United States Patent Office 2,830,873
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2,830,873 United States Patent Office Patented Apr. 15, 1958 2 active, so that any recovery process must be capable of being carried out by remote control. Second, plutonium 2,830,873 and uranium are members of the actinide rare earth FLUORDE voLATILITY PROCESS FOR THE family and, although they do not have identical charac RECOVERY OF URANUM 5 teristics, the chemical characteristics are sufficiently close Joseph J. Katz and Herbert H. Hyman, Chicago, and that it does increase the difficulty of separation of these Erving. Sheft, Oak Park, I., assignors to the United two elements by chemical methods. States of America as represented by the United States An ideal separation process for the recovery of ura Atomic Energy Commission nium from neutron-irradiated uranium would include the No Drawing. Application May 10, 1956 O following characteristics. The process should be one capable of continuous operation. The process must be Serial No. 584,153 one which can be operated by remote control because of 25 Claims. (CI. 23-145) the radiation hazards involved. Furthermore, it is desir able that the non-radioactive uranium be separated in an The present invention is concerned with the separation 15 early step of the process from the radioactive fission and recovery of uranium from contaminants by a halo products, so that the further processing of uranium may genation and volatilization method. The invention is par be carried on without the shielding required for process ticularly concerned with the recovery of uranium from . ing radioactive materials. The efficiency of the separa contaminants arising from the neutron irradiation of ura 20 tion of the uranium from the plutonium and fission prod nium. w - lucts must be very good. If complete separation of ura At the present time nearly all nuclear reactors employ nium, plutonium and fission products is not achieved in uranium in one form or another as the primary fuel, a single continuous process, it is desirable that the frac The employment of uranium as a nuclear fuel in reactors tions containing the plutonium and/or fission products has produced a great need for efficient methods for sepa should be in as small bulk as possible. Thus a plutonium rating uranium from contaminants. The uranium used 25 fraction or a fission product fraction having a large bulk in reactors must be very pure. Therefore it must be sep of materials added during the processing is undesirable. arated from contaminants native to uranium ores as well It is desirable that the uranium fraction be obtained as as those introduced in processing the ores. After the the metal or in the form of a compound such as uranium uranium is neutron-irradiated in a reactor for a period hexafluoride which can be readily converted to the metal. of time, it must be separated from the nuclear reaction 30 Uranium hexafluoride also may be used directly as the products. These include the fission products which are feed material in isotopic separation processes. the elements having atomic numbers 32 to 64, inclusive, It is an object of the present invention to provide a and if the isotope U238 is present, it will also include the Volatilization method of separating uranium from con higher actinide elements such as neptunium and pluto taminants. nium. There are also various additional uranium mix 35 It is an additional object of the present invention to "tures from which it is desirable to recover purified ura provide a method of recovering purified uranium from nium. For example, a great deal of neutron-irradiated neutron-irradiated uranium. uranium has been processed to remove the plutonium Other objects of the present invention will be apparent from the uranium without removing the fission products 40 from the description which follows. from the uranium. Therefore it is now desirable to sep In accordance with the present invention uranium con arate and recover uranium from this partially processed taminated with other elements, for example the radio uranium containing the fission products and various chem active fission products, may be conveniently recovered icals which were added during the plutonium removal from such contaminants by a process the initial step of process. 