[en] Preparation of ammonium diuranate easy to handle with spherical grains of mean diameter between 40 to 100 microns, of unpressed apparent specific weight between 2 to 2.8 g/cm³ and with a SO₄ ion content between 0.5 to 1 %. It is obtained by reaction of uranyl sulfate on ammonia and precipitation at a pH value between 6.6 to 7.2

[en] The main regularities of the effect of various surfactant classes on the properties of ammonium diuranate precipitates, prepared by the action of ammonia concentrated solution on uranyl nitrate nitric acid solution, are established. It is shown, that monomolecular cationogenic surfactants promote the increase in ammonium diuranate sedimentation rate. High-molecular catiogenic surfactants affect negatively the rate of suspension sedimentation and filtration, increase the precipitate humidity. The effect of high-molecular nonionogenic surfactants is similar to the effect of monomolecular surfactants of the same type. Anionogenic polyelectrolytes are shown to be the most effective flocculants of ammonium diuranate. Insignificant concentrations of the substances in suspension permit to increase the rate of sedimentation and filtration, to decrease ammonium diuranate precipitate humidity due to the formation of stable, resilient flakes

[en] One of the products from Monazite ore processing is yellow cake which is Ammonium diuranate with thorium impurity. Continuous liquid-liquid extraction in laboratory scale was simulated to purify uranium by scrubbing thorium using various scrub solutions and flow ratios. The results indicated that the uranium extraction efficiency at flow ratio (solvent : feed) of 3:2 and 6 stage numbers is higher than 99.8 percents. The thorium scrub efficiency is higher than 80 percents when 52,950 ppm uranyl nitrate is used as scrub solution at flow ratio (feed : scrub solution) of 7:1 and 4 stage numbers

[en] During 1964 mining at Randfontein estates ceased, and the mine was put on a caretaker basis in 1965. Five years later in the intervening period the importance of uranium had gradually assumed new proportions worldwide, and a feasibility study that REGM had been conducting about 15 km south of the mine proved payable values of both gold and uranium. This was the start of the Cooke section. The development of this section led to the re-opening of the South Deep 32 and no 16 shafts at the old mine, the re-commissioning of the old Millsite gold plant in 1973, and the old uranium plant in 1977. Today the emphasis at the old mine is essentially on uranium production with gold taking very much a back seat

[en] The quality of sintered UO_2 fuel pellets, in terms of density and pore size distribution is influenced to a large extent by the method of powder preparation and associated thermal treatment. The microstructure of a Uranium dioxide pellet is directly the result of the different transport mechanisms, some of which are efficient at lower temperatures while others need high temperatures. In addition uniformity and homogeneity of particle packing in the green body has an enormous impact on how well the green body will densify during sintering. Nuclear grade uranium dioxide powders are prepared, pressed and sintered to yield pellets of high density and homogeneous microstructure. UO_2 powder used in this study is produced by ADU route. The green pellets are sintered at various temperatures starting from,1173 °K to 1973°K. All the sintering tests were performed in reducing atmosphere in high temperature dilatometer. Temp vs. dimensional shrinkage plots were obtained from dilatometric studies for all the pellets. Data obtained thus were analysed using different methods to find out the kinetics and microstructural changes occurring during the sintering process. Microstructural observations helped in correlating reasons for some of the low density pellets in the production lots

[en] The concepts of spray drying process and pebble-bed fluidized drying process for ADU slurry is presented. And the effects of ADU powder and UO₂ powder/pellet by these processes using the statistic results from series production are discussed. It is believed that these drying methods have no influence on structure and shape of ADU particle, and thereby no difference will be made to the properties of UO₂ powder and pellet. Thus, spray drying process can really be replaced by pebble-bed fluidized drying process. (10 figs., 6 tabs.)

[en] Uranium is the starting fuel material for many nuclear energy programs. Metallic uranium fuel is used in research reactors to ensure compact design and good thermal conductivity. The purity requirement of this metal is extremely stringent to improve neutron economy in reactors. Present paper intends to discuss above developmental activities in production of U-metal

[en] Ammonium diuranate particles generated by an outside gelling method are heated in air at about 400degC to 800degC to remove a gelling aid such as polyvinyl alcohol thereby forming UO₃ or U₃O₈ particles. The particles are heated/sintered in a slightly oxidative atmosphere. The slightly oxidizing atmosphere comprises an inert gas such as N₂ having an oxygen concentration of from 10^-3 to 5 x 10²ppm or a CO/CO₂ gas having the same oxygen concentration. The heating temperature is set to about 1000 to 1400degC. Then, they are heated in a reducing atmosphere containing hydrogen at about 1000 to 1400degC so as to determine the O/U ratio of UO₃ or U₃O₈ particles to 2.0±0.05. Fuel particles having a large grain size for high burn-up degree to be used in a HTGR type reactor are thus formed by conducting a low temperature oxidation and reduction sintering method without adding U₃O₈. (I.N.)

[en] The demand for uranium concentrate, as defined in the Brazilian nuclear program, requires the construction of a new industrial plant in the beginning of the nineties. One of the alternatives for that new industrial plant is the Lagoa Real uranium ore deposit in Bahia. The process development studies carried out by Nuclebras, using Lagoa Real ore samples, led to the definition of an acid leaching process, with uranium solubilization into a sulphuric acid solution in the presence of an oxidant, followed by filtration, clarification, solvent extration and ammonium diuranate precipitation. An uranium recovery of over 90% is possible with this process. (Author)

[en] The final quality of a sintered ceramic depends on starting powder characteristics, forming and firing conditions. The powder characteristics are, in turn, dependent on the characteristics of the precursor from which the powder is obtained by thermal decomposition. The precursor precipitate ammonium diuranate is dried, calcined and reduced at specific temperatures and heating rates to yield UO₂ powder. The final acceptance of sintered UO₂ has been found to be high with a combination of a low precipitation temperature, intermediate precipitate aging, precipitate washing and controlled thermal decomposition that would not only preserve precursor morphology, but also develop sufficient porosity. These conditions yield agglomerate-free soft powders that do not require milling or binder addition before compaction. The powders, after granulation, pack well in compaction and yield homogeneous high density microstructures on sintering. (UK)