Radiation-Chemical Behavior of TBP in Hydrocarbon and Chlorohydrocarbon Diluents under Conditions of Reprocessing of Spent Fuel from Nuclear Power Plants

Experiments were performed for comparative assessment of the effect of ionizing radiation on the service characteristics of 30% TBP solutions in various diluents: hexachlorobutadiene (HCBD), mixtures of n-paraffins (RED diluent), and fraction of naphthenic hydrocarbons (RZh diluent). The following main parameters were chosen for comparative assessment of the quality of irradiated extractant solutions: composition and behavior of diluent radiolysis products, effect of diluents on the TBP radiolysis, and aggregative stability of emulsions in the main operations of the extraction cycle. The service life of the extraction mixtures was estimated from variation of the above parameters with the irradiation dose. Principles for choosing solvents with increased service life under irradiation were substantiated.     

Extraction of Long-Lived Radionuclides from High-Level Alkaline Waste with <Emphasis Type="Italic">p</Emphasis>-Alkylcalix[8]arene

p-Alkylcalix[8]arene containing six tert-butyl and two isononyl groups on the upper rim of the macrocycle was suggested for extraction recovery of long-lived β- and α-emitting nuclides from high-level alkaline waste. The influence of the compositions of the organic and aqueous phases on the extraction efficiency was examined. After four contacts of the extractant solution with the real high-level alkaline solution, the activity of the major dose-producing radionuclide, ¹³⁷Cs, decreases by two orders of magnitude, and that of α-emitting radionuclides, by a factor of 3.5–40 depending on the initial solution pretreatment. The degree of stripping of the radionuclides after the first contact of the loaded organic phase with the acid exceeds 99%. p-Alkylcalix[8]arenes show promise for treatment of high-level alkaline waste at the Mayak Production Association.     

Radiation resistance of a series of organophosphorus extractants

Extraction of U(VI), TUE, and REE from acid process solution with solutions of mono-and bidentate neutral organophosphorus compounds (NOPCs), phenyloctyl(N,N-diisobutylcarbamoylmethyl)phosphine oxide (CMPO), 2-ethylhexyl (N,N-dibutylcarbamoylmethyl)phenylphosphinate (CMPP), and unsymmetrical phosphine oxide (UPO) was studied as influenced by γ-irradiation at different absorbed dose rates. In all cases extraction of the target radionuclides decreased with increasing absorbed dose of γ-radiation. The resistance of the NOPCs to radiolysis decreases as CMPO>CMPP>UPO owing to the difference in the structures of their molecules.     

Anomalous effects in extraction of lanthanides and actinides with bidentate neutral organophosphorus extractants. Role of proton hydrate solvates

Extraction of europium, lithium, and acids from nitric acid and perchloric acid media with solutions of bidentate neutral organophosphorus compounds (BNOPCs) in polar diluents (dichloroethane, meta-nitrobenzotrifluoride, and trifluoromethyl phenyl sulfone) was studied. It was found that cationic complexes of BNOPCs with proton hydrates or lithium cation are formed in the organic phase. BNOPC hydrate solvates H⁺ · nH₂O · mBNOPC extract europium substantially better than do free BNOPCs. The main differences of BNOPCs from monodentate extractants are anomalous aryl effect (AAE) and perchlorate and synergic (the latter is observed in the presence of chlorinated cobalt dicarbollide) effects, which are connected with specific properties of proton hydrate solvates with BNOPC. The existence of BNOPC cationic complexes found by IR spectroscopy in polar diluents was confirmed by ESI-MS. The effect of preorganization of the extractant molecule and the change from the solvate mechanism of the metal ion extraction to the cation-exchange mechanism are apparently responsible for the high extraction ability of proton hydrate solvates with BNOPCs.     

Extraction of U(VI), Th(IV), Pu(IV), and Am(III) from nitric acid solutions with polyfunctional organophosphorus acids

Extraction of microamounts of U(VI), Th(IV), Pu(IV), and Am(III) nitrates from aqueous HNO₃ solutions with solutions of (diphenylphosphinylmethyl)phenylphosphinic, (di-p-tolylphosphinylmethyl)phenylphosphinic, and (dioctylphosphinylmethyl)phosphinic acids and of butyl hydrogen (diphenylphosphinylmethyl)phosphonate in organic diluents was studied. The metal: extractant stoichiometric ratio in the extractable complexes was determined, and the diluent effect on the extraction efficiency was examined. The possibility of using a macroporous polymeric sorbent impregnated with (dioctylphosphinylmethyl)phenylphosphinic acid for concentrating metal ions from HNO₃ solutions was demonstrated.     

