Vol 61, No 2 (2019)

Actinide(VI) complexes with succinate anions [PuO₂(succ)(H₂O)] and Cs₂[(AnO₂)₂(succ)₃]·H₂O (An = U, Np, Pu), where succ = [C₄H₄O₄]^{2 −}, were synthesized and studied by single crystal X-ray diffraction. The compound [PuO₂(succ)(H₂O)] is isostructural with [UO₂(succ)(H₂O)] [1] and forms a three-dimensional electrically neutral framework in the crystal. The equatorial plane of the Pu(VI) pentagonal bipyramid is constituted by the O atoms of four [C₄H₄O₄]²⁻ anions and one water molecule. The [C₄H₄O₄]²⁻ anions are bridging; each anion is bound in the monodentate fashion with four Pu atoms. The structure of the complexes Cs₂[(AnO₂)₂(succ)₃]·H₂O is based on an anionic framework. The equatorial plane of the An(VI) hexagonal bipyramid is constituted by O atoms of three [C₄H₄O₄]²⁻ anions, with each anion acting as a chelating and bridging ligand binding two An(VI) atoms. The electronic absorption spectra of [PuO₂(succ)(H₂O)] and Cs₂[(PuO₂)₂(succ)₃]·H₂O were measured.

The extraction of microamounts of REE(III), U(VI), and Th(IV) from perchlorate solutions with solutions of tetraphenyl(o-oxyphenylenemethylene)diphosphine dioxide (I) in 1,2-dichloroethane was studied. The stoichiometry of the extractable complexes was determined, and the influence of the aqueous phase composition on the efficiency and selectivity of the extraction of U(VI), Th(IV), and REE(III) into the organic phase was analyzed. In going from nitric to perchloric acid solutions, the efficiency of the extraction of REE(III), U(VI), and Th(IV) with solutions of I considerably decreases, whereas the selectivity of the U(VI)/REE(III) separation increases.

Dowex 1×4-trioctylphosphine oxide powder (DTP) was prepared, characterized, and studied as an adsorbent for the adsorption of Th(IV) from aqueous solutions. The adsorption of Th(IV) strongly depends on pH. The adsorption follows the pseudo-second-order kinetics, and the adsorption isotherms agree well with the Langmuir model with a maximum adsorption capacity of 132.1 mg g⁻¹.

The use of fission products present in relatively large amount in the spent fuel itself for preparing compounds for long-term storage or disposal of transuranium elements is suggested. One of such fission products is Pd whose content in NPP fuel is relatively high (apparently, natural Pd cannot be used because of its high cost and short supply). A distinctive feature of Pd is its ability to dissolve in HNO₃. Therefore, if there will be a need for recovering TPE from Pd-based materials, it will be sufficient to dissolve these materials with the subsequent recovery of the required elements (e.g., Am, Cm). The technical solutions allowing the use of reactor Pd as a material for immobilization of transuranium elements are analyzed.

The behavior of Cl, Ca, Be, Ni, and Cs radionuclides in the course of heating of radioactive graphite in steam was studied by thermodynamic modeling. Complete thermodynamic analysis at temperatures in the interval from 373 to 3273 K was performed using the TERRA program with the aim of determining the possible composition of the gas phase. The modeling shows that chlorine occurs in the form of gaseous HCl in the temperature interval from 873 to 1973 K and in the form of gaseous HCl and Cl at temperatures from 1973 to 3273 K. Calcium in the temperature range from 1973 to 3273 K occurs in the form of gaseous Ca(OH)₂, Ca, and CaOH and ionized CaOH⁺ and Ca⁺. Beryllium in the temperature interval from 1873 to 3273 K occurs in the form of gaseous Be(OH)₂, BeOH, Be, and BeOH. Nickel at temperatures from 1673 to 2173 K occurs in the form of gaseous NiH, Ni(OH)₂, NiOH, and Ni, and at temperatures from 2173 to 3273 K, in the form of gaseous NiH, NiOH, and Ni. Cesium at temperatures from 973 to 1473 K occurs in the form of gaseous CsCl and CsOH and of ionized Cs⁺, and at temperatures from 1473 to 3273 K, in the form of ionized Cs⁺. The main reactions within separate phases and between the condensed and gas phases were determined, and their equilibrium constants were calculated.

