The results of an investigation of the combined vitrification of chloride and phosphate wastes, which were obtained as a result of experimental reprocessing of irradiated nuclear fuel by the pyroelectrochemical method, are presented. The optimal composition of the glass matrix is determined, the characteristics of the model and real samples obtained are presented, and the hydrolytic stability and the thermal stability of the samples are studied. The proposed method of combined vitrification makes it possible to salvage more than 1.5 times more wastes per unit mass of the glass block than separate vitrification.Two main types of solid radioactive wastes are formed when spent uranium-plutonium oxide nuclear fuel is reprocessed by the pyroelectrochemical method [1, 2]: an electrolyte (salt melt of alkali-metal chlorides NaCl-2CsCl), used as a solvent, and a phosphate precipitate from the regeneration of the electrolyte, which is performed in order to reuse the electrolyte in the technological cycle. The composition of the phosphate precipitate is as follows (mass %): Investigations of the immobilization of each type of waste [3,4] have shown that these wastes can be incorporated into the alumofluorophosphate glass matrix, developed at the Institute of Physical Chemistry of the Russian Academy of Sciences [5]. The present paper presents the results of experiments on the combined immobilization of these wastes in a glass matrix and a study of the hydrolytic and thermal stability of the samples obtained.The sample preparation method and the properties of the samples were investigated on model materials and real products obtained with experimental reprocessing of spent oxide fuel. The thermal stability was studied by differential-thermal analysis at 20-800°C. The rate of heating was 10°C/min. The phase transformations occurring in the material were recorded on the recording chart of a KSP-4 potentiometer after the signal on a F-116 microvoltmeter-microammeter (for real objects) and on a MOM derivative meter (Hungary) was recorded. Annealed aluminum oxide was used as a control substance. The leachability of the radionuclides and the components of the glass maatrix were studied in compliance with GOST 22114-91. The ratio of the water volume to the surface area of the glass samples was 10 cm. The quantitative and qualitative composition of the radionuclides was determined by the γ spectrometric method using a DGDK-32B Ge(Li) detector and an AMA-02-f-1 analyzer with a DVK-3 computer. The measurement error did not exceed 20%. The components (cesium, sodium, aluminum) which passed into solution during the hydrolytic tests were analyzed with a STÉ-1 spectrograph in the wavelength range 250-340 nm. The error was 25-30%. The x-ray diffraction analysis was performed by the photomethod using a RKU-114 M Debye camera and CuK α radiation.
A model of a centrifuge is developed, critical centrifuge speeds are determined by the Dunkerley and Krylov method, and the expected endurance with centrifuge vibration is determined.In the design, manufacture, and operation of centrifugal equipment, evaluation of their vibration reliability is recommended in order to provide accident-free operation. Here, a knowledge of the range of critical velocities, expected life with vibration, makes it possible to optimize the construction parameters of a device so that during its operation resonance phenomena are avoided, that lead to total breakdown of the device, and also to reduce development costs due to a reduction in the number of full-scale tests [1][2][3][4].Vibration reliability theory describes common approaches to analytical study of vibratory systems with a finite number of degrees of freedom and linear systems with distribution parameters, and also for determining the form and values of natural frequency vibrations of a complex structure. Additional studies should be carried out for a specific device, mechanism or class of devices.Well-known methods for evaluating the vibration reliability of centrifugal devices [1-5] are common for a whole variety of rotary machines. However, these methods do not make it possible, for example, to construct a simple mathematical model for evaluating the range of most probable critical velocities and the number of outbursts in a unit of time specifically for a loaded centrifuge of the vertical type, intended for separating suspensions by centrifugal deposition [1,6,7]. This centrifuge is related to continuously operating machines with inertial discharge of deposit. It may be used in the chemical and petrochemical industries for extracting solid deposits and suspensions of liquid media, and separation of medium-and highly-concentrated suspensions [6][7][8][9][10][11].The aim of this work is a study of the parameters of vibration reliability (range of critical velocities and expected life with vibration) of a loaded centrifuge of the vertical type for separating suspensions, development of a simple model for calculating these parameters, implemented in a personal computer, and also checking this model for conformity with experimental data with full-scale tests.The terms and definitions used herein are provided in [1,3,4,[12][13][14][15][16]. Mathematical Model of CentrifugeThe shaft of a centrifuge is placed on two supports. At the free end of the shaft through a rod a collector is fastened, that is a hollow thin-walled cylinder with an open lower base for loading a suspension and four holes in a cylindrical shell for discharge of clarified liquid. The center of gravity of the collector does not coincide with the area of its fastening to the shaft.
The method of carbothermic synthesis produced 260 g tablets of mixed nitrides of uranium, plutonium, americium and neptunium with a mass fraction of americium 0.61%. For the production of tablets were used uranium oxide manufactured by the water method, as well as plutonium dioxide containing impurities of uranium and americium oxides with a mass of 0.9 g americium, obtained by volumetric crystallization method in a NaCl — 2CsCl melt. Neptunium dioxide and americium oxide were added to the mixture of uranium and plutonium oxides before carbothermic synthesis. The resulting tablets had a density of 11.6-11.9 g / cm3. By methods of gamma-spectrometry, scanning electron microscopy and x-ray microanalysis is showed that the heat treatment of the mixture of the source chemicals - oxides of uranium, plutonium, americium, neptunium with carbon black at a temperature 1600-1500 °C for 72 h (24 h in nitrogen and 48 h in nitrogen-hydrogen atmospheres), and also the subsequent sintering synthesized by the press powders for 48 h at a temperature of 1800°C in nitrogen-hydrogen atmosphere doesn't leads in average to the significant losses of americium.
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