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El-Khayatt A.M.,Egypt Atomic Energy Authority
Annals of Nuclear Energy | Year: 2010

The shielding of γ-rays and fast neutrons by concrete has been studied for concretes containing different lime/silica ratios. Calculations were carried out for six different concrete samples. The total mass attenuation coefficients (μ/ρ, cm2 g-1) have been computed at photon energies of 1 keV to 100 GeV using the personal computer software package WinXCom. Also the macroscopic effective fast neutron removal cross-sections (ΣR, cm-1) have been calculated using MERCSF-N program and the removal cross-section database for all required elements. The obtained results showed that the lime/silica ratio of concrete has significant and insignificant effects on μ/ρ and ΣR values, respectively. © 2010 Elsevier Ltd.

Saleh H.M.,Egypt Atomic Energy Authority
Nuclear Engineering and Design | Year: 2012

Phytoremediation is based on the capability of plants to remove hazardous contaminants present in the environment. This study aimed to demonstrate some factors controlling the phytoremediation efficiency of live floating plant, water hyacinth (Eichhornia crassipes), towards the effluents contaminated with 137Cs and/or 60Co. Cesium has unknown vital biological role for plant while cobalt is one of the essential trace elements required for plant. The main idea of this work i.e. using undesirable species, water hyacinth, in purification of radiocontaminated aqueous solutions has been receiving much attention. The controlling factors such as radioactivity concentration, pH values, the amount of biomass and the light were studied. The uptake rate of radiocesium from the simulated waste solution is inversely proportional to the initial activity content and directly proportional to the increase in mass of plant and sunlight exposure. A spiked solution of pH ≈ 4.9 was found to be the suitable medium for the treatment process. The uptake efficiency of 137Cs present with 60Co in mixed solution was higher than if it was present separately. On the contrary, uptake of 60Co is affected negatively by the presence of 137Cs in their mixed solution. Sunlight is the most required factor for the plant vitality and radiation resistance. The results of the present study indicated that water hyacinth may be a potential candidate plant of high concentration ratios (CR) for phytoremediation of radionuclides such as 137Cs and 60Co. © 2011 Elsevier B.V. All rights reserved.

El-Morshedy S.E.-D.,Egypt Atomic Energy Authority
Nuclear Engineering and Design | Year: 2012

One of the most limiting critical phenomena, which nuclear designers must consider, is the onset flow instability (OFI) phenomenon. It is the critical phenomenon limiting the reactor power from the thermal-hydraulic point of view especially material testing reactors (MTR). In the present study, an empirical correlation is developed to predict OFI in narrow vertical rectangular channels simulating coolant channels of MTR. The developed correlation involved almost all parameters that affecting OFI phenomenon in a dimensionless form. The coefficients involved in the proposed empirical correlation are identified by experimental data of Whittle and Forgan (1967) that covers the wide range of MTR operating conditions. The correlation predictions for subcooling at OFI are compared with predictions of some previous correlations where the present correlation gives much better agreement with the experimental data of Whittle and Forgan with relative standard deviation of only 6.6%. The present correlation is then used to predict the void fraction and pressure drop in subcooled boiling where the S-curves of Whittle and Forgan for OFI are predicted with good accuracy. Based on the present correlation, the OFI locus for the IAEA 10 MW MTR generic reactor is predicted and plotted against the flow velocity, exit coolant temperature and bubble detachment parameter under both fast and slow loss-of-flow transients where a vast safety margins for OFI phenomenon are predicted in both the steady and transient states as well. © 2011 Elsevier B.V. All rights reserved.

El Abd A.,Egypt Atomic Energy Authority
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2014

Void fraction simulating stratified air-water flow in cylindrical tubes of different radii was measured using transmission and scattering of gamma rays. A simple experimental set-up using 137Cs γ-ray point source of 10 μCi and NaI(Tl) detector was used. The void fractions determined from Compton-Compton scattering and transmission peaks were found in good agreement with the real void fractions. However, deviations were noticed between the results obtained from traditional Compton scattered gamma rays and real void fraction. It was shown that sensitivity of gamma ray scattering is better than the transmission measurements. The set-up used in the present work is simpler than those existing in literature and radiation safety and shielding requirements are minimized. © 2013 Elsevier B.V.

A systematic liquid-liquid extraction of lanthanum and neodymium from aqueous nitric acid solutions using a mixture of two neutral extractants, namely trioctylphosphine oxide (TOPO) and trialkylphosphine oxide (TRPO) in kerosene has been investigated. The different factors influencing the extraction affinity of those metals have been studied in detail. The extracted species for both metals have been found in the form of [M(NO3)3(TOPO)(TRPO)̄], where M refers to the metal ion. The temperature had a negative effect on the extraction of the metals where the extraction process has been found to be spontaneous in nature and associated with exothermic reaction. Since yttrium is accompanied with these metals in monazite ore, the extraction of Y(III) has also been studied. Based on the results obtained, a proposed method has been suggested to extract and separate the above metals from the hydrous oxide cake resulted by alkaline leaching of Egyptian monazite and a schematic diagram explaining the process has been presented. © 2012 Elsevier B.V. All rights reserved.

