Vol 58, No 2 (2016)

New Np(VI) and Pu(VI) dimolybdates Rb₂NpO₂(MoO₄)₂·H₂O (I), Cs₂NpO₂(MoO₄)₂·H₂O (II), Cs₂PuO₂(MoO₄)₂·H₂O (III), and Rb₂PuO₂(MoO₄)₂·H₂O (IV) were synthesized under hydrothermal conditions. The crystal structures of the compounds were determined, and their absorption spectra in the UV, visible, and IR ranges were measured. The compounds crystallize in the monoclinic system. Their crystal structure is based on [AnO₂(MoO₄)₂]_n^2n– anionic layers (An = Np, Pu) formed by (AnO₂)O₅ pentagonal bipyramids and MoO₄ tetrahedra, sharing common vertices. Each An atom in the layer is bonded to other five An atoms via MoO₄ tetrahedra with the formation of a 4343² network. The effect of the ionic radius of the outer-sphere cation on the parameters of the crystal structure and features of the absorption spectra is discussed.

Previously unknown sodium uranate of the composition Na₂U₂O₇·6H₂O was synthesized by precipitation from solution under hydrothermal conditions at 200°С. The composition and structure of this compound were determined by chemical analysis, X-ray diffraction, IR spectroscopy, and thermal analysis. The dehydration and thermal decomposition of the compound were studied.

Gas-phase conversion of U₃O₈, MoO₃, SrO, ZrO₂, and their mechanical mixtures into water-soluble compounds in an HNO₃ (vapor)–air atmosphere was studied. In the course of the gas-phase conversion, U₃O₈ and SrO transform into water-soluble compounds (nitrates, hydroxynitrates), whereas MoO₃ and ZrO₂ undergo no changes. The principal possibility of separating U from Mo and Zr by gas-phase conversion of the oxides in the HNO₃ (vapor)–air atmosphere was demonstrated.

The database on the influence of concentrations of salting-out agents with different cation valence (Li⁺, Na⁺, K⁺, Cs⁺, NH₄⁺, Mg2+, Ca²⁺, Cu²⁺, Zn²⁺, Al³⁺, Fe³⁺, La³⁺, Pu⁴⁺, UO₂²⁺ nitrates) and of H₂SO₄ on the HNO₃ distribution between liquid and vapor at atmospheric pressure was verified and expanded by performing equilibrium evaporation experiments in an evaporator without reflux with circulation of the bottoms. This equilibrium can be described by the equation \(\log {\kern 1pt} {\alpha _H} = - 2.35 + 2\log \;{X_{\Sigma N{O_3}}}\) (where \({X_{\Sigma N{O_3}}}\) is the total concentration of nitrate ions in aqueous solution), taking into account partial binding of water due to hydration of the salting-out agent and apparent hydrolysis of polyvalent cations, and also incomplete dissociation of sulfuric acid. The suggested model is valid at \({X_{\Sigma N{O_3}}}\) from 3 to 16 M (azeotrope); at \({X_{\Sigma N{O_3}}}{\text{ < }}\;3\), Raoult’s law is observed (α_H = const), which is confirmed by a number of examples. In this model, the additivity of the properties of the salting- out agents, taking into account the concentration of “free” water, is assumed, which allows calculation of the composition of the bottoms and distillate when evaporating waste of any composition from radiochemical plants.

The possibility of measuring the ¹³⁷Cs concentration in seawater by its own β-radiation using liquid scintillation spectrometry after preliminary sorption on cellulose fiber impregnated with copper(II) ferrocyanide was studied. This measurement procedure allows the ¹³⁷Cs detection efficiency to be increased to 50% and the sample volume to be decreased from 1000 (as in γ-ray spectrometry) to 50 L and less.

The paper deals with the preparation and quality control of ³²P-labeled albumin particles used in therapy of inoperable solid tumors with remarkable vascularization. A process was developed for preparing ³²P-labeled albumin particles by combining biocompatible human serum albumin and [³²P]phosphoric acid salt. Factors affecting the process were investigated, and labeling conditions were optimized. The size distribution, shape, and radiochemical stability of particles were determined. The biodistribution of the particles was examined after intravenous injection in Wistar rats. The in vivo stability and distribution of the radioactive particles in mice were studied with different administration methods. Optical microscopic examinations revealed that the particles had a narrow size distribution (20–50 μm) after sterilization and dispersion in a mixture of normal saline and human serum albumin or in Tween 80 solution. The particles prepared had high radiochemical stability and 99% purity. Experiments on the distribution in animals showed that high radioactivity was accumulated in the lungs as a vascular tumor model.

α-Radiolysis of tributyl phosphate in Sintin n-paraffin diluent in equilibrium with HNO₃ solutions at single “internal” irradiation from the extracted ²³⁸Pu was studied. The radiation-chemical yields (molecules/100 eV) of butyl hydrogen phosphates (BHP), carboxylic acids, carbonyl compounds, and nitro compounds upon irradiation of 20% TBP in the treated Sintin in equilibrium with 3 M HNO₃ were 0.4 (at dibutyl hydrogen phosphate to monobutyl dihydrogen phosphate ratio HDBP: H₂MBP = 4.3), 1.4, 0.2–0.3, and 0.2–0.3, respectively. The degradation and oxidation processes occur more deeply than under γ-irradiation. A simple volumetric method for determining carboxylic acids in the extract was developed. In the course of irradiation, the Pu(IV) oxidation state in the extract does not change, and its retention is due to the interaction with BHP at the ratio BHP: Pu = 2 in stripping with 0.02 M HNO3 and BHP: Pu = 4 in stripping with Fe(II). The retention can be eliminated by the displacing action of Np(IV).

Borobasalt systems were studied as host materials for incorporation of radioactive waste from pyroelectrochemical technology. For all the examined compositions, the leach rates are of the order of 10^–7 g cm^–2 day^–1, which is quite acceptable for radionuclide immobilization. The synthesis temperature ensuring formation of homogeneous glasses is about 1250°С for all the examined compositions. The host material is capable to incorporate up to 40 wt % phosphate wastes, which seems quite sufficient from the viewpoint of technology. The system is only weakly sensitive to variations of the boric anhydride content.