AT A R | j HEEARCH ) IBRARY b4/ AR : N / ORNL-2530 Chemistry=-General SOLUBILITY AND STABILITY OF PuF3 IN FUSED ALKALI FLUORIDE-BERYLLIUM FLUORIDE MIXTURES C. J. Barton W. R. Grimes R. A, Strehlow OAK RIDGE NATIONAL LABORATORY operated by UNION CARBIDE CORPORATION for the U.5. ATOMIC ENERGY COMMISSION CENTRAL RESEARCH LIBRARY DOCUMENT COLLECTION LIBRARY LOAN COPY DO NOT TRANSFER TO ANOTHER PERSON If you wish someone else to see this document, send in name with document and the library will arrange a loan. -1 - ABSTRACT The solubility of PuF; in one NaF-LiF-BeF, mixture, three NaF-BeF; mixtures and four LiF-BeF, mixtures was determined at tempefatures ranging from about 550 to 650°C. Solubility- -compositiqn diagrams for the binary systems at 565°C show that in the LiF-BeF, system a minimum solubility of 0.25 mole % PuF; occurs at about 63 mole % LiF while in the NaF-BeF, system the minimfim solubility of 0.18 mole % PuF; occurs at approximately 57 mole % NaF. In both systems, the solubility increases rather slowly on adding BeF, to the composition exhibiting minimum soiubility but increases quite rapidly on adding alkali fluoride to this composition. The highest solubility observed at 565°C was 1.2 mole % PuF; in the mixture NaF-LiF- BeF2 (56.5-17.5-26 mole %). In fused LiF-BeF,-PuF, mixtures, the only plutonium species observed with the help of a polar- izing miéroscope was PuF,; but another compound believed to have the formula NaPuF, was found in the fused NaF-BeF, -PuF; mixture containing 64 mole % NaF and in the mixture resulting from the addition of PuF; to the ternary solvent composition. No evidence of disproportionation of PuF; was found in the course of the solubility studies. -2 - SOLUBILITY AND STABILITY OF PuF; IN FUSED ALKALI FLUORIDE-BERYLLIUM FLUORIDE MIXTURES C. J. Barton, W. R. Grimes and R. A. Strehlow INTRODUCTION An extensive series of studies conducted by W. R. Grimes | § | 2 | | | | a and co-workers in the Chemistry Division of Oak Ridge National A SRR e o Laboratory demonstrated that UF, can be dissolved in a number of fused fluoride solvents to provide fuel for fused salt reactors. The feasibility of the circulating fused salt reactor concept was established by the successful operation of the Aircraft 3 e Oty o S R o e U o 1 L D) 23 Y T Reactor Experiment.z’ The only fissionable species that have . . 35 been considered for a fused fluoride burner reactor are v Fy 5 235 3 3 and U F; but the possibility of a ThF,-U 33F4 fused salt breeder reactor seems promising,l Some consideration has also been given to the use of UZ35C14 or U?3°Cl, as the fissionable material in a fast neutron fused salt reactor.l Thermodynamic 4 data which indicate that PuF; is more stable than UF; and that PuF, is much more corrosive than UF,; prompted the choice of PuF; 1. W. R. Grimes et al., Reactor Handbook, Vol. 2, Section 6, AECD-3646, May 1955. 2. A. M. Weinberg and R. C. Briant, "Molten Fluorides as Power Reactor Fuels," Nuclear Science and Engineering, 2, 797-803 (1957) . | T 3. E. S. Bettis, W. B. Cottrell, E. R. Mann, J. L. Meem, and G. D. Whitman, "The Aircraft Reactor Experiment--Operation,” Nuclear Science and Engineering, 2, 841-853 (1957) . 4. Alvin Glassner, ''The Thermochemical Properties of the Oxides, Fluorides, and Chlorides to 2500°K," ANL-5750. | | | g % g @ % % ] ! it fi | i as the examin: materi: seems than U reCOgn§ obtain; prelimé the sd solvené in the intere includ tempef of oth is bei: Equip@ shown chambé of neg Isotop pluton micros .;as the plutonium-bearing species for the first experimental ziexamination of the possibility of using Pu,;, as the fissionable fmaterial in a fused fluoride power reactor (see Appendix A). It ;seems reasonable to expect that PuF; will not be more corrosive ithan UF,; under proposed power reactor conditions but it is recognized that data to support this belief will not be easy_to_ obtain. This report gives the results obtained to date of a preliminary investigation of one aspect of this problem, namely, the solubility and stability of PuF; in suitable fused salt solvents. Alkali fluoride-beryllium fluoride systems were used ;in these studies since