مجله علوم و فنون هسته ای
سال چهلم شماره 2 (پیاپی 88، تابستان 1398)

The main purpose of the work is to develop a valid physical model and an accurate numerical technique to describe the occurred phenomenon of the VVER-1000 fuel rod, during its lifetime, especially for high burn up conditions. There are many factors involved in the fuel rod performance, which each of them, intricately affect its behavior during normal operation. The accurate prediction of the fuel behavior is obligatory and will be utilizable for the fuel designers. In geneval, fuel rod behavior is affected by the various chemical, mechanical, and thermo neutronic phenomena. For a detailed assessment of the fuel behavior inside the reactor core, the mentioned factors and the dominant aspects must be modeled accurately. The physical models and correlations used in this paper, are chosen in such a way that all the simulation results be in a good agreement with the available post-irradiation examination data (PIE) and outputs of the FRAPCON-3.3 fuel rod performance code.

The article aims in the studying of thermal-hydraulic simulation of the VVER-1000 reactor core fuel assemblies’ reaction to the mass flux changes which are caused by the lose of coolant accident and its sudden pressure drop. The analysis of mentioned accident is performed in concise periods (mili second) by the use of the sound effect. Time-related thermal-hydraulic equations were analyzed by the method of a compressible fluid in a single heated channel and were evaluated by the results of the mentioned transient, in a PWR reactor. The mentioned transient was simulated in RELAP5 code and results were compared to the previous ones. Then, 28 reactor fuel assemblies were studied, considering the 1/6 symmetry of VVER-1000 reactor and unique features of every assembly. Mass flux drop was happened the end of the channel, after a few seconds. It was observed that mass flux is at dependent on the role of every assembly in the production of core heat power. The acoustic effect reveals some of the perturbations in mass flux changes, considering every fuel assembly features.

Safety is one of the most critical issues in any test. The flexural test is a significant one to obtain material specifications. In this paper, a standard sample dose rate was calculated for the graphite flexural test in Tehran research reactor. Using different standards, the dose was computed at different distances and two periods of radiation, 15-40 days. Our calculations were performed with the ORIGEN and MCNPX codes. The impurity amounts of the material were measured by two methods of X-ray Fluorescence (XRF) and Inductively Coupled Plasma, Atomic Emission Spectroscopy (ICP-AES). The obtained results show that the Claiborne & Trubey standard is more stringent than other standards, and it has less than 2 μSv/h dose with the observance of 100cm distance and 20 days after irradiation. Moreover, calculations of the transfer chamber indicate that there is no limitation for the transport of the samples. Finally, it can be concluded that the considered method of this research can be used also for other materials at the reactor core.

In this paper, a Helicon plasma system with Nagoya Type III antenna was designed and simulated by using COMSOL Multiphysics 5.2. In our simulation, all effective interactions and parameters in the plasma production process are considered. Besides, the cross-sections of the reactions which are occurred in the plasma with the energy range from 0.001 eV to 1MeV are applied in the software. Meanwhile, the Argon-Helicon plasma is produced by using Nagoya Type III antenna considering the following conditions: the magnetic field of 600 G, the antenna current 6 Ampere, with the operating gas pressure 10 mTorr and inlet gas flux of 50 (SCCM). Finally, the plasma density of the order 2×1018 m-3 and a temperature of 2.6 eV were obtained by using the Nagoya antenna. The effect of the variations of the current, which was applied to the Nagoya antenna, on the density and absorbed power of the Helicon plasma was also investigated. This simulation was made for seven operational helicon devices, and the results have seemed reasonable.

In this work, the hybrid configuration was used to produce the single longitudinal mode operation of pulsed CO2 laser with 14 cm long active volume at the pressure 3 atm. For this resean, a low pressure continuous wave CO2 laser with 120 cm long active volume is used. It was found that the emitted pulses of the system exhibit single mode behavior in above threshold condition and also at the pressures up to 7 mbar below threshold condition. To characterize the system performance, various parameters of the single mode pulses at different pressures and powers of the continuous wave laser were analyzed. Furthermore, the threshold pressure of the continuous wave laser for the single mode operation was obtained at about 9.5 mbar. It is shown that in both above and below threshold conditions, the single mode pulses have higher durations and rise times and also lower build up times.

