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THERMAL EXPANSION O F URANIUM DIOXIDE

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Prepared for:

Metallurgy and Materials Branch United States Atomic Energy Commission Washington, D.

Division of Research C .

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.

Apri l 15, 1959 1

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Fina l Repor t

THERMAL EXPANSION 0 F URANIUM DIOXIDE

By: F. A. Halden H. C. Wohlers R . H. Reinhar t

S R I P r o j e c t No. SU-2542

P r e p a r e d for:

Metallurgy and Mater ia l s Branch United States Atomic Energy Commiss ion Washington, D. C.

Division of R e s e a r c h

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Approved:

Contract No. AT(04-3)-115 Agreement No. 6

J a 07- !%-

0. F. Senn, Chai rman Department of Chemis t ry

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Copy No. 1 7

PREFACE

This r e p o r t has been p repa red in a manner suitable f o r publication in The preface i s intended to the Journa l of the Amer ican C e r a m i c Society.

p re sen t conclusions pertinent to the sponsored r e s e a r c h p r o g r a m and to indicate regions which appear t o war ran t additional exploration.

In this investigation an at tempt was made to obtain high t empera tu re t h e r m a l expansion data on uranium dioxide actually employed f o r r eac to r fuel e lements . c ia l suppl ier . s inter ing p r o c e s s samples were p repa red to provide var ia t ion in density and g ra in s ize . Although no firm answer was obtained to the problem of the volume change of uranium dioxide on melting, s eve ra l significant r e s u l t s can be de te rmined f r o m this work.

F o r this r eason specimens were obtained f r o m a c o m m e r - In o r d e r to de te rmine the influence of changes in the

1. The rma l expansion data have been extended f r o m the region of 900 to 1000°C to the melting point of uranium dioxide.

0 2. An expansion anomaly w a s observed in the region of 1000 to 1500 C. F u r t h e r study would be requi red t o de te rmine i f th is is a r e su l t of nonstoi- ch iometry of uran ium dioxide o r a n ac tua l s t ruc tu ra l change occurr ing a t the s e tempe r a t u r e s .

3 . The t h e r m a l expansion of l a rge gra in , dense uranium dioxide, s in te red f o r a n extended per iod, w a s somewhat l e s s than that of m a t e r i a l having the same density but with a no rma l gra in s ize .

4. Unique heating techniques f o r obtaining high t empera tu re physical data have been explored, and the i r advantages and l imitat ions m o r e f u l l y defined.

5. Exploration of the t empera tu re region around the melt ing point of uran ium dioxide has suggested that the volume change on melt ing i s probably l e s s than t h r e e percent . should p e r m i t improved m e a s u r e m e n t of th i s change.

F u r t h e r ref inement of the techniques explored

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THERMAL EXPANSION OF URANIUM DIOXIDE

ABSTRACT

The t h e r m a l expansion of commerc ia l u ran ium dioxide spec imens have been m e a s u r e d up to the melting point. n o r m a l gra in s ize U 0 2 follows closely the equation:

The l inear expansion of dense,

An anomalous expansion was noted in the t e m p e r a t u r e range of 1000 to 15OOOC. necess i ta te the application of heating techniques which provide rapid heating and quenching in o r d e r to obtain rel iable data. mel t ing furnaces 6or this type of m e a s u r e m e n t is descr ibed.

Above 250OoC the rapid vaporization and c rys t a l growth of U 0 2

The use of so la r and a r c -

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Fina l Report

THERMAL EXPANSION OF URANIUM DIOXIDE

Int r o duc tion

The d e s i r e to opera te nuclear r e a c t o r s a t i nc reased t e m p e r a t u r e s h a s i n the pas t ten y e a r s s t imulated extensive r e s e a r c h on c e r a m i c fuel e lement m a t e r i a l s . s tud ies on the uranium-oxygen s y s t e m , prepara t ion of s in te rab le powders , and fabr ica t ion techniques, in addition to de te rmina t ion of t h e r m a l con- ductivity, t h e r m a l expansion, and i r r ad ia t ion effect . However, knowledge oE the p rope r t i e s of uranium dioxide a t t empera tu res above 1000 C is s t i l l quite l imi ted .