they are the only solvents currently of finterest in the fused salt power reactor program. The studies included determination of the effect of solvent composition and temperature on the solubility of PuF;. The effect of addition ~of other fluorides on the solubility of PuF; in fused LiF-BeF, is being studied and will be reported at a later date. EXPERIMENTAL Equipment Two glove boxes constructed for fused salt studies are hown in Figures 1 and 2. They are connected by an interchange fchamber and constitute an extension of an inter-connected series ;of negative-pressure glove boxes used by personnel of the sotopes Division, Oak Ridge National Laboratory, for handling fplutonium isotopes separated by use of the calutron. The microscope glove box shown in Figure 1 has plywood back, bottom , sealed and sides while the front and top are made of clear plastic _ used to material for maximum visibility. The eyepiece of a Zeiss polar- ; : . i arrange izing microscope protrudes through an opening in the slanting at Los front of the glove box which is sealed with an airtight bellows the fro arrangement permitting vertical movement of the eye piece. The . . , which a microscope support is constructed of transparent plastic mate- o rial to facilitate observation of ohjects beneath the microscope Scobe a - OX ., - which are illuminated with light from a bulb in the base of the box ( insid s microscope. The microscope glove box is a modification of one h © of 3" I used at Los Alamos Scientific Laboratory for microscopic exam- HF from ination of highly toxic materials. The stainless steel glove _m _ ] ] ) _ in seri box shown in Figure 2 is a modification of a muffle box built _ . _ , vent ca for plutonium isotope work. Some of the more interesting _ _ L while t! features of this glove box are: (1) A heating well consisting : ) _ plete ri of a 1-1/2" length of 6" I.D. pipe welded around an opening in Th the bottom of the box and connected to an 8'" length of 4" I.D. ) . ] below tl pipe closed at the bottom. The interior of the well is heated ) . Air £fil to a maximum of approximately 800°C by means of a 5" I.D. 2700~ - to the | watt tube furnace mounted on a jack beneath the box so that it imatel can be lowered to facilitate rapid cooling of the well. The tmately . . istu: box is kept cool by water flowing through a copper coil soldered (mois 1 to the bottom of the box around the well. (2) A discharge chute on a pa s . . argon, ° consisting of a 12" length of 4" I.D. pipe welded to the right N . itl side of the box at an angle of 60° from the vertical, loosely tus witl sealed on the inside of the box by a sliding door and tightly supply hydroger Scope : the one ;ted é?OOM it e idered ;chute ght 1y 5137 sealed at the other end by a long plastic sock which is also used to encase materials removed from the box. This discharge arrangement is similar to that used on a number of glove boxes at Los Alamos Scientific Laboratory. (3) A small protrusion on the front of the box at the left side having a glass top over which a low-power long focal length (9X and 18X) binocular micro- - scope and light is mounted for examination of objects inside the box. (4) Sodium fluoride traps (not visible in Figure 2) mounted - inside of the box on the back wall, consisting of two 30" lengths ~of 3" I.D. copper tubing filled with 1/8" NaF pellets to remove - HF from exhaust gases. The first one of the traps connected in series is heated to 100°C by means of a heating coil to pre- vent caking of the NaF through formation of HF-rich complexes, '.While the second trap is unheated in order to effect more com- - plete removal of HF. The pressure in the boxes is maintained 1/2 to 1" of water :ibelow that of the laboratory by means of an exhaust system. “Air filtered through a CWS filter can be alternately supplied I;to the box from the room (50% RH), from an '"Lectrodryer" (approx- fimately 15% RH) or from a drying tower packed with Drierite - (moisture content not determined). Bellows-type valves mounted ;on a panel below the front face of the box control admission of ;_argony 95% argon-5% hydrogen mixture, HF, and vacuum to appara- ;fus within the