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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 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.