مجله علوم و فنون هسته ای
سال چهل و یکم شماره 4 (پیاپی 94، زمستان 1399)

In this study, the role of multi-electron effects on the high harmonics generation by the interaction of femtosecond laser with Argon atom and N2O molecule has been investigated. First, the effect of multi-electron contribution to the generation of harmonics has been studied. It is observed that the presence of more than one electron leads to an increase in harmonics yield, especially in the cutoff region. This effect is more obvious in the systems in which their highest occupied level is degenerate. The effect of exchange and correlation interaction on the high harmonic generation is also investigated. The results showed that the effect of correlation interaction on harmonics is negligible, but the effect of exchange-correlation interaction is significant. Indeed, this remarkable influence is due to exchange interaction which constitutes 17% and 23% of the total energy of Argon atom and N2O molecule. By considering the exchange-correlation interaction for the argon atom and N2O, the harmonics yield decreased by one order of magnitude and the cutoff frequency increased by 4-5 harmonic order.

Li2TiO3 as a tritium breeder has a significant role in nuclear fusion reactors. The aim of this study was the synthesis of Li2TiO3 powder by solution combustion in the explosive mode as an inexpensive and efficient method. Fuel type and nitric acid, as an oxidizer, have vital roles in this method. Hence, the effect of nitric acid content and citric acid, glucose, and glycine fuels were investigated. Results showed that the use of glucose fuel was not appropriate, because the combustion didn't occur, neither the desired phase was not synthesized. Moreover, synthesis in the presence of glycine fuel led to the synthesis of the desired product, however, no pure single-phase product was obtained. Contrary to the two mentioned fuels, citric acid was a suitable fuel for the synthesis of Li2TiO3 by solution combustion method, which resulted in a single-phase product. The optimum amount of nitric acid was determined to be 9 liters per mole of fuel. Using more than the optimal amount of nitric acid also resulted in LiTiO2 impurities being left. While using less than the optimal amount resulted in an incomplete combustion reaction.

BaxSr1-xSO4:Dya%, Tbb% nanoparticles were synthesized by the chemical co-precipitation method. The orthorhombic lattice structure was confirmed by X-ray diffraction (XRD) pattern and an average size of 63.5nm was obtained using Deby-Schere`s formula. The shape and size of particles were also observed by scanning electron microscopy (SEM). EDX spectra proved the presence of Dy and Tb in the sample. The TL glow curves of samples showed the maximum sensitivity at 0.12, 0.88, 0.5, and 1.5 mol% for Sr, Ba, Dy, and Tb, respectively. The thermoluminescence (TL) glow curves of the sample (in the range of 0.05-100 mGy) had two glow peaks at 534 and 615 K. Dosimetry characteristics of the selective combination were studied. The best heat rate was 2 K/s. The TL intensity was increased by increasing the dose up to 7 kGy and after that, it was increased very slowly. Studies of the fading indicated that the reduction of dose-response of the sample in 1000 mGy dose is negligible within 21 days. Energy response was studied in the range of 80-1250 keV and showed the sample was energy-dependent.

In SOOREH Co, a significant amount of uranium-containing phosphoric acid wastewater from analytical operations is produced on a large volume of process samples. Uranium recovery and its optimal use in the UF6 gas production cycle is the most important goal of this research. To achieve this goal, two methods for the recovery of uranium from this wastewater have been investigated. The first method is to use TBP and D2EHPA extractant diluted with kerosene. The results of this study showed that up to 98% of uranium is extracted from laboratory wastewater, 95% of which can be stripped from the organic phase by ammonium bicarbonate solution. The second method is to precipitate uranium using sodium dithionite. In this study, the two-step process of uranium recovery from phosphoric acid wastewater has been studied. The results of this method show that using sodium dithionite with two-stage precipitation, the concentration of uranium in the filtered solution of sediments is reduced to less than 0.2 ppm and this reduction in concentration is equal to the efficiency up to 99.99%. Therefore, the use of the sedimentation method to recover uranium from phosphoric acid wastewater by sodium dithionite is a more appropriate method compared to the solvent extraction method and is recommended for this type of wastewater.