box. The argon-hydrogen mixture was used to fsupply a reducing atmosphere over the melts instead of pure hydrogen because of safety considerations. The gas tanks and vacuum pump are located outside of the laboratory. Materials Plutonium trifluoride used in these studies was high-purity material supplied by Los Alamos Scientific Laboratory. Solvent mixtures were purified prior to being introduced into the glove box by treating fused mixtures with gaseous HF and H, at about 800°C and cooling under an inert atmosphere. The composition of some of the purified mixtures was modified either by addition of crystalline BeF, purified by the above-described procedure or by addition of Harshaw optical grade LiF. Apparatus A picture of the filtration apparatus used in this inves= tigation is shown in Figure 3. This apparatus is a modification f of that used earlier in these laboratories for solubility determinations,* the main change being a reduction in the diam- eter of the sample container in order to permit smaller charges to be used. The copper bellows permit the filter medium to be kept out of contact with the charge material prior to the actual filtration in order to minimize clogging of the filter medium. The apparatus shown in Figure 3 was assembled by heliarc welding in the Special Services Shop of the Y-12 Plant. An improved version of the apparatus used for the last few experiments per- formed was assembled in the Welding and Brazing Facility, ORNL, * Designed by B. H. Clampitt, formerly a member of the Chemistry Division, Oak Ridge National Laboratory. by braz hydroge: use of effecte Thi thermoc: platinu proport: recoxrde: the rec: was alse The rec; 2°c. T colils wé Th controlj mocouplé to a poé controlé Experime The the gasf the stai Toom ten tained,: sisting .purity Slvent %glove 1 bout tion of tion of 2 Oor by AVES - ication diam~ harges to be dium. ved S per-— ORNL, éctual; Welding: by brazing the top part together with gold-nickel alloy in a ydrogen atmosphere at about 1000°C. This procedure permitted use of thin-wall tubing for the thermocouple well and also effected remcval of oxide film from the nickel surfaces. The temperature of the melt surrounding the tip of the thermocouple well was measured and controlled by means of a platinum-platinum 10% rhodium thermocouple connected to a Brown roportional controller. It was recorded on a 300-1000°C ecorder. A portable potentiometer provided an e.m.f. to keep he recorder on scale while the temperature was below 300°C and as also used to check the potential of the thermocouple junction. The recorder and potentiometer readings generally agreed within :OC, The temperature near the center of the furnace heating coils was indicated on a Brown Protect-0O-Vane controller. The temperature of the heated NaF trap was measured and controlled by means of a chromel-alumel thermocouple, in a ther- mocouple well extending from the center of one end of the trap to a point near the middle, connected to a Brown Pyr-0O-~Vane controller. Experimental Procedure The filtration apparatus (Figure 3) was first connected to the gas tanks and vacuum pump through the manifold system below the stainless steel glove box (Figure 2) and vacuum tested at ?oom temperature. After a vacuum of about 50 microns was Ob- tained, the filter stick was removed and charge material con- Sisting of 5.0 to 5.5 grams of solvent mixture and enough PuFj to give 6.0 grams total charge was transferred from plastic vials into the filter apparatus through a long-neck metal funnel. The ratio of solvent to PuF,; was adjusted to provide at least-twice the amount of'PuF3 that was expected to be dissolved. After the filter stick was replaced, the filter apparatus was re-connected and vacuum tested. It was then filled with argon-hydrogen mix- ture introduced through the filter stick, which was positioned so that its lower end was close to the fused salt mixture, providing' reducing atmosphere to help keep the plutonium in the trivalent state. Argon-hydrogen mixture was used in preference to pure hydrogen because of safety considerations. Gaseous HF was mixed with the argon-hydrogen mixture before the temperature