The propagation of the small amplitude ion-acoustic solitary waves (IASWs) is studied in a plasma containing cold fluid ions and multi-temperature electrons (cool and hot electrons) with the nonextensive distribution. In this paper, we were firstly written a set of fluid equations in the spherical geometry. Then, spherical Korteweg–de Vries (KdV) equation was derived using a reductive perturbation method. The obtained spherical Korteweg–de Vries equation was solved using a homotopy perturbation method (HPM). Furthermore, the impact of the electron nonextensivity, the density ratio of electrons and ions and the temperature ratio on the characteristics of ion- acoustic solitary waves were studied. The analytical results show that a decrease in the electron nonextensivity increases the soliton ion- acoustic width. On the other word, it was observed that a reduction in the nonextensivity parameter increases the nonlinear coefficient of the KdV equation.

In this paper, we used a coherent beam combination to design a 50 kW high power laser beam for energy applications. Because of the strong environmental turbulence, degrade the coherent beam combination advantages, low turbulence level is considered. Combining elements are composed of 19 polarized single mode 3 kW high power fiber lasers where are arranged in the co- two centric hexagonal rings. Each of the fiber a lasers has a collimator with a 30 mm beam spot size output. We extended the transmitting range to z=10 km and the improved filling factor up to f=0.91. Therefore, power loss at the side lobes are minimized and resulted in the rise of combination efficiency to 88%, which is the highest published result. The central spot size radius on the target is R=5.9 cm, where indicate 0.45 kW/cm2 power density. Also, the effect of Phase errors of the combining elements at the far- field, which cause the ray intensity scattering from the center spot to the side lobes is investigated.

In the present work, a hybrid material, as an adsorbent based on a mesoporous silica nanoparticle Sainta Barbara Amorphous-15 (SBA-15) and inorganic adsorbent, tin tungsto-molybdo-phosphate (TWMP), was synthesized for the investigation of adsorption behavior of uranium in aqueous solution under ambient conditions. The synthesized hybrid was characterized by the X-ray diffraction, Fourier transfer infra-red, thermogravimetry, and N2 adsorption-desorption analysis. The obtained results confirm that TWMP has been immobilized on SBA-15 very well. Furthermore, the experimental results show that uranium adsorption on the hybrid is strongly influenced by the hydronium ion concentration, contact time, and initial concentration of uranium. The values of the calculated correlation coefficients of the linear regressions (R2) indicate that, the adsorption data are fitted by the Langmuir isotherm model very well. The obtained amount of RL (0.1) shows that the adsorption process is favorable. The amount of E obtained by the Dubinin-Radushkevich model, suggests that the predominant reaction mechanism is a physisorption process. Kinetic data of adsorption indicate that the adsorption process can be described by the pseudo second-order reaction rate model. Finally, the obtained maximum adsorption capacity of uranium (193.6 mg.g-1) on hybrid, indicates that the prepared material is a perfect candidate for the adsorption and removal of the uranium from wastewater.

The existence of heavy metals in nature is one of the pressing concerns because of their toxicity and threat to human life. The aim of this study is the preparation of suitable adsorbent for heavy metal adsorption from the waste water using nanotechnology. In this work, modified graphene/ZnO (MG/ZnO) nanocomposite was first synthesized. The as-prepared composite was then used as an adsorbent for heavy metal removal, and its adsorption efficiency was compared with the modified graphene and ZnO nanoparticles. Adsorption efficiency of the modified graphene/ZnO was found higher than modified graphene and ZnO nanoparticles. The influence of the effective parameters on the adsorption process was studied and optimized. The obtained optimum conditions were: time = 30 min, an adsorbent dosage of 0.03 g/L, pH of 6, and T = 25˚C. The experimental data were best described by the pseudo-second-order kinetic and Langmuir isotherm models. The obtained thermodynamic parameters indicate that the adsorption process was exothermic and spontaneous.

