[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 invention discloses a method for the continuous manufacture of ammonium diuranate (ADU) from ammonium hexafluoride (UF₆) and its conversion to uranium dioxide (UO₂) through calcination. The method is characterized by the following steps: dissolving UF₆ in water with the formation of UO₂F₂ and HF; partially neutralizing the aqueous solution by concentrated NH₄OH; transferring the partially neutralized solution into a precipitation vessel; adding concentratred NH₄OH for precipitating ADU (by injecting a suspension of the precipitate, large-area ADU-particles are obtained); continuously drawing off about 10% of the suspension for preparing, by eliminating water, a slurry comprising at least 35% of ADU, by weight; ADU is used for manufacturing UO₂ fuel pellets

[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] The ammonium nitrate bearing effluent after ADU precipitation can be recycled as strippant in the stripping process of solvent extraction during uranium refining process. The nature of stripping of uranium with various concentration of ammonium nitrate as strippant was studied experimentally and a suitable theoretical model developed for the estimation of Distribution coefficient. The theoretical values of equilibrium constant distribution coefficient was estimated after employing the correction factors due to the activity coefficients each species at higher ionic strength. The activity coefficients of salts in aqueous solution were estimated the correlations developed by 'Bromley' for activity coefficients of multiple salt solutions. The model equations were developed by the mass balance of uranium at equilibrium for biphasic system. Solubility of TBP in water is not considered in the equation so developed. Also the model does not take into account for the ideality of organic phase

[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)

No abstract available

[en] Published in summary form only

[en] This study was carried out in order to select the optimum conditions for ammonium diuranate (ADU) precipitation to obtain high density uranium dioxide. The data were collected for ADU precipitation reactor design. The precipitation temperature was controlled at 50⁰C. The stirrer speeds are 5.9 and 7.1 Hz. The properties namely : specific filtration resistance, initial settling rate and agglomerate size of ADU precipitates obtained at various pH were investigated. The results indicated that when the pH of precipitation increases, specific filtration resistance increases but ADU agglomerate size decreases and causing difficulty in filtration

[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] Three preparation methods of high-density U₃O₈ powder have been studied: grinding of sintered U₃O₈ pellets, sintering of calcined U₃O₈ granules; and sintering of ammonium diuranate (ADU) granules. Experiments have been carried out varying ADU calcination time and temperature as well as sintering time, yielding ten U₃O₈ batches. Powder characteristics, granulometric yield, and number of process steps have been taken into account for comparison purposes. Impurity content, specific surface area, stoichiometry, morphology, density, porosity distribution and phase identification have been considered as parameters for powder characterization. The main conclusions show that the second method (following a 600⁰C/3h ADU calcination) gives the best results. Moreover, the third method gives also good results, but there were some difficulties with ADU handling. (author)