of the filter bottle reached 250°C in order to minimize hydrolysis resulting from adsorbed water on the surface of the fused salt and PuF; crystals or to recoavert any hydrolysis products to fluorides. The filter bottle and contents were held at the desired filtration temperature ¥ 5°C for two hours with a slow flow of the mixed gases over the surface of the liquid and then filtra- tion was effected'by applying a vacuum to the filter stick and argon pressure of 3 to 6 1lbs to the surface of the liquid while the bellows was compressed to bring the filter stick into con- tact with the liquid for a period of 5 to 10 minutes. The filtrate and residue were allowed to cool slowly to room temper- ature in an argon atmosphere. The filter stick was then removed - and cu of sol filtra the ab peratu comple cut op remove: A filtra: Flexibj leading bottle. filtrat the fij quite rx 300°0) . of the cooling availafi after fi arrange moving are thé the glo The wice ;r the iected mix- 1lent ire mixed the - yials oned SO sviding and cut intoc sections for removal of the filtrate. A new charge of sclvent and PuF, was added to the residue from the previous filtration, a new filter stick was inserted in the apparatus and the above filtration procedure was repeated at a different tem- perature. After the required number of filtrations had been completed with each solvent composition, the filter bottle was cut open and the residue from the final filtration experiment was removed for examination and analysis. A variation of the above-described procedure was used in filtration experiments with one solvent (71.3 LiF-28.7 BeF,). Flexible hose connections were placed in the three gas lines leading to the filtration apparatus. This permitted the filter bottle to be withdrawn from the furnace at the conclusion of the filtration period while argon gas was still being pulled through the filter stick, causing the filter bottle and contents to cool quite rapidly (approximately 100° per minute between 600 and 300°C). This procedure eliminated any possibility of a portion 0of the filtrate running through the filter medium during the cooling period and it had the advantage of making the filtrate available for examination at room temperature about 30 minutes after the end of the filtration. It was also possible with this arrangement to agitate the contents of the filter bottle by fmoving the apparatus up and down. The principal disadvantages fare the hazards associated with the handling of hot objects in jthe glove box and the extremely small crystal size of the - 10 - rapidly cooled mixtures which makes microscopic identification of crystals difficult. Results Table I gives the composition of solvent mixtures which were analyzed chemically. The first column shows the nominal or intended composition of the mixtures while the last column shows the composition calculated from analytical data. The composi- tion of solvent mixtures not included in Table I was calculated. Solubility data obtained with LiF-BeF, mixtures are given in Table II; NaF-BeF, solubility data are contained in Table III; | and the solubility of PuF; in one NaF-LiF-BeF., mixture is shown in Table IV. The data are shown graphically in Figures 4 and 5, omitting doubtful results, as a plot of the log of the molar concentration of PuF; versus 1/T (PK). Figure 6 shows solubility'i data at three temperatures as a function of solvent composition for LiF-BeF, mixtures while Figure 7 shows a similar plot for NaF-BeF, compositions. The data obtained with the ternary mix- ture (Table IV) were used to extend the data in Figure 7 by considering 56.5% NaF and 17.5% LiF as equivalent to 74 mole % NaF. A comparison of the two systems, using interpolated solu- bility values at 565°C is shown in Figure 8, again using data on the ternary system to extend the NaF-BeF, curve. Dissolved portions of seven samples were examined spectro- photometrically for Put* content. No Pu™ was detected in any of the samples. The limit of detection varied from 0.2 to 3.0%, "SOTJI01BIOQR] OM] AQ PSBUTIRIQO SIINS8JI JO 98BIDAY 4 TT 68°¢ ‘qed 0°92=dTT §°LT-dBN G°96 %86 °§ BN 98°0¢ cdeg @Z=ATT 9T=dEN 99 ¢qed