Extraction of cesium and americium with <Emphasis Type="Italic">p</Emphasis>-alkylcalix[8]arenes from alkaline solutions

Previously unknown isononylcalix[8]arene was synthesized from commercially available isononylphenol. The properties of the product (solubility, extraction ability, tendency to aggregation) were compared with those of the known tert-butylcalix[8]arene. The extraction of ¹³⁷Cs, ^99mTc, and ²⁴¹Am from alkaline carbonate solutions with solutions of p-alkylcalix[8]arenes (alkyl = tert-butyl, isononyl) in tetrachloroethylene was studied. The dependence of the distribution ratios on pH of the aqueous phase in the interval from 11 to 13.9 and on the nature of functional groups in the calixarene core was determined. The composition of extractable solvates of cesium and americium with calix[8]arenes was found. Calix[8]arenes extract cesium from alkaline solutions more efficiently than p-tert-butylphenol, their nonmacrocyclic analog, does. tert-Butylcalix[8]arene exhibits the highest performance, which may be due to formation of aggregates 5.7 ± 0.8 nm in diameter in the organic phase at pH 13.5 of the aqueous phase. The isononyl derivative exists in the monomeric form (particle diameter 1.9 ± 0.5 nm).     

Extraction of Strontium and Yttrium from Alkaline Carbonate Media with Functionalized Calix[8]arenes

The extraction of ⁹⁰Sr and ⁹⁰Y from alkaline carbonate media with tetrachloroethylene solutions of p-tert-butyl and p-isononylcalix[8]arenes with various substituents in the lower rim was studied. The dependences of the ⁹⁰Sr and ⁹⁰Y distribution ratios on pH of the aqueous phase in the interval from 11 to 14 were studied. Among the calixarenes tested, p-alkylcalix[8]arenes with a bridging group in the lower rim show the highest performance in the extraction of ⁹⁰Sr and ⁹⁰Y.     

Extraction of U(VI), Th(IV), and REE(III) from nitrate solutions with diaryl(dialkylcarbamoylalkyl)phosphine oxides containing a dialkylcarbamoylmethyl substituent in the alkylene bridge

The extraction of microamounts of U(VI), Th(IV), and REE(III) from HNO₃ and NH₄NO₃ solutions with solutions of diaryl(dialkylcarbamoylalkyl)phosphine oxides containing a dialkylcarbamoylmethyl substituent in the alkylene bridge was studied. The stoichiometry of the complexes extracted from nitric acid solutions with N,N,N',N'-tetrabutyl-2-(di-p-anisylphosphinyl)butanedioic diamide I was determined. The influence of the extractant structure and aqueous phase composition on the efficiency and selectivity of the extraction of U(VI), Th(IV), and REE(III) into the organic phase was examined. Introduction of the–CH₂C(O)NAlk₂ fragment into the methylene bridge of the diaryl(dialkylcarbamoylmethyl)phosphine oxide molecule considerably enhances the extraction of REE(III) from neutral nitrate solutions. Such modification of the extractant molecule only slightly influences the extraction of REE(III) from nitric acid solutions, but leads to a considerable increase in the U(VI) extraction and to a decrease in the Th(IV) extraction. The selectivity of the extraction of U(VI) and REE(III) is thus considerably increased.     

Exothermic processes in mixtures of TBP with nitric acid

Causes of initiation of exothermic self-accelerating oxidation processes in mixtures of TBP with HNO₃ are analyzed. The main condition is heating of the mixtures to temperatures (Т _st) above which the heat release in the chemical reaction starts to exceed the heat removal from the system. After the initiation of selfaccelerating exothermic reactions, their development and intensity depend on whether the vessels are sealed, on the HNO3 concentration, and on the heating time. Heat treatment and radiolysis of the extractant slightly decrease Т _st of its mixtures with HNO₃ compared to the values for the “fresh” extractant.     

Extraction of Am and Eu with N,N′-substituted pyridine-2,6-dicarboxamides in fluorinated diluents

Extraction of Am and Eu with N,N′-substituted pyridine-2,6-dicarboxamides in fluorinated diluents was studied. N,N′-Diethyl-N,N′-di(p-tolyl)pyridine-2,6-dicarboxamide (EtTPDA) is readily soluble in fluorinated diluents, and its solutions allow the extraction of TPE and REE from nitric acid solutions. The extraction ability of EtTPDA in fluorinated polar diluents is higher than in CHCl₃. In the extraction with EtTPDA, the Am/Eu selectivity is independent of the extractant concentration and decreases with an increase in the acidity of the medium. Americium is extracted with EtTPDA better than Eu, which allows selective recovery of Am at moderate HNO₃ concentrations.     

