Dec. 12, 1961 F. L. HORN 3,012,849 DISSOLUTION OF ZIRCONIUM-CONTAINING FUEL ELEMENTS Filed April 6, 1959 ZRCONIUM CLAD - URANUM, CORED SPENT FUEL ELEMENT

(ACD FLUORDE) HF HYDROGEN, VOLATILE DSSOLUTION FSSON PRODUCTS (COMPLEXING AGENT) NO2 AND DECAY PRODUCTS LIQUID PHASE: URANUM DISSOLVED IN HF-NO2. SOLVENT SOLID PHASE: ZRCONUM HF AND NO FLUORIDE COMPLEX RECYCLE

F LTRATON SOLDS (ZIRCONUM PLUS FSSION PRODUCTS)

EVAPORATION

(FLUORINATING AGENT) J BrF FLUORNATION

RECYCLED BrF. UFe, EXCESS BrF, VOLATLE FISSIO PRODUCT FLUOR DES SOLIDS (ZIRCONIUM PLUS FSSION PRODUCTS)

DST LLATION VOLATLE

FSSION PRODUCTS

UFs

INVENTOR. FREDER!CK L. HORN BY 122-- 2a-74---- artz 3,012,849 United States Patent Office Patented Dec. 12, 1961

2 novel and simple process for the recovery of uranium 3,012,849 from spent fuel elements in which the uranium is mixed DSSOLUTION OF ZIRCONUM-CONTANN FUEL ELEMENTS with, clad with or alloyed with zirconium metal or its Frederick L. Horn, Sayville, N.Y., assignor to the United alloys. A further object of this invention is to provide a States of America as represented by the United States process which effects dissolution of spent fuel elements Atomic Energy Commission of the type described at relatively low temperatures and Filed Apr. 6, 1959, Ser. No. 804,553 pressures and under relatively controllable conditions. 7 Claims. (CI. 23-14.5) Another object of this invention is to provide a process which can use inexpensive, readily available materials r The present invention relates to a method of separat 10. for the construction of process vessels. A still further ing and recovering uranium from spent nuclear reactor object of this invention is to provide a process for re fuel elements. More particularly, the invention relates covering uranium in a volatile form from spent fuel ele to a method of separating and recovering uranium from ments of the type in which uranium is clad with or alloyed fuel elements in which the uranium is mixed with, with zirconium or its alloys. A still further object of alloyed with or clad with zirconium metal or alloys there 5 this invention is to provide a process for recovering ura of. nium from spent fuel elements by which the volume of In the processing of neutron-irradiated nuclear fuel waste fission products is minimized and wherein said elements to separate and recover the uranium from the fission products are in a concentrated and easily-handled nuclear reaction products, a highly advantageous method form. Still another object of this invention is to provide comprises a method the initial step of which involves 20 a continuous process for the recovery of uranium from a dissolving the contaminated uranium in a non-aqueous mixture containing uranium and zirconium. halogen fluoride in the liquid phase. This dissolution Certain acid fluorides, of which hydrogen fluoride (HF) step effects a partial phase separation of the uranium and difluorophosphoric acid (HPOF2) are examples, re and certain other contaminants and converts the uranium act with uranium under anhydrous conditions. However, to the halogen fluoride soluble and volatile uranium hexa 25 the reaction of zirconium with these acids results in the fluoride compound. When this is followed by one or formation of an essentially insoluble fluoride, salt. I more distillation steps, the volatile uranium hexafluoride have found that if the uranium is clad with or alloyed can be separated from the solvent and any volatile im with zirconium or its alloys, or otherwise combined with purities. Such a fluoride volatility process for the recov zirconium, the uranium cannot be separated from Zir ery of uranium is described in United States patent, 30 conium. Zirconium, as well as certain other metals, Serial No. 2,830,873, dated April 15, 1956. forms an insoluble, tightly adherent coating thus pre While the described process has wide utility in the cluding further reaction to effect recovery of the uranium processing of spent nuclear reactor fuel elements it can from the zirconium...... not be used for the recovery of the uranium from fuel The present invention is predicated on the discovery elements in which the uranium is alloyed with, clad 35 that zirconium metal or a zirconium alloy can be at with or otherwise combined with zirconium metal or least partially solubilized in anhydrous acid fluorides by alloys of zirconium. It has been found that the halogen the addition thereto of a complexing agent thus avoiding fuoride reacts with the zirconium to form a tenacious the formation of an insoluble adherent fluoride coating fluoride coating thus precluding dissolution or reaction on the metal surface to be treated. In the absence of a of the metal underlying the coating. For this reason, it 40 tightly adherent fluoride coating the uranium is then has become necessary to turn to other processes for the rendered free to react with an acid fluoride to form a recovery of uranium from reactor fuels in which the ura soluble uranium complex compound which can be Suit nium is combined with zirconium metal or its alloys. ably treated with a halogen fluoride to form the volatile One process which is used for recovery of uranium uranium hexafluoride. . . m from spent nuclear reactor fuels of the type described 5 In accordance with the present invention, uranium