h e previous s e c t i o n (3820 g of TBP i n a one-ton uranium b a t c h ) , and t h a t TBP oxida t ion r e l e a s e s as much hea t per g of TEP oxidized as t h e r eac t ion

(C+Hg0)3P04+ 15.6 "03 -f H3P0,~ + 1 2 C 0 2 + 1 9 . 8 H20 + 7 .8 N2

From publ ished da ta , AH f o r t h i s r e a c t i o n i s -1634 kcal /mole.16 '17 The volume of combustion products generated i s assumed t o be 20 mol/mol TBP, ignoring steam and assuming t h a t a t l e a s t a small amount of n i t rogen i s emit ted as oxides . The temperatu?; r i s e i s ca l cu la t ed assuming the hea t capac i ty i s (2.32 c a l / g 'C; hea t capac i ty v a r i e s with t h e s t a g e of d e n i t r a t i o n . However, a t a cons tan t hea t ing r a t e , t h e melt temperature inc reases about l i n e a r l y with time, ind ica t ing a nea r ly constant hea t capac i ty . The d e n i t r a t o r i s operated t o heat-up a t a r a t e no t exceeding 1°C/min over t h e c r i t i c a l range from 120 t o 200°C. Table 17 shows t h a t cons iderable oxida t ion must occur t o have a major e f f e c t i n acce le ra t ing t h i s hea t ing r a t e . To es t imate t h i s e f f e c t , t h e TBP decomposition r a t e was ca l cu la t ed f o r var ious amounts of TBP oxida t ion i n t h e mel t . The c a l c u l a t i o n assumed a homogeneous d i spe r s ion of adduct i n t h e l i q u i d , a hea t ing r a t e of l"C/min, and t h e thermal parameters prev ious ly given. The hea t - up r a t e , t h e mass of t h e d e n i t r a t i o n ba tch , and t h e s p e c i f i c hea t were used t o der ive an e f f e c t i v e hea t input i n t o the system; t h i s hea t input was then compared with t h e heat added by r e a c t i o n (Table 18) . The following conclusions can be der ived:

the ac tua l

O x i d a t i o n o f TBP i n c r e a s e s t h e h e a t i n g r a t e , p r i n c i p a l l y a t t h e h igher temperature .

0 The temperature a t which t h e maximum TBP decomposition occurs s h i f t s upward; f o r >SO% oxida t ion , it can be above 200°C.

The e f f e c t of d i l u t i o n by combustion products overwhelms t h a t of t h e increased hea t ing r a t e , and t h e amount of a i r f low requi red f o r d i l u t i o n decreases s t e a d i l y as t h e amount of oxiuaLion inc reases .

The volume of d i l u t i o n a i r r equ i r ed t o d i l u t e t h e maximum volume of flammable gases ( 3 moles of b u t y l compounds per mole of TBP) below t h e lower l i m i t of f lammabil i ty w i l l be adequate a t any degree of TBP oxida t ion . This conclusion i s v a l i d so long as t h e TBP concent ra t ion i s l i m i t e d , and t h e TBP i s wel l mixed wi th t h e aqueous phase during t h e d e n i t r a t i o n s t e p . Revised A-Line opera t ing procedures have been w r i t t e n t o ensure t h a t s a f e opera t ing condi t ions w i l l be maintained.

TABLE 1 7

Ca lcu la ted Heat and Gas Generated by TBP Ox ida t i on i n A-Line D e n i t r a t o r

TBP Oxid ized , % 0 25

mol/mol TBI' 3 2.15

Emi t ted , mol/mol TBI' 0 5

Heat Generated pe r g Velt , c a l 0 3 . 3

Temperatute R i se , "C 0 1 0 . 3

T o t a l Gas Volume Generated 49 118 p e r t on U , f t 3 ( a t 1 2 0 " ~ )

Combustible Content of 100 31 Emitted Gas, '6

D i l u t i o n Fac to r Required 66 .7 20.;

Volume of Room Air Required 3270 2450 t o D i l u t e below 1.5%," f t 3 ( a t 1 2 0 ' ~ )

Volume of Room A i r Required, 2480 1860 f t 3 ( a t 2 5 ' ~ )

Flanunable Gas Emi t ted ,

Combust ion Products

( t o 1 .5%)

a. Lower explos ion l i m i t f o r b u t y l n i t r a t e

TABLE 18

50

1 . 5

10

6 . 6

20.6

187

13

8 . 7

1630

1240

75 100

0 .75 None

15 20

9 .9 1 3 . 2

30.9 4 1 . 2

257 326

4 . 8 None

3 . 2

820

620

See Table 16

Ca lcu la ted Decomposi t ion Rates and D i l u t i o n Requirements f o r Var ious Degrees o f TBP Ox ida t i on

(Assumptions: 3820 g TBP/ton U; nominal hea t ing ra te , l "C/min)

TBP ox id ized , % 0 25 50 75 100

Maximum h e a t i n g r a t e , 1 .0 1 . 3 1 .8 2 .4 3 . 5 "C/min

Maximum TBP decomposition 92 111 134 168 2 1 7 r a t e , g/min

Temperature of maximum 191 194 198 -705 2 1 2 decomposition r a t e , "C

A i r r equ i r ed t o d i l u t e below 63 55 4 4 27 ?Jane flammable l i m i t , f t ' /m in