The separation of metal ions from nuclear waste is an important issue in the nuclear industry. Cyclic chemical compounds including ether groups are called crown ethers. These compounds strongly bind to certain cations, forming complexes. Successive oxygen substitution with nitrogen leads to form new structures called Azacrown. In this work, quantum mechanical calculations based on density functional theory (DFT) has been used to investigate the stability of complexes formed between various Azacrowns and selective transition metals (M) ( M= Mn2+, Fe2+ , and Co2+). The results showed that binding energies (ΔE) for titled metals are enhanced by increasing the number of replaced oxygen atoms in crowns structure. For example, the fully substituted Azacrown complexes of Mn2+, Fe2+ , and Co2+ are about 16.8, 22.4, and 37.2 kcal/mol more stable than corresponded crown ethers complexes, respectively. Analogous trends were found for ΔH and ΔG of complexation reactions.

One of the significant phenomena in the operational conditions of the enrichment cascades is the sudden crash of a number of separate machines along the cascade. In order to investigate the effect of gas centrifuge crash on cascade performance, separation of the cascade in a transient condition should be modeled. In this paper, the performance of two-component symmetric enrichment cascades was modeled, using partial mass balance equations in the transient condition. Nonlinear equations of the model were also discriminated against using Crank Nicholson's finite difference method and the q iteration method was used to solve the equations. The results of the computer simulation of the model cascade for the enrichment of uranium 235 showed that if the crash of gas centrifuge machines occurs at the end of the enrichment part of the cascade, the product concentration will decrease more and more, and it takes a longer time to reach new steady-state condition. For the cascade and the conditions used in this paper, with the crash of a machine, the greatest reduction in product concentration compared to the pre-incident state is, 0.5% percent and the highest increase in waste stream concentration compared to the pre-incident state is 0.2 percent. It was also observed that the cascade performance of machines with a higher separation factor is less affected by the crash of machines. The results showed that the gas hold up has a small effect on the variation of the 235 isotope concentration in the product stream and only affects the time to reach equilibrium in the cascade.

Due to the special and difficult conditions for the fuel rods inside the reactor core, inspection and quality control of the fuel after the production at the factory and before loading in the core of the reactor is essential. This process is carried out using various non-destructive tests. Generally, neutron radiography is one of the most important non-destructive tools for fresh fuel inspection. In the present work, neutron computerized tomography (CT) of a depleted TRIGA fuel rod is investigated using a digital detection system which includes a scintillator screen, a mirror, and a CCD camera. The experiments were performed in the INUS neutron radiography facility. The results show that the structure and components of the fuel rod such, as pellets and springs, are well visible by using the neutron tomography technique and it can be utilized for precise investigation of the fuel rod’s structure after production at the factory.

In this study, two methods of nano-particle coating, by boiling and electrophoretic, have been used to investigate the effect of surface modification on the Critical Heat Flux of stainless steel plates. In each of these two methods, the coating was performed for 20, 40, and 60 minutes while other parameters remained constant. The SEM1 and EDS2 images were captured and then the contact angles were measured using the Stadler technique to study the effect of surface properties on Critical Heat Flux.  Finally, the boiling curves of the hydrophilic and superhydrophilic surfaces were obtained and then the Critical Heat Flux (CHF) is determined. The CHF values were compared with the existing experimental data and empirical correlations. It was found that the CHF for nanoparticle coating by pool boiling, is significantly higher than those of electrophoretic coating. Also, a comparison of the present Critical Heat Flux results with those obtained by the empirical correlations that are a function of surface properties showed better agreement

In the present study, for the first time the R cascade under normal and optimal conditions with the constant and specified total number of cascade stages, the feed flow rate to the cascade, the factor of separation based on the unit mass difference, and the maximum and optimal of the feed flow into the centrifuge machine is assessed. The algorithm used for optimization is TLBO algorithm and the objective function is considered as a function of separation work for a single machine and match abundance ratio. The results show that in the cascade with the match abundance ratio for isotopes k1 and k2 the separation work in optimal cascade is more than conventional. If the abundance ratio is adapted for two pair of components, i.e., the “first and third” and the “second and third, the separation power in the optimal mode for the first and second cases is 1% and 9% more than those of conventional, respectively. Finally, a computational code named MISCC is written to determine and analyze the parameters of the match abundance ratio cascade in optimal and normal conditions.

