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The liquid radioactive waste (LRW) management at the Ukrainian nuclear power plants is an urgent problem since the scheme of treatment of radionuclide-bearing solutions by deep evaporation with subsequent crystallization of radionuclides in the form of soluble salts has a number of serious drawbacks and the final products of the treatment (vat residue, spent sorbents and sludges, salts) do not meet the ac-ceptance criteria for long-term storage and disposal. One of the promising LRW treatment schemes is the one using methods of selective sorption by natural and modified sorbents. The article presents the results of the study of the kinetics of 90Sr and 137Cs sorption by natural, acid- and alkaline-modified zeolites from Sokirnyt’ske deposit. The maximum degree of sorption on natural zeolite during the experiment (14 days) was 55% for 90Sr and 90% for 137Cs. The maximum degree of 90Sr and 137Cs sorption on alkaline-modified zeolite was 62.2% and 98.78%, respectively. For acid-modified zeolite, the maximum sorption degree of 90Sr was 18% and of 137Cs – 85%. Thus, it can be infered that among the studied zeolites, the most effective sorbent of 90Sr and 137Cs is alkaline-modified zeolite (Na-form). Sodium hydrox-ide modification of the natural zeolite increases the sorption degree of both 90Sr and 137Cs by 10 15%. The results of determining the forms of being of the adsorbed radionuclides indicated that the sorption of 90Sr on natural and alkaline-modified zeolites is characterized by up to 20% predominance of ion-exchangeable forms, and sorption on acid-modified zeolite – by the equality of exchangeable and non-exchangeable forms. The sorption of 137Cs on natural and alkaline-modified zeolites is characterized by up to 10% predominance of ion-exchangeable form. In the case of the alkaline-modified zeolite, 10% predominance of non-exchangeable adsorbed cesium form was observed during the first 2 days of the experiment. During the sorption of 137Cs on alkaline-modified zeolite, double predominance of the exchangable form over the non-exchangeable was observed during the whole experiment (14 days).

The article presents the results of an experimental modelling of the influence of Ca2+ ion concentration and pH of a model solution on the elemental composition and sorption capacity of natural (NB) and sodium-modified (SMB-20) bentonites from the Cherkasy deposit for 137Cs and 90Sr. The processes of the Cs and Sr sorption from multicomponent solutions with different pH, Eh and salt composition depend on the insoluble or sparingly soluble compounds precipitated on the bentonite surface. Based on the computer simulation data, it was found that small amounts of sediments, mainly oxides, hydroxides, Fe oxyhydroxides (hematite, goethite, limonite), and Ca carbonates (calcite, aragonite, dolomite) were present in the model solution with alkaline pH after adding CaCl2 solutions. Oxides and hydrated oxides of Fe, and calcium carbonates play an important role in the Cs and Sr sorption processes on bentonites. They can concurrently sorb radionuclides and block the sorption centres in montmorillonites. The concentration of the main structural elements (Si, Al) in the bentonites practically does not change with the increased pH and Ca2+ ion concentration in the model solution compared to the initial samples of NB and SMB-20, which indicates their structural stability. At the same time, an increase in the calcium concentration and a decrease in the sodium concentration were found in the ionexchange complex of montmorillonite — the main bentonite mineral if compared to the initial samples. This can eventually lead to the transformation of SMB-20 bentonite from Na, Ca form to Ca, Na form. The 137Cs and 90Sr sorption on NB is shown to proceed more effectively, compared to SMB-20 in conditions of the increased pH and Ca2+ ion concentration. The results of this research may justify the bentonite clay application as a component of the isolating engineered barriers of radioactive waste disposal facilities. [ABSTRACT FROM AUTHOR]

