Vol 66, No 6 (2024)

The results of thermochemical denitration of U and Pu nitric acid solutions to obtain mixed salts of uranium-plutonium formates and subsequent reduction in Ar–H₂ (5 vol %) of the mixture to obtain a powder of mixed U–Pu dioxide are presented. The obtained products were investigated and characterized by X-ray diffraction, fluorescence, and Raman spectroscopy. According to the analysis results, a (U,Pu)O₂ solid solution containing 5 wt % Pu was obtained, and UO₂ was identified in the powder. After processing the powder by vortex mixing, pellets of high density with a homogeneous structure were produced.

The behavior of a number of REE and Am(III) during their extraction from nitric acid solutions with iron and manganese compounds with dibutyl phosphoric acid (HDBP) in various solvents was studied. It was shown for the first time that, with an increase in the concentration of iron and manganese in the organic phase, an increase in the REE distribution coefficients and, in some cases, a noticeable change in the element separation factors are observed. There is a significant difference in the element separation factors in different solvents. The increase in the separation factors of pairs of elements can reach significant values. For example, the Er/Dy separation factor in toluene increases by a factor of 5, and the Dy/Tb separation factor in chloroform, by 7. The use of decalin as a solvent leads in most cases to a maximum increase in the REE distribution coefficients. In the system with an o-nitrotoluene (ONT) solvent, at a certain ratio of HDBP to Fe(III), the separation factors of americium and REE (except cerium) are high enough to allow their separation. The influence of the transition metal and solvent on the distribution and separation of REE is discussed.

The extraction of ytterbium with solutions of mono(2-ethylhexyl) ether of 2-ethylhexylphosphonic acid (HEH[EHP]) in hexane from nitric acid solutions at an HEH[EHP] concentration of 0.5–2.0 mol/L, acidity of 0.1–2.0 mol/L, and lanthanide concentration from 0.1 to 5 g/L was studied. It is shown that the dependences of the ytterbium distribution coefficients on the acidity of the solution are described by expressions such as logD = alog[H⁺] + b, with the value of the coefficient a depending on the extractant and lanthanide concentrations and varying in the range from –1.26 to –3.0. The probable cause is extraction by both cation-exchange and solvation mechanisms. A model describing the dependence of the ytterbium distribution coefficient on its concentration in the aqueous phase at various extractant concentrations and acidities is proposed. The model reasonably agrees with the experimental data.

In the Khlopin Radium Institute, during development of extractive partitioning of the liquid high level radioactive waste (HLW), a strip solution containing up to 6.0 × 10¹¹ Bq/dm³ (16.3 Ci/dm³) of ¹³⁷Cs in the form of a nitric acid solution was collected and temporary stored. To solidify this solution, a batch process using «Gubka^» porous inorganic material (PIM) was developed and performed. Since that time, about 18 dm³ of HLW was solidified into 12 sets of «Gubka^», reducing the liquid HLW volume by a factor of about 50. «Gubka» sets were placed into special containers, which were sent to the site of the RosRAO Branch in Sosnovy Bor after sealing by welding.

The possibility of introducing deuterium into dopaquine, a compound consisting of quinone and dopamine fragments, has been studied. It has been established that isotope exchange can be carried out with deuterated water in the presence of trifluoroacetic acid (TFA) and HCl. Optimal conditions are the use of TFA at a temperature of 80°С. To activate isotope exchange, catalysts based on iridium or palladium (5%Pd/Al₂O₃, cycloocta-1,5-dienylyridium(I) 1,1,1,5,5,5-hexafluoropentane-2,4-dionate) were added to the reaction mixture in addition to the acid component. The preparative synthesis of [D]dopaquine was carried out by isotope exchange with deuterated water (D₂O : TFA 5 : 1, 80°С, 3 h). [D]Dopaquine was obtained in 20% yield of with the deuterium content in the interval 1.2–1.4 atoms per molecule. The deuterium content in the dopamine fragment is 1.2–1.3 atoms per molecule. The quinone fragment contained approximately 4–7% of the isotope.