Improvement of radiation stability of semi-insulating gallium arsenide crystals by deposition of diamond-like carbon films

We studied the properties of optical elements for the IR spectral range based on semi-insulating gallium arsenide (SI-GaAs) and antireflecting diamond-like carbon films (DLCF). Particular attention has been paid to the effect of penetrating γ-radiation on transmission of the developed optical elements. A Co⁶⁰ source and step-by-step gaining of γ-irradiation dose were used for treatment of both an initial SI-GaAs crystal and DLCF/SI-GaAs structures. It was shown that DLCF deposition essentially increases degradation resistance of the SI-GaAs-based optical elements to γ-radiation. Particularly, the transmittance of the DLCF/SI-GaAs structure after γ-irradiation with a dose 9⋅10⁴ Gy even exceeds that of initial structures. The possible mechanism that explains the effect of γ-radiation on the SI-GaAs crystals and the DLCF/SI-GaAs structures at different irradiation doses was proposed. The effect of small doses is responsible for non-monotonic transmission changes in both SI-GaAs crystals and DLCF/SI-GaAs structures. At further increasing the γ-irradiation dose, the variation of properties of both DLCF and SI-GaAs crystal influences on the transmission of DLCF/SI-GaAs system. At high γ-irradiation dose 1.4⋅10⁵ Gy, passivation of radiation defects in the SI-GaAs bulk by hydrogen diffused from DLCF leads to increasing the degradation resistance of the SI-GaAs crystals coated with DLCF as compared with the crystals without DLCF.     

Extraction of U(VI) and Th(IV) ions from nitric acid solutions with <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>′,<Emphasis Type="Italic">N</Emphasis>′-tetra-2-ethylhexylglutaramide

N,N,N′,N′-Tetra-2-ethylhexylglutaramide (TEHGA) was used as a new extractant for the extraction of U(VI) and Th(IV) from nitric acid solutions. Toluene was found to be the most suitable diluent for TEHGA. The extraction of nitric acid was also studied. The influence exerted on the distribution ratio (D) of U(VI) and Th(IV) by the concentrations of HNO₃, TEHGA, and LiNO₃ as salting-out agent, and also by the equilibration time, temperature, and kind of diluent was examined. Good U–Th separation can be achieved using 2–3 M HNO₃. The results obtained show that U(VI) and Th(IV) are mainly extracted as UO₂(NO₃)₂·2TEHGA and Th(NO₃)₄·TEHGA, respectively. The IR spectra of the extracted species were analyzed. The thermodynamic functions of the process were calculated. Back-extraction of U(VI) and Th(IV) from the organic phases was also studied.     

Extraction Properties of Butyl Bis(dibutoxyphosphinylmethyl)phosphinate in Nitric Acid Solutions

The extraction of HNO₃ and microamounts of U(VI), Th(IV), Sc(III), REE(III), and Am(III) nitrates from HNO₃ solutions with solutions of butyl bis(dibutoxyphosphinylmethyl)phosphinate in organic diluents was studied. The stoichiometry of the extractable complexes was determined, and the apparent extraction constants were calculated. The capability of the extractant to recover the examined elements from nitric acid solutions grows with an increase in the number of phosphoryl groups in its molecule. The recovery of the metal ions into the organic phase becomes more efficient in going to more polar organic diluents.     

Thermal properties of 2,2′-bipyridine-6,6′-dicarboxylic acid bis(<Emphasis Type="Italic">N</Emphasis>-ethyl-4-hexylanilide), an extractant for radioactive waste components

Thermal properties of 2,2′-bipyridine-6,6′-dicarboxylic acid bis(N-ethyl-4-hexylanilide) (DYP-7) were studied by DSC-TG with the aim of evaluating its fire and explosion hazard. Heating at a rate of 1 K min^–1 is accompanied by exothermic effects with the onset temperatures of 202, 312, and 432°С for the initial extractant and 62, 297, and 412°С for the extractant saturated with nitric acid. The presence of extracted nitric acid decreases the self-ignition point of DYP-7 by at least 20°С. The onset temperatures of the exothermic effects tend to increase with increasing heating rate. The extractant thermolysis products characteristic of the exothermic effect with the onset temperature of 202°C were identified by GC-MS. These are the deethylation product, 2,2′-bipyridine-6,6′-dicarboxylic acid N,N′-bis(4-hexylphenyl)amide, and product of further dearylation/reduction, 6′-formyl-N-(4-hexylphenyl)-2,2′-bipyridine-6-carboxamide.     