L e%~dTT €°96 *2T "T11 86 °0T tqeg v¥—dTT 9§ M ‘asd ¢°8%—dTT L 164 0° 2T 06°6 ‘qed 0S=dTI1 06 J ‘qod 6°T¢~dTT T1°89 x08 ° 8 LY FT tded ¢ree~dATT L°99 ‘ded 9°9g=deN ¥°¢9 *x8% ° L 21 ¢¢ ‘god 9¢=deN %9 ‘god 0°¢H—dEN 0°LS *¥9°8 Y1°62 ‘deog ¢h-deN LG tged £°0s=deN L 6¥ x90°0T 25°G¢ ‘dad 0g~deN 0% (6 oTOW) % “IM) % “IM) (0 o1owU) uorylirsodwo) palrernore)d ag T JO BN uotlrsodwo) TeUTWON SOJIN}XTN JUSATOS JOo uoritrsodwo) I 9T19®eL for \ shows yle IIT any 0 3.0%, ?ctro~ sition data on 7 mix— Dy 316 Yo ‘solu- - 12 - Table 11 Solubility of PuF, in LiF-BeF, Mixtures Solvent Filtration ' _ | _ - Cfi Composition Temperature Plutonium in Filtrate T Mole % Li (°c.) Wt. % Pu Mole % PuF, 51,7 - 463 | 1.02 | 0.16 " 549 | 2,44 0.38 " 599 . 2.96% 0.47% " 654 5,76 0.93 56,3 494 1,04%* 0,15 i 560 | 1,89%x 0.28 " 602 3.15%% 0.48 " 653 5.47%% 0.86 " 550 1.98 0.30 i 599 2.04% 0.31% " 649 6.24% 0.98% 65. 4 532 - 1,15 0.16 " 600 o 1.78% 0.27% " 643 4.30 - 0.63 71.3 546 | ,' 4,00 0.56 " 597 | 5.90 0.85 * " 650 8.48 1.26 * Doubtful result, excluded from Figure 4. / ** Results obtained with a pre-fused mixture. Other results with this composition were obtained with mixtures pre- " pared by mixing LiF, Li,BeF, and PuF, in the filter bottle 27% s 56 85 26 iresults - pre- er bottl Table III Solubility of PuF, in NaF-BeF, Mixtures Solvent Filtration Composition Temperature . Plutonium in Filtrate Mole % NaF (°C) Wt. % Pu Mole % PuF, 49.7 552 1.18 0.22 " 600 1.73 0.33 " 600 1.79 0.34 " 651 2.72 0,52 57.0 538 1.17% 0,22+ " 552 1.63% 0.31% " | 600 1.35 0.26 " 600 1.26 0.24 " 609 1.26 0,24 " 650 1.48% 0,28%* " 652 2.21 0.42 m 706 3.40 0.66 63.4 550 1.54 0.29 " 598 2,43 0.46 " 600 2.00% 0,38% " 650 4,40 - 0,85 * Doubtful result, excluded from Figure 5. - 14 - Table IV Solubility of PuF; in NaF-LiF-BeF, (56.5-17.5-26 mole %) Filtration Temperature (°C) 500 554 565 600 634 655 Plutonium in Filtrate Wt. % Pu Mole % PuF, 2.92 0.51 7.68 1.43 2,61% 0.,46% 7.59 1.41 13.0 2.58 6.45% 1.18%* * Doubtful result, excluded from Figure 5, depend. size o a care: micros sampléa chemi c: examins graphig Appendi S ] have b{ or by t resulti ed witt similar were ifi nickel | such mé total fi NaF, Be contacfi 6500C 1 two sam snding upon the plutonium concentration in the samples and the » of the sample analyzed. Since these results, coupled with féful examination of each sample by means of the petrographic iéscope, demonstrated that all of the plutonium in these _lés wfis in the trivalent form, other samples were analyzed mically only for total plutonium content but microscopic mination of the samples continued. A summary of the petro- fphic observations made by R. A. Strehlow is contained in pendix B. Since Pu™™ produced by disproportionation of PuF; could e been reduced by hydrogen in the atmosphere above the melt ;fby the nickel walls of the container, it seemed advisable to ok for other evidence of the absence of disproportionation of uF; . In similar studies with UF;-containing melts, U metal _E$ulting’from disproportionation of UF; was found to have alloy- 'fijwith the container wall. In order to determine whether a ’milar ailoying effect occurred when PuF;-containing melts re in contact with nickel, the bottom section of two welded hickel filter bottles (Figure 3) that had been in contact with Such melts were scraped as clean as possible and analyzed for otal plutonium content. One sample had contacted a mixture of NaF, BeF, and PuF; at 600°C for two hours while the other had contacted a similar mixture at temperatures varying from 550 to 6509C for approximately eight hours. The plutonium found in the two samples, amounting to 0.05 and 0.17 mg respectively, could be accounted for by the trace of fused salt remaining on the nickel. ©No evidence of disproportionation of PuF; in fused alkali fluoride-~beryllium fluoride melts under the conditions maintained in these solubility studies has been observed to date. Discussion Straight lines correlate the data in Figures 4 and 5 with- in the limits of reproducibility of the results. Changes in composition of the solvent mixtures seem to have little effect on the slope of the lines. It appears, therefore, that