Radiochemistry最新文献

Invaluable experience of the designing, construction, and operation of sodium-cooled fast reactors, of prolongation of their lifetime, and of their decommissioning has been accumulated in Russia. The BN-600 reactor facility is being prepared for repeated prolongation of the lifetime up to the year 2040. The problem of preparing BN-600 for the decommissioning becomes topical, because this final step of the life cycle of the power unit is time-, material-, and labor-consuming and requires expensive measures for reducing dose loads, the more so as this reactor type is unique. To reduce these expenditures, it is necessary to choose the most effective technologies. Problems of sodium pretreatment to remove radioactive impurities and thus to minimize the staff dose loads when draining the BN-600 sodium coolant and decommissioning the reactor facility are being discussed today. The paper presents data on the radioactive contamination of hot and cold parts of sodium circuits and on the ways of sodium treatment to remove impurities. The processes of sodium decontamination from cesium with MAVR small adsorbers and cesium-accumulating traps are considered in detail for the BN-350 reactor facility as example. The paper objectives are to inform specialists on the experience on treatment of sodium from the primary circuit and to recommend the positively assessed technologies. The study is aimed at justifying the need for removing cesium isotopes from sodium as a preliminary step to reduce the staff dose loads prior to the decommissioning of fast sodium-cooled reactors.

This study examined the effectiveness of using aminotrimethylenephosphonic acid (ATMP) as a chelating agent to remove iron from Abu Zeneima sulfate leach liquor (AZSLL) and recover uranium as a result. Key parameters including pH, ATMP to sample volume ratio, contact time, and temperature were systematically examined to find the ideal conditions for iron removal. The findings revealed a remarkable selectivity in iron removal by precipitation with 0.05 M aminotrimethylenephosphonic acid (ATMP) per 10 mL of the sample: 90% of iron was precipitated, which is equivalent to approximately 20.5 mg, without adversely impacting uranium content. The iron amputation provided a favorable opportunity for the subsequent recovery of uranium, employing trioctylamine (TOA) as the extracting agent. TOA dissolved in benzene demonstrated efficiency in uranium recovery. The effect of the type of stripping solution, organic/aqueous phase volume ratio, contact time, and temperature on the uranium stripping was examined. Under the optimized conditions, with a maximum stripping efficiency of 98%, the uranium concentration in the resulting solution reached 451.58 mg/L.

The paper analyzes the causes of the appearance of steps with plateaus of different lengths in sorption isotherms, based on experimental and literature data. Examples of step-shaped isotherms are given to illustrate each type of causes. It is shown that the following factors can cause the deviation of sorption isotherms from linearity and the appearance of steps: sorbent polyfunctionality, the presence of sorption sites with significantly different specificity to sorbate; sorbate heterogeneity, the presence of inert sorbable sorbate species; chemical transformation of sorbents in the course of sorption with the formation of new phases, including processes involving solution components; sequential change of sorption mechanisms.

It is known that the concentration ratio of chemical elements in an aqueous aerosol (AA) can differ significantly from that of the same elements in the aqueous medium (AM) from which this AA was formed. Different accumulation (fractionation) of elements in AA occurs in the surface microlayer of water and is observed only for water-soluble microimpurities, whereas dissolved salts present in macroscopic concentrations undergo no accumulation. For radionuclides, the relative fractionation coefficient F(X/Cs) is defined as the degree of accumulation of the activity of radionuclide X in AA relative to another, reference radionuclide (¹³⁷Cs). The values of F(X/Cs) were determined previously under natural conditions in the region of V-9 intermediate-level liquid radioactive waste storage reservoir (Lake Karachay) by analyzing the ratio of the volume activities of the radionuclides in water, R^W(Cs/X), and in AA (in air), R^A(Cs/X): F(X/Cs) = R^A(Cs/X)/R^W(Cs/X). Attempts to estimate the absolute fractionation coefficient of ¹³⁷Cs, F(Cs), in AA relative to its content in AM failed. A procedure was suggested for determining the absolute fractionation coefficient of ¹³⁷Cs, F(Cs), in AA relative to its content in AM under laboratory conditions. The procedure was tested with a model AM with the parameters close to those of V-9 reservoir (¹³⁷Cs volume activity 0.17 MBq/L, dry residue ~10 g/L). The integral value of F(¹³⁷Cs) for the model AM (for all the aqueous aerosol particles of size smaller than ~100 μm) varied from 4.4 to 6.5.

