Vol 59, No 1 (2017)

Crystal-chemical analysis of actinide baric polymorphs was performed on the basis of Voronoi–Dirichlet (VD) tessellation. The second moment of inertia of the VD polyhedron (G₃) and the displacement of the atom nucleus from the center of gravity of its VD polyhedron (D_A) were suggested as descriptors acting as criteria for revealing 5f interactions between the actinide atoms. Pressure elevation is accompanied, as a rule, by an increase in G₃ for Th, Pa, Am, Cm, Bk, and Cf, whereas for U and Pu it leads to a decrease in G₃. Topologically equivalent flat (Th-hP) or corrugated (Pa-hP, α-U, Вk-III) 4⁴ networks are formed in these high-pressure phases owing to the shortest (covalent) bonds between the actinide atoms, whereas a diamond-like framework is formed in the structures of An-III or An-IV (An = Am, Cm, Cf) and Cm-V, and Pu₄ molecules are formed in hexagonal Pu-hP.

The electrochemical behavior of Tc–Ru alloys (Ru content, at. %: 3.2, 5.2, 20.1, 24.7) in 1 M HNO₃ was studied. The transpassivation potentials (E_tp) of Tc–Ru alloys were determined by linear voltammetry. The results show that the transpassivation potentials of the alloys increase with the Ru content. To understand the dissolution mechanism, electrolysis experiments at 1.2 V vs. Ag/AgCl were performed; the corrosion products of the alloys were characterized in solution by UV-visible spectroscopy and electrospray ionization mass spectrometry (ESI-MS). For Ru, a polymeric Ru(IV) species was detected, while for Tc the speciation was dominated by TcO₄^–.

As shown by thermodynamic modeling, accumulation of fission products in the course of irradiation of mixed uranium–plutonium nitride containing 0.25 wt % C impurity leads to the formation of a multicomponent carbonitride solid solution containing U, Pu, Am, Np, Zr, Y, lanthanides, and also separate carbide (UMoC₂, U₂RuC₂, URu₃C_0,7, BaC₂, SrC₂) and nitride (U₂N₃) phases and intermetallic compounds U(Ru, Rh, Pd)₃. The β⁻-decay of metallic radionuclides in separate carbide phases of spent nuclear fuel leads to changes in their chemical compositions. The transformation kinetics of separate dicarbide (⁸⁹SrC₂ → ⁸⁹YC₂, ⁹⁰SrC₂ → ⁹⁰YC₂ → ⁹⁰ZrC + C, ¹⁴⁰BaC₂ → ¹⁴⁰LaC₂ → ¹⁴⁰CeC₂) and complex carbide (U⁹⁹MoC₂ → UC₂ + ⁹⁹Tc) phases was calculated.

Sorption of tracer amounts of ¹³⁷Cs and ⁹⁰Sr radionuclides from model solutions of various compositions onto synthetic titanosilicates, framework ivanyukite and layered SL3, both synthesized at the Center for Nanomaterials Science, Kola Scientific Center, Russian Academy of Sciences, was studied. Synthetic ivanyukite and titanosilicate SL3 well compete with Termoxid-25 ferrocyanide sorbent in the ability to take up cesium from neutral NaNO₃ solutions and from a simulated solution of bottom residue from a nuclear power plant with RBMK reactors. The maximal sorption of ¹³⁷Cs onto ivanyukite is observed at pH 6–7. The dependence of the ¹³⁷Cs distribution coefficient (K_d) on ivanyukite on the concentration of sodium and potassium ions in the solution was studied. Potassium ions affect the cesium sorption more strongly than sodium ions do. In the ability to take up ⁹⁰Sr, synthetic ivanyukite well competes with synthetic zeolite of type A and with the sorbent based on modified manganese dioxide. The dependences of K_d of ⁹⁰Sr on the concentrations of the Na⁺ and Ca²⁺ ions in the solution were determined. Calcium ions affect the strontium sorption more strongly than sodium ions do. Ivanyukite and SL3 show promise as sorbents for removing cesium and strontium radionuclides from multicomponent salt solutions.

Sorption of CH₃¹³¹I and ¹³¹I₂ from water vapor–air medium onto SiO₂–C (2 wt %) composite material and a mixture of SKT-3I with SiO₂–Cu⁰ (10 wt %) was studied. SKT-3I shows high performance in sorption of ¹³¹I₂ and CH₃¹³¹I. The degree of localization of ¹³¹I₂ and CH₃¹³¹I exceeds 99.99% at ~60°С and gas phase–sorbent contact time τ of ~0.45 s. The degree of sorption of ¹³¹I₂ and CH₃¹³¹I onto the SiO₂–C (2 wt %) composite material under similar conditions does not exceed ~87 and ~8%, respectively. Experiments on ¹³¹I₂ and CH₃¹³¹I sorption onto mechanical mixtures of SiO₂–Cu⁰ and SKT-3I in the weight ratio varied from 1: 4 to 1: 1 showed that the degree of the ¹³¹I₂ and CH₃¹³¹I sorption at ~60°С and τ ~0.45 s exceeded 99.95 and 99.0%, respectively. The scheme of layer-by-layer arrangement of SiO₂–Cu⁰ and SKT-3I in the column was examined. It shows promise for use in AUI-1500VM filters in ventilation systems of nuclear power plants.

Timonacic acid (TCA) was successfully labeled with ^99mTc. The influence exerted on the reaction by the substrate and reducing agent concentrations, pH of the reaction mixture, and reaction time was examined, and in vitro stability of ^99mTc-TCA was evaluated. The maximum labeling yield was 98.5 ± 0.6%. The complex was stable throughout the working period (6 h). A study of in-vivo biodistribution in mice showed that the maximum uptake of ^99mTc-TCA in the liver was 22.3 ± 0.3% of the injected activity per gram of the tissue or organ (% ID/g) at 30 min post injection. The clearance from the mice appeared to proceed via the circulation mainly through the kidneys and urine (approximately 56% of the injected dose at 1 h after injection). The liver uptake of ^99mTc-TCA is higher than that of ^99mTc-UDCA (ursodeoxycholic acid); therefore, ^99mTc-TCA shows more promise for liver SPECT.

The radon exhalation rate from soil and building materials collected from the Hassan district of southern India was studied by the sealed can technique. The surface exhalation rates of the building materials were found to vary from 13.07 ± 0.19 to 430 ± 9 mBq m^–2 h^–1 with a mean value of 141 ± 4 mBq m^–2 h^–1. The surface exhalation rates of the soil samples were found to vary from 36.5 ± 0.8 mBq m^–2 h^–1 to 376 ± 7 mBq m^–2 h^–1 with a mean value of 140 ± 4 mBq m^–2 h^–1. Good positive correlation was observed between the effective radium content and radon exhalation rate for both soil and building materials. Annual effective dose and α-index have also been estimated for the population of the region.