45 which comprises dissolving said contaminated uranium There are several factors which make the recovery of in a halogen fluoride in the liquid phase. This dissolution uranium from neutron-irradiated uranium a particularly Step effects a partial phase separation of the uranium and difficult problem. The normal starting material for a sep certain contaminants. The uranium is converted to the ... aration process for the recovery of uranium from neutron halogen fluoride-soluble uranium hexafluoride compound irradiated uranium is a metal uranium slug which has 50 whereas the fluorides of certain contaminating elements been irradiated in a neutronic reactor for a sufficient time are insoluble in liquid halogen fluorides and the reaction to produce fission products, and plutonium. These fission rate of halogen fluorides with certain other solid ura products and plutonium are normally present in about 1. nium contaminants is sufficiently slower than the reac part fission products and 1 part plutonium per 1000 parts tion rate with uranium that substantial portions of these ... uranium. A successful separation process must separate 55 contaminating elements will remain as solids in the liquid the uranium from the fission products and plutonium so phase halogen fluoride. These foregoing solids are then that the recovered uranium has not more than 1 part of Separated from the solution by a distillation step, or other fission products in 109 parts of uranium and not more convenient method of separating solids from liquid, such than 1. part of plutonium in 108 parts of uranium. There as filtration, centrifugation, etc. The uranium hexaflu are two main factors which complicate recovery proc 60 oride (UF6) is then separated from the balance of the esses. First, these fission products are exceedingly radio impurities and solvent by one or more distillation steps, 2,880,873 3 4. as will be more fully described in the following para portant factor in the reactivity of these solutions towards graphs. other materials such as uranium. Some measure of the The use of the halogen fluorides as fluorinating agents reactivity may be correlated with the conductivity of in the liquid phase provides several advantages over the the halogen fluorides. The order of the conductivity of use of fluorine. A liquid phase fluorination greatly re various halogen fluorides is as follows: duces the corrosion of equipment that is found with gase ous fluorination. Hurthermore, the health hazard in the TABLE I fluorination of radioactive fission products or materials containing fission products by gaseous fluorinating agents Compound Conductivity at 25° is greatly reduced by the fluorination in the liquid phase. 0 C. (ohm-1 cm.-1) The halogen fluorides are extremely reactive with wa BrF3--------------------------------------------- 8.0XO-3 ter so that every precaution must be taken in the proc IFs---- 2.3XO-5 ess to avoid bringing the halogen fluorides in contact BrFs------------------- ------- 8.4X107 with any aqueous phase. The materials of construction ClF3-------------------------------------------- 3X10-9 (at 0° C.) for reactors also must be selected with some care. It has been found, however, that such common metals as iron, nickel, aluminum and copper readily form co The reactivity of the halogen fluorides toward uranium herent protective films in the presence of halogen fluo masses is in substantially the same order. However, it rides which make their use as construction materials tnust again be emphasized that by suitably increasing the 20 temperature and pressure of the reactor in which distill for handling the liquid halogen fluorides practical. Of lation is carried out any of these halogen fluorides will these construction materials nickel and high nickel al dissolve uranium masses. loys appear to be least affected by halogen fluorides and One aspect of the present invention is concerned with accordingly are favored for reactor construction. Alu a method of increasing the rate of dissolution of uranium minum, however, is nearly as satisfactory from the cor and similar metals by the halogen fluorides, such as bro rosion standpoint, and much less expensive for use in mine trifluoride. It has been found that the rate of reactor construction. dissolution of uranium metal in pure bromine trifluoride While the process of the present invention is particu is very slow at room temperature. It is believed that larly adapted to the recovery of uranium from con this is probably due to the absence of the bromine tri taminated uranium metallic masses, it may also be used fluoride system cations which are believed to be the to recover uranium from contaminated uranium con prime cause of the attack on the metal. However, where tained in other forms. Thus, any uranium salt or salf uranium is maintained in contact with bromine trifluoride mass may be dissolved by the present process by a suit for a substantial period of time, it is found that the slow able adjustment of reaction temperature and pressure. initial rate of reaction will be followed after a period by The present process is particularly applicable to the re a much faster rate of reaction between the uranium and covery of purified uranium from the uranium wastes bromine trifluoride. This may be due to the accumula which are by-products of the recovery of plutonium from tion of a substantial amount of bromine trifluoride sys uranium by precipitation processes. These wastes are tem cations in the solution as a result of the formation usually primarily in the form of uranium salts such as of bromine and bromine fluoride in the initial, or "incu uranyl ammonium phosphate containing 200-600 parts 40 bation' stage of the reaction.