[en] A study was made on the dependence of the rate of Pu⁶⁺ macroconcentration reduction to Pu⁴⁺ (2-40 g/l) when bubbling mixture of gaseous nitrogen oxides (oxide and dioxide) on nitric acid concentration (3-8 mol/l, initial Pu⁶⁺ content (20-95 %) total plutonium concentration in processable solution temperature (50-80 deg C), the rate of gaseous nitrogen oxides and composition of the given gaseous mixture, as well as the presence of uranium (6) and stable isotopes of some fission products in processable solution. Empirical kinetic equation for the rate of studied process enabling to calculate the apparent rate constants of gas-chemical reduction of Pu⁶⁺ to Pu⁴⁺ using experimental data is suggested. Applicability of derived equation for decribing the studied process under steady conditions during regeneration of NPP spent fuel is shown

[en] Method for decreasing plutonium losses during Pu(6) to Pu(4) reduction by nitrogen oxides in nitric acid solutions at temperatures above 60 deg C is suggested. Nitric acid solution (4-5 mol/l), saturated preliminary by nitrogen oxides at 22-25 deg C is used as source of nitrogen oxides at that. This results to sufficient decrease of plutonium losses with aerosol and 5-30 time decrease of the flow-rate of gaseous nitrogen oxides. The method can be used for reprocessing of plutonium-containing materials and for reprocessing of NPP spent fuel in particular

[en] By means of catalytic hydroisomerization of the n-paraffinic raw material in a reactor using alumino-platinum catalysts, there was attained a 45-90% degree of conversion of n-paraffins into branched iso-paraffins with mono- and dimethyl structure. From a batch of extensively isomerized n-paraffins, by carrying out the operations of distillation of the light (benzine) fraction, dearomatization, de-n-paraffinization and fractional distillation on a rectification column, isoparaffinic (99%) concentrates were obtained with a constant molecular weight, from iso-C₁₀ to isoC₁₅. The solubility of plutonium and thorium nitrates in 30% solutions of TBP in iso-paraffins (mixtures of iso-paraffins with the same number of C-atoms) increases with decrease in the molecular weight of the iso-paraffin; a system with a 30% TBP in a mixture of iso-decanes practically does not stratify (∼104 g Pu/liter, 22-25 degree C). Nevertheless, a twofold increase (compared with NP) of the maximally permissible (up to the formation of the third phase) concentration, is attained when iso-paraffins are introduced into NP with a similar molecular composition in a 1:1 ratio. With respect to the main requirements demanded of diluents for radiochemical extractional operations, such as density, viscosity, boiling point, flash point, and freezing point, the chemical stability and radiation resistance, content of radioruthenium and radiozirconium, rate of stratification of two-phase systems, the synthetic iso-paraffin-containing solvents are as suitable as n-paraffins