Radiochemistry最新文献

The mechanical strength and chemical stability of the radioactive cement waste forms obtained by solidification of iron hydroxide slurries containing α-emitters were assessed with the aim to evaluate the effect of elevated temperatures in the range from 150 to 250°С. The dehydration of the waste forms in this temperature range exerts no significant negative effect on the extent of fixation of the radionuclides in the matrices and on the strength characteristics of the waste forms. The water loss on heating to 150°C is 11–13%, and further heating to 250°С leads to no more than 10% additional water loss.

At the Khlopin Radium Institute, during the 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 was stored. To solidify this solution, a batch process using Gubka (sponge) porous inorganic material (PIM) was developed and implemented. 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 after sealing by welding were delivered to the long-time storage of the RosRAO Branch in Sosnovy Bor.

Suggestions are made for potentially promising coolants for molten salt reactors from a mixture of six lithium, sodium, and potassium fluoride and chloride salts having high entropy of mixing. These compositions, which contain less lithium salts, should have higher thermodynamic stability than FLiNaK or FLiBe because of their high entropy. The chemical formula of the maximum high-entropy solution, Li_1/6Na_1/6K_1/6F_1/4Cl_1/4, may result from mixing the variety of alkali halides like MX (M = Li, Na, K and X = F, Cl) taken in an equimolar ratio. Molecular dynamic estimations of the density, heat conductivity, and viscosity demonstrate reasonable values of these properties between those of the fluorides and chlorides.

The characteristics of an extraction-chromatographic sorbent for lanthanide separation, prepared by impregnation of Prefilter resin with 2-ethylhexyl hydrogen 2-ethylhexylphosphonate, were studied. As demonstrated by the example of the Yb/Lu separation, in sorption from nitric acid solutions ([HNO₃] < 4 M) under batch conditions, the logarithm of the lanthanide distribution ratio is a linear function of the solution acidity. In column experiments, the flow rate of the mobile phase exerts the strong influence on the Yb/Lu separation efficiency. The temperature and sorbent particle size exert weaker influence. The characteristics of the suggested sorbent are identical to those of its analog, LN2 sorbent (EiChrom, USA). The sorbent based on Prefilter resin ensures lower, compared to LN2, extractant leaching.

Conditions were determined for preparing a suspension of detonation synthesis nanodiamonds (NDs) with immobilized scandium in solutions, meeting the requirements to solutions for intravenous administration of radiopharmaceuticals based on the medicinal isotopes ⁴⁴Sc and ⁴⁷Sc. The possibility of the quantitative binding of scandium with ND samples in isotonic solutions having the required pH and containing the minimal ND amount was demonstrated. The Freundlich and Langmuir adsorption isotherm parameters and ΔG of adsorption were determined for the most promising ND sample under the optimum conditions. The conditions found for preparing NDs with immobilized scandium isotopes will allow in vivo studies in the future.

The behavior of a number of REE and Am(III) during their extraction from nitric acid solutions with iron and manganese dibutyl phosphoric acid (HDBP) compounds in various diluents was studied. An increase in the concentration of iron and manganese in the organic phase leads to an increase in the REE distribution ratios and, in some cases, to a noticeable change in the element separation factors. The element separation factors significantly differ depending on the diluent. The increase in the separation factors of pairs of elements can reach high 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 a factor of 7. The use of decalin as a diluent leads in most cases to a maximum increase in the REE distribution ratios. In the system with an o-nitrotoluene (ONT) diluent, 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.

Thermochemical denitration of nitric acid solutions of U and Pu to obtain mixed uranium–plutonium formates was performed. It was followed by the reduction of the mixture in Ar–H₂ (5 vol %) to obtain a powder of mixed U–Pu dioxide. The products obtained were studied and characterized by X-ray diffraction, X-ray fluorescence analysis, and Raman spectroscopy. The analysis of the powder revealed the formation of a (U,Pu)O₂ solid solution containing 5 wt % Pu and of UO₂. After the powder treatment by vortex mixing, high-density pellets of homogeneous structure were fabricated.

The extraction of ytterbium from nitric acid solutions with solutions of 2-ethylhexyl hydrogen 2-ethylhexylphosphonate (HEH[EHP]) in hexane was studied. The HEH[EHP] concentration was varied from 0.5 to 2.0 M; acidity, from 0.1 to 2.0 M; and lanthanide concentration, from 0.1 to 5 g/L. The dependences of the ytterbium distribution ratio on the solution acidity are described by equations of the type log D = a log[H⁺] + b, where the coefficient a depends on the extractant and lanthanide concentrations and varies from –1.26 to –3.0. Its variation is probably caused by the occurrence of the extraction by both cation-exchange and solvation mechanism. The model describing the dependence of the ytterbium distribution ratio on its concentration in the aqueous phase at different concentrations of the extractant and acid was suggested. The data predicted by the model reasonably agree with the experimental data.

The possibility of using new anion-exchange resins AM-4VP, AM_pu, AMP-p, AM-p, and AM-2B produced by Smoly Group of Enterprises for plutonium recovery from nitric acid process solutions was examined. The physicochemical characteristics of the resins, the thorium distribution coefficients as functions of the nitric acid concentration, and the static exchange capacities of the resins were determined. The plutonium recovery from process solutions was studied in column experiments. The physicochemical properties and sorption ability of the anion-exchange resins were compared to those of the previously used VP-1Ap resin. AM-4VP resin shows promise for plutonium recovery from nitric acid process solutions.

The efficiency of the extraction of lanthanide(III), americium(III), and thorium(IV) ions from nitric acid solutions with tetraoctyldiglycolamide significantly increases in the presence of an ionic liquid, didecylammonium di-2-ethylhexyl sulfosuccinate, in the organic phase. The effect of the aqueous phase acidity on the distribution ratios of the extracted elements was considered, and the stoichiometry of the extractable complexes was determined.