the heat of solution of PuF; in these solvents is essentially constant for the temperature and composition ranges studied. The solubility-composition plots, Figures 6, 7, and 8, show that the solubility of PuF; in the melts goes through a minimum with a sharp increase on the alkali fluoride side and a gradual increase on the BeF, side of the minimum. This result is not unexpected since the BeF,-PuF; eutectic probably contains a very low concentration of PuF; while the alkali fluoride-PuF; eutectics almost certainly contain a much higher PuF; concentra- tion. Inspection of Figure 8 and the phase diagrams of the binary systems LiFmBeFZS and NaF—BeFZ6 shows that a higher solubility 5. D. M. Roy, R. Roy, and E. F. Osborn, J. Ceram. Soc. 37, 300 (1954); Novoselova, Simanov, and Yarembash, J. Phys. Chemn. USSR, 26, 1244 (1952). 6. D. M. Roy, R. Roy, and E. F. Osborn, J. Ceram. Soc., 33, 85 (1950); Ibid, 36, 185 (1953); E. Thilo and H. Schroder, Z. physik. chem., 197, .41 (1951). of F the temg molé molé melt mole PuF, temy sSOlv Tab] were the$ of equ] des] men; £1ue sib: dat: sol med of ', 300 ?hem. 3, der, of PuF, at 565°C can be achieved in the LiF-BeF, system than in the NaF-BeF, system for solvent mixtures having the same liquidus temperature. For example, the LiF-BeF, mixture containing 69 mole % LiF which is liquid at 520°C, will dissolve about 0.50 mole % of PuF; at 565° while the comparable NaF-BeF, mixture melting at 520°C contains 62.5 mole % NaF and will hold 0.26 mole % PuF,; in solution at 565°. If much more than 0.5 mole % PuF; is needed for a circulating fuel reactor having a minimum temperature of 5652, it may be necessary to resort to a ternary solvent in order to keep the liquidus temperature of the sclvent at an acceptably low figure. Approximation 25% of the filtration data recorded in Tables II, III, and IV (those results marked with asterisks) were excluded from Figures 4 and 5 and some of the points in these graphs do not lie very close to the lines. This scatter of data reflects to some extent the difficulty in obtaining equilibrium data with small amounts of fused salts. It was desirable to use small amounts of materials for these experi- ments because of neutron production in plutonium~beryllium fluoride melts. However, an analysis of factors having a pos- sible influence on the results may be of help in evaluating the data. Low results could be due to failure to saturate the solvent because of inadequate equilibration time, absence of a means of agitation (see page 9), or lack of a sufficient amount of PuF; in the mixture. There are two fairly obvious explana- tions of high results. A temperature gradient is known to exist in the heated zone occupiéd by the filter bottle during filtration experimenté, with the temperature decreasing in going from the bottom to the top of the chamber. If the thermocouple junction was above the surface of the liquid in the%filter bottle, the temperature indicated by the thermocouple was prob- ably lower than that of the liquid. Some of the filter bottles used in these studies had thermocouple wells too short to reach the surface of the liquid and it is also possible that éfrors in the determination of the‘temperature of the melts resulted from the thermocouple being inadvertently pulled part way out of the thermocouple well. The other possibility is that a portion of the solvent or a low-melting ternary eutectic having a lower plutonium content than that of the original filtrate ran back through the filter after partial solidification of the filtrate occurred. (See Experimental Procedure, p. 7) Confidence in plutonium values reported by the analytical laboratory was strengthened by having a number of samples reanalyzed under different sample designations. The results, shown in Appendix C, indicate that satisfactory reprdducibility was obtained although the differences for some samples were greater than expected from the precision of the potentiometric plutonium determination. It is possible that some of the early samples which were ground but not sieved were not entirely homo- geneous . ng going uple brOobh- fitles reach :rs in from f the er ack irate