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122-- 2A-74---- Artz 3,012,849 United States Patent Office Patented Dec

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122-- 2A-74---- Artz 3,012,849 United States Patent Office Patented Dec 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.
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