is employs an initial step which comprises dissolving the separated from its fission products and its zirconium spent fuel element in an aqueous solution of hydrogen containing cladding and alloying constituents by a process, fluoride and nitric acid. This process has a number of the initial step of which comprises, dissolving the con disadvantages. The uranium salt (uranium tetrafluoride) taminated uranium in the liquid phase of a non-aqueous recovered from the dissolution step is not volatile, and 50 solvent containing an acid fluoride and a complexing further processing is required to purify the uranium and agent. The uranium is thereby converted to an acid convert it to a form suitable for reconstitution into re fluoride-soluble uranium fluoride complex compound, actor fuel elements. Moreover, the dissolving medium is whereas the zirconium forms a complex of limited solu extremely corrosive and requires the use of unusual con bility. This insoluble compound is then separated from tainer materials such as an alloy of gold and nickel. the solution by conventional phase separation methods It has been estimated that for each kilogram of uranium which may include filtration or decantation. The ura recovered from spent fuel elements containing about nium-containing filtrate is then evaporated to dryness. 0.6% by weight uranium, the remainder being zirconium, The solid residue which contains uranium and a small about 1,000 gallons of aqueous waste liquid is produced percentage of other metal contaminants is then treated contaminated with radioactive fission products. 60 Other processes which have been used for the recovery with a halogen fluoride in the liquid phase. The ura of uranium from spent fuel elements in which the urani nium is thereby converted to the volatile uranium hexa um is clad with or otherwise combined with zirconium or fluoride compound. The uranium hexafluoride (UFs) its alloys all have their complications because high tem so formed is separated from the solvent and from any peratures and highly corrosive reagents are employed contaminating volatile fluorides by one or more distilla which result in excessive corrosion of the containing tion steps, following conventional distillation practice. vessels and present the hazard of run-away reactions. . For a more complete underestanding of the invention, It is therefore an object of this invention to provide a reference may be made to the following description and 3,012,849 3. 4. accompanying flowsheet which illustrates one embodi fluoride and other volatile contaminants, by distillation ment of the process of the present invention. In the to yield a uranium hexafluoride product which is sub composition to be treated, the uranium may be uranium stantially free of these contaminants. metal or a uranium compound such as one of its oxides. The materials of construction for reactors to contain The uranium may be alloyed with another metal such halogen fluorides must be selected with some care. Cer as a uranium-zirconium alloy. The zirconium may form tain common metals such as iron, nickel, aluminum and part of the core of the fuel-element or part or all of the copper have been found to form coherent protective cladding. Indeed, the metal mixture may be any coin films in the presence of halogen fluorides which make position in which the uranium and zirconium are phys their use as construction materials practical for handling ically and/or chemically combined. In the embodiment O the liquid halogen fluorides. Nickel and high nickel al to be described, it will be assumed that the starting ma loys are favored as materials for reactor construction terial is a neutron irradiated fuel element wherein such based upon corrosion resistance although aluminum, element has a uranium core and a zirconium cladding. which is nearly as satisfactory from the corrosion stand The spent fuel element containing uranium and zirconi point, is less expensive and is therefore also satisfactory um is dissolved in the liquid phase in an anhydrous so 15 for this purpose. lution of an acid fuoride represented by the chemical In the dissolution step, halogen fluorides are not pres compound hydrogen fluoride (HF) and a complexing ent. Accordingly, fluorinated hydrocarbon materials agent represented by nitrogen dioxide (NC). The dis such as perfluoroethylene can be used for reactor con Solution step is advantageously carried out at a tem struction and should be used where temperatures below perature in the range of 90-110° C. although the re 20 150° C. are encountered, as in the evaporation step. action will proceed at a satisfactory rate at a tempera In the present process, the acid fluorides which can ture of about 70° C. Higher temperatures, up to as be used as the dissolving medium include various acid much as 150 C., may also be used subject to strength of fluorides which are liquid at or about room temperature. materials of construction. The minimum operable Hydrogen fluoride, which boils at 19.4° C. at atmos amount of nitrogen dioxide in the dissolution medium is 25 pheric pressure, has been found to be satisfactory as a about 7 mole percent; a solution of about 7-35 mole per solvent. The hydrogen fluoride and other acid fluorides cent nitrogen dioxide and about 6.5-93 mole percent may be maintained in the