Determination of the leaching rate of radionuclide 134Cs from the solidified radioactive wastes in Syrian Portland cement and cement–microsilica matrixes

The suitability of Syrian Portland cement for disposal of solidified low-level radioactive waste was assessed by measuring the leaching rate of ¹³⁴Cs. In ordinary cement concrete, a leaching rate of 1.309 × 10^?3 g/cm² per day was measured. Mixing this concrete with microsilica reduced significantly the leaching rate to 3.106 × 10^?4 g/cm² per day for 1% mixing, and to 9.645 × 10^?5 g/cm² per day for 3% mixing. It was also found that the application of a latex paint reduced these leaching rates by about 10%. These results, along with mechanical strength tests (under radiation exposure, high temperature, long water immersion and freeze–thaw cycling) indicate that Syrian Portland cement is suited for the disposal of low-level radioactive waste.     

Optimization of Nb-substitution and Cs+/Sr+2 ion exchange in crystalline silicotitanates (CST)

Crystalline silicotitanate inorganic ion exchanger, with a sitinakite structure is a candidate material for remediation of aqueous nuclear waste streams. Niobium substituted crystalline silicotitanates (Nb-CST) with varying concentrations of Nb (2, 4, 8, 12 and 24 mmol) and with constant concentrations of Ti-12 mmol, Si-16 mmol, Na-165 mmol were prepared hydrothermally and the products were characterized using techniques viz., XRD, SEM/EDS, DTA/TGA, surface area respectively. Batch experiments were carried out to study the kinetics of uptake of Cs¹³⁷ and Sr⁹⁰, to estimate the decontamination factor (DF) values and distribution coefficients (K _d) for the above synthesized Nb-CST samples from actual radioactive waste solutions. The DF values for uptake of Cs and Sr by Nb-CST for the optimized Nb-concentration of 4 mmol after 24 h of equilibration was 355 and 136 respectively. The K _d values for uptake of Cs and Sr for Nb-CST (Nb-4 mmol) after 24 h of equilibration was found to be 35,490 and 13,500 ml/g respectively. The ion exchange capacity of Nb-CST (Nb-4 mmol) towards Sr ⁹⁰ and Cs¹³⁷ was estimated to be 11.8 and 3.2 meq/g respectively.     

Sorption and removal of iodate from aqueous solution using dried duckweed (<Emphasis Type="Italic">Landoltia punctata</Emphasis>) powder

Dried duckweed (Landoltia punctata) powder is applied to remove IO₃^? from aqueous solutions under various conditions. The results indicate the K_d is 150 ml g^?1 under general conditions. The sorption kinetics follow the pseudo-second-order equation, and the isotherm is well described by the Freundlich model. Hydroxyl and carbonyl groups contribute to IO₃^? sorption by ion-exchange, electrostatic attraction and redox reactions. Spectroscopic analyses prove that IO₃^? is reduced to I₂ and I^? by hydroxyl groups. These results demonstrate that duckweed (Landoltia punctata) is a promising biosorbent for environmental remediation of radioactive iodine pollution.     

Radiochemical methodologies applied to determination of zirconium isotopes in low-level waste samples from nuclear power plants

The ⁹³Zr determination in low-level radioactive wastes generated at nuclear power plants is an important issue for waste disposal purpose. This paper describes an analytical methodology developed for ⁹³Zr determination based on selective separation using extractive resins associated with inductively coupled plasma mass spectrometry (ICP-MS) and liquid scintillation counting (LSC) measurements. The ⁹³Zr results obtained for waste samples were in a good agreement for both techniques and the detection limits of 0.045 μg L^?1 and 0.05 Bq L^?1 were obtained for ICP-MS and LSC techniques respectively.     

Development of a practical decontamination procedure for uranium-contaminated concrete waste

Practical decontamination procedure and equipments have been developed to decontaminate uranium-contaminated concrete waste generated from a uranium conversion plant. The direct burning of mortar block coated with epoxy and then the mechanical removal of the burned surface reduces the amount of sludge by preventing the dissolution of whole cement paste in concrete block. And the removal of calcium from the concrete washing solution for the use of electrokinetic equipment decreases the volume of waste by a recycling of the solution. This improved decontamination procedure makes more than 70 % of concrete waste be self-disposed and remarkably reduces secondary radioactive waste.     

