Radiochemistry最新文献

The uranium(VI) sorption in organogenic and mineral horizons of peaty-podzolic-gleyic and alluvial sod-gley soils collected in Nelidovo raion, Tver oblast was studied. The fraction of adsorbed uranium and the process kinetics are determined by the soil horizon composition. In deep horizons with high content of nonsilicate iron, the uranium adsorption occurs rapidly (within less than a day) and quantitatively. In upper horizons with high organic matter content, the fraction of adsorbed uranium showed pronounced dependence on time and on the amount of dissolved organic matter in the solution. The local surrounding of uranium was analyzed by X-ray absorption spectroscopy and by sequential extraction. The uranium valence state and the main soil components responsible for uranium binding were determined by X-ray absorption spectroscopy. The uranium availability fractions were analyzed by sequential extraction. The set of data obtained using independent analysis methods significantly supplements the existing views on the uranium(VI) behavior in soils.

The chemical behavior of silicon in the initial steps of reprocessing of spent uranium silicide nuclear fuel (U₃Si₂-SNF) in nitric acid solutions was studied. The composition of voloxidation products of triuranium disilicide (U₃Si₂) and their solubility in nitric acid solutions were determined. The U₃Si₂ oxidation products are U₃O₈, elemental silicon, and silicon dioxide (SiO₂). The influence of the voloxidation and dissolution conditions on the silicon distribution into uranium-containing nitric acid solutions was studied for powders of voloxidized U₃Si₂.

Borosilicate glasses with different amounts of incorporated PdO were studied. The palladium behavior in borosilicate melts was determined. As found by the digital element mapping system, the degree of PdO incorporation into the glasses prepared does not exceed 0.10 wt % at 1150°С. Excess palladium separates in the form of the metal phase.

Modern methods for concentrating radionuclides are reviewed with a focus on their advantages and limitations. The experimental part of the work consisted of five preconcentration cycles on a 300 L batch of simulated solution. The results show that reverse osmosis helps to reduce sample preparation time as compared to the other methods. However, it causes substance mass loss of up to 23% in a permeate stream. With increasing number of cycles, the membrane selectivity decreases owing to an increase in the solution concentration. The results were validated by evaporating the permeate, and the presence of unaccounted loss was confirmed. The paper demonstrates high potential of reverse osmosis for radionuclide analysis of water discharges from nuclear fuel cycle enterprises, as well as the need to take into account the mass loss across multiple preconcentration cycles.

The carbonate-alkaline leaching technique for the separation of the ⁹⁰Sr–⁹⁰Y pair in nuclear waste processing was studied. The influence of potassium carbonate concentration, alkali metal cation, temperature, and stirring speed on the yttrium extraction was examined using stable isotopes of strontium and yttrium in the carbonate form. The highest degree of yttrium extraction (99.9 %) was achieved under the following optimum conditions: 2 M K₂CO₃ solution, 70°C, stirring speed 500 rpm, liquid-to-solid ratio 20 mL/g, Sr : Y weight ratio 10 : 1, and leaching time 2 h. Under these conditions, the leaching process is primarily diffusion-controlled, as evidenced by the strong dependence of the extraction efficiency on the stirring speed and the apparent activation energy of 13.9 kJ mol^–1.

The modern data on ^99mTc radiopharmaceuticals, namely, their chemical features, synthesis methods, safety, and clinical efficacy, are analyzed. Data on the procedures for preparing ^99mTc-labeled complexes, on factors influencing their stability and radiochemical yield, and on the approaches to choosing chelators are systematized. Particular attention is paid to coordination cores, to structural features of technetium complexes, and to vector fragments determining the properties of radiopharmaceuticals. The main fields of using ^99mTc radiopharmaceuticals for the diagnostics of cardiovascular, tumor, renal, and inflammatory diseases are analyzed in view of the fact that efficient diagnostics and therapy of these diseases is still an unsolved clinical problem. The safety requirements including the radiation protection, quality control, and process standardization are discussed. The problems of the development, quality control, and use of ^99mTc radiopharmaceuticals are considered. The modern trends and prospects for the development of ^99mTc radiopharmaceuticals are summarized.

The fire and explosion safety of solvent samples unirradiated and γ-irradiated to a dose of 0.5 MGy from a ⁶⁰Co source was evaluated by the flash point determination, simultaneous thermal analysis, and adiabatic reaction calorimetry. Samples of the fresh extraction mixture and of the used solvent taken from contactors of the RT-1 plant, containing 10 or 30% tributyl phosphate (TBP) in hydrocarbon diluents of grades С₁₃ and С₁₀, were studied. In the course of operation of the recycled solvent prepared using the С₁₀ diluent, its flash point gradually increases by at least 10°С [1]. The experimental data suggest that the safe operation limits for extraction systems based on TBP in linear hydrocarbon diluents can be determined using the data on the open-crucible flash point.

An electrochemical deposition procedure was developed for forming the active part of a linear ⁵⁷Co source for SPECT system calibration. The effects of copper substrate preparation, current density, stable cobalt concentration, anode material, and deposition time on the coating quality and on the activity distribution along the length were studied. Under the parameters chosen, the ⁵⁷Co deposition yield reaches 92–93 %; the coatings exhibit high adhesion, and the maximum nonuniformity of the activity distribution along the length does not exceed 10% with a standard deviation of ≤2.5%. Edge effects influencing the activity distribution were identified. The results confirm the feasibility of fabricating a linear ⁵⁷Co active part with characteristics meeting the requirements for calibration sources.

The incorporation of the material simulating high-level perlite-containing sludge accumulated at the Mayak Production Association into sodium aluminum phosphate glass was studied in laboratory experiments. Crystalline phases present in the samples prepared were identified by X-ray diffraction analysis. These include graphite, silicon oxide, sodium aluminosilicate, and aluminum phosphate. The sample homogeneity was evaluated by scanning electron microscopy. The ultimate strength was determined for the most homogeneous sample. The compliance of the sample homogeneity and strength with the regulatory requirements to glassy compounds was assessed. The acceptable percentage of the perlite-containing sludge in sodium aluminum phosphate glass was determined.

The possibility of the deep partitioning of the raffinate from the extractive SNF reprocessing using a mixture of di-2-ethylhexyl hydrogen phosphate (HDEHP), polyethylene oxide (PEO), and chlorinated cobalt dicarbollide (CCD) in a polar diluent was demonstrated. The improved solvent containing a synergistic mixture of CCD and HDEHP efficiently extracts cesium, strontium, transplutonic elements (TPEs), and rare earth elements (REEs) from a nitric acid high-level waste (HLW) solution and allows obtaining separate fractions of the elements. Based on the results obtained, a flowsheet for the extractive HLW partitioning was developed; it has a number of advantages over the flowsheets described previously. Dynamic trials of the flowsheet with a simulated solution were performed. Efficient separation of REEs and TPEs (decontamination factor of TPEs from REEs about 200) and efficient recovery and separation of other elements being partitioned were achieved.