Numerous investigations have been devoted to phase

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Calculat ions of t h e r m a l s t r e s s e s and heat t r a n s f e r a t e leva ted t e m p e r - a t u r e s r equ i r e accu ra t e knowledge of t he rma l expansion and t h e r m a l con- ductivity. have o c c u r r e d as a r e su l t of the volume change of uranium dioxide upon melting i n the core’ , This investigation was ini t ia ted to explore unique heating techniques for obtaining the rma l expansion data up to the melting t e m p e r a t u r e of uranium dioxide, with pa r t i cu la r emphas i s on the d e t e r - m’ination of volume change of uranium dioxide on melting.

It h a s been suggested that some fa i lu re s of fuel e lements may

Me tho d

The technique used fo r measu r ing the rma l expansion w a s to heat spec imens of known dens i t ies and dimensions under a tmosphe res of a rgon , hel ium, o r hydrogen and to photograph the profile of these spec imens by the i r emi t ted light a t t empera tu re . l a r g e d , approximately ten t i m e s spec imen s i z e , on g l a s s p la tes to prevent dimensional changes that normal ly occur with the use of photographic pape r , The profile dimensions w e r e m e a s u r e d with a t ravel ing microscope C a l i -

b r a t ed to 1 mil .

These photographs w e r e then en-

It w a s proposed that i f l iquid UO, fo rmed a contact angle g r e a t e r than 90° on a leveled tungsten plaque, i t should be possible to calculate the densi ty of molten uranium oxide as well a s i t s su r f ace tension by the s e s s i l e d rop technique desc r ibed by Kingery a n d Humenik’. does occur , i t w a s felt that this information might s t i l l be obtained by melt ing the top port ion of a UO, cyl inder to fo rm a self-supported bead.

If wetting on tungsten

EauiDment and P rocedure

In o r d e r t o mee t the heating requi rements for measu remen t s of th i s

The so lar furnace a t Stanford R e s e a r c h

0 4 type a t t empera tu res around 2860 C (melting point of UOZ) a so la r furnace was employed in this investigation. Insti tute, shown in F igu re 1, has been descr ibed in previous publications4- A d iag ram of the furnace chamber employed i s shown in F igu re 2. 24-inch focal length cameras , placed 9 0 graph the specimen a t elevated t empera tu res and t o indicate uniformity of the specimen shape.

Two a p a r t , were employed to photo- 0

In such a furnace , only the specimen under investigation i s heated direct ly; the furnace chamber r ema ins ju s t above ambient t empera tu re . Thus, many of the difficulties encountered a t these t empera tu res with conventional furnaces , such a s insulation requi rements , sagging of s t ruc - t u r a l components, a tmosphere contamination due to outgassing of hot e lements , e t c . , a r e eliminated. Close observat ion of the spec imen i s possible through g la s s windows. i ne r t i a of such a furnace , the specimen can be heated rapidly and quenched - - a consideration of par t icu lar importance f o r ma. ter ia ls having high vapor p r e s s u r e s where i t i s des i rab le t o minimize weight l o s s during heating (v. p. uOZ = 1 mm a t melting tempera ture5) .

In addition, as a r e su l t of the low t h e r m a l

One m a j o r l imitation in the use of a so l a r furnace f o r this type of

Normal optical technique s a r e unsuited because of ref lect ions investigation is the difficulty in making accu ra t e t empera tu re m e a s u r e - ments . f r o m the sun; cal ibrat ions of f lux with m a t e r i a l s of varying melt ing points a re unsuited because of t empera tu re dependence on the emiss iv i ty of the specimen. but the complex optical requi rements placed development of this technique out of the scope of this p rogram. F o r this r eason the so l a r furnace w a s considered to provide data only in the region of the melting point of UOZ.