The safety of near-surface and deep radioactive waste storage facilities is based on a system of engineered and natural barriers. Significant degradation of the engineered barrier system composed of cemented waste matrixes covered by cement mixture, concrete compartments, and structures at the basement of the storage facility may cause radionuclide transfer from the facility to groundwater. Mixing of the cement and concrete with water leads to the formation of several various hydration products with subsequent leaching of Ca2+ ions and formation of hydroxyl ions (OH-), which affects the alkalinity of the water environment and the sorption properties of bentonite, as a component of the engineered barrier at the basement of near-surface facilities. The article presents the results of an experimental study of the influence of Ca2+ ion concentration and pH of the model solution (similar to groundwater composition at Vector Site in Chornobyl Exclusion Zone) on the elemental composition and sorption properties of natural (NB) and Na-modified (PBA-20) bentonites from the Cherkasy deposit concerning 137Cs at the Solid: Solution ratio of 1: 100. Geochemical modeling suggests that addition of CaCl2 to test solution and resulting alkaline pH leads to precipitation of solids, mainly oxides, hydroxides, Fe oxyhydroxides (hematite, goethite, limonite), and Ca carbonates (calcite, aragonite, dolomite). Their role in Cs adsorption was evaluated. The concentration of structural elements (Si, Al) in bentonites practically does not change with Ca2+ ion concentration increase in the model solution, demonstrating the bentonite structure's stability under these conditions. At the same time, an increase in the Ca concentration and a decrease in the Na concentration was found in the ion exchange complex of the bentonites if compared to the initial natural bentonite. This results in the transformation of Na-modified bentonite from Na, Ca-form to Ca, Na-form. The total sorption capacity of NB and PBA-20 bentonite concerning Cs+ ions at increased concentrations of Ca2+ ions and pH of the solution slightly decreases, though retaining high values of the degree of absorption (> 90 %). The total adsorption of Cs+ ions on NB and PBA-20 bentonites from model groundwater with the addition of CaCl2 from 16 to 960 mg/dm³ and increase of рН from 7.4 to 11.8 decreases with the increase in ionic strength, in particular, due to competition with Са2+ and Na+ ions. NB and PBA-20 bentonites of the Cherkasy deposit remain a reliable component of the liner at the repository basement owing to their main functional property - high absorption capacity for 137Cs, which is an important dose-forming radionuclide of short-lived low- and medium-level waste. [ABSTRACT FROM AUTHOR]

The article reveals the regularities of the overall process of ozonolytic destruction of organic components of model drain water from nuclear power plants and sorption of imitators of the main dose-forming radionuclides (Cs — with the isotopic 137Cs label; stable isotopes of Co, Sr, Mn salts) by natural zeolite of the Sokyrnytsky deposit and sorption-reagent compounds — salts of ferrous and manganese (II). The chemical composition of the main elements of zeolite after ozonation with the addition of iron and manganese salts practically does not differ from the composition of natural zeolite. Its phase composition in the ozonation process in the presence of ferrum salts is represented by the main rock-forming mineral clinoptilolite and the secondary mineral — quartz. The main ferrum-containing phase on the zeolite surface is goethite. Secondary phases include Fe(II)-Fe(III) layered double hydroxides (Green Rust) and lepidocrocite, but their relative content is insignificant. For zeolites, after ozonation with the addition of both ferrous and manganese (II) salts, the main phases are clinoptilolite and quartz. Manganese-containing phases on the zeolite surface are represented by hausmannite Mn3O4, manganese(II) oxide, and manganese oxyhydroxide MnO(OH)2. The iron- and manganese-containing phases deposited on the surface of the zeolite in the process of ozonation are mainly characterized by a weakly crystallized or amorphized structure. The main sorbent of dose-forming radionuclides is zeolite, not the iron- and manganese-containing compounds that formed on its surface during ozonolysis. The maximum degree of sorption of 137Cs by zeolite is up to 90% when the concentration of Fe 2+ is increased to 50 mg/dm³ or Mn2+ to 100 mg/dm³. The degree of cobalt sorption is 97.5% at the initial typical concentration of competing cations (Fe 2+ —5 mg/dm3 ; Mn2+ — 10 mg/dm³ ) and when Mn2+ concentration increases to 100 mg/dm³. The maximum degree of extraction of Sr 2+ and Mn2+ is 99.4% and 99.9%, respectively. For effective extraction of 137Cs and Co2+ by zeolite in the ozonation process, an increase in the concentration of competing Fe 2+ cations is permissible — 50 mg/dm³; Mn2+ — 100 mg/dm³ in solutions. The efficiency of extraction of Sr2+ and Mn2+ practically does not depend on the concentration of competing cations (Fe2+, Mn2+) in the drain water solutions. [ABSTRACT FROM AUTHOR]

