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[en] The authors measure the oxidation potential of the Bk(IV)-Bk(III) pair in H3PO4 solutions by a direct spectroelectrchemical method. When the phosphoric acid concentration is increased from 3 to 10 M, its value decreases from 1.123 to 1.065 V (with respect to a normal hydrogen electrode)

[en] The electrochemical reduction of americium, thulium, erbium, samarium and europium has been investigated in acetonitrile. Am, Tm and Er, like Eu and Sm, have been suggested to be converted to the divalent state during the reduction. The divalent cations are oxidized at different rates by water that is present in the solvent to form the hydrolyzed trivalent ions. Their reduction is completed by precipitation of basic salts. Stability of the divalent cations to oxidation by water determines the extent of the transference of these elements to the amalgam and to the basic salt precipitate. (author)

[en] The pyrochlore-type matrices containing up to 10% wt. of U, Np, Pu and Am oxides were produced by self-propagating high-temperature synthesis (SHS) proposed as a method of preparation of the ceramic mineral-like matrices for immobilization of actinides. It was shown that basically the matrices consist of a phase of yttrium titanate having pyrochlore structure with actinides incorporated isomorphically. Stability of these matrices relative to hydrothermal leaching of the actinides at 90 C was studied: the leaching rate does not exceed 1 * 10^-7 g/(cm² day). (authors)

[en] It has been found for the first time that diphenyl[dibutylcarbamoylmethyl]pho sphine oxide (DPDBCMPO) is able to extract effectively actinide and rare-earth elements from acidic solutions, without its preliminary dissolution in an organic solvent. DPDBCMPO, taken initially as a solid powder, is established to form an oily liquid complex DPDBCMPO.HNO₃.nH₂O ('liquid reagent') on contact with 4 M HNO₃. Behavior of Pr(III), Np, Pu and Am in various oxidation states in the process of their extraction by 'liquid reagent' is studied. It has been shown that distribution coefficients of the elements extracted by the 'liquid reagent' ('LR') are greater than is observed in conventional solvent extraction ('SE'). The use of aluminum phosphate matrix, containing DPDBCMPO, for isolation of the actinide and rare-earth elements and for their subsequent vitrification is suggested. (orig.)

[en] Dissolution of individual actinide oxides (Th, U, Pu, Np), or their mechanical mixtures, as well as of solid solutions U-Pu, U-Np, U-Am and U-Pu-Eu oxides in supercritical fluid carbon dioxide (SF-CO₂) containing the complex of tri-n-butyl phosphate (TBP) with nitric acid (TBP-HNO₃) has been investigated. The effect of the calcination temperature of solid solutions of dioxides on the separation of actinides during supercritical fluid extraction (SFE) has been studied as well. It was shown for the first time that milligram amounts of uranium dioxide could be quantitatively dissolved in (SF-CO₂) containing the TBP-HNO₃ complex and efficiently separated from Pu, Np, and Th during SFE of mechanical mixture of these oxides. On the contrary, both U and Pu are quantitatively dissolved in SF-CO₂-TBP-HNO₃ during SFE from solid solutions of U-Pu dioxide. An increase of the calcination temperature of the mixed U(IV)-Pu(IV) dioxide from 850 to 1200 C has no influence on the relative extraction yield of these actinides during SFE. (authors)

[en] It has been found for the first time that diphenyl(dibutyl carbamoylmethyl) phosphine oxide (DPDBCMPO) is able to extract effectively actinides in various oxidation states and lanthanides from acidic solutions without its preliminary dissolution in organic solvents. The system of DPDBCMPO-metal-nitric acid has been studied in detail by the methods of physicochemical analysis. The composition, the structure of complexes forming in this system under solvent less extraction process have been evaluated. The use of inert matrices, containing DPDBCMPO, for isolation of the actinides and lanthanides for their subsequent vitrification is suggested

[en] Studies on extraction of californium(III) from alkaline solutions containing pyrophosphate and tripolyphosphate or carbonate by dioctyl pyrocatechol (DOP) in octane have been made. This element is also quantitatively extracted from pyrophosphate media between pH 4 and 5 by di-(2-ethylhexyl) phosphoric acid (HDEHPA), and back-extracted with 1 M H₂SO₄. About 330 μg of californium(III) has been recovered. (author). 4 refs

[en] Samples of zirconolite, pyrochlore, and murataite based ceramics potentially suitable for immobilization of actinide waste and excess weapons plutonium have been prepared via melting in a resistive furnace and a cold crucible, and examined with X-ray diffraction. Melting temperature ranged between 1400 C and 1700 C. The samples with zirconolite, pyrochlore, and murataite as major phases were obtained after melting under oxidizing conditions. An extra phase in the most of the samples was perovskite. The highest perovskite content was found to be in the murataite-based ceramics produced under reducing conditions (in glassy carbon crucibles). The reason of this effect is formation of trivalent plutonium entering the perovskite phase. Pu leach rate from the murataite ceramic measured by 7-day MCC-1 test at 90 C was found to be ∼10 -6 g/(m².day). (author)

No abstract available