liquid state by suitable adjust hydrogen fluoride is a satisfactory reactive dissolution ment of temperature and pressure. Other acid fluorides mixture. - Optimum dissolution rates are obtainable at which can be used in the dissolving mixture include di about 20 mole percent nitrogen dioxide. There is no 30 fluorophosphoric acid, monofluorophosphoric acid, fluo advantage in using solutions wherein nitrogen dioxide phosphoric acid, factors of cost, stability, reactiveness, concentration is about 35 mole percent. Any excess over availability, etc., enter into the choice of a particular this limit causes an undue amount of gaseous reaction acid fluoride agent to be used under specific circum products to evolve and excess pressure to build up. The stances. On the basis of these and other factors, hy gaseous reaction products of the dissolution are hydro 35 drogen fluoride and difluorophosphoric acid have been gen and volatile fission products and decay products found to be the most satisfactory acid fluorides for use which are vented from the dissolution chamber. The in the present process. Of these two, hydrogen fluoride hydrogen acts as a sweep gas to remove the gaseous has been found to be most suitable, chiefly because it fission products and any entrained nitrogen dioxide. The may be used in the present invention at moderate tem uranium forms a soluble complex with the nitrogen di 40 peratures and pressures, i.e., of the order of 70 to 150 oxide while the zirconium forms a complex with nitro C. at 1 to 20 atmospheres. gen dioxide of limited solubility. The complexing agent component of the dissolving me The liquid and solid phases are then separated by con dium can be selected from chemical compounds which ventional phase separation methods. Any of the well readily ionize in the liquid acid fluorides to form cations known methods of separating solids from liquids, such 45 capable of forming soluble or slightly soluble complex as filtration, centrifugation, fractional crystallization, etc. fluorides of zirconium and with other metals which form may be employed for this purpose. Filtration has been tenacious adherent fluoride coatings. Suitable complex found to be a desirable separating procedure. The bulk ing agents of this class include inorganic fluoride salts of the zirconium and fission products are separated and such as the fluorides of potassium, sodium, cesium, silver, removed from the uranium containing solution as in 50 mercury, manganese and thallium; inorganic chlorides soluble or sparingly soluble fluorides and nitronium such as those of silver and cesium, and nitrogen oxides complex fluoride compounds. The acid fluoride solvent such as nitric oxide and nitrogen dioxide. The halide salt contains uranium as a soluble uranium connplex and a complexing agents are presumed to react with the divalent small percentage of soluble zirconium and other soluble zirconium hexafluoryl anion to yield complex double fission product metal fluorides. The solvent is then evap metal hexafluorides which permit dissolution of the ad orated at a temperature in the range 20-150° C. The herent fluoride coatings on the uranium, thus making the selection of the evaporation temperature in an operating uranium available for reaction. Nitric oxide and nitrogen process will depend upon such economic considerations dioxide appear to act in a manner similar to the cations of as cost of condensers, coolant circulation means, asso the inorganic fluorides and chlorides in the formation of ciated piping and the like, and will be affected by such 60 complex fluorides. The choice of a complexing agent is limitations as available coolant temperature, etc. Thus, chiefly determined by its effect on the zirconium dissolu for a particular plant site and local conditions of op tion rate, extent of recovery of a uranium product, and erations, it may be preferred to operate the evaporation also by ease of handling and economic considerations. Of step at elevated temperature and pressure or at a lower the metal halides, KF and CsF were found to be the most temperature at essentially atmospheric pressure. 65 desirable because their use provides a relatively high dis The volatilized solvent which by now is essentially solution of recoverable uranium. Fluoride salts of sodium, hydrofluoric acid can be recycled for reuse in the disso silver and manganese did not give as high dissolution rates ution step. The solids are then treated with bromine or percentage of uranium recovery as was the case with trifluoride (BrF3) to convert the uranium to the volatile potassium or cesium fluoride. The use of nitric oxide or uranium hexafluoride. It is desirable to carry out the 70 nitrogen dioxide is especially advantageous in this process conversion of the uranium to the hexafluoride at a tem since, in addition to providing a relatively high dissolution perature between 60 and 110° C. and preferably at a rate Substantally complete uranium recovery was obtained. temperature of about 90° C. The volatile uranium hexa Furthermore, complex nitronium fluoride salts which are fluoride can then be separated from any residual zir believed to be formed can be decomposed and the result conium fluoride, fission products fluorides, bromine tri 75 ing nitrogen oxides recycled to the dissolution step. The