The dissolution of uranium oxides of various chemical compositions at different nitric acid solution concentrations and flow rates with obtaining uranyl nitrate solutions with a deficiency of NO₃^– anions was studied. The dependences of the solubility of uranyl hydroxonitrates on the nitric acid deficiency relative to stoichiometry and temperature were determined. It was shown that the solubility of hydroxonitrates in these solutions is higher than the solubility of uranyl nitrates obtained with stoichiometric or excess nitric acid content. In addition, the solubility of hydroxonitrates increases with temperature. The kinetics of uranium oxide dissolution in various temperature regimes with the formation of solutions with nitric acid deficiency relative to stoichiometry were studied. The initial dissolution rate of U₃O₈ in uranyl nitrate solution was determined in the temperature range from 40 to 104°C.

The article presents the results of studies of the effect of heat and ionizing radiation on oil extraction from natural bitumen sands (BS) of Azerbaijan. The combined effect of heat (20–500°C) and ionizing radiation at dose rates of 1 and 470 Gy/s was studied. The reactions of radical products generated by ionizing radiation depend on the temperature and rate of their generation, determined by the radiation power. The ratio of the rates of thermal and radiation-thermal reactions is the most universal characteristic. This value is a function of temperature and dose rate. The temperature and dose rate intervals for radiation-thermal processing of oil bitumen sands are calculated. The results obtained allow the evaluation of possibility of obtaining oil products by the radiation-thermal (RT) method. The use of radiation technologies for the organization of industrial production of synthetic oil from natural bitumen sands and heavy oils will have a positive effect from the point of view of environmental protection, since materials that pollute the environment are used in the production of electricity.

It was established that the content of the main clay minerals in the loam sample from the Fanipolskoye deposit is 13.6 wt % for montmorillonite and 3.3 wt % for illite. It was determined that the pH of solution in the range of 4–12 has virtually no effect on ¹³⁷Cs⁺ sorption by the loam. The distribution coefficient (K_d) of ¹³⁷Cs for the specified loam sample with a K⁺ concentration in the solution of up to 0.01 mol/dm³ is higher than 10³ dm³/kg, which indicates that the ¹³⁷Cs sorption is efficient. The loam contains two types of sorption sites, T₁ and T₂, with different selectivity and capacity toward Cs⁺. The sorption capacities of sites T₁ and T₂ for Cs are 4.0 × 10^–5 and 1.2 × 10^–2 mol/kg, respectively, and the values of K_d of Cs for these sites differ by a factor of 20 and are 1.6 × 10⁴ and 7.9 × 10² dm³/kg. The loam from the Fanipolskoye deposit is shown to be suitable as a buffer backfill for the disposal site of very low-level radioactive waste from the Belarusian NPP.

By the methods of thermodynamic modeling, sorption diagnostics, analysis of particle zeta-potential, and UV-Vis spectrometry the equilibrium conditions of sorption interaction of CrO₄^2–, MoO₄^2–, WO₄^2–, SeO₃^2– oxygen anions in the region of chemical stability of Al₂O₃||C composite have been analyzed. The anion sorption isotherms are shown to follow the Langmuir model for a monoenergetic sorbent. The Henry region is observed at concentrations less than 1 μM. According to the established mechanism of surface complexation, the value of anions protonation constant (K₁) in the investigated pH range determines the sorption activity of the composite to these anions. This explains the correlation found between the ratio of parameters of acid–base sites {Al–O^–}, {Al–HO⁰}, and {Al–OH₂⁺} of composite K_M(1,2) and the protonation constant of anion K₁. It is shown that the Al₂O₃||C composite concentrates from dilute solutions both cations of d-, f-elements and oxygen anions of d-elements with the value of log K_d [mL/g] > 4, thereby exhibiting the properties of collective action sorbent.

Thermal degradation of radioactive concentrates in the oxidizing medium at temperatures of up to 900°C was studied by DSC–TG. The presence of significant amounts of organic compounds in the concentrates was confirmed. The degradation of organic compounds in the concentrates occurs in steps and is accompanied by thermal effects in the temperature range 170–900°С. Oxidative treatment of the concentrate with Fenton’s reagent decreases the content of organic compounds by a factor of 2–5. High-temperature drying of the concentrate at a temperature higher than 450°С allows virtually complete removal of organic compounds from the waste, which improves the safety of the long-term waste storage. The concentrate weight loss decreases as the drying temperature is increased. The high-temperature drying opens prospects for preparing compounds that will be safer from the viewpoint of final disposal.