In the present work, the effect of the external magnetic field of = ( T 0 -1000 Bext ) on the energy deposition of the relativistic electrons into high density fuel of 3 ρc ( ) 200 1000 g.cm   in fast-shock ignition concept has been investigated by using the Geant4 simulation toolkit. In our simulation model, two types of the energy distribution function including exponential energy distribution and quasi-two temperature energy distribution function, for relativistic electrons with an initial kinetic energy of 0 E   ( ) 1.5 6.5 MeV were considered. The results of simulations in the presence of an external magnetic field show that the dynamics of the relativistic electrons are strongly affected by the external magnetic field which results in the optimum energy transfer into the fuel. The comparison of the results indicates that the optimal energy deposition is obtained for the density of 3 ρc 300 g.cm in the presence of a magnetic field of about Bext 600 T with an ignitor laser wavelength of λif   0.35 m and laser intensity of 21 2 I 10 W.cm  . It can therefore be concluded that by increasing the external magnetic field of 600 T ext B  , the energy deposition rate increases slowly. Keywords: Geant4 simulation toolkit, Fast-shock ignition, External magnetic field, Exponential energy distribution, Quasi-two temperature energy distribution.

The aim of present study is to evaluate thedisinfection efficiency and regrowth control of microorganism in urban wastewater effluent using cold atmospheric plasma. Two voltages of spark of 20 and 25 kV were applied to wastewater samples of Tehran wastewater treatment plant, Tehran, Iran on 1, 3, and 6 min using oxygen gas supply. The physicochemical characteristics of the effluent sample were determined before and after the treatments. The disinfection efficiency was assessed based on the total colony count and total coliform. The results showed that the COD, BOD5, and the total nitrogen became less than the maximum allowed for agriculture purposes in both treatments, however, this reduction was significantly more in the higher voltage. In terms of bacterial regrowth after disinfection, disinfection efficiency was 100 percent at the beginning of the experiment in all spark treatments, however, total coliform population has become higher than the allowed limit after only one day. This confims the importance of investigating microbial regrowth in wastewater disinfection studies. The spark plasma had no effect on permanent and irreversible inactivation of the total coliform and microbial regrowth occurred.

Environmental hazards of wastewater containing metals, including lead, have attracted researchers' attention on their cleanup using novel methods such as bioremediation. In the present study, the biosorption ability of lead by Bacillus sp. Strain STG-83 was evaluated. Response surface methodology with central composite design by the Design Expert software was used to optimize parameters such as pH, biomass concentration, and initial lead concentration. The results showed that the quadratic model proposed by Design Expert software with a correlation coefficient of R2=0.9938 predicted the process behavior properly; lead biosorption by the bacteria was optimized at pH=4.5, initial concentration of lead 297.95 mg. L-1, and the amount of adsorbent 1 g.L-1, which is equal to 149.595 mg. g-1 dry weight. Also, the experimental data were fitted with Langmuir and Freundlich isotherms. The results showed that the Langmuir model is more suitable with R2=0.961. Kinetic studies showed that adsorption capacity reached its maximum value within 5 minutes. Ultimately, due to the valuable potential of this bacterium in rapid and high biosorption of lead, Bacillus sp. strain STG-83 is introduced as a valuable bacterial sorbent for lead bioremediation processes and performance of response surface methodology in modeling and optimizing lead biosorption process by Bacillus sp. strain STG-83 is confirmed.