Some a t tempts were made to employ two-color pyrometry ,

To de termine the suitabil i ty of the so l a r furnace fo r s e s s i l e d rop measu remen t s , a 1 -g ram nickel spec imen was mel ted in a rgon on a Morgani te plaque and photographed. Surface tension, density, and con- tac t angle of molten nickel were calculated f r o m the tab les of Bashforth and Adams8. The sur face tension was found to be 1375 compared to the repor ted value2 of 1615 dynes/cm. 7. 36 -f. 0. 14 gm/cm3 was obtained as compared to 8. 0 gm/cm3 repor ted in the l i terature9. appear quite reasonable consider ing that no a t tempt was made to obtain

20 dynes /cm A density of

The contact angle was 125 -f. 3 degrees . These values

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ext remely pure nickel o r a luminum oxide o r to purify the a rgon a tmosphere employed. In addition, no par t icu lar c a r e was taken t o maintain the nickel t empera tu re a t the melt ing point; consequently. i t m a y have been consider- ably higher.

0 To obtain the rma l expansion data below 2500 C, the tungsten r e s i s -

tance furnace i l lus t ra ted in F igu re 3 w a s constructed. The all- tungsten heating chamber cons is t s of top plate, side s p a c e r s , and a slotted 0 . 050- inch base plate 1-inch square . The heating chamber r e s t s on two upright 0. 050-inch tungsten plates fi t ted into 1/2-inch tungsten e lec t rodes . top plate and side s p a c e r s of the heating chamber were ground to thick- n e s s e s that provided a total e l ec t r i ca l r e s i s t ance equa.1. to that of the b a s e plate. tungsten spr ings , ,as shown. 1 inch square by 1/4 inch high. w a s provided. A thin slit in one side space r pe rmi t t ed t empera tu re measu remen t of the specimen whi1.e main- taining essent ia l ly black body conditions. The 1/4-inch square openin.gs on opposite f aces permi t ted profile photographs to be taken of the hea,ted specimens. The hot chamber w a s surrounded with molybdenum radi.atjon shields and a water-cooled shell . Power w a s provided by a t r a n s f o r m e r var iab le au to t ransformer combination supplying a maximum of 1500 a m p s a t 14 volts. heat in hydrogen and then flushed with a rgon fo r high t empera tu re m e a s u r e - ments . In o r d e r to a s s u r e the rma l equi l ibr ium a t each t empera tu re , the spec imen w a s held a t constant t empera tu re for ten minutes before taking photographs. Tempera tu re measu remen t s were made with a standa.rdized optical py romete r . A 13 degree t empera tu re cor rec t ion was ma.de fo r the Pyrex furnace window.

The

The en t i re chamber w a s held in positi,on by 1/8-inch diamet.er In this way, a uniform t empera tu re chamber

During operation this furnace was norma.lly heated to r e d

Mate r i a l s

The uranium dioxide employed in this investigation w a s obtained f r o m the Nuclear Mate r i a l s Corporat ion of Appollo, Pennsylvania in the f o r m of cy l inders 3/16 inch in d i ame te r and 1/4 to 1 inch long. This m a t e r i a l was fabr ica ted by no rma l cold press ing and s inter ing techniques. dens i t ies of 77 and 9 3 percen t of theoret ical were obtained, with the high densi ty m a t e r i a l s in te red in a manner to provide spec imens of no rma l and l a rge gra in s ize . Density values f o r the th ree types of uran ium dioxide, m e a s u r e d on all spec imens by d i r ec t dimensional m e a s u r e m e n t and m e r c u r y i m m e r s i o n techniques, a r e shown in Table I.

Specimen

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Table I

DENSITY OF UOZ SPECIMENS

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8. 45 -b 0. 10 gm/cm3

10, 19 2 0. 11 gm/cm3

! Low densi ty , no rma l g ra in

I High densi ty , n o r m a l gra in i

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i ! High density, l a rge g ra in i 10. 19 3 0. 12 gm/cm3 i

Microphotographs of typical polished sect ions of the th ree types of spec imens a r e shown in F i g u r e 4. revea led the p re sence of 100 ppm sil icon, copper .