3,012,849 5 6 inorganic fluoride and chloride salts useful as complexing form the uranyl nitrate. The results are summarized in agents in this process form uranium complexes which are Table 1 below: not decomposed as readily as the nitrogen oxide com Table. I plexes. The halogen fluorides which can be used to convert the Uranium non-volatile uranium complex to the volatile hexafluoride Analytical Sample Milligrams. Analysis, in this process include various fluorides which are liquid at Percent or near room temperature such as chlorine trifluoride. First Distillate------83 64.5 Othere halogen fluorides which are included within the Second Distillate 85 30 scope of uranium fluorinating agents for this invention in 0. Pot Residue 15.5 5.5 clude bromine monofluoride, bromine trifluoride, bro Total Uranium 283.5 00 mine pentafluoride, and iodine pentafluoride, although for considerations of cost, stability, reactiveness, availability, The recovery of 382.5 milligrams of uranium from the etc., bromine trifluoride has been found to be the most dissolution of the 7 gram specimen shows, allowing for satisfactory halogen fluoride. It has been found that the 5 experimental error, substantially complete recovery of conversion of uranium complex to the volatile hexafluo uranium. ride will take place so long as there is any bromine tri EXAMPLE II fluoride present to react with the uranium complex. How The following example illustrates the effect of tempera ever, at least a stoichiometric amount of bromine tri ture on the dissolution rate of Zircaloy-2 in a nitrogen fluoride and generally an amount equivalent to about 100 20 dioxide-hydrogen fluoride dissolution solvent medium. percent in excess of the stoichiometric amount is preferably Each sample was immersed in a solution of 11 mole used. The amount of excess bromine trifluoride does not percent nitrogen dioxide and 89 mole percent hydrogen appear to be critical and in a large scale process will be fluoride at the temperature ranges indicated in Table 2 limited by engineering and economic considerations. below. With respect to the particular embodiment previously 25 ... The dissolution rate for each sample was calculated in described and illustrated in the flowsheet, it will be noted accordance with the following general formula: that some of the steps of the process can be combined Dissolution rate (mg/cm2-unit time) = without departing from the scope of the invention. For Initial weight of sample-final weight of sample example, the halogen fluorides can be added to the initial after exposure to dissolution medium for 1 hr. dissolving medium (acid fluoride and complexing agent) 30 7Surface area of untreated sample so that the uranium of the zirconium clad fuel element is - -- surface area of treated sample dissolved and simultaneously converted to a volatile prod 2 - uct. The only additional step required would be to frac tionally distill the uranium hexafluoride from the fluorinat The results are summarized in Table 2 below. ing agent and other volatile components of the solvent 35 Table 2 medium. Of course, in this modification, the purified Temperature, C.: Dissolution rate, mg./cm.-hr. uranium hexafluoride will appear at different distillation 35-39------man na -- and as a sm - - - 88.2 cuts than in the previously discussed embodiment. 38-40------33.0 - Having described the process, it may be further illus 66-68------960.0 trated by the following examples: 40 54-78------1038.0 EXAMPLE I 93-100------2610.0 This experiment demonstrates that uranium fuel ele 96-99------3474.0 ments having a cladding of zirconium or alloys thereof The data show that the dissolution rate does not become can be dissolved in non-aqueous liquid phase medium at a significant until a temperature of about 70° C. is reached. . practical rate and that the uranium can be quantitatively At about 100° C. the dissolution rate was of the order of separated as a pure uranium hexafluoride product. 3500 mg/cm2-hour. An unirradiated fuel plate section having a Zircaloy-2 cladding and containing approximately 4% uranium by EXAMPLE III weight (about 280 mgms.) was immersed in a liquid solu 50 The effect of a halogen fluoride, such as bromine tri tion of 12.5 mole percent nitrogen dioxide 25 mole per fluoride, on the dissolution rate of a zirconium alloy, cent bromine trifluoride, and 62.5 mole percent hydrogen Zircaloy-2, is illustrated in the following example. fluoride in a polyfluoroethylene container. The container Samples of Zircaloy-2 were prepared and immersed in was provided with an internal monel metal cooling coil a dissolution medium for varying periods of time at con for controlling the solution temperature. The solution, 55 trolled temperatures and the dissolution rates calculated with the sample immersed therein, was heated to a tem as in Example II. In this experiment, however, the rela perature in the range 90 to 120° C. During the dissolu tive proportions of the components of the solution were tion period, there was an initially rapid reaction while the varied. The calculated dissolution rates are shown in cladding was being dissolved, followed by a slower reac Table 3. tion with little evolution of heat while the uranium was Table 3 60 being dissolved. Dissolving Solution After the sample had dissolved, the solution was trans Composition, Mole Dissolu ferred to another polyfluoroethylene vessel and distilled. Percent Tempera tion iRate, Initially, brown fumes of nitrogen dioxide evolved and ture, C. mg.fcm.2. these were collected in a condenser. This was followed 65 hr. by white hydrogen fluoride vapor which condsensed to a clear liquid. The next fraction recovered was bromine. 17. 8. Finally, white, solid uranium hexafluoride was collected. 8. After all the solution was vaporized and the solid residue 8. 8. ; was reduced to dryness, an additional volume of bromine 70 ii. trifluoride was added to the residue and this was distilled 24. O i to recover any uranium remaining in the solids. - . . . 0. The residue, first and second distillate fractions, were 0. then analyzed for uranium by colorometric methods after I 00 . hydrolysis of uranium hexafluoride with nitric acid to 75 3,012,849 7 3 These data indicate that the dissolution rate of Zirca tion rate was found to be about 395 mg/cm.”