The behavior of salts (chlorides, nitrates, sulfates, phosphates, borates, ferri- and ferrocyanides) of various alkali metals (Li, Na, K, Cs) and ammonium in the course of nanofiltration (NF) of their aqueous solutions was studied. The NF polymer membrane at high salt concentrations (>30 g dm⁻³) retains alkali metal and ammonium ions to a low extent (1–5%). At lower salt concentrations, the retaining ability of the NF membrane increases. In nanofiltration of solutions of Na and K salts with anions of different charge, the retaining ability of the NF membrane increases with an increase in the anion charge. The pH dependence of the ability of the NF membrane to retain sodium nitrate was studied. This parameter was constant at pH in the ranges 2.0–5.5 and 7.5–13.0, but at pH in the range 5.5–7.5 the retaining ability decreased approximately by half. Experiments on retention of sodium borates of various compositions showed that the solutions containing bulky polynuclear anions consisting of 4–5 boron atoms were retained by the NF membrane with 45–50% efficiency, whereas neutral boric acid molecules were not noticeably retained by the membrane. Thus, nanofiltration can be used for selective separation of inactive alkali metal salts from radioactive components of liquid radioactive waste.

The ability of inorganic hydroxide sorbents Termoxid-5 (T-5) and Termoxid-39 (T-39) heat-treated at temperatures from 100 to 950°C to take up radionuclides of the ²²⁵Ac subfamily was examined in a wide range of solution acidities and salt compositions. T-5 and T-39 are principally suitable for the development of both direct and inverse ²²⁵Ac/²¹³Bi generators with the activity of hundreds of millicuries of ²²⁵Ac.

Total synthesis, quality control, and preclinical evaluation of [¹¹¹In]-DOTA-Triptorelin ([¹¹¹In]-DOTA-TRP) for diagnostic SPECT imaging have been made. For ¹¹¹In labeling, the peptide synthesis was followed by conjugation with DOTA using pSCN-Bn-DOTA. The synthesized conjugate prepared at optimized conditions was purified with a reversed-phase semipreparative column using gradient of water: acetonitrile mixture. The molecular mass was confirmed by mass spectroscopy. The conjugated Triptorelin was labeled with 500–550 MBq of ¹¹¹In chloride (in 0.2 M HCl). The radiochemical purity of the product prepared under optimized conditions was about 98% (RTLC) and >95% (HPLC). The serum stability of the tracer was determined up to 24 h. The ¹¹¹In-peptide chelate exhibits high stability. The binding affinity of Triptorelin peptide was determined in a binding assay for both human and rat GnRH receptors. For in vivo studies, ¹¹¹In-peptide was injected intravenously via the tail vein to rats. In vitro radioligand binding assays were performed with GnRHR-expressing human cell lines using [¹²⁵I]Triptorelin as the standard radioligand. The receptor affinity of the new radioligand was IC₅₀ = 0.35 ± 0.08 nM vs. 0.13±0.01 nM for Triptorelin, and the internalization efficiency was 3.4 ± 0.7% at 1 h and 11.8 ± 1.9% at 4 h.

Labetalol was labeled with ¹⁸⁸Re. The reaction conditions (amounts of stannous chloride and substrate, pH, time) were optimized, and the radiochemical yield as high as 95 ± 0.4% was reached. Biodistribution in mice was studied. ¹⁸⁸Re-Labetalol showed excellent initial heart uptake and good retention. The heart/liver ratios were 5.16, 2.70, and 2.15 at 30, 60, and 120 min post injection, respectively.

The efficiency of the conservation of the radioactive waste (RW) repository at the former radium extraction plant in Komi Republic was confirmed by comparative analysis of the dynamics of the ²²⁶Ra release into the river and groundwater. High mineralization of the surface and ground waters on the territory of the RW repository favored the dissolution of contaminant compounds present in RW. Owing to the supply of ²²⁶Ra dissolved in water and incorporated in suspended particles of 0.45–3.5 and >3.5 µm size, the activity concentration of ²²⁶Ra in water bodies under the impact of the plant increased by a factor of 1.3–3 relative to the background values. The RW isolation by making physical and geochemical (based on bentonite clays) barriers on the radionuclide migration pathway reduced the release of ²²⁶Ra into the hydrographic network. After the RW conservation, a tendency toward improvement of the groundwater quality with respect to the content of ²²⁶Ra and its chemical analogs is observed in the region of the study, which is confirmed by the results of the ecotoxicological evaluation of drainage waters from the object. Increased content of ²²⁶Ra is observed on the sites of discharge of melioration trenches from other industrial sites of the plant into the river.