Emiss ion spec t rographic ana lys i s 15 ppm aluminum, and 2 ppm

X - r a y diffraction pa t t e rns showed a la t t ice constant of 5 .47 ? 0. 01 8. Resu l t s

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Linea r t h e r m a l expa.nsion data f o r uranium dioxide a r e plotted i n

Typical expansion values for these runs a r e shown F i g u r e s 5 through 8. heated to 2OOO0C. in F i g u r e 5. Considerable sca t t e r of data points wa.s found during these t e s t s in the c a s e of the two dense g rades . n o r m a l g ra in m a t e r i a l w a s s o g r e a t that it i s not shown in F i g u r e 5. Sintering w a s observed above 140OoC in a1.I c a s e s on the low densi ty m a t e r i a l , and during these ini t ia l runs the densit.y i n c r e a s e d f r o m 8. 4 5 to 9. 3 3 gm/cm3. The rma l expansion data of Bel l and Makin6 and M u r r a y and ThacKray;' to t e m p e r a t u r e s of looo°C and 900°C, respec t ive ly , a r e showr-for c o m p a r i s o c .

During the initial. heating, each spec imen w a s

The sca t t e r f o r the high densi ty ,

The shaded points indicate data obtained during cooling.

Upon reheat ing these spec imens to 2500OC the t h e r m a l expansion c u r v e s in F i g u r e s 6 , 7 , and 8 were obtained f o r the t h r e e types of uran ium dioxide pel le ts . shown. These values were highly reproducible . The low densi ty ma te r i a l f u r t h e r s in te red at e levated t e m p e r a t u r e s and then during cooling followed closely the expansion curve of the l a r g e gra in , dense m a t e r i a l , reaching a r o o m t e m p e r a t u r e densi ty of 10. 27 gm/cm3. No s inter ing w a s observed in the n o r m a l grain, dense m a t e r i a l , and the l i nea r t h e r m a l expansion is r ep resen ted by the equation:

Typical data points f o r individual r u n s a.re

L = Lo( 1 + 6. O x IO-% i- 2 . 0 x 10-st2 t 1. 7 x 10'ILt3)

The l a r g e gra in , dense UOZ inc reased slightly in density to 10. 25 grn/cm3.

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In all c a s e s , during he,ating and cooling of dense uranium dioxide, a n i r r egu la r i ty was noted in the expansion curve between 1000 and 15OO0C. NO a t tempt was made to explore this region in detail .

The volume expansion of uranium dioxide up to the melting point is presented in F igu re 9 f o r the two dense g rades studied. calculated f r o m the l i nea r expansion values of the previous cu rves and i l lus t ra te m o r e c lear ly the l a rge inc rease in volume occurr ing a t t empera - t u r e s above 20OO0C.

These data were

0 Above 2450 C excess ive vaporization and c r y s t a l growth on the sur face A polished section of the spec imens were observed in the tungsten furnace.

of th i s c rys t a l growth is shown in F igu re 10. mate ly 270O0C in helium o r hydrogen, weight l o s s was v e r y rap id and whiskers of U 0 2 up to 1/8 inch long appeared. reduced this vaporization somewhat, and a t a t empera tu re sl ightly above 281OOC (maximum reading on optical pyrometer ) UOZ mel ted and com- pletely wet the tungsten plaque.

At t e m p e r a t u r e s of approxi-

An argon a tmosphere

During this investigation i t w a s found that uranium dioxide could not be me l t ed in a controlled manner in the so la r furnace. c ipal r e a s o n s fo r this w a s the high vapor p r e s s u r e of UOz n e a r the melt ing point. vapor was observed to f o r m which ac ted as a f i l t e r fo r the so l a r energy and coated the g l a s s cover on the furnace chamber . growth occur red on the specimen, and melting s t a r t ed on the top su r face , but before sufficient melting could occur to pe rmi t measu remen t , the su r face resolidified. the rad ian t flux would be sufficient to accomplish melting in spite of this difficulty. Attempts t o f o r c e vapor out of the so l a r radiation path by means of a rgon circulation were unsuccessful. furnace chamber by providing a thin-wall g l a s s hemisphere top o r by removal of the top g l a s s plate to locate the spec imen in a n open column of a rgon did not significantly incre,ase the t empera tu re .