Molybdenum metal with atomic number 42 belongs to the sixth group of the periodic table of elements. This element has many usages in various industries. The most important molybdenum mineral is molybdenite (MoS2 ). Different leaching methods are used for the extraction of molybdenum. One of the methods is bioleaching, which requires a high potential for extraction of molybdenum, in addition to applying other special leaching conditions. In this study, in order to use a bioleaching method for extraction of molybdenum from its mineral, the native thermophilic archaebacteria of Sulfolobus solfataricus and Acidianus ambivalens were isolated from the Narigan mine and registered on the NCBI site, also they were gradually adapted for resistance against to the high potential. The result of the adaptation was positive and archaebacteria were able to resist potentials higher than 1000 mV and had a good growth and proliferation rate. In the following, these archaebacteria have been used for the bioleaching of the Narigan ore for the extraction of molybdenum. Because molybdenum recovery has a strong dependency on the redox potential, recovery was increased to 80%. By increasing the potential from 400 mV to 1000 mV. While the molybdenum recovery was 43% by non-adapted bacteria against high potential.

The Boltzmann equation which describes binary collisions between molecules is a very important equation in physics and fluid dynamics. Direct Monte Carlo simulation is one of the methods to solve the Boltzmann equation. The moisture can leak to the fluid pipelines in the various places of cascades so many times through the enrichment operations since the pressure of the most enrichment process units is less than the atmospheric pressure. It causes the solid uranium precipitation on the inner surfaces of rotor and HF production upon the reaction with UF6. In the present work, the effect of concentration and total pressure inside a hypothetical centrifuge for binary component conditions (ZUF6=0.97, ZHF=0.03), (ZUF6=0.93, ZHF=0.07), (ZUF6=0.9, ZHF=0.1), (ZUF6=0.85, ZHF=0.15), and three component conditions (ZUF6=0.9, ZHF=0.05, ZAir=0.05) and (ZUF6=0.8, ZHF=0.1, ZAir=0.1) have been investigated. The results have been compared with those of the Boltzmann distribution function. Moreover, increment in the amount of light gas along with UF6 results in the decrement of ρνz.

In this study, the mass transfer performance of the Horizontal pulsed sieve plate column for the extraction of uranium from Bandar Abbas sulfate leach solution with Alamine 336 was investigated using a dispersion model. The organic phase contained 6% (v/v) Alamine 336 as extractant and 5% (v/v) isodecanol as a modifier in kerosene as diluent. The sulfate solution of Bandar Abbas containing 0.22 M sulfate and 250 ppm Uranium was used as the aqueous phase. The axial dispersion model was used to determine the mass transfer parameters and modeling of this system. Also, the effect of operating parameters such as pulsation intensity, the rate of phases flow on the volumetric overall mass transfer parameters was investigated; namely total volumetric coefficients of continuous phase mass transfer (Koca) and axial scattering coefficients of continuous and scattered phase (Ec and Ed). The obtained results showed that the mass transfer parameters are strongly dependent on the pulse intensity and turbulence degree of the system. In addition, the mass transfer performance of this column is high for the uranium extraction from sulfate leach liquors. Moreover, the practical and novel correlations have been determined for prognostication of mass transfer parameters which are closely matched with the experimental results in the horizontal pulsed column.

The multi-objective optimization methods are widely used in various areas of science and engineering. In this paper, a multi-objective optimization algorithm has been used to design the optimal placement of fuel assemblies in the KWU reactor with the purposes of power flattening and increasing the multiplication factor. Also, thermal-hydraulic analysis has been performed to investigate the new arrangement during a hypothetical loss of coolant accident. For this purpose, the PESA-II algorithm is coupled with Nodal expansion code (for neutronic calculations) and COBRA-EN code (for thermal-hydraulic calculations). The results showed that the neutronic parameters including power flattening and the multiplication factor (increases from 1.0047 to 1.0058) improved by optimizing the fuel assemblies’ placement. It was also investigated that during a hypothetical loss of coolant accident up to 15%, the reactor could continue to operate in the safe mode. In addition, the results have emphasized the better performance of the PESA-II algorithm than the SPEA algorithm.

