Vol 59, No 6 (2017)

The facilities operating in the world are today incapable of reprocessing the whole amount of the already accumulated and annually unloaded NPP spent fuel. Therefore, the spent nuclear fuel (SNF) reprocessing is not considered today as the only alternative of the nuclear fuel cycle. The paper attempts to analyze measures aimed at reducing expenditures for NPP fuel reprocessing. In the author’s opinion, the existing approach to the SNF reprocessing technology should be revised taking into account prospects for using REMIX fuel, with possible expansion of the range of fission products suitable for further use.

The oxidation state of Fe and U and the coordination surrounding of Fe in uranium-containing sodium aluminum iron phosphate glasses were determined by analysis of the FeK and UL₃ X-ray absorption nearedge structure (XANES), X-ray photoelectron spectroscopy (XPS), and Mössbauer spectroscopy on ⁵⁷Fe nuclei. Uranium is present in the glasses in the form of U(V) and U(VI), and iron, in the form of Fe(III) and Fe(II), mainly in the distorted octahedral surrounding. The fraction of U in various oxidation states depends on the form of untroducing uranium (UO₂ or UO₃) and on the oxide concentration. With an increase in the UO₃ concentration in glasses, the fraction of U(VI) increases and the fraction Fe(III) relative to Fe(II) decreases.

Solvent extraction of Ce(IV) and Th(IV) from 8 M HNO₃ with TBP in kerosene was studied. The dependence of the extraction on the TBP concentration, kind of diluent, O/A phase ratio, and contact time was examined. The extraction efficiency reaches 99.3 and 97.7% for Ce and Th, respectively, at 5% TBP in kerosene, 1/1 O/A phase ratio, and 5 min contact time. Successive selective stripping of Ce(III) and Th(IV) from the loaded organic phase was reached at 1.1 M H₂O₂ concentration, 10 min contact time, 3/1 O/A phase ratio, and room temperature (25 ± 2°C). After stripping of cerium, the remaining organic was contacted with H₂O for thorium stripping at 5 min contact time, 2/1 O/A phase ratio, and room temperature (25 ± 2°C).

Hydrolysis is the prevalent mechanism of decomposition of benzo- and caprinohydroxamic acids (HAs) in nitric and perchloric acid solutions and in the equilibrium organic phase based on heptanol, decanol, and 30% TBP in С13 paraffin diluent. In the nitric acid system with alcohols, HAs undergo autocatalytic oxidation at temperatures raised over 50°С. In the case of BHA, the process occurs in both phases taken separately and on their mixing. In the case of caprinohydroxamic acid poorly soluble in HNO₃ solutions, the autocatalytic process occurs only at 70–80°С on mixing the phases; it tends to fade as the phase ratio n = О/A is increased from 1 to 10. This trend determines the conditions for Mo stripping in this system. In the practice of the ⁹⁹Mo production, the stripping efficiency can be increased by repeated contact with the addition of non-salt complexing agents (H₂O₂, H₂C₂O₄, CH₃CONHOH) into the system.

Thermal properties of 2,2′-bipyridine-6,6′-dicarboxylic acid bis(N-ethyl-4-hexylanilide) (DYP-7) were studied by DSC-TG with the aim of evaluating its fire and explosion hazard. Heating at a rate of 1 K min^–1 is accompanied by exothermic effects with the onset temperatures of 202, 312, and 432°С for the initial extractant and 62, 297, and 412°С for the extractant saturated with nitric acid. The presence of extracted nitric acid decreases the self-ignition point of DYP-7 by at least 20°С. The onset temperatures of the exothermic effects tend to increase with increasing heating rate. The extractant thermolysis products characteristic of the exothermic effect with the onset temperature of 202°C were identified by GC-MS. These are the deethylation product, 2,2′-bipyridine-6,6′-dicarboxylic acid N,N′-bis(4-hexylphenyl)amide, and product of further dearylation/reduction, 6′-formyl-N-(4-hexylphenyl)-2,2′-bipyridine-6-carboxamide.

^99mTc-oxiracetam was prepared. It can be used as a radiotracer for brain imaging. Under the optimum conditions (0.5 mg of oxiracetam, 50 μg of SnCl₂·2H₂O, pH 7, room temperature, 30 min), the radio-chemical yield determined by chromatographic methods reached 96%. Biodistribution studies with mice showed that the brain uptake of the complex was 5.1% injected dose per gram (% ID/g) at 5 min post injection. In this parameter, the complex surpasses the commercially available ^99mTc-ECD (4.7% ID/g) and ^99mTc-HMPAO (2.25% ID/g).

An efficient method was developed for radioiodination of melatonin with ¹²⁵I. Chloramine-T and iodogen were used as oxidizing agents. The radioiodination was carried out via electrophilic substitution of the H atom with the I⁺ cation. Indirect iodination using Bolton–Hunter reagent was also performed. The influence exerted on the radiochemical yield by the melatonin concentration, pH of the reaction mixture, type of oxidizing agent, and reaction time was studied. The shelf life and specific activity of the product were determined. The radiochemical yield and product purity were determined by HPLC and paper electrophoresis. The immunoreactivity of the tracer was checked using its specific antibody. Specific and sensitive polyclonal antimelatonin was prepared using two New Zealand rabbits, which were injected with 5-methoxy-N-acetyltryptamine–bovine serum albumin conjugate as immunogen. The tracer prepared by the indirect method with iodogen had high specific activity, high yield, and long shelf life; it was also more selective in the melatonin assessment using radioimmunoassay technique.