The stoichiometric relation for the extraction of thorium(IV) from acidic nitrate solutions with Cyanex272 was investigated. The effects of the extractant and nitric acid concentrations were studied. The extracted species at three different acidities (low, middle, and high levels) were found to be [Th(NO3)(OH)3.HA], [Th(NO3)(OH)2A.HA], and [Th(NO3)4.HA], respectively, based on the slope analysis method. The results showed that the extraction of thorium follow solvation mechanism in low, 0.001 M and high, 8 M concentration Nitric acid medium. While, in the middle acid conditions, 1 M, is in the form of cation exchange. The extracted Th(IV) species contain one CYANEX 272 molecule in the all acidic ranges.

Mineralogical examination of the gangue and ore parts of the Se-Chahun magnetite-apatite ore deposit revealed the existence of Th and REE bearing minerals with paragenetic relationships with amphiboles, magnetite and calcite. Trace and REE host minerals are found in both of the gangue and the magnetite-apatite ore showing remarkable concentration in a phase referred to as the brecciated phase. This zone (phase) is characterized by high amounts of trace (Th) and light rare earth elements including La, Ce, Pr and Nd that were revealed in geochemical analysis. Mineralization of these elements is related to fluids appeared after magnetite mineralization in the region and resulted in metasomatism of the host rocks and a part of the ore and also concentration of the REE and trace elements as phosphates and silicates, respectively. There is not a clear key concerning the origin of these fluids but based on the geochemical evidence, the probable provenance is thought to be related to the magmas derived from the arc related subvolcanic bodies injected in subduction zones. Based on the paragenetic and geochemical evidence, a part of these elements is transported by carbonate complexes and accumulated in the brecciated rocks.

The aim of this study is preparing a conductive tissue equivalent composite similar to expensive and limited access commercial A-150 plastic, in which, the Conductive Carbon Nanotubes (CNT) are used instead of black carbon. For this rescan, to obtain more conductivity nanocomposites of polyamide/polyethylene (PA/PE) containing 1 to 4% carbon nanotube were made by melt mixing. The resulting electrical conductivity of the composite with 3% CNT reached to 3× 10-6 S/cm which is in the range of semi-conductive materials. The Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) pictures show an electrical network formation in continuous PA phase and at the interface of two phases. In the studies of mechanical properties, a significant increase in the modulus of PA/PE/CNT nanocomposite with 3% CNT was observed. Meanwhile, determination of the density and percentage of the elements ​​of this nanocomposite indicated that the obtained amounts were similar to that declared for the muscle tissue and A-150 plastic. Farther, Microdosimetry calculations showed that the linear energy distributions obtained from the microdosimeters with a wall of PA/PE/CNT nanocomposite and A-150, are well compatible. Therefore, this composite could be a suitable substitute for A-150, as an electrode of the gaseous microdosimeters

Uranium (VI) solvent extraction from the acidic sulfate solutions by Alamine 336 diluted in kerosene has been investigated. The effect of the contact time between phases, sulfuric acid concentration, extractant concentration, uranium concentration, organic/aqueous phase ratio, and temperature were studied. The results demonstrated that the uranium extraction was a fast, exothermic, and spontaneous reaction. Log Kex is calculated to be 5.94. The process parametric variation studies indicated a strong influence of sulfuric acid concentration on the extraction percentage of uranium. The extraction percentage was increased with an increase in the extractant concentration as well as the organic/aqueous phase ratio and decreased with an increase in the uranium concentration. Using 0.05 mol L-1 Alamine 336˚C at 25˚C with organic/aqueous phase ratio of 1:1, an extraction percentage of about 99.72% was achieved when the H2SO4 concentration was 0.15 mol L-1. The uranium extraction from the leach liquor solution was done under these optimum conditions, and iron (ІІІ) removal has investigated. Uranium stripping from the loaded solvent was carried out by many salt and acid solutions in the four steps. The effect of temperature was studied, and for the first time in this study, the enthalpy change of stripping reaction by using various chemical agents was obtained. 99.87% of uranium loaded in the organic phase was removed by 0.5 mol L-1 (NH4)2CO3 in a single stripping step.