Nayl A.A.,Egypt Atomic Energy Authority
Journal of Hazardous Materials | Year: 2010

Extraction and separation of Co(II) and Ni(II) from acidic sulfate solutions by solvent extraction technique were studied using different forms of Aliquat 336 diluted with kerosene. The extraction percent of each metal ion was found to increase with increasing pH and extractant concentration. Co(II) was preferentially extracted by different forms of Aliquat 336 over Ni(II) under the same extraction conditions. From analysis of the experimental results, the extraction mechanism of R4N-forms was proposed with Co(II). It was found that the highest separation factor (SCo/Ni) value of 606.7 was obtained with 0.36 M R4N-SCN in kerosene from 2.0 M H2SO4 solution at pH 4.8 and shaking time of 20 min. Stripping of the two metal ions from the organic phase was also investigated. Based on the experimental results, a separation method was developed and tested to separate high purity Co(II), Ni(II) and Ln(III) from Ni-MH batteries leached by 2.0 M H2SO4. Based on the experimental results, a flow sheet was developed and tested and 0.34 g Co, 1.39 g Ln and 5.2 g Ni were obtained from the leaching process. © 2009 Elsevier B.V. All rights reserved.

Nanocrystalline potassium zinc hexacyanoferrate loaded on nanoscale magnetite substrate was successfully synthesized for significantly enhanced removal of cesium from low-level radioactive wastes. A description was given for preparation and properties of these precursors. The physicochemical properties of these nanocomposites were determined using different techniques including Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). Data clarified that supporting potassium zinc hexacyanoferrates on iron ferrite nanoparticles increased their thermal stability. Further, Fourier transform infrared spectra confirmed that the nanocomposites were well coordinated and incorporated in the polymer matrix. The average particle sizes, of these nanoparticles, determined by SEM had a good agreement with XRD results. Based on characterization data, the prepared zinc hexacyanoferrates were proposed to have a zeolitic rhombohedral structure with cavities can host alkali metal ions and water molecules. The magnetic analysis showed a super-paramagnetic behavior. Batch technique was applied to evaluate the influences of initial pH value, contact time, and competing cations on the efficiency of cesium removal. The sorption process was fast initially, and maximum separation was attained within 2h of contact. Cesium exchange was independent from pH value and deviate from ideal exchange phenomena. In neutral solutions, Cs + was retained through exchange with K +; however, in acidic solution, phase transformation was proposed. Sorption capacity of these materials attained values amounted 1965mgg -1. The synthesized nanocomposites exhibited different affinities toward Cs(I), Co(II), and Eu(III) elements and showed a good ability to separate them from each other. © 2012 Elsevier Inc.

The total mass attenuation coefficients, effective atomic numbers and electron densities of different types of solid state track detectors have been calculated for total and partial photon interactions in the wide energy range of 1 keV-100 GeV using WinXCom program. The values of these parameters have been found to vary with photon energy and chemical composition of the detectors. The variations of these parameters with energy are shown graphically for all photon interactions. The results of this work can stimulate research for other detectors and different materials. © 2011 Elsevier Ltd. All rights reserved.

Salama A.,Egypt Atomic Energy Authority
Annals of Nuclear Energy | Year: 2011

Three dimensional CFD full simulations of the fast loss of flow accident (FLOFA) of the IAEA 10 MW generic MTR research reactor are conducted. In this system the flow is initially downward. The transient scenario starts when the pump coasts down exponentially with a time constant of 1 s. As a result the temperatures of the heating element, the clad, and the coolant rise. When the flow reaches 85% of its nominal value the control rod system scrams and the power drops sharply resulting in the temperatures of the different components to drop. As the coolant flow continues to drop, the decay heat causes the temperatures to increase at a slower rate in the beginning. When the flow becomes laminar, the rate of temperature increase becomes larger and when the pumps completely stop a flow inversion occurs because of natural convection. The temperature will continue to rise at even higher rates until natural convection is established, that is when the temperatures settle off. The interesting 3D patterns of the flow during the inversion process are shown and investigated. The temperature history is also reported and is compared with those estimated by one-dimensional codes. Generally, very good agreement is achieved which provides confidence in the modeling approach. © 2011 Elsevier Ltd. All rights reserved.

Badr H.M.,Egypt Atomic Energy Authority
International Journal of Food Microbiology | Year: 2012

This study aims to control the presence of Listeria monocytogenes and Vibrio parahaemolyticus and the formation of biogenic amines in cold-smoked salmon by gamma irradiation. Irradiation at doses of 3 and 1. kGy inactivated 6.59 and 6.05. log cfu/g of L. monocytogenes and V. parahaemolyticus in the inoculated samples, respectively. Furthermore, irradiation of the un-inoculated samples significantly decreased their microbial populations of mesophilic aerobic bacteria, anaerobic bacteria, psychrophilic bacteria, lactic acid bacteria, and molds and yeasts. The Enterobacteriaceae were almost undetectable in samples irradiated at 2. kGy dose. The concentrations of biogenic amines significantly decreased in the irradiated samples due to microbial inactivation. However, irradiation of samples had no significant effects on their moisture and salt contents as well as on their pH values, total volatile base nitrogen, and trimethylamine nitrogen contents, but significantly decreased their amounts of phenolic compounds and increased their levels of thiobarbituric acid reactive substances. Moreover, irradiation treatments at doses up to 3. kGy showed no significant effect on the sensory acceptability of samples. Therefore, gamma irradiation at dose of 3. kGy can be successfully applied to provide significant improvement in the safety of cold smoked salmon with respect to L. monocytogenes, V. parahaemolyticus, and biogenic amines without adverse effects on chemical or sensory quality attributes of the product. © 2012 Elsevier B.V.

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