One of the p r in -

A s the melting point was approached a considerable amount of

Excess ive c r y s t a l

It is probable that with a l a r g e r col lector m i r r o r

Modifications of the

In o r d e r t o obtain values of the volume of UOz at the melt ing point

A d iag ram of this furnace is shown in F igu re 11. s e v e r a l t e s t s were made using an a rc -me l t ing furnace , available in the laboratory. F o r this work, the viewing po r t and cover were rep laced with a polystyrene plate so that photographs of the drop prof i le could be taken. technique for measu r ing the volume change of U 0 2 on melt ing was f i r s t proposed by Dr. L. M. Pidgeon of the Universi ty of Toronto and i s being studied in detai l t he re a t the p re sen t t ime.

This genera l

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The method employed in this p rogram consis ted of placing a 1/4-inch- thick tungsten electrode on the water-cooled copper hea r th in o r d e r to reduce the t empera tu re gradient through the UOZ specimen. The d. c. a r c wa.s d i rec ted onto the top of a 1/2-inch UOZ cylinder (3 /16 inch d iameter ) placed on the tungsten plaque. on the top of the UOz, high speed movies (32 f r a m e s / s e c ) were taken as the a r c was turned off and the specimen cooled. taken of the maximum bead d iameter and dis tance f r o m the equator to the top of the bead during cooling. room t empera tu re in o r d e r to calculate the volume change on cooling.

When a molten bead was fo rmed

Measuremen t s were then

P i c t u r e s were a l s o taken of the bead a t

In each c a s e , when the a r c w a s placed on the specimen, the UO2 Consequently the molten bead fo rmed was not symmet-

Measuremen t s cyl inder f rac tured . r i c a l and calculations of sur face tension w e r e not possible. of the bead prof i le during cooling a r e shown in F igu re 12. These values a r e normal ized on the room tempera tu re measu remen t s . It can be seen that during a r c cutoff a l a rge volume change occurred . P r i o r to this t ime the dimensions var ied considerably, probably due to s t i r r ing of the m e l t by the a r c . constant for approximately th ree seconds and then s t a r t ed contract ing without a sha rp discontinuity. p e r a t u r e a r r e s t point where solid and liquid a r e in equi l ibr ium and i t w a s used to calculate the expansion of solid UOZ a t the melting point ( F i g u r e s 7 and 8).

Following the a r c cutoff, the bead dimensions remained

This constant region is fe l t to be a tem-

The ini t ia l volume change during a r c cutoff does not appea r to be a change due to solidification. Ra the r , i t m o r e l ikely i s caused by the act ion of the a r c on the me l t , by superheating of the m e l t sur face , and by overexposure of the film due to the br ight a r c f lame around the bead. If th i s change were a t rue volume change i t would mean a change of 40 to 50 percent , which a p p e a r s unreasonable f r o m pas t observations1.

If solidification actually o c c u r r e d during the uniform-volume per iod i t would indicate that the volume change on solidification mus t be less than th ree percent ( the es t imated accu racy of these measu remen t s ) . exceeded th is , some dis tor t ion of the drop sur face should have occur red during solidification, o r a hollow zone should have fo rmed in the bead. This was not observed on the bead surface.. f r a c t u r e occur red in the bead, which was revea led by polished sect ions, so that the latter possibil i ty cannot be eliminated.

If i t

However, extensive in te rna l

CONCLUSIONS

The t h e r m a l expansion of uranium dioxide has been m e a s u r e d at t empera tu res up to the melting point (286OOC). dense, no rma l gra in s ize UOZ follows closely the equation:

The l i nea r expansion of

An anomaly was observed in the expansion curve i n the region of 1000 to 15OOOC. rap id in i n e r t a tmosphe res and hydrogen.