Experimental and FLUKA study relevant to the production of <Superscript>124</Superscript>I through <Superscript>nat</Superscript>Te(p,xn) reaction at a medium-sized cyclotron

A radiochemical methodology for the determination of ⁹⁴Nb in low-level radioactive wastes from nuclear power plant was proposed. Although ⁹⁴Nb is a strong gamma emitter, its concentration in radioactive waste samples is usually several orders of magnitude lower than that of other β–γ emitters, whose emissions interferes in the detection of the emission lines of ⁹⁴Nb. The procedure involves acid digestion, precipitation, cation exchange chromatography by using Amberlite IRA120 resin, extraction chromatography by using TEVA resin to isolate the Nb and the gamma spectrometry to its measurement. The chemical yield was 70% in average. Samples of evaporator concentrate and spent resin were analyzed. For the samples of the evaporator concentrate, the results obtained were below L _D = 9.59 × 10^?4 Bq g^?1. For the spent resin an average result of 1.54 × 10² Bq g^?1 was obtained.     

Thermodynamic analysis of radioactive graphite reprocessing by incineration in air and oxidation in molten salt

Reactor graphite waste of nuclear industry contains various radionuclides. This study deals with the behaviour of radioactive elements during thermal treatment of waste. Two thermal processes were simulated: incineration of graphite in air and oxidation of graphite in a molten salt, containing Na₂CO₃ + K₂CO₃ + 20 mass% PbO. Carbon oxides CO and CO₂, containing radioactive ¹⁴C, are the main components of the gaseous phase with partial pressures approximately 10⁴ Pa in both cases. More gaseous radionuclides are observed during incineration of graphite in air than during oxidation of graphite in the molten salt. In the latter case radionuclides are in the condensed state in the melt of sodium and potassium carbonates.     

NMR studies of interactions of new CB2 cannabinoid receptor ligands with cyclodextrins hosts. Correlation with micellar electrokinetic chromatography and reversed phase high performance liquid chromatography

Three selective CB₂ cannabinoid receptor ligands have recently been discovered to be promising anti-inflammatory agents but their low water solubility hinder their per os administration. The popularity of the cyclodextrins, from a pharmaceutical standpoint lies on their ability to interact with poorly water-soluble drugs and improve their solubility. Herein, three experimental approaches for calculating the stability constant of complexes between the selective CB₂ ligands and either the β-CD or the HP-β-CD, were tested: nuclear magnetic resonance, micellar electrokinetic chromatography and high performance liquid chromatography in reversed phase. In NMR studies the calculated K values were relatively high and were between 1486 and 3571 M^?1 with β-CD. With HP-β-CD they were between 1203 and 2650 M^?1. Concerning the two others techniques the K values were found lower. In MECK studies with β-CD they were between 308 and 792 M^?1 and with HP-β-CD between 124 and 764 M^?1. Finally in RP-HPLC studies with β-CD, they were between 539 and 1144 M^?1 and with HP-β-CD between 196 and 396 M^?1. These calculated constants suggest that a complexation phenomenon occurs. A model for inclusion of one of the CB₂ ligands in the β-CD was then proposed from molecular modeling studies.     

Solvent extraction of cesium into nitrobenzene by using sodium,potassium and rubidium dicarbollylcobaltates in the presence of polypropylene glycol PPG 425

Extraction of microamounts of cesium by nitrobenzene solutions of sodium dicarbollylcobaltate (Na⁺B^?), potassium dicarbollylcobaltate (K⁺B^?) and rubidium dicarbollylcobaltate (Rb⁺B^?) in the presence of polypropylene glycol PPG 425 (L) has been investigated. The equilibrium data have been explained assuming that the complex species ML⁺ (M⁺ = Na⁺, K⁺, Rb⁺, Cs⁺; L = PPG 425) are present in the organic phase. The stability constants of the cationic complex species ML⁺ (M⁺ = Na⁺, K⁺, Rb⁺) in nitrobenzene saturated with water have been determined; they were found to increase in the series of Rb⁺ < K⁺ < Na⁺.     

The MEDINA facility for the assay of the chemotoxic inventory of radioactive waste packages

A new analytical facility called MEDINA (Multi Element Determination based on Instrumental Neutron Activation) and based on Prompt- and Delayed-Gamma-Neutron-Activation-Analysis (P&DGNAA) using a 14 MeV neutron generator is developed for the determination of non-radioactive elements and substances in 200-l radioactive waste drums. The qualitative performance of MEDINA is studied by measuring (1) the gamma-ray spectra for the empty chamber, (2) for an empty 200-l steel drum in presence or not of ⁶⁰Co and ¹³⁷Cs sources and (3) for a 200-l steel drum filled with concrete in order to determine the level of interferences induced by activation products of the facility components and to investigate further optimization steps to improve the measurements sensitivity. The measurement carried out for the empty drum with the radioactive sources show the possibility to characterize radioactive waste packages containing both ⁶⁰Co and ¹³⁷Cs with activities ranging between 20 and 80 MBq at least.     