Effect of Fe(III) on the extraction of U(VI), Th(IV), and REE(III) from HCl solutions with diphenyl(dibutylcarbamoylmethyl)phosphine oxide

The extraction of U(VI), Th(IV), and REE(III) from HCl solutions with solutions of diphenyl(dibutylcarbamoylmethyl)phosphine oxide in dichloroethane in the presence of Fe(III) was studied. An increase in the Fe concentration in the organic phase leads to a considerable increase in the distribution ratios of U(VI), Th(IV), and REE(III), which is caused by transfer into the organic phase of mixed complexes MCl _m?n (FeCl₄) _n solvated by the extractant molecules. A macroporous styrene-divinylbenzene copolymer impregnated with diphenyl(dibutylcarbamoylmethyl)phosphine oxide can be used for concentrating U(VI), Th(IV), and REE(III) from HCl solutions in the presence of Fe(III).     

Extraction of americium and europium with functionalized thiacalix[4]arenes from alkaline solutions

The extraction of ²⁴¹Am and ¹⁵²Eu from alkaline carbonate solutions with solutions of functionalized thiacalix[4]arenes in m-nitrobenzotrifluoride was studied. The dependence of the radionuclide distribution ratios and separation factors on pH of the aqueous phase in the interval from 10 to 13.5, kind of the organic diluent, and position and electronic characteristics of functional groups in the thiacalixarene platform was examined. The composition of the extractable solvates of Am and Eu with functionalized thiacalix[4]arenes was determined by slope analysis. The hydrolytic stability of tert-butylthiacalix[4]arene in alkaline and acid solutions was evaluated. Thiacalix[4]arenes efficiently extract Am from alkaline solutions. The bromine-substituted thiacalix[4]arene exhibits the maximal selectivity, with the Am/Eu separation factor in extraction with this agent exceeding 30.     

Using γ-irradiation to synthesize Ag nanoparticles

Aqueous dispersions of Ag nanoparticles (NPs) were obtained after γ-irradiation of solutions containing AgNO₃, sodium citrate, and ethanol. The dose of γ-irradiation influences the diameter of the Ag NPs, as evidenced from UV–Vis absorption spectra and scanning electron microscopy (SEM) images. When the γ-irradiation dose increased from 60 to 530 Gy, the particle diameters decreased continuously as a result of irradiation-induced Ag NP fragmentation. At a constant γ-irradiation dose (ca. 100 Gy), we obtained Ag NPs that had highly reproducible particle diameters. This study reveals that γ-irradiation-mediated synthesis is a promising method for the preparation of stable Ag NPs when “clean” metal surfaces are required, e.g., for use in sensing devices.     

Effect of γ-irradiation on the thermal decomposition of nitric acid saturated solutions of TBP in С13 diluent

The dynamics of gas evolution in the course of thermal oxidation of 30% solutions of tri-n-butyl phosphate (TBP) in C13 diluent, equilibrated with 12.9 M HNO₃, was studied in open vessels in the temperature interval from 70 to 150°С. The total volumes of the released gases were measured, and the effect of the preliminary γ-irradiation of the TBP–С13–HNO₃ system on the thermolysis of nitric acid and accumulation of liquid products of TBP decomposition was studied. The boundary temperature parameters for the development of the oxidation process in the autocatalytic mode were estimated. On heating of the single-phase systems in open vessels, the conditions for the development of the autocatalytic oxidation are not created.     

Rare-earth-doped PbTiO<Subscript>3</Subscript>-PbZrO<Subscript>3</Subscript> solid solutions

(Pb_{1 ? x} Ln _x )(Zr_0.53Ti_0.47)O₃ and (Pb_{1 ? x} Ln _x )(Zr_0.65Ti_0.35)O₃ (x = 0.02, 0.06; Ln = La, Pr, Gd, Yb) solid solutions have been prepared by modified solid-state synthesis using organic-ligand precursors. The solid solutions have been characterized by thermal analysis, IR spectroscopy, x-ray powder diffraction, and atomic force microscopy. All of them have a rhombohedrally distorted perovskite structure (sp. gr. R3c).     

Coordination of V<Superscript>4+</Superscript> in Vanadium Titanium Oxide Xerogels

V_{2 ? y}Ti _y O_{5 ? δ} · nH₂O (0 < y < 1.33, layered structure) and Ti_{1 ? y}V _y O_{2 + δ} · nH₂O (0 < y < 0.25, anatase structure) solid solutions are synthesized by a sol-gel process. ESR spectra are used to assess the state of tetravalent vanadium in the solid solutions before and after calcination at 350°C and after intercalation with K⁺. Six types of ESR signals arising from paramagnetic ions in different environments are identified. Computer simulation is used to evaluate the ESR parameters of the materials studied.