I

a t 25OC

- 3 4 -

APPENDIX - COMPUTER PROGRAM FOR DENITRATOR OFF-GAS CALCULATIONS

C C C C C C C C C C C C C C C C C C C C C C C C

( M A Y 72 1 C S / 3 6 0 F D R T R A h H

C O M P I L E R OPT 1 q N S - NAME= 4A I N ~ O J T + C O . L I Y E C N T = 5 8 r SI Z E = 0 0 0 0 K . SOURCE.EBCCIC. N 3 L [ S T I N O D E W t LOAD1 MAPI NOEO I T 1 I D v N O XREF

PR’IGRAM O F F S A S TEYP=CFNT I W A O E TE MPK=ABSOLUTE OGTEMP=OFFGAS TEYPESATU?E (PSSUMED T O @E 6 0 C L E S S THAN POT) T I N V S = I N V E R S E OF ABSOLUTE T I 4 P E R A T U q E T L h K = N A T U R A L LCG CF R A T ? CCdSTANT TLOGK-LOG OF RATE,CONST$NT T K = R A T E C C M T A N T H A L F T = H A L F L I F E OF R E A C T I C N E A C T = A C T I V A T I O N ENERGV SROY SLOPE OF LOG K V S 111 PLOT Y I N T C P = Y I N T E R C E P T OF L J G K JS 111 PLOT TEYPl=LOWER END OF T E Y P Z R 4 T J t E RANGE CF I N T E R E S T N=NUMRER O F T E M o E R A T U 4 E S IY OWE DEGREE I N T E R V A L S VOLADO=VOLUME OF ACDUCT I h J E N I T R A r O R I N GALLOYS AMTADD=WEIGHT OF A D D X T I Y J G Y I T R A T O R A T T I M E T I N LBS. TLOCAD=LOG OF Y E I G I - T I F ACOUCT T L N A D D = N I T U R A L LCG OF hEIGHT OF ADDUCT HTRATE=HEAT UP R A T E F3R D E N 1 TRATDR FL*IRT=OFF GAS FLOW RATE B E I I ( G A ’ P L I E D TO D E N I T R A T 3 R I N CFM AMTDCP=AMOUNT OF ADDUCT ’3ECZMPOSED I h EACH T I M E I N T E R V b L VCLGAS-VOLUME O F GAS E V I L J E I D U R I N G EACH T I Y E I N T E R V A L VOLPCT=VOLUME PERCENT OF F L A q Y A B L E GAS IN D E N I T R A T J R O F F GAS T I M E = T I M E E L A P S E D F R C Y I Y I T I 4 L TEMPERATURE T O PRESENT TEMPERATURE TPDCP=T I U E A L L W E C FOR D E C O 4 ~ O S I T I O Y A T EACH TEMPERATURE REAL*B T E M P ( 5 0 0 ) r T E M P K ( 5 0 0 ) 1 T I N V S ( 5 0 0 1 1 T L N K ( 5 0 0 )1TLOGK ( 5 0 0 ) ~

A W T A C C 1 5 0 3 ) r T L ~ G A C ( 5 3 5 ) r T L N A D O ( 5 0 0 ) v A M T D C P ( 500) t 1 TI< ( 5 0 0 ) r H A L F T ( 5001

I R E A L * 8

VOLGASt 500) r V O L P C T ( 5 0 0 ) S T [ M Z (530 1 .OGTECP(500 I 1 2 3 4 5 6 7 8

9 10 11 12 13

50

R E A D 2 1 E A C T i V I N T C P ~ T E 4 P l r Y F C R M A T ( 3 F 1 0 .O, I5 1 TEMP( l I = T E M P l 00 5 Iz2.N TEMP( I I = T E M P I 1-1 1 +1.0 OD 13 I = l * N T E M P K ( I ) = T E M P ( I ) + 2 7 3 . 3 T I N V S t I ) = l . O / T F M P K ( I ) OGTEWPI I l = T E M P K ( 11-60.0 TLCGK ( 1 1 =- ( EACT/4 .583 I * ( T I N J S ( 1 I 1 +I I N T C P T L N K ( I ) = T L O G K I I ) * 2 . 3 0 3 T K t I I =DEX P( T L NK ( I I 1 H A L F T ( 1 ) =0.693/TKlI) C O Y 1 INUE P R I N T 50 F O Q M A T ( I X . 1 3 H T E M F E R A T J R f C . 5 X . 3 H l / T .1OX .5HLDG KI LOX. 1Ws 7X.