Use of Capillary Zone Electrophoresis and Micellar Electrokinetic Chromatography for Separations of Anthraquinone Derivatives

The behavior of seven hydroxy anthraquinone derivatives was studied by capillary zone electrophoresis and micellar electrokinetic chromatography. The effects of buffer pH (6.5–10.8) and sodium dodecyl sulfate concentration (10–20 mmol L^?1) on the effective mobilities of the analytes and their separation were tested. A comparison of the two optimized separation systems showed that micellar electrokinetic chromatography was superior as it permits separation of all the seven analytes within 15 min, using 15 mmol L^?1 sodium dodecyl sulfate in 10 mmol L^?1 tetraborate buffer, pH 8.5, at a voltage of 20 kV. The calibration curves were linear in the concentration range from 5.0 · 10^?7 to 5.0 · 10^?4 mol L^?1 for most of the analytes, at a detection wavelength of 254 nm. LOD and LOQ values of the analytes were in the ranges of 2.10 · 10^?7–1.28 · 10^?6 mol L^?1and 6.99 · 10^?7–4.25 · 10^?6 mol L^?1, respectively. The proposed separation conditions were applied to determination of 1,2-dihydroxy anthraquinone (alizarin) and 1,2,4-trihydroxy anthraquinone (purpurin) in Rubia tinctorum aglycone and of the recently described 1-acetyl-2,4,5,7-tetrahydroxy-9,10-anthraquinone and 1-acetyl-2,4,5,7,8-pentahydroxy-9,10-anthraquinone in the mycelium of fungi Geosmithia lavendula.     

Determination of adsorption heats of individual adsorption complex by combination of microcalorimetry and FTIR spectroscopy

Adsorption of CO as a probe molecule on K-FER zeolites differing in Si/Al ratio was investigated. Successful determination of adsorption heats of individual adsorption complexes formed upon adsorption of CO molecules on K-FER zeolites at 300 K by combination of IR spectroscopy with adsorption microcalorimetry is reported. Adsorption heat of bridged carbonyl complexes, where CO molecule interacts with two nearby extraframework K⁺ cations, was experimentally determined for the first time. It was found that bridged complexes on dual cationic sites exhibit adsorption heat of 34.8 kJ mol^?1, whereas monodentate carbonyls on single isolated K⁺ cation exhibit adsorption heat of only 26.2 kJ mol^?1 and adsorption heat of isocarbonyls was 21.5 kJ mol^?1.     

Characterization of very low thermal conductivity thin films

Characterization of thermal transport in nanoscale thin films with very low thermal conductivity (<1 W m^?1 K^?1) is challenging due to the difficulties in accurately measuring spatial variations in temperature field as well as the heat losses. In this paper, we present a new experimental technique involving freestanding nanofabricated specimens that are anchored at the ends, while the entire chip is heated by a macroscopic heater. The unique aspect of this technique is to remove uncertainty in measurement of convective heat transfer, which can be of the same magnitude as through the specimen in a low conductivity material. Spatial mapping of temperature field as well as the natural convective heat transfer coefficient allows us to calculate the thermal conductivity of the specimen using an energy balance modeling approach. The technique is demonstrated on thermally grown silicon oxide and low dielectric constant carbon-doped oxide films. The thermal conductivity of 400 nm silicon dioxide films was found to be 1.2 W m^?1 K^?1, and is in good agreement with the literature. Experimental results for 200 nm thin low dielectric constant oxide films demonstrate that the model is also capable of accurately determining the thermal conductivity for materials with values <1 W m^?1 K^?1.     

Selective removal of cesium and strontium by crystalline silicotitanates

Crystalline silicotitanate ion exchanger (58.5 mmol Ti, and 620 mmol Na) with 6 mmol of SiO₂ after 10 days of hydrothermal synthesis was optimized for selective removal of ⁹⁰Sr. Studies on X-ray diffraction, scanning electron microscope and energy dispersive spectroscopy revealed that the silicotitanate is highly crystalline with bright cubic and rod like morphology with varying amounts of Ti, Si, Na, and O. The decontamination factor and distribution coefficient values for uptake of ¹³⁷Cs and ⁹⁰Sr from actual radioactive waste solutions by the ion exchanger after 24 h of equilibration was found to be 40 and 176 and 4025 ml g^?1 and 7525 ml g^?1, respectively. The exchange capacity for ⁹⁰Sr and ¹³⁷Cs was estimated to be 14.6 and 4.4 meq g^?1, respectively.     