ical ility &ric early ~ homo- Acknowledgments The writers are grateful to F. N. Case of the Isotopes Division of ORNL, for help in planning the glove boxes used in this investigation; to R. J. Sheil, Chemistry Division, ORNL, for designing the gas manifold system; to H. Insley, Consultant, ORNL, for help in designing the microscope glove box; to personnel of the Analytical Division of ORNL under the direction of L. T. Corbin, J. H. Cooper and W. R. Laing for performing the numerous analyses required in these studies; and to personnel of the Los Alamos Scientific Laboratory including R. D. Baker, W, J. Maraman, Charles Metz and K. W, R. Johnson for helpful advice during the planning stage of the project and for furnishing the high purity PuF, used in this investigation. - 20 - Appendix A Thermodynamic Calculations for Reactions at IOOOOK. AF for Reaction AF per Gm. Atom Reaction as written (k Cal) of F, k Cal 4UF, — 3UF, + U° + 12 + 1.0 4PuF, — 3PuF, + pu’ + 214 + 18 2UF, + Cr° — 2UF, + CrF, + 31 + 3.9 2UF, + 3Cr® — 20° + 3CrF, + 120 - + 20 2PuF, + Cr® — 2PuF, + CrF, -~ 80 - 10 2PuF,; + 3Cr° — 2pu® + 3CrF, + 194 + 32 1 fc ST Un ap mi of “Atom Cal ) Optical Properties of Fluoride Mixtures Containing PuF, and residues obtained in the study with a principal objective of identifying the plutonium containing phase. preparations for the work were made in a glove-port plexi- . glas box (Figure 1) scope. - 21 - Appendix B R. A. Strehlow Petrographic examinations were carried out on filtrates The optical character of the various plutonium All of the slide in which was mounted a polarizing micro-= compounds permitted distinction to be made from the crystals of the various solidified solvents. contained one or more of the compounds: 2 . 1 NaBeF,, LiBeF, 1 refractive indices of less than 1.4. fractive indices an initial observation was made of the growth form of all phases of higher index by examining the crushed Li,BeF, , ' Na,BeF,, and BeF, . All of these compounds have Inasmuch as the plutonium phases had much higher re- specimen in an oil with a refractive index of about 1.35. The solvents generally 2 Under these conditions all phases of appreciably higher index appear quite heavily bordered and are easily located in the microscope field. of the phase indicated which of the possible compounds con= 1. 2. D. M. Roy, 300 (1954) D. M. Roy, 85 (1950). R. Roy and E. F. Osborn, R. Roy and E. F. Osborn, J. Ceram. J, Ceram, Soc., Soc. 37 33 r— 7 g Observation of the color and birefringence - 22 - taining plutonium was present: Pu(III) fluorides are blue and Pu(1V) fluorides tan. (No PuF, was observed in the fil- trates or residues in this study.) The maximum birefringence of PuF; observed in this study is about 0.003. The inter-~ ference color (observed with crossed polarizing discs) is approximately that of the crystal observed in "white"™ light, pale blue. The compound NaPuF, appears reddish blue and has a maximum birefringence of about 0,02. The optical properties of these compounds are compared in Table B-1 with those of some Ce*3, U*®, and Ut4 compounds. The Pu(III) ion is about the same size as the Ce(III) and U(III) ions and differs from them in its polarizability which is, of course, shown by the differences in refractive indices. The most common growth form of PuF, as crystallized from the solvents used in the study was that of thin sheets which could be observed with their maximum birefringence only when they existed as platy inclusions in the»solvent crystalso. Under these conditions they exhibited their maximum bire- fringence and parallel extinction. No compound was found which could be considered a LiF-PuF, binary compound in LiF= BeF,~PuF, melts and no change in the refractive index of PuF; was seen which would indicate solid solution of LiF in the PuF, . The growth form of the PuF, is strongly dependent on the Lue filw Lgence s ght, l'hés erties of some Table B-1 Refractive Indices and Optical Character of Some Plutonium, Cerium, and Uranium Fluorides Me N Description PuF, 1.683 1.685 Uniaxial (-); blue* UF, ~2 Isotropic; red Cel, 1.607 1.613 Uniaxial (-); colorless Ty | ”7 Description PuF, 1.577 "16629 2v = =65° pink green-brown UF, 1.550 . 