Considering the radioactivity of radiopharmaceuticals compounds, there are strict rules and regulations regarding their quality control aspects. One of the essential parameters in quality control is to determine the type and amount of radiopharmaceuticals impurities in order to ensure the prescribing of the correct dose. Impurity values are usually small, but these small amounts are also important and should be measured with high accuracy. The purpose of this study is to evaluate the simultaneous production of 186Re and 188Re with one target material and to investigate the production of probable impurities. To achieve the goal of this research, the work was carried out in two phases. In phase 1, a model based on the MCNPX code is designed to simulate target irradiation. In phase 2, the experimental assessment will be carried out using natural rhenium irradiation in Tehran research reactor. Both simulation and practical results showed that 186Re and 188Re can be produced with appropriate and nearly equal activities, simultaneously. Also, the amount of impurities is negligible compared to the main products. Our findings indicated that experimental data are in good agreement with simulation data (bias error less than 5%) and as a result, the simulation method is the powerful and useful technique to investigate different aspects of radioisotope production in reactor.

In this study, the removal of Zr (IV) from aqueous solutions was investigated using magnetic Fe3O4@PEG@TBP nanoparticles as a new adsorbent. Experiments were conducted to study the effects of initial pH, amount of adsorbent, shaking time, and initial Zr (IV) concentrations on zirconium sorption efficiency. The sorption of zirconium on Fe3O4@PEG@TBP nanoparticles was pH-dependent, and the optimal pH was 6.0. In kinetics studies, the sorption equilibrium was reached within 10 min, and the experimental data were well fitted by the pseudo-second-order model, and the equilibrium sorption capacities calculated by the model were almost the same as those determined by experiments. The maximum zirconium sorption capacity onto magnetic nanoparticles was estimated to be about 50 mg/g at 25 °C. Sodium acetate, sodium nitrate, sodium fluoride, and ammonium oxalate were used as desorbing agents. The highest values of zirconium desorption (100 %) was achieved using 0.5 M sodium fluoride as the desorbing agent. The present study suggested that this method is simple, fast, and highly efficient for zirconium removal from aqueous solutions by using magnetic nanoparticles.

In this study, recovery of uranium from leach liquor using solvent extraction technique in a horizontal pulsed sieve plate column was experimentally investigated. Extraction of uranium from an aqueous sulfate solution with 0.25M concentration acid, by using TOA solvent, diluted in kerosene and n-decanol modifier of 5%, 90% and 5% v/v respectively was studied and the influences of operation parameters including the phase flow rates along with pulsation intensity on the dispersed phase holdup, drop size and drop size distribution, as well as extraction efficiency, were evaluated. Increasing pulsation intensity along with the dispersed phase flow rate and decreasing the continuous phase flow rate caused to increase the extraction efficiency. Results showed that the horizontal pulsed sieve plate column has high efficiency for extraction of the uranium from leach liquor. Moreover, a comparative evaluation of available correlations proposed for the prediction of mean drop size and hold up in such columns have been conducted. New correlations for estimating mean drop size and hold up in a horizontal pulsed sieve-plate column were presented, which provided AARE of 7.7% and 8.2%, respectively.

Increasing the current, beam lifetime and, the quality of dynamic properties of the stored electron beam in the storage ring are the important purposes of synchrotrons. One of the phenomena affecting the beam quality is the longitudinal and transverse instabilities that increase as the beam current increases. Longitudinal instability in radiofrequency cavities has the greatest impact due to the high-quality factor of their higher order modes. As a result of these modes, one electron bunch affects the next one and it has a long-range nature. Longitudinal instabilities increase the energy spread and lead to loss of the beam current and reduce the intensity of the output synchrotron radiation. Considering the current and emittance of the Iranian light source which is 400 mA and 270 picometer-radian in the final phase of project, it is important to evaluate the higher order modes and identify the most effective ones. Simulation studies using CST Studio Suit software show that there are 13 monopole modes up to 1500 MHz in the project's 100 MHz radio frequency cavity. Seven modes are dangerous, and two modes at frequencies of 624.67 and 1432.55 MHz, with shunt impedances of 70.8 and 115 kHz, are very effective and must be dealt with in all phases of commissioning.