At t empera tu res above 250OoC vaporization of UOZ is ex t r eme ly

3 ACKNOWLEDGEMENT

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This work w a s conducted under the sponsorship of the R e s e a r c h Division of the Atomic Energy Commission. edge the a s s i s t ance of Mr . E. F a r l e y and Mr . L. Murphy who pe r fo rmed the a r c - mel t ing experiments .

The au thors wish to ackmowl-

REFERENCES

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1. (a) Bel le , J. Resume/ of Uranium Oxide Data-V, WAPD-PWR-PMM- 429 (Del) p. 24 (1956).

2.

(b) Bel le , J. and L. J. Jones. Resume'of Uranium Oxide Data-VI, WAPD-PWR-PMM-466 (Del ) , p. 24 (1956).

( c ) Bel le , J. and L. J. Jones. Resume' of Uranium Oxide Data-VF. WAPD-PWR-PMM-491: p. 24 (1956).

(d) Eichenberg, J. D. e t al. Effects of I r radiat ion on Bulk UOt, WAPD-183, pp. 51-7 (1957).

Kingery, W. D. and M. Humenik, Jr. Surface Tension at Elevated Tempera tu res I. , J. Phys. Chem. P 57, 359 (1953).

3. E h l e r t , T. C. and J. L. Margrave. Mel.ting Point and Spectra.1 Emiss iv i ty of Uranium Dioxide, J. Am. C e r . SOC. - 41, 330 (1958).

4. (a) R e s e a r c h f o r Industry News Bulletin 9 , No. 5, p. 3 . Stanford R e s e a r c h Institute (September 1957).

5.

6.

7.

8.

9.

(b) Cohen, R . K. and N. K. Hies te r . A Survey of Solar F u r n a c e Installations i n the United States. J. of Solar Energy Science and Engineering - - 1 (2, 3 ) , 115 (1957). /

Ackermann, R . J. The High Tempera tu re , High Vacuum Vapori- zation and Thermodynamic P r o p e r t i e s of Uranium Dioxide, ANL-5482, p. 67 (September 14, 1955).

Bell , J. P. and S . M. Makin. Fast Reac tor - Phys ica l P r o p e r t i e s of Mater ia l s of Construction, RDB (C)/TN-70 ( Ju ly 5, 1954).

Mur ray , P. and R . W. Thackray. The Therma l Expansion of Sintered UOz, A. E. R. E. M/M22 ( n . d. )

Bashforth, F. and S . C. Adams, An Attempt t o T e s t the Theor i e s of Capillari ty. Cambridge University P r e s s , 1883.

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Kurkjian, C. R. and W. D. Kingery. Surface Tension at Elevated Tempera tu res 111; E f fec t of C r , In, Sn, a n d T i on Liquid Nickel Surface Tension and Interfacial Energy with A120,. J. Phys. Chem. 60, 961 (1956). -

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FIGURES

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FIG. 1 SOLAR FURNACE AT STANFORD RESEARCH INSTITUTE

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RC- 2542-2

FIG. 2 SOLAR FURNACE SPECIMEN CHAMBER: (a) PYREX OPTICAL PLATE, (b) SIGHT PORT, (c) GAS INLET, (d) GAS OUTLET, (e) COPPER SUPPORT, ( f ) GRAPHITE BASE PLATE,

(g) TUNGSTEN SETTER PLATE, (h) UO2 SPECIMEN

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R C - 2542 - 3

FIG. 3 TUNGSTEN RES I STANCE FURNACE

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R P - 2 5 4 2 - 4 ( C )

FIG. 4 PHOTOMICROGRAPHS OF U R A N I U M DIOXIDE SPECIMENS AS RECEIVED: (a) LOW DENSITY,

GRAIN, (c) H I G H DENSITY, LARGE GRAIN (BOX) NORMAL GRAIN, (b) H I G H DENSITY, NORMAL 1

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@ 0 .45 gm/cm3 NORMAL GRAIN A 10.19 gm/cm3 LARGE GRAIN

