Vol 60, No 4 (2018)

Coordination of the Am and Cm atoms in the crystal structures of oxygen-containing compounds was analyzed using Voronoi–Dirichlet polyhedra (VDPs). These actinides (An) form coordination polyhedra AnO_n (6 ≤ n ≤ 9) of eight types. At a fixed oxidation state of An, the volume of the corresponding VDP is virtually independent of the coordination number n. Analysis of the characteristics of atomic VDPs in the An sublattices revealed compounds with binding An–An 5f interactions in the crystals.

Two new U(VI) compounds templated with organic molecules, [(CH₆N)₃(H₂O)][(CH₆N)₂(C₃H₁₀N)· (H₂O)][(UO₂)₅(CrO₄)₈(H₂O)] (1) and [(C₆H₁₀N₃O₃)(H₅O₂)₂(H₂O)][(H₅O₂)₃(H₂O)][(UO₂)₅(SO₄)₈(H₂O)] (2), were prepared by combination of hydrothermal synthesis and isothermal evaporation methods. Compounds 1 and 2 crystallize in the monoclinic system, space group P2₁/n, a = 21.921(5), b = 11.016(2), c = 22.021(5) Å, β = 90.571(5)° for 1 and P₂/c, a = 18.1693(17), b = 10.0732(10), c = 30.098(3) Å, β = 103.427(2)° for 2. The reflections from the single crystals were collected at 100 K. The structures were solved by the direct methods and refined to R₁ = 0.053 and 0.070 for 1 and 2, respectively. The crystal structures of 1 and 2 are based on [(UO₂)₅(TO₄)₈(H₂O)]^6– modular layers (T = S⁶⁺, Cr⁶⁺) between which protonated organic molecules, water molecules, and hydroxonium ions are located. Specific features of the crystal chemistry of U(VI) compounds with tetrahedral oxoanions with the ratio UO₂: TO₄ = 5: 8 (T = S⁶⁺, Cr⁶⁺, Se⁶⁺, Mo⁶⁺) are considered.

Physicochemical processes occurring in a UHF furnace were analyzed. The information structure of the process as a management object was constructed. A system of differential equations describing the processes that occur in a UHF furnace in the course of evaporation of actinide nitrates was constructed. A mathematical model of preparation of actinide oxide powders by denitration in a UHF furnace was developed. It allows the calculation experiments to be performed and the operation of the installation and control systems to be optimized.

Three types of ionic groups with different pK_i values were revealed for T-5 sorbent by potentiometric titration: for acid groups, pK₁ = 7.5 ± 0.5, pK₂ = 10.2 ± 0.5, and pK₃ = 11.0 ± 0.2; for base groups, pK₄ = 6.5 ± 0.2, pK₅ = 4.5 ± 0.2, and pK₆ = 2.7 ± 0.2. Thus, titanium hydroxide is an amphoteric ion exchanger. Each exchange group of T-5 sorbent, characterized by its definite pK_i value, was assigned to a definite hydroxy group. T-5 and T-52 sorbents exhibit high specificity to Mo in acid and neutral solutions. All the isotherms logC_S–logC_L are described by the Langmuir equation for the polyfunctional sorbent for at least two exchange sites in both nitric and sulfuric acid solutions, irrespective of the Mo speciation. Two groups of values were obtained and confirmed for T-5 and T-52 sorbents depending on the Mo concentration: k_d ≈ 10⁴ mL g^–1 at concentrations lower than 10^–5 M and k_d = 1000–2000 mL g^–1 at a concentration of 10^–5 M. The exchangeable hydroxy groups in T-5 sorbent exhibit high heat resistance, and even the sorbent calcined at 900°C preserves certain reliably measurable capacity for Mo. For T-5, the capacity for Mo only slightly depends on the solution acidity and composition and is about ~1 mmol g^–1.

A composite material based on magnetite and K₂[CoFe(CN)₆] was prepared. Structural and morphological studies of the sorbent were carried out, and the specific surface area was determined. The crystal structure of the material was studied by X-ray diffraction, and the composition was evaluated by energy-dispersive X-ray spectroscopy. Sorption of radionuclides was studied in batch experiments in relation to pH of the solution, mass of the adsorbent, and contact time. The adsorption kinetics was examined, the adsorption isotherm was constructed, and the adsorption capacity was determined. The resistance of the material to radiation to a dose of 250 kGy was evaluated. The material efficiently removes Cs and Am radionuclides from aqueous solutions. The sorbent seems to be sufficiently stable for practical use in the treatment of radioactive waste.

The distribution coefficients of Hf(IV) and Lu(III) between Dowex 50W×8 cation exchanger or Dowex 1×8 anion exchanger and mixed HCl–H₂C₂O₄ solutions and between Dowex 50W×8 cation exchanger or Dowex 1×8 anion exchanger and citric acid solutions were determined. A number of modifications of the ¹⁷²Hf → ¹⁷²Lu generator, based on reverse separation schemes, were examined. Systems consisting of an anion-exchange resin and a solution of appropriate organic acid were taken as a chemical basis of the generator. Irreversible sorption of ¹⁷²Lu in generator columns was studied. The optimum operation mode of the ¹⁷²Hf → ¹⁷²Lu generator based on the reverse-tandem scheme with periodic transfer of the parent radionuclide into the liquid phase was determined.

Samples of aluminum (iron) phosphate glasses containing weighable amounts of rare earth and transuranium elements were synthesized. The quenched glasses obtained are X-ray amorphous, and in the course of annealing they undergo partial crystallization with segregation of a poorly soluble phase of monazite structure. However, the hydrolytic durability of the glasses remains on the level meeting the requirements to immobilized high-level waste (no more than 10^–7 g cm^–2 day^–1). Plutonium in the surface layer of the glass samples occurs in oxidation state IV, and neptunium, mainly in oxidation states IV and V.

The scale material in TENORM waste from petroleum industry was characterized using nuclear and non-nuclear techniques. The scale TENORM samples were collected from the Ras Shukeir area on the west bank of the Suez Gulf in Egypt during gas and oil production. These scales represent the TENORM deposits formed in the pipelines and removed during the periodical maintenance. X-ray fluorescence analysis showed that the main elements in all investigated fractions were Si, Fe, Mg, Ca, Sr, and Ba in addition to traces of some heavy elements, e.g. Pb, Cr, and Zn. The radioactivity concentrations of natural radionuclides ²²⁶Ra, ²³²Th, and ⁴⁰K in seven particle size fractions were found to be in the range from 14.1 ± 0.4 to 28.9 ± 0.9, from 5.0 ± 0.2 to 9.5 ± 0.4, and from 0.25 ± 0.02 to 0.43 ± 0.02 kBq kg^–1, respectively. The radiation hazard parameters were calculated. The values obtained are much greater than the accepted values. The results were compared to the values reported for other countries.