The mineral composition and sorption properties of precipitates formed during ozonation of a model solution simulating nuclear power plant wastewater (total mineralization 7 g/dm³, pH = 11.5, T = 60 °C, t = 2 hours) 137Cs were studied. The precipitate is represented by finely dispersed spherical particles of metal oxides ranging in size from 20 to 30 nm, forming microaggregates and their associates of various shapes. The composition of the precipitates, along with X-ray amorphous phases, includes Fe(II)-Fe(III) layered double hydroxides (Green Rust), as well as LDH of mixed composition, in particular Fe-Co, and iron oxyhydroxides - goethite and lepidocrocite. The precipitates also contain manganese- containing phases represented by manganese (IV) hydroxide and manganese (II) carbonate with an admixture of manganese oxides, such as Mn2O3 · H2O, MnO, Mn3O4 (gaussmanite). In the process of ozonation, organic compounds that are part of the solutions undergo destruction, co-precipitation with other components of the solution, which is accompanied by the sorption of 137Cs radionuclides on the surface of mineral particles. An increase in the concentration of Fe2+ and Mn2+ cations by 10 times (up to 50 and 100 mg/dm³, respectively) in wastewater reduces the concentration of 137Cs in the initial solution by 50.5%. [ABSTRACT FROM AUTHOR]

The article is devoted to the study of the barrier properties of bentonite clays from the Cherkasy deposit (Ukraine) as the most promising material for engineered barriers in near-surface disposal facilities for low-level radioactive waste. The work presents a description of the Cherkasy bentonite deposit, in particular, of the most promising II layer of the Dashukivka site, and the composition and properties of the natural and soda-modified (PBA20) bentonites which can be used for safe long-term storage and disposal of radioactive waste. The scanning electron microscope (SEM) images of the samples were made and the chemical and mineral composition of the samples was determined. Based on the obtained data, the Dashukivka bentonite was classified as Al-Fe-montmorillonit. The main rock-forming minerals of the bentonite are montmorillonite (75 ± 3 wt. %) and quartz (20 – 25 wt. %). Infrared spectra of the bentonites in the range of 4000 – 400 cm-1 are typical for dioctahedral Al-smectites and are almost identical both for the natural and modified samples. The derivatographic analysis (DTA) of the bentonite samples allows us to conclude that the modified bentonite PBA-20 has greater thermal stability than the natural bentonite. The total weight loss of the samples is about 10.3% and 17.8%, respectively. From the experimental study of 137Cs adsorption from a simulated ChEZ water solution (mineralization – 0.2 g/dm3), it was found that the equilibrium in the sorbent-solution system is established within 12 to 14 h, and the degree of adsorption on the modified bentonite PBA-20 reaches 93%. The degree of adsorption on the natural bentonite is 7 – 10% lower. Analysis of the partition coefficients (Kd) also indicates a higher efficiency of the Na-modified bentonite compared to the natural, and that ion exchange is the main mechanism of caesium adsorption. Increasing of the pH of the initial solution results only in a slight increase of the degree of adsorption. The degree of 137Cs adsorption on Na-modified bentonite is practically independent of the initial concentration of Ca2+ (from 16 to 160 mg/dm3) and Na+ (from 6 to 60 mg/dm3) in the solution. However, 137Cs adsorption on natural bentonite decreases with the increase in Na+ concentration. Thus, the bentonite clays from the Cherkasy deposit (Dashukivka site, II layer) having good barrier properties can be recommend as anti-migration engineered barriers for radioactive waste repositories, in particular, near-surface storage facilities I and II line of Vector complex.

Identification of the novel HLA-A*68:99:02 allele that differs from HLA-A*68:99:01 in exon 2 and intron 7., (© 2022 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)