-hr. A loy-2 in nitrogen dioxide-bromine trifluoride is much lower slight increase in temperature (150-175 C.) of the dis than the dissolution rate in nitrogen dioxide-hydrogen solution medium is required in order to obtain dissolu fluoride. It will especially be noted that in all cases where tion rates for aluminum clad elements comparable to the the nitrogen dioxide complexing agent was not used, the high zirconium dissolution rates. Practical dissolution zirconium did not dissolve. A similar pattern of results rates for stainless steel clad, uranium-bearing fuel ele has been found to occur when the other complexing agents ments are comparable to those for zirconium or aluminum embraced by the present invention were used in place of at temperatures in the range 150 to 190° C. For example, nitrogen dioxide. - at a temperature in the range 150-190 C. a sample of O 304S stainless steel was dissolved in a HF-NO2 solvent EXAMPLE IV (2:1 by volume) at an average rate of reaction of 410 The effect of the addition of various halide salts to the mg./cm.2-hr. In all cases substantially complete recov bromine trifluoride-hydrogen fluoride dissolution medium ery of uranium was obtained from compositions contain is illustrated by the following example. ing these metals. Several samples of Zircaloy-2 were treated as in the 15 It will thus be seen that I have described a process for previous examples, and dissolution rates were determined facilitating recovery of uranium from mixtures of urani at various temperatures in solutions of bromine trifluoride um a metal which forms an insoluble and tenacious and hydrogen fluoride to which metal halide salts had fluoride coating which, prior to my invention, precluded been added. The amount of salt used was the same in efficient and quantitative recovery of uranium from such 20 mixtures. each case. The dissolution rates are tabulated in Table 4. Whenever reference was made to an insoluble zirconi Table 4 um complex it will be understood that the zirconium complex is termed insoluble relative to the corresponding Temperature, C. Dissolution uranium complex on a mole for mole basis. Addition Agent to 15m. EIF and Rate, 5 ml. BrFs ng.fc.m.2- 25 Since many embodiments might be made in the present Initial Final hour invention and since many changes might be made in the embodiment described, it is to be understood that the 77 21 92 88 foregoing description is to be interpreted as illustrative 73 115 only and not in a limiting sense. 92 12 30 I claim: 93 120 89 28 132.0 1. An anhydrous process for separating uranium from 9. 121 a mixture of uranium and zirconium which comprises heat 30 99 ing said mixture at a temperature in the range of 70 to 150° C. with a liquid consisting essentially of a stoichio While all of the fluoride salts studied increased the 35 metric amount of an inorganic acid fluoride and nitrogen dissolution rate of zirconium to some extent, the dissolu dioxide, a complexing agent, which ionizes in said acid tion rate for cesium fluoride and potassium fluoride was fluoride to convert the uranium to a soluble uranium con higher by a degree of magnitude as compared to other plex and the zirconium to an insoluble zirconium complex halide salts used. The reason for the difference in disso respectively, and thereafter separating said zirconium com lution rates between the various halide salts, and espe 40 plex from said uranium complex. - cially the enhanced dissolution rate achieved with KF and 2. An anhydrous process for separating uranium from CsR is not understood. It has been suggested that in the a mixture containing uranium, zirconium and fission prod solvent system used here KF and CsP are stronger basic ucts of uranium which comprises heating said mixture in fluorides than the other useful fluorides used. a liquid consisting essentially of as active ingredients a stoichiometric amount of an acid fluoride and nitrogen EXAMPLE V 45 dioxide, a complexing agent which reacts with said ura In this example, diffuorophosphoric acid was used as nium and said zirconium to form a soluble uranium fluor the acid fluoride and potassium fluoride was used as the ide complex and an insoluble zirconium fluoride complex complexing agent. The results are shown in Table 5. respectively, separating said zirconium complex from said uranium complex, heating said uranium complex and said Table 5 50 fission products with a halogen fluoride in the liquid phase. to thereby convert the uranium to uranium hexafluoride Dissolution Medium Tempera Dissolution and at least a portion of said fission products to volatile ture, C. Rate,ngf fluorides and thereafter separating said uranium hexafluor KF, EIPOF, cm.2-hour ide from said volatile fission product fluorides by frac Grains ml. 55 tional distillation. 9 50-250 30.0 3. An anhydrous method for separating uranium from 4. 116 552.0 a mixture containing uranium, zirconium and fission prod ucts of uranium which comprises reacting said mixture in a liquid consisting essentially of a stoichiometric amount The enhanced dissolution rate achieved by adding po 60 of an acid fluoride and nitrogen dioxide at a temperature tassium fluoride to the halogen acid dissolving medium in the range 70 to 150° C. to convert the zirconium to a will again be noted. . . Although the foregoing discussion has been concerned non-adherent insoluble zirconium complex compound, primarily with the dissolution of uranium-bearing fuel contacting the resultant reaction mixture with a liquid elements in which the uranium is alloyed with zirconium 65 halogen fluoride to thereby convert the uranium to ura or its alloys or is clad or sheathed in Zirconium or nium hexafluoride and at least a portion of said fission its alloys, this invention is also applicable to the dis products to volatile fluorides, and thereafter distilling said solution of fuel elements and other compositions in which uranium hexafluoride from said volatile fluorides. uranium is combined with aluminum or stainless steel 4. The method according to claim 3 wherein the con instead of zirconium and zirconium alloys. These metals 70 centration of nitrogen dioxide is at least 7 mole percent. have also been found to form tenacious fluoride coatings. 5. The method according to claim 3 wherein the acid so that dissolution and subsequent recovery of uranium fluoride is selected from the group consisting of hydrogen becomes a difficult problem. At a temperature in the fluoride, fluophosphoric acid, monofluophosphoric acid range 120-180 C. a sample of 2S aluminum was dis and difluophosphoric acid. solved in HF-NO, solvent (2:1 by volume). The reac-75 6. The method according to claim 3 wherein the halo