Removal of some radionuclides from contaminated solution using natural clay: bentonite

Clays and specially bentonite are widely used as natural adsorbents for wastewater treatment and as a barrier in landfills to prevent the contamination of subsoil and groundwater by leachates containing radioactive materials. The adsorption of four radionuclides, ¹³⁴Cs(I), ⁹⁰Sr(II), ¹³³Ba(II) and ¹⁵²Eu(III) by an Egyptian bentonite (Bent) and its modified Na⁺ form (Na-Bent) collected from a deposit within Alexandria governorate was investigated as a function of different parameters. The batch equilibrium technique was used and the kinetic results showed that the equilibrium was mostly reached within 10 min and the kinetic data fit well to the pseudo-second order model. The Langmuir model fits well the experimental data of all metals adsorption on Bent and Na-Bent except for adsorption of ¹³³Ba on Bent, while ¹⁵²Eu adsorption on Na-Bent fits better to the Freundlich model rather than to the Langmuir. Both Bent and Na-Bent fit well to the D-R model with adsorption energy of E > 8 kJ mol^?1 that means that the adsorption reaction is expected to be controlled by both cation exchange and surface complexation reactions. At lower concentrations, the values of distribution coefficient (K _d), follow the order of ¹⁵²Eu > ⁹⁰Sr > ¹³⁴Cs > ¹³³Ba for Bent and Na-Bent. The K _d of ¹⁵²Eu is higher than that of ¹³⁴Cs in Bent up to 150 mg L^?1. This order changes at higher concentration where the K _d of ¹³⁴Cs becomes higher than ¹⁵²Eu after 150 mg L^?1 for Bent and after 200 mg L^?1 for Na-Bent. Na-Bent is preferred than Bent for the uptake of ⁹⁰Sr and ¹³⁴Cs especially at high concentration.     

Preparation of ultra-and nanoporous glasses and study of their structural and electrokinetic characteristics in 1: 1 electrolyte solutions

Nano-and ultraporous glass membranes with pore radii of 4.5–150 nm are prepared from sodium borosilicate glasses of various compositions. Structural parameters (structure resistance coefficient, volume porosity, and filtration factor) and electrokinetic characteristics (conductivity, counterion transport numbers, and electrokinetic potential ζ _α ^* ) of membranes are determined at various KCl and NaCl solution concentrations (10^?4?10^?1 M) in a neutral pH region. The passage from nano-to ultraporous glasses is accompanied by an increase in |ζ _α ^* | values, which is apparently related to a decrease in the thickness of a gel layer due to the removal of ion-permeable secondary silica from pore channels. The comparison of electrokinetic characteristics of glass membranes (counterion transport numbers, efficiency coefficients, and electrokinetic potentials) measured in NaCl and KCl solutions indicates a higher specificity of K⁺ counterions as compared to Na⁺ ions.     

<Superscript>99m</Superscript>Tc production via the (<Emphasis Type="Italic">γ, n</Emphasis>) reaction on natural Mo

In this paper, cheap liquorice residue was used to prepare activated carbon (AC), thioacetamide (TAA) was used to modify the AC, and the adsorption experiments were conducted in the simulated acid radioactive wastewater with low uranium concentration to study the adsorption behavior and mechanism for uranium by TAA modified AC (TAA–AC). The removal efficiency by TAA–AC was 92.1–98.2% from the 1 mg L^?1 uranium solution at pH 2–6. The adsorption equilibrium data were well fitted by Dubinin–Radushkevich model, and the maximum adsorption capacity was estimated to be 340 mg g^?1. TAA–AC showed an enhanced selectivity for uranium in the presence of competitive ions. Furthermore, the adsorption experiments were conducted in the actual acid radioactive wastewater with low uranium concentration from an in situ leach uranium mine. The high adsorption rate (98.3%) and selectivity (K_d?=?3.78×10⁴ mL g^?1) for uranium were observed in the actual acid radioactive wastewater, and the adsorption rate was found to maintain 96.2% over six cycles of adsorption–desorption.     