B MURRAY AND THACKRAY' 1.02 - A BELL AND MA KIN^ -

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TEMPERATURE - 'C R A - 2 5 4 2 - 5

FIG. 5

(Shaded points ind icate measurements on cooling) LINEAR THERMAL EXPANSION OF UO,: I N I T I A L HEATING AFTER FABRICATION

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B MURRAY AND THACKRAY

1.02

0.96 ' " ' I " I I I ' I ' I " I " ' " I 0 500 1000 1500 2000 2500

R I - 2 5 4 2 - 6 TEMPERATURE - "C

' FIG. 6

LINEAR THERMAL EXPANSION OF LOW DENSITY UO, UPON REHEATING TO 2500°C ( I n i t i a l densi ty, 9.33 grnlcm3)

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I .oo

A BELL AND MA KIN^ B MURRAY AND THACKRAY'

FIG. 7

LINEAR THERMAL EXPANS I ON OF DENSE (10.19 gm/cm3) , NORMAL G R A I N S I Z E UO2 UPON REHEATING

J

Ji J a I J

1

I .06

I . 0 5

% + .04 - I z 0 a a

1 .03

X W

-J

I

I l-

a 5 1 .02

a a w z 7 1.01

1.00

0.99

A BELL AND MA KIN^ B MURRAY AND THACKRAY7 It

t- z 0 a W

c -I w

f

z

0 3

N

I l l l l l l l I l l l l l l ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ' ~ 0 500 IO00 1500 2 0 0 0 2 5 0 0 3000

R 4 - 2 5 4 2 - 8 TEMPERATURE - O C

FIG. 8

LINEAR THERMAL EXPANSION OF DENSE (10.19 gm/cm3), LARGE GRAIN S I Z E UO;1 UPON REHEATING

17

I

J

3 J Ii I ii

3

I .24

I .20

1.16 + - I z I2 cn 1.12 z

X w W I 3

0 >

2

1 1.00

I .04

I .oo

0 10.19 gm/cm3 NORMAL GRAIN

10.19 grn/crn3 LARGE GRAIN

500 Io00 1500 2000 2 5 0 0 3000 TEMPERATURE-%

R I - 2 5 4 2 - 9

FIG. 9

(Shaded points ind icate measurements o n cool ing) VOLUME EXPANSION I N HEATING UO2 TO THE MELTING POINT

18

J

I 3 a

a

a

a

I

FIG. 10

PHOTOMI CROGRAPH SHOW I NG CRYSTAL GROWTH AT THE SURFACE OF UO;I SPECIMEN HEATED ABOVE 2500°C (80x1

3 d

I J J

J 1 1 3 3

J

V

&- COOLING WATER I N L E T

COOLING WATER OUTLET

(-1 STINGER ELECTRODE

FLEXIBLE BELLOWS

VIEWING PORT

COPPER HEARTH

SAMPLE WELLS

"H \\ ' COOLO:NTGLF?TER

( + I VACUUM LINE HEARTH ELECTRODE

COOLING WATER I N L E T

R A - 2 5 1 0 - 1

FIG. 11

ARC-MELT1 NG FURNACE

20

J 1

J 3

3

1

I .40

I .30

41 -J

I + -

z v) z 0

2 x 1.20

a I a W r I- tY a W z -J

W J

-

I . I 0

I .oo

LL LL 0

u a a

0 10.19 g m / c m 3 NORMAL GRAIN

El 10.19 g m / c m 3 LARGE GRAIN

SOLIDIFICATION

i / DECREASING TEMPERATURE

-I 0 + I + 2 3 4 5 6 2

T I M E FROM ARC CUTOFF - s e c o n d s R 4 - 2 5 4 2 - 1 2

FIG. 12

LINEAR DIMENSIONAL CHANGE OF UO, I N COOLING THROUGH THE MELTING POINT

2 1

a STANFORD

RESEARCH

INSTITUTE

MENLO PARK. CALIFORNIA

3 R E G I O N A L O F F I C E S A N D L A B O R A T O R I E S

J 1

J J J a a a

Printed in U.S.A

J

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