Nitrate (UO2 (NO)) 4

July 7, 1970 H. VETZKE ETA 3,519,403 METHOD FOR THE PREPARATION OF URANIUM DIOXIDE POWDER (UO) WITH GOOD PRESSING AND SINTERING PROPERTIES FROM URANIUM HEXAFLUORIDE (UF) OR AQUEOUS SOLUTIONS OF URANYL Fied Dec. 18, 1967 NiTRATE (UO2 (NO)) 4. Sheets-Sheet l mixer nozzles --race to fitter Fig.1 Schematic drawing of a batch process for the precipitation of AUC. July 7, 1970 H. VETZKE EA 3,519,403 METHOD FOR THE PREPARATION OF URANIUM DIOXIDE POWDER (UO) WITH GOOD PRESSING AND SINTERING PROPERTIES FROM RANIUM HEXAFLUORIDE (UF) OR AQUEOUS SOLUTIONS OF URANYL Filed Dec. 8, 1967 NiTRATE (UO2 (NO)) 4. Sheets-Sheet 3. mixer nozzles UF6 Of U02 (NO3)2ad tC92--X Ex-Ns / to filter cooling precipitation Vessel vessel Fig. 2 Schematic drawing of a continuous process for the precipitation of AUC July 7, 1970 H, VETZKE ETAL 3,519,403 METHOD FOR THE PREPARATION OF URANIUM DIOXIDE POWDER (UO) WITH GOOD PRESSING AND SINTERING PROPERTIES FROM URANIUM HEXAFLUORIDE (UF) OR AQUEOUS SOLUTIONS OF URANYL Filed Dec. 18, 1967 NiTRATE (UO (NO)2) 4. Sheets-Sheet 3 Off gas Off gas 487\m Nx UO2 powder XXX.& X.X S& steam / H2 Fig. 3 Ot Schematic drawing of a fluidized bed furnace for the reduction of AUC to U02, July 7, 1970 H. VEZKE ETAL 3,519,403 METHOD FOR THE PREPARATION OF URANIUM DIOXIDE POWDER (UO) WITH GOOD PRESSING AND SINTERING PROPERTIES FROM URANIUM HEXAFLUORIDE (UF) OR AQUEOUS SOLUTIONS OF URANYL NITRATE (UO2 (NO)a) Filed Dec. 18, 1967 4. Sheets-Sheet 1 -- Offgas Step 1: Decomposition, reduction and pyrohydrolysis i Step 2: Pyrohydrolysis Step 3: Controlled oxidation an o- are as an un- Fig. 4 Schematic drawing of a continuous fluidized steam fair bed process for the reduction of AUC to U02. 3,519,403 United States Patent Office Patented July 7, 1970 2 This description shows clearly in what complicated 3,519,403 way UO2 powder of good pressing and sintering prop METHOD FOR THE PREPARATION OF URANUM erties has been prepared up to now. The multitude of DIOXDE POWDER (UO) WITH GOOD PRESSING AND SINTERNG PROPERTIES FROM URANUM these process steps, the parameters of which can hardly HEXAFLUORIDE (UF) OR AQUEOUS SOLU be kept constant, gives rise to noticeable differences in the TIONS OF URANYL NITRATE UO(NO), quality of separate UO2 charges, which again causes con Horst Vietzke, Grossauheim (Main), Fritz Ploger, Klein siderable difficulties during pressing and sintering. ostheim (Main), Klaus Wegner, Hanau am Main, and Now, a wet chemical process for converting UFs to Hans Pirk, Dornigheim (Main), Germany, assignors to UO2 with (NH4)(UO2(CO)3 as an intermediate prod Nukem Nuklear-Chemie und Metallurgie G.m.b.H., 10 uct, has been developed, which shows none of these Wolfgang, near Hanau am Main, Germany difficulties. Filed Dec. 18, 1967, Ser. No. 691,581 This process is carried out by converting vaporous Claims priority, application Germany, Dec. 17, 1966, N 29,688; Mar. 1, 1967, N 30,086 UF6 with gaseous NH, CO2 and water, or with an int. Cl. C01g 43/02 aqueous solution of ammonium carbonate or with solid 15 ammonium carbonate, whereby AUC is precipitated and U.S. C. 23-355 14 Claims Subsequently decomposed to pure uranium dioxide powder as set forth hereinafter. ABSTRACT OF THE DISCLOSURE The invention will be understood best when considered in connection with the drawings wherein: Uranium dioxide of good pressing and sintering be 20 FIG. 1 is a schematic drawing of a batch process for havior is prepared by precipitating ammonium uranyl car the precipitation of ammonium uranyl carbonate (AUC) bonate by continuously introducing as gases UF6, NH3 according to the invention; and CO2 into an ammonium carbonate solution having a FIG. 2 is a schematic drawing of a continuous process constant pH of 7.8 to 8.6 followerd by spontaneously de for the precipitation of AUC; composing and gas reducing the ammonium uranyl car 25 FIG. 3 is a schematic drawing of a fluidized bed furnace bonate in a furnace to obtain a pure uranium dioxide for the reduction of AUC to UO; and powder. The reduction is preferably carried out in a FIG. 4 is a schematic drawing of a continuous fluidized fluidized bed at 500 to 600° C. using a mixture of hy bed process for the reduction of AUC to UO. drogen and water vapor. Referring more specifically to FIG. 1 of the drawings, 30 there is shown a process wherein UF6 gas and CO gas are fed to mixer nozzles where they are mixed with am This invention relates to a method for the conversion monia gas and introduced to an aqueous solution of of uranium hexafluoride (UFs) or aqueous solutions of ammonium uranyl carbonate (AUC), whereby the AUC uranylnitrate UO(NO3)2 into the ammonium uranyl is precipitated. A portion of the resulting AUC suspen carbonate (NH4)(UO2(CO)3) and the conversion of sion is pumped to a filter where the AUC is removed. The that product