Том 60, № 5 (2018)

The review substantiates the desirability of developing spent nuclear fuel reprocessing technologies alternative to the Purex process. The practical use of radiochemical technologies based on alkaline and carbonate media, such as extraction of radiocesium from alkaline high-level waste and CARBEX process, is considered. Extraction of actinides with aliphatic amines, β-diketones, phenol derivatives (alkylpyrocatechols, aminomethylphenols, alkylphenol oligomers, calixarenes), and carboxylic acids, as well as extraction in two-phase aqueous systems based on water-soluble polymers, is discussed. The extraction of technetium is considered separately.

Two new U(VI) compounds, [((CH₃)₂CHNH₃)(CH₃NH₃)][(UO₂)₂(CrO₄)₃] (1) and [CH₃NH₃][(UO₂)· (SO₄)(OH)] (2), were prepared by combining hydrothermal synthesis with isothermal evaporation. Compound 1 crystallizes in the monoclinic system, space group Р2₁, a = 9.3335(19), b = 10.641(2), c = 9.436(2) Å, β = 94.040(4)°. Compound 2 crystallizes in the rhombic system, space group Рbca, a = 11.5951(8), b = 9.2848(6), c = 14.5565(9) Å. The structures of the compounds were solved by the direct methods and refined to R₁ = 0.041 [for 5565 reflections with Fo > 4σ(Fo)] and 0.033 [for 1792 reflections with Fo > 4σ(Fo)] for 1 and 2, respectively. Single crystal measurements were performed at 296 and 100 K for 1 and 2, respectively. The crystal structure of 1 is based on [(UO₂)₂(CrO₄)₃]^2– layers, and that of 2, on [(UO₂)(SO₄)(OH)]^– layers. Both kinds of layers are constructed in accordance with a common principle and are topologically similar. Protonated isopropylamine and methylamine molecules are arranged between the layers in 1, and protonated methylamine molecules, in 2. Compound 1 is the second known example of a U(VI) compound templated with two different organic molecules simultaneously.

New complexes of hexavalent actinides with cyclobutanecarboxylic acid (Hcbc) anions, Na₄[NpO₂· (cbc)₃]₄·H₂O (I), K[NpO₂(cbc)₃] (II), Cs[NpO₂(cbc)₃] (III), and Cs[PuO₂(cbc)₃] (IV), cbc = C₄H₇(COO)^–, were synthesized and studied by single crystal X-ray diffraction. The structures of I–IV are based on the anionic complexes [AnO₂(cbc)₃]^– surrounded by alkali metal cations. The AnO₂²⁺ cation in the anionic complex is bonded with three chelating C₄H₇COO^– anions, and the coordination polyhedron (CP) of An is a hexagonal bipyramid with the O atoms of the AnO₂²⁺ cations in apical positions. The coordination number (CN) of the alkali metal cations in the structures of II–IV is the same and equal to 6; the coordination surrounding of the K⁺ and Cs⁺ cations is constituted by the O atoms of six C₄H₇COO^– anions. The crystal structures of II–IV are examples of cubic 3-connected networks (10,3) built of alkali metal and actinide cations. In the structure of I, there are four kinds of crystallographically different NpO₂²⁺ and Na⁺ cations. The coordination surrounding of the NpO₂²⁺ cations differs only in the conformational characteristics of the C₄H₇COO^– ligands. Four independent Na⁺ cations differ from each other in the structure of the coordination surrounding. The CPs of the Na(1) and Na(4) atoms can be described as distorted octahedra (CN 6); that of Na(3), as a trigonal prism (CN 6); and that of Na(2), as a tetragonal pyramid (CN 5) with one of the basal vertices occupied by the Ow(1) atom of a water molecule. In the structure of I, the configuration of the network formed by the Na and Np cations differs from the cubic 3-connected network found in the structures of II–IV.

An electrolytic method for preparing chemically resistant Am–Ni alloys was studied. Optimum electrolysis conditions ensuring the maximal (up to 95%) recovery of Am from the electrolyte with the alloy formation were found. The compositions of the alloys formed in the process were determined.

Molal activity coefficients of uranyl nitrate and nitric acid in mixed solutions were calculated on the basis of Mikulin’s equations. Analytical equations for calculating these quantities at different concentrations were obtained. These equations are compatible with published activity coefficients for binary solutions, which allows their use for calculating the equilibria in uranium extraction from nitric acid solutions.

A radiotracer technique has been used to achieve the carrier-free separation of ^115mIn from its parent ¹¹⁵Cd in hydrochloric acid medium on a chromatographic column packed with TODGA-impregnated silica gel. At 8 M HCl, both cations are bound at the chelating site, which results in maximum adsorption. When the column is treated with 2 M HCl, the daughter complex gets desorbed and is eluted from the column, whereas the parent remains undisturbed. Pure silica gel does not adsorb radioactivity under these conditions. The radiochemical purity of daughter was checked by its half-life (4.49 h).

To examine the possibility of disposal of irradiated graphite in ground near-surface repositories, the concentration and spatial distribution of radionuclides in the volume of irradiated graphite sleeves of industrial uranium–graphite reactors was studied, and the efficiency of decontamination using liquid reagent treatment methods was evaluated. The radionuclide distribution in the graphite volume is extremely heterogeneous on the 10–100 μm scale. The degree of decontamination using solutions with high acid concentrations and fluoride ions added does not exceed 16–25% for ¹⁴C and 15–19% for ³⁶Cl. Under these treatment conditions, no structural changes occur in graphite, and ¹⁴С bound with the graphite surface via sorption is removed. Significant differences in the efficiency of the reagent decontamination of irradiated graphite from various producers were revealed.