Radiochemistry最新文献

The work investigated the sorption of no-carrier-added ¹⁷⁷Lu isolated from neutron-irradiated ¹⁷⁶Yb₂O₃, and carrier-added ¹⁷⁷Lu obtained by irradiation of ^natLu₂O₃, by commercial and oxidized nanodiamonds (NDs) of various grades from aqueous solutions to identify among them a promising carrier for further research in the field of nuclear medicine. A promising sorbent was found: oxidized NDs of the STP grade (ox-STP); conditions for the fast sorption of lutetium with it in an amount equivalent to 1.2 GBq of no-carrier-added ¹⁷⁷Lu were determined, which corresponds to the activity used in therapy.

Using through diffusion method at room temperature, migration of simulants of RW elements (P, Se, Br, Mo, Cs, U) in compacted samples of clay materials of various mineral compositions was studied during porous diffusion from model solutions: underground water and leachates of phosphate waste forms having a total salt content of up to 500 mg/L. Based on the results of experiments, effective diffusion coefficients and sorption distribution coefficients of elements in barrier materials were determined. Numerical models are proposed to describe diffusion transfer of selenium, cesium, and uranium depending on porosity, mineral composition of materials, and concentration of elements in pore solution. Patterns of diffusion of elements from solutions of different salt composition were revealed.

Materials based on Portland cement and concrete are widely used for radioactive waste solidification and construction of engineered safety barriers at radioactive waste repositories. As compared to other candidate matrices, cement also exhibits the potential for chemical immobilization by reacting with many radionuclides and binding them. The water permeation through the bulk of concrete leads to its degradation, to a change in the composition of its pore water, and to transformations of solid mineral phases constituting the concrete. The long-term degradation of concrete can be estimated using geochemical modeling. A procedure for forecasting the degradation of materials based on Portland cement concrete is described. The model takes into account the stages of cement hydration and chemical degradation. The geochemical changes in the course of concrete degradation were calculated using numerical modeling with the PhreeqC code. Schemes of the stepwise concrete degradation are considered for estimating the radionuclide transport. Relevant radionuclide distribution coefficients are applied to each stage. The duration of concrete degradation stages largely depends on the filtering water composition.

The decomposition processes of plutonium hydroxo compounds formed under ozonation conditions in MOH (M = Li, Na, K) solutions of various concentrations were studied by UV-Vis spectroscopy using a modified nonlinear least squares method. The influence of the nature of alkali on the kinetics and mechanisms of spontaneous reduction of alkaline solutions of hydroxo compounds of plutonium(VII) was discovered. This influence and the “anomalies” in the UV-Vis spectra for ozonized plutonium solutions are associated with the presence in the systems of iron compounds in the form of impurities in commercially available LiOH, NaOH, and KOH (analytically pure, chemically pure, and ultrapure grade). Even trace amounts of impurities in alkaline solutions of plutonium compounds change the mechanisms of their reduction through the active participation of iron in redox processes. They include the oxidation of iron to ferrate(VI) ions FeO₄^2–, followed by reduction to Fe³⁺, probably through the stage of formation of an intermediate with a hydroxo derivative of plutonium(VI). As a result of the analysis of large arrays of spectral data, the spectra of individual components corresponding to compounds of plutonium(VI, VII) and iron (VI) were isolated.

Experiments on high-temperature reprocessing of VVER-1000 SNF with a burnout depth of 47 GW day/t U were carried out in order to determine the dependence of the extent of semi-volatile fission product removal on the time of SNF reprocessing in an oxidizing atmosphere for subsequent optimization of operating modes of this process. It was found that, during high-temperature reprocessing at 1200°С for 8 h, more than 30% of Mo, 90% of Cs, and 100% of Ru and Tc are removed.

The structure of the crystals of Li(UO₂)₂(C₅H₆O₄)₂F‧6H₂O (I), NaUO₂(C₅H₆O₄)F‧4H₂O (II), and Sr(UO₂)₂(C₅H₆O₄)₂F₂‧8H₂O (III) was studied by X-ray diffraction analysis for the first time. The uranium-containing structural units in crystals of I are 1D complexes [UO₂(C₅H₆O₄)F_0.5(H₂O)]^0.5– with the crystal chemical formula AQ⁰²M²_0.5M¹, where A = UO₂²⁺, Q⁰² = C₅H₆O₄^2–, M² = F^–, M¹ = H₂O, and in II and III, 1D complexes of the same composition and structure [UO₂(C₅H₆O₄)F]^– with the crystal chemical formula AQ⁰²M². In all compounds, the U(VI) atoms implement hexagonal-bipyramidal coordination, forming coordination polyhedra UO₂FO₅ (I) and UO₂F₂O₄ (II and III). It was found that the uranyl fluoroglutarate {UJUBEG}, for which the composition [UO₂(С₅H₆O₄)F]‧2H₂O contradicting the of electroneutrality principle was previously erroneously indicated, should be considered as (Н₃O)[UO₂(С₅H₆O₄)F]‧H₂O.

