Radiochemistry最新文献

This work examines cast stone matrices (CSM) fabricated by comelting of basalt with both uranium-bearing perlite (M150 grade) and U₃O₈ at a temperature of 1623 K in air for 5 h. As a result of comelting of basalt with uranium-free M150 grade perlite, matrices are obtained containing glass and spinel as the major phases. When basalt is comelted with uranium-bearing perlite (M150 grade) CSMs are formed, the major phases of which are two Cr-spinels of different compositions, uranium-bearing glass, and dendritic aluminosilicate crystals. In the case of fusion of basalt and U₃O₈ taken in the initial weight ratio of 1 : 1, CSM is generated as the major phases containing UO₃, CaU₃O₁₀, (Al,Cr,Fe)₂U₂O₉, plagioclase, and uranium-bearing glass. The leaching rate of uranium from a basalt melt with uranium-bearing perlite (M150 grade, ~7.2 wt % U) and that of CSM made by comelting of basalt with U₃O₈, (~42.5 wt % U) after 28 days contact with water at 298 K was investigated.

Sorption of tributyl phosphate (TBP) on a polymer sorbent Polysorb-1 in aqueous solutions and sorption of butylphosphoric acids onto layered Mg-Al double oxides and hydroxides in a 70% solution of TBP in dodecane was studied. It was found that the Polysorb-1 is suitable polymer sorbent to remove TBP in aqueous solutions in the static and dynamic modes, and LDH-Mg-Al-CD-OH is suitable sorbent to remove acidic products of the decomposition and hydrolysis of TBP in TBP solutions in dodecane.

Centrifugal contactor rig trials of the partitioning flowsheet were carried out using simulated and real high level waste solutions obtained by reprocessing of WWER-100 spent nuclear fuel with burn-up of 47 MW day/t. 40% TBP in Isopar M was used as a solvent with magnesium nitrate as a salting-out agent. Complete removal of Cs, Sr, Zr, and Mo to raffinate was achieved. Rare earth elements, Am and Cm were totally concentrated in TPE and REE product. Comparison of the results of this work and previous trials with iron(III) nitrate as a salting-out agent [1] demonstrated that the use of magnesium nitrate instead of iron(III) nitrate resulted in higher decontamination factors of TPE and REE fraction from Cs (about 10 000) while in the case of iron(III) nitrate they are >7500.

This work examines cast stone matrices (CSM) fabricated by comelting basalt and Sr, Ln (Ce, Nd, Gd) oxides. Matrices containing glass and clinopyroxene as the major phases were established to be resulted from the comelting of basalt with SrO. Strontium partially replaces calcium in clinopyroxene, but mostly enriches the melt in contact with crystallizing clinopyroxene. When this melt cools, glass is formed containing up to 31 wt % SrO. The doping of basalt with oxides of rare earth elements (REE) M_xO_y: CeO₂, Nd₂O₃, Gd₂O₃ taken in a weight ratio of 4 : 1 and 2 : 1, results in the formation of CSM, the main permanent phases of which are glass and clinopyroxene. In addition, magnesioferrite can crystallize from a basaltic melt upon cooling, and phases of cerianite CeO₂ or britholite Ca(Nd,Gd)₄(SiO₄)₃O can crystallize depending on the basalt/M_xO_y weight ratio.

The content of ²³⁷Np, ^239,240Pu, and ²⁴¹Am in seawater, suspended matter, and bottom sediment cores of the Ussuri and Amur Bays, sampled in July 2021 and August 2022, was analyzed. The activity concentrations of ²³⁷Np, ^239,240Pu, and ²⁴¹Am in the water of Peter the Great Bay were determined for the first time and were found to be equal to (19–105) × 10^–3, 2.0–5.3, and 24.1–33.5 mBq/m³, respectively. The activity concentrations as well as the ²³⁹Pu/²⁴⁰Pu isotope ratio (⁓0.18) in the bottom sediments definitely indicate that global fallout is the main source of plutonium in the investigated territory. The sedimentation rates were determined for the Amur Bay (in the Razdolnaya River estuary), 0.9 mm/year, and for the Ussuri Bay, 4.1 mm/year. Actinide transfer coefficients were determined for Peter the Great Bay in the system dissolved forms (including colloids)–suspended matter–bottom sediment.

The method of fabrication of solid solution powder of uranium/plutonium (38%) oxides from the pulp of ammonium uranyl-plutonyl carbonate process (AUPuC) by microwave radiation in reducing and atmospheric environments was proposed and tested at the laboratory level. For research the pulp was prepared, obtained by co-precipitation of uranium and plutonium from nitrate solution (simulator for stripping product). The process consists of three main stages: oxidation of Pu(IV) to Pu(VI), precipitation, and conversion in a laboratory microwave unit. According to data of the X-ray diffraction analysis the powders synthesized in a reducing atmosphere and an atmospheric environment are a solid cubic solution (U_xPu_1–x)O₂ and (PuO₂, U₃O₈) mixed oxide, respectively. Scanning electron microscopy and electron probe microanalysis of the powder obtained in an atmospheric environment showed a fairly uniform distribution of U, Pu, and O in the solid phase.

Thermal analysis of non-irradiated and irradiated carbohydrazide solutions in 3 and 7 M HNO₃ to doses 100, 250, and 500 kGy was carried out. The onset temperature, time, and rate of the exothermic reaction were determined; the specific thermal effect of the reaction and self-heating value of the solution were calculated. Irradiation of the solution rises the onset temperature of the exothermic reaction and reduces its specific heat release. At radiation dose of 500 kGy, the main characteristics decrease by 70%, which is associated with the decomposition of carbohydrazide.

The decontaminating power that Vybor technical detergents (Vybor-K, Vybor-KS) produced by Kembrin Sole Proprietorship (Perm) exhibit in washing of facing and structural materials to remove α- and β-emitting nuclides in combination with ultrasonic treatment and without it was studied. The corrosion action of the detergent solutions on stainless and carbon steels was evaluated. The results of laboratory studies and semicommercial trials on washing of the process equipment of a radiochemical plant are reported.

The water pollution with Cs⁺ and Sr²⁺ radionuclides in the nuclear fuel cycle is a pressing environmental problem. The selective adsorption of radionuclides onto inorganic sorbents of zeolite structure, exhibiting the ion-sieve effect, is a promising procedure for the treatment of the liquid radioactive waste formed. Titanosilicate of the CST structural type, corresponding to the formula Na_1.64H_0.36Ti₂O₃SiO₄(H₂O)_1.84, was prepared by hydrothermal synthesis performed at 190°С and a pressure of 1.3 MPa for 24 h. This sorbent allows efficient removal of the Cs⁺ and Sr²⁺ cations from liquid media. The sorption exchange capacity q_eq is 1.58 mg-equiv/g for Cs⁺ and 2.56 mg-equiv/g for Sr²⁺. Preliminary oxidation of Ti³⁺ to Ti⁴⁺ with H₂O₂ increases the sorption capacity for Cs⁺ and Sr²⁺. The phase composition, elemental composition, specific surface area, and pore size of the materials synthesized were determined. The titanosilicates obtained can be used as sorbents for liquid radioactive waste treatment.

The characterization system and automated database on vitrified high-level waste (VHLW) accumulated at the Mayak Production Association were developed for assessing and substantiating the waste disposal safety. All the available analytical data on VHLW are accumulated in the database. Calculations based on the developed integral algorithm for estimating the content of radiologically significant radionuclides (RSRNs) in containers with VHLW were made.