8,012,849 - 9 10 gen fluoride is selected from the group consisting of chlo- References Cited in the file of this patent rine trifluoride, bromine monofluoride, bromine trifluo ride, bromine pentafluoride and iodine pentafluoride . UNITED STATES PATENTS 7. An anhydrous process for separating uranium from 2,758,024 Feder ------Aug. 7, 1956 luctsa mixture of uranium containing which uranium, comprises zirconium adding and to saidfission mixture prod- 5 2,811,413 McMillan Oct. 29, 1957 in a liquid consisting essentially of as active ingredients. HER RE . stoichiometric amounts (1) a halogen fluoride, (2), an in- OT FERENCES organic acid fluoride, and (3) nitrogen dioxide as a com- Paramonova et al.: NSA 12, No. 20, Oct. 31, 1958, No. plexing agent which ionizes in said acid fluoride to convert 0 13734. the uranium to a soluble uranium complex, heating the Abstracting Zhur., Neorg. Khim, 3, pages 215-21 resultant mixture to thereby convert the uranium to vola (1958). tilefission uranium products hexafluoride to volatile fluoridesand at least and thereaftera portion separatof said TID-7534, May 20-25, 1957, Book 1, pp. 244-250 and ing the uranium hexafluorides from the other volatile con- 15 Book 2, pp. 560-573. taminants by fractional distillation.