into a very pure, free flowing UO2 powder balance of the AUC suspension is recirculated with the which is without further treatment pressed and sintered aid of a pump to the mixing nozzle. to give ceramic bodies of high quality. In the existing FIG. 2 illustrates a modification of the process of FIG. generation of light water moderated nuclear reactors 1, whereby the process can be carried out continuously. mainly dense, sintered UO containing up to 5% U-235 40 The UF6, CO2 and N are continuously mixed and fed is used as nuclear fuel. into a first precipitation vessel containing water and AUC, At this time the starting material is almost without ex the AUC suspension overflows into a second cooling ception uranium hexafluoride (UFs), which, after vessel which is stirred. The suspension goes to a filter chemical conversion to UO2 powder is worked into UO2 where the AUC is removed and water is removed. A por bodies of high density and surface quality by oxide 45 tion of the suspension in the first precipitation vessel is ceramic methods. continuously pumped through the mixing nozzles. The wet chemical processes developed up to now for As shown in FIG. 3, hot fluidizing gases, e.g. a mix the preparation of UO2 powders from UFs and uranyl ture of water vapor and hydrogen, are introduced in a nitrate solutions comprise numerous steps with partly sintered metal bottom plate in the furnace. Moist AUC limited specific throughput. So for instance UF is re 50 filter cake is fed into the top of the furnace through a acted with water to give an aqueous solution of suction hose. The gases leaving the fluidized bed pass UOF-4HF, from which by addition of ammonia the through sintered metal filters (indicated by the dotted uranium is precipitated as ammonium diuranate lines near the top of the furnace) to hold back entrained (NH4)2UO (ADU). In succeeding steps these precipi UO2 powder. The UO is maintained at 600° C. to re tates will be filtrated, dried, calcined and reduced, where 55 duce the fluorine content of the UO and then the hy by during the calcination and/or reduction at tempera drogen shut off and air introduced to stabilize the UO, tures near 700° C. the oxide is steam-treated to remove formed which is then recovered. the large amounts of fluorine (2-4%) which are un FIG. 4 shows the continuous fluidized bed formation avoidably contained in the precipitate. - of UO2 wherein AUC filter cake is added at the top of This multi-step, labour intensive process with small 60 a three Zone furnace. It is injected into a first fluidized specific throughput gives rises to a UO2, product of un bed where it is reduced with a mixture of hydrogen and satisfying quality especially with regard to its pressing and steam to give a UO2 powder which is passed to a second sintering properties, as well as its purity. fluidized bed wherein the steam and hydrogen mixture This UO can not be pressed directly but must be present removes the last traces of fluorine. The UO milled, granulated under addition of several weight per 65 powder then passes to the third or bottom fluidized bed cent of an organic binder, broken up and sieved prior to where a mixture of steam and air provide controlled pressing. Before sintering the pellets pressed from this oxidation to stabilize the UO2. The off gases from the two granulate the organic binder must be removed by a lower fluidized beds are introduced above the upper separate dewaxing step. To better the poor sinterability fluidized bed and form a part of the off gases. of this powder the milling must be carried out with a jet 70 By freeding gases NH3, CO2 and UF6 continuously into mill, if an oxidation reduction treatment of the powder a measured quantity of water, the uranium content in the should not be sufficient. Suspension can be increased up to 250 g. U/l, without 3,519,403 3. 4. any increase in the soluble uranium component beyond through an overflow into a cooling vessel which is also 20 g. U/1., with the result that no ammonium uranyl provided with an overflow through which the cooled sus double fluorides are formed. Accordingly, the precipitated pension (20° C.) is delivered to a filter. During cooling product contains only a very small quantity of fluorine. the pH-value of the suspension is preferably raised to In order that the components may be uniformly mixed above 9. Since in the processing of uranium which is en and completely absorbed by water, it has proved to be of 5 riched with the lighter isotope U-235, the geometrically advantage to circulate the water contained in a suitable 'safe' diameters are determined in dependence upon the reaction vessel through the mixer nozzles and to feed the level of enrichment, it is possible to obtain a really high gases to these mixer nozzles.

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