2 1 3 t ” A L F L I F F 1 kR 5 I 14 CC 17 I = l . N 15 P R I N T 1 6 ~ T E M P ~ I ~ r T I N ~ S ~ I 1 r T L ~ G K ~ I ~ ~ T K l I l ~ H A L F T ~ I ~ 16 17 C G N T I N U E

80 FCPMAT f 15 )

18 READ ~ ~ , V O L A D D ~ H T R A T E I F L O ~ R ~ 19 F C P m A T ( 3 F L O . O )

FORMAT ( 4 x 1 F5.0,6X,FLO. 1 5 ~ 4 x 1 F 10.61 3x1 F 10.614X.F 10.61

R E A D BOrNORUNS

OC 42 J* l .NOPUNS

35-

20 2 1 22 23 24 25 26 27 28 29 30 3 1 32 33 34

C C C C

C 35

36 3 7

100

60

A)rTADD( 1 I = V C L A O D * l 2 . 2 2 8 TMDC P = l . O / H T R A T E COUNT= 1 .O T I M E ( 1 I =O.O TLOGAD( 1 ) =DLOG 1 O( AMTAOOI 1 I 1 AWTOCP ( 1 )=O .O V O L G A S ( 1 I=O.O M L P C T l 1)=0.0 T L N A D D ( l ) = O L O G l A Y T A D C ( I I I 90 37 I c 2 . N T I M E t I I=TMOCP*COUNT COUNT =cm NT +1 .o TLOGAOI I I =-I T K I I I / I 2 -303) I * I TMDCP/50 -0 ) +T LOGAC I 1-1 I T L N A D O t I ) = T L O G A O l I J * 2 . 3 0 2 5 8 5 0 9 D 00 A W T O C P ~ I I ~ t C E X P l T L N A D D ( I - l ) J I - ( D M P l T L N A D O l Ill)

CCWPIAJNDS .ALL C C N V E R S I O J F A C T J S S A * € COMBINED. THE N E X T STAlEMEhT CCNVERTS T H E VOLUME O F OFFGAS T O VOLUME PERCENT A T THE E S T I N A T E ) O F F G A S TEMPERATURE ( P O T T E M F E R A T U R E - 6 3 C ) V C L G A S ( I l = A M l C C P ( I )*O;TEMPl I)u).0085154 THE D I L U T I C N A I A I S CONVERTEC T O T H E OFFGAS T E M T E R A T U R E VOL P C T ( I ) = I VOL GA 51 I I 1( F L O CR 1 * TNOC P * I CG TEMP I ) 1298. ) I I 1 00.0 AWTAOOI I ) = O E X P l T L N A O C ( I) 1 P R I N T 100 F 0RW AT I 1H1I

THE N E X T S T A T E K Y T C C N V E R T S UEIGHT aF ADDUCT T O VOLUME BUTYL

PR I N 1 60 r V O L A r 0 t HT RAT E t FLOU RT F O R M A T ( 4 X r 2 5 H I N I l I A L VCLUME 3F A O O U C T = r F I . l . l X r 3 H G A L r 4 X . l 3 P H E A T U P 4 RAT E=* F5 21 l X t 5 H t / Y I '41 4x1 19HK I Y a 4 TE= r f 5.0.1X e WCF M I

P R I N T 6 5 65 F O R M A T I LHO)

PRINT 70 70 FORMA T I 4x1 8 H T I ME r M I N r CX r 11H T E NPE RAT J RE r 4 X * l O H ADDUCT t L B S t 4 X t 3 ~ ~ P ~ E C O M P O S E O I L ~ S ~ ~ X ~ 1 3 H C i S V O L U H E r C F r 4 X 1 1 4 H V O L U M E P E R C E N T )

.38 OC 41 I * l r N 3 9 PR I N 1 40

4011INEl I I . T E M P ( I I r A ) r T A O D I I ) r A C T O C P ( 1 ) r V O L G A S I I ) . V O L P C T 11 8 F O R M A T ( F l O . l r 4 X r F 10.116X. F 13. h SX1F10.4r7XrF10.4 .9X.F 10.6)

4 1 C O N T I N U E 42 C O N T I N U E

S T C P E NO

- 3 6 -

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2 . C . D . Hodgman, ed. Handbook of Chemistry and Physics. 42nd Edi t ion , Chemical Rubber Publ ishing Co., Cleveland, Ohio (1961).

3. E . Stenhagen, S . Abrahamsson, and F . W. McLafferty, eds . Registry of Mass Spectral Data. New York (1974).

Volume 1, John Wiley and Sons,

4 . W . Davis, J r . , J . Mrochek, and R . R . Judkins . "Thermodynamics of t h e Two-Phase System: Phosphate-Amsco 128-52." J . Inorg. Nucl. Chem. 32, 1689 (1970).

Water-Uranyl N i t r a t e -Tr ibu ty l

5 . . S. C . Lind, ed . Chemistry Division Quarterly Progress Report. USAEC Report ORNL-1116, Oak Ridge Nat ional Laboratory, Oak Ridge, Tennessee (1952).

6 . J , Kennedy and S. S . Grimley. Radiometric Studies wi th Phos- phorus-32 Labelled Tri-n-buty 1 Phosphate, Part I , So lub i l i t y and Distr ibut ion Studies . Atomic Energy Research Establishment, Harwell, England (1953).

B r i t i s h Report AERE-CE-R-1283,

7. L . L . Burger. The Chemistry of TributyZ Phosphate-A Review. USAEC Report HW-40910, Hanford Works, Richland, Washington (1955).

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