Determination of <Superscript>129</Superscript>I using volatilization method and liquid scintillation spectrometry

A simple and rapid separation method for ¹²⁹I determination in radioactive waste samples was developed. Suitable conditions for iodine volatilization were tested. Iodine was trapped in 1.5 mol L^?1 NaOH and precipitated as PdI₂·H₂O by addition of PdCl₂ with recoveries higher than 80%. The method was applied for analysis of contaminated soil, radioactive sludge, evaporator concentrate and heterogeneous waste samples from nuclear power plants in Slovak Republic. ¹²⁹I was measured on liquid scintillation counter TRI CARB 2900 TR using Ultima Gold AB scintillation cocktail.     

Hermetic thermal behaviors and specific heat capacities of bis(aminofurazano)furazan and bis(nitrofurazano)furazan

Thermal behaviors of bis(aminofurazano)furazan (BAFF) and bis(nitrofurazano)furazan (BNFF) were studied by the differential scanning calorimetry (DSC) method with a special hermetic high-pressure crucible and compared to that with a common standard Al crucible. The exothermic decomposition processes of the two compounds were completely revealed. The extrapolated onset temperature, peak temperature and enthalpy of exothermic decomposition at the heating rate of 10 °C min^?1 are 290.2, 313.4 °C and ??2174 J g^?1 for BAFF, and 265.8, 305.0 °C and ??2351 J g^?1 for BNFF, respectively. The apparent activation energies of the decomposition process for the two compounds are 115.7 and 131.7 kJ mol^?1, respectively. The self-accelerating decomposition temperatures and critical temperatures of thermal explosion are 247.5 and 368.7 °C for BAFF, and 249.6 and 268.1 °C for BAFF, respectively. Both BAFF and BNFF present high thermal stability. The specific heat capacities for the two compounds were determined with the micro-DSC method, and the specific heat capacities and molar heat capacities at 298.15 K are 1.0921 J g^?1 K^?1 and 257.9 J mol^?1 K^?1 for BAFF, and 1.0419 J g^?1 K^?1 and 308.5 J mol^?1 K^?1 for BNFF, respectively.     

Green and efficient extraction strategy to lithium isotope separation with double ionic liquids as the medium and ionic associated agent

The paper reported a green and efficient extraction strategy to lithium isotope separation. A 4-methyl-10-hydroxybenzoquinoline (ROH), hydrophobic ionic liquid—1,3-di(isooctyl)imidazolium hexafluorophosphate ([D(i-C₈)IM][PF₆]), and hydrophilic ionic liquid—1-butyl-3-methylimidazolium chloride (ILCl) were used as the chelating agent, extraction medium and ionic associated agent. Lithium ion (Li⁺) first reacted with ROH in strong alkali solution to produce a lithium complex anion. It then associated with IL⁺ to form the Li(RO)₂IL complex, which was rapidly extracted into the organic phase. Factors for effect on the lithium isotope separation were examined. To obtain high extraction efficiency, a saturated ROH in the [D(i-C₈)IM][PF₆] (0.3 mol l^?1), mixed aqueous solution containing 0.3 mol l^?1 lithium chloride, 1.6 mol l^?1 sodium hydroxide and 0.8 mol l^?1 ILCl and 3:1 were selected as the organic phase, aqueous phase and phase ratio (o/a). Under optimized conditions, the single-stage extraction efficiency was found to be 52 %. The saturated lithium concentration in the organic phase was up to 0.15 mol l^?1. The free energy change (ΔG), enthalpy change (ΔH) and entropy change (ΔS) of the extraction process were ?0.097 J mol^?1, ?14.70 J mol K^?1 and ?48.17 J mol^?1 K^?1, indicating a exothermic process. The partition coefficients of lithium will enhance with decrease of the temperature. Thus, a 25 °C of operating temperature was employed for total lithium isotope separation process. Lithium in Li(RO)₂IL was stripped by the sodium chloride of 5 mol l^?1 with a phase ratio (o/a) of 4. The lithium isotope exchange reaction in the interface between organic phase and aqueous phase reached the equilibrium within 1 min. The single-stage isotope separation factor of ⁷Li–⁶Li was up to 1.023 ± 0.002, indicating that ⁷Li was concentrated in organic phase and ⁶Li was concentrated in aqueous phase. All chemical reagents used can be well recycled. The extraction strategy offers green nature, low product cost, high efficiency and good application prospect to lithium isotope separation.