The present study addresses transformation of physicochemical forms (species) of artificial radionuclides in bottom sediments (BS) of the Yenisei River after the shutdown of the reactors at the Mining-and-Chemical Combine (MCC) at Krasnoyarsk. The BS samples collected from the Yenisei at the MCC in 2018–2021 contained ⁶⁰Co, ¹³⁷Cs, ¹⁵²Eu, ¹⁵⁴Eu, ¹⁵⁵Eu, and ²⁴¹Am. The species of radionuclides were studied using sequential extraction procedure. Considerable proportions of ⁶⁰Co (48–100%) and ¹³⁷Cs (72–83%), which are still released to the Yenisei with controlled discharges, were irreversibly bound to BS mineral solids. The percentages of europium isotopes, which have not been released to the Yenisei as part of controlled discharges since 2013, were lower in the irreversibly bound fraction (4.6–9.3% of ¹⁵²Eu), but their representation as relatively mobile species was more diverse compared to ⁶⁰Co and ¹³⁷Cs. Interestingly, some percentage of ¹⁵²Eu (up to 15.5%) was retained in the most mobile, exchangeable, form. The species of ¹⁵⁴Eu and ¹⁵²Eu differed, which can be explained by dissimilar origins of these isotopes. Further research is needed to investigate the mechanisms of physicochemical transformation of radionuclides in BS that enable them to be present in mobile species over long time periods and mechanisms of immobilization of artificial radionuclides in the environment.

Sorption of pertechnetate on pyrrhotite Fe_nS_n+1 (I) and stibnite Sb₂S₃ (II) from distilled water was evaluated. The distribution coefficients were found to be 185 and 223 cm³/g, respectively. The XPS study of the chemical state of ^99Tc absorbed on the surface of pyrrhotite and stibnite from aqueous solution of potassium pertechnetate (KTcO₄) was carried out. It was found that Tc(IV) ions are present mostly on the surface of the studied samples, their concentration was 5.7 times higher on the surface of pyrrhotite compared to that on the surface of stibnite. A 13% admixture of Tc(VII) ions on the surface of pyrrhotite was observed.

The release of ¹³⁷Cs into an Ar flow during the reaction of ¹³⁷CsI and ¹³⁷CsOH–¹³⁷Cs₂CO₃ with molten lead at a temperature of ~852 K was studied. It was determined that during the heating of Pb⁰ with ¹³⁷CsI, ¹³⁷CsOH–¹³⁷Cs₂CO₃, and ¹³⁷CsI–¹³⁷CsOH–¹³⁷Cs₂CO₃ from 2 to 8% of ¹³⁷Cs can pass into the gas flow. Based on the distribution of ¹³⁷Cs among the elements of the gas purification system, it was concluded that the chemical and disperse composition of the compounds containing ¹³⁷Cs in the gas phase is fairly heterogeneous. Volatile ¹³⁷Cs compounds formed on heating ¹³⁷CsI, ¹³⁷CsOH–¹³⁷Cs₂CO₃, and ¹³⁷CsI–¹³⁷CsOH–¹³⁷Cs₂CO₃ with Pb⁰ in a gas flow at ~852 K can contain both charged aerosols and aerosols without an electric charge.

The effect of gamma radiation on olefins was studied under static conditions at an absorbed dose of 65 kGy and at a dose rate of P = 0.076 Gy/s. The effect of radiation on the physicochemical characteristics and structural and group composition of the resulting olefins has been established. Post-radiation effects were studied immediately after irradiation and during 1, 2, 4, and 7 months later. When fuels are irradiated, polymerization of unsaturated hydrocarbons occurs. After the irradiation cessation, there occurs postpolymerization process. The chemical instability of olefins in fuels leads to the formation of carbon deposits in the engine system, tanks, and valves. IR spectra, iodine values, density, and kinematic viscosity of irradiated samples were measured.