1.594 2v = -57° blue-green green-brown Mgy | Ne Description NaUF, 1.552 1.564 Uniaxial (+) NaPuF, 1.534 | 19552 Uniaxial (+) (length slow) NaCeF, 1.494 S 1.512 Uniaxial (+) * The sign ofPuF; as observed in this work does not agree with that listed by E. Staritsky and A. L. Truitt in "The Actinide Elements,' NNES, IV-14A, McGraw-Hill Book Co., cooling rate and is described in Table B-2, Table B-2 The Effect of Extremes in Cooling Rates On Appearance of PuF; in LiF-BeF, Mixtures Rate Appearance Rapid Asterisms <5l across frequently imbedded in glassed solvent. Occasional identifiable crystals near 3-84 in diameter. Slow Large plates (>50n across, 5 thick) gifiing the uniaxial (~) interference figure; solvent well crystallized. A sample prepared by mixing LiF-NaF-PuF; (50-33.3-16.7 mole %) was examined petrographically after fusing. A 1arge amount of a plutonium containing phase, LiF crystals, and NaF-LiF eutectic aggregates were observed. Since the plutonium: compound was found only in mixtures containing sodium fluoride and since the optical properties were similar to those for the known compounds NaCeF, and NaU¥,, this plutonium compound was designated as NaPuF, . It is interesting to note that NaPuF, was observed as the sole plutonium containing phase in the filtrate from the mixture NaF-LiF-BeF, (56.5-17.5-26 mole %). Some NaPuF, was seen in the residue from the mixture containing 64 mole % NaF but not;in ’ the filtrate. This indicates that the isotherms as shown in Figure 7 probably cross the NaPuF, -PuF,; primary phase field in ing lvent 6.7 ;rge ?tonium ?oride Qr the d was és the mixture in the t in - 1 1in 2 1d —~ 25 - boundary at a relative composition of very near 64-36 mole NaF per mole BeF,. PuF,; was observed in both filtrates and residues of other NaF content. A comparison was made of transmission spectra by means of a Leitz pupillary spectroscope., The principal difference between NaPuF, and PuF,; is an absorption band between 6500 2 and 6650 K for PuF; which exists at 6660 K to 6800 & for NaPuF, . For the PuF; there is also more transmission between 5200 fi and 6000 ® which presumably accounts for the difference in color between NaPuF, and PuF,. S oVt e g o T i Appendix C Analysis of Re~submitted Samples Original Sample % Pu Re-Check % Pu A5 1.36 G2 1.33 B5 1.41 E8-C9 1.15-1.22 A7 2.16 G3 2.25 B3 1.37 Gé6 1.60 D6 1.77 ' G7 1.68 B7 1.82 H3 1.74 ET : 2.88 H8 3.03 02867 OLOHd A313185y 10NN 1.22 /@% = . PR U U R s SYZ0t OLOHd a3a1dISSYTIONN m wwm el . 3 /M/%&wa L X T 1 NCL ASSIF) PHOTO 298 650 TEMPERATU 600 RE (°C) 550 UNCLASSIFIED ORNL—LR—DWG 29605 500 \//74.3 LiF-2 8.7 B(-'aF2 | N\ N v ONONL AN N N, N\ NN o, ~ 0.5 N\ A ~ ~ PuF, (mole % ) N N A NN 65.4 LiF-34.6 BeF,” ® N\ N\ = 51.7 LiF-48.3Bef, _| 0.2 56.3LiF-4 | | 3.7BeF, | 0.1 10.5 11.0 11.5 2.0 1 10%/°K 2.5 13.0 Fig. 4. Solubility of PuF3 as a Function of Temperature for LiF-BeFy Solvents. 13.5 14.0 05 0.5 PuF; (mole %) 0.2 O -31- UNCLASSIFIED ORNL—LR—DWG 29606 TEMPERATURE (°C) 650 600 550 500 | 1 | | NJ{_56.5 NoF-17.5 LiF- 26 BeF, l / / 7/ './ o /| \\ \\ | 57.0NaF-43.0BeF~ ~ ~ ~ ~ \\ \+ 49.7NaF-50.3Be R 10.0 105 10 1.5 120 125 10%/°K 13.0 13.5 Fig. 5. Solubility of PuF3 as a Function of Temperature for NaF-BeFy and NaF-LiF- BeFy Solvents, -32- UNCLASSIFIED ORNL-LR-DWG 29607 e Pl o \M/ i 650°C 600°C 550°C 1.4 1.2 1.0 D O (% ®jow) © O €4ng 0.4 0.2 60 65 70 75 LiF (mole %) 55 50 . Solubility of PuF3 as a Function of Solvent Composition for Li -BeFy Fig. 6 Mixtures. Fig. 7. Mixtures. 2.5 2.0 1.5 PuF3(moIe %) 0.5 0 Solubility of PuF3 as a Function of Solvent Composition for NaF-BeF, -33- UNCLASSIFIED ORNL-LR-DWG 29608 / ~. / N 650°C 600°C_~ yd / / 56.5 NaF — {7.5 LiF ————a——\ \ 550°C | 50 5 5 6 0 6 5 70 NaF (mole %)} -34- UNCLASSIFIED ORNL-LR-DWG 29609 1.2 o8 32. 0.6 ;) NaF PuFz (mole %) 0.4 NLE N N0 47. 56.5 NaF =17.5 LiF —1————3m— £ < 50 55 60 65 70 75 27 NaF OR LiF (mole %) 59. Ei L‘ L A L J ] E E S M GE J R H F A A M 44, K T A c c D D F D J M W G C J ¥ E . G Fig. 8. Solubility of PuF3 in LiF-BeFy and NaF-BeFp at 565°C, 62, S R E F ¥ E I‘ £ C. E. 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