Publication Date: 2014
International Journal of Modern Physics E (2183013)(8)
A plasma boundary reconstruction code has been designed by using current filament method to calculate the magnetic flux and consequently plasma boundary in Damavand tokamak. Hence, a computer-based code "The Plasma Boundary Reconstruction Code in Tokamak (PBRCT)" was developed to make a graphical user interface and to speed up the plasma boundary estimation algorithm. All required tools as the plasma boundary and magnetic surface display (MSD), error display, primary conditions and modeling panel as well as a search motor to determine a good position and number of the current filaments to find a precise model have been considered. The core is a 3000 lines Matlab code and the graphical user interface is 10,000 lines in C# language. © 2014 World Scientific Publishing Company.
Publication Date: 2016
Journal of Materials Science (15734803)51(22)pp. 9991-10004
In this study, a novel PAN/NaX/ZnO nanocomposite absorbent was introduced and its ability to remove of uranium anionic species, which are the most dominant species of uranium in water at natural pH, from contaminated waters was studied. In this regards, micro and nano sized NaX zeolite and PAN/NaX/ZnO nanocomposite were successfully synthesized and characterized using various methods, including X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Fourier transforms infrared spectroscopy (FT-IR), atomic absorption spectroscopy (AAS), and Brunauer–Emmett–Teller (BET) specific surface area analysis. Batch technique was used to study the adsorption behavior of uranium ions from contaminated water as a function of solid–liquid ratio, initial uranium concentration, contact time, and temperature. Results showed that although NaX nanozeolite due to its negative framework charge, showed low sorption capacity for adsorption of uranium anionic species but the composite of it with ZnO nanoparticles and polyacrylonitrile (PAN) effectively improved its uranium adsorption capacity. The novel PAN/NaX/ZnO nanocomposite could selectively remove uranium ions from contaminated water with removal efficiency of more than 98.65 % in the presence of all anions and cations which are available in waters. © 2016, Springer Science+Business Media New York.
Publication Date: 2018
Radiation Physics and Chemistry (18790895)152pp. 1-5
In the present research, polyvinyl butyral film was prepared and irradiated by gamma-ray at various doses up to 250 kGy. Then, the effects of irradiation on the PVB were studied through the tensile test, FTIR, 1H-NMR and AFM techniques. The results of tensile tests show the existence of ‘necking’ up to 100 kGy and an increase in the toughness up to 70 kGy. Structural study by spectroscopic techniques show the formation of new groups as a result of increased conjugated double bonds. At higher doses, however, the polymer began to decompose due to degradation of the main chains, which led to reduced mechanical strength. Finally, AFM examination of the samples revealed less rough surface by irradiation. © 2018 Elsevier Ltd
Publication Date: 2011
Radiation Protection Dosimetry (17423406)147(1-2)pp. 296-299
Cardiac disease is one of the most important causes of death in the world. Coronary artery stenosis is a very common cardiac disease. Intravascular brachytherapy (IVBT) is one of the radiotherapy methods which have been used recently in coronary artery radiation therapy for the treatment of restenosis. 90Sr/ 90Y, a beta-emitting source, is a proper option for cardiovascular brachytherapy. In this research, a Monte Carlo simulation was done to calculate dosimetry parameters and effective equivalent doses to the heart and its surrounding tissues during IVBT. The results of this study were compared with the published experimental data and other simulations performed by different programs but with the same source of radiation. A very good agreement was found between results of this work and the published data. An assessment of the risk for cardiac and other sensitive soft tissues surrounding the treated vessel during 90Sr/ 90Y IVBT was also performed in the study. © The Author 2011. Published by Oxford University Press. All rights reserved.
Publication Date: 2012
Progress in Nuclear Energy (01491970)56pp. 61-70
Steam Generator (SG) is a crucial component of nuclear power plant. The proper water level control of a nuclear steam generator is of great importance in order to secure the sufficient cooling source of the nuclear reactor and to prevent damage of turbine blades. The water level control problem of steam generators has been a main cause of unexpected shutdowns of nuclear power plants which must be considered for plant safety and availability. The control problem is challenging, especially at low power levels due to shrink and swell phenomena and flow measurement errors. Moreover, the dynamics of steam generator vary as the power level changes. Therefore, it is necessary to improve the water level control system of SG. In this paper, an adaptive estimator-based dynamic sliding mode control method is developed for the level control problem. The proposed method exhibits the desired dynamic properties during the entire output tracking process independent of perturbations. Simulation results are presented to demonstrate the effectiveness of the proposed controller in terms of performance, robustness and stability. Simulation results confirm the improvement in transient response obtained by using the proposed controller. © 2011 Elsevier Ltd. All rights reserved.
Publication Date: 2018
Annals of Nuclear Energy (03064549)121pp. 382-405
Load-following is the most important operation in the nuclear reactors. In the nuclear reactors, imbalance of axial power distribution induces xenon oscillations. These oscillations must be maintained bounded within acceptable limits. Otherwise, the nuclear reactor could become unstable. Therefore, bounded imbalance of axial power distribution is considered to be a restriction for the load following operation. Also, in order to design the nuclear reactor control systems, xenon concentrations and delayed neutrons precursors densities must be available. But, physical measurement of these parameters is impossible. In this paper, for the first time, in order to estimate the xenon concentrations and delayed neutrons precursors densities and ensure imbalance of axial power distribution are kept bounded within acceptable limits during Load-following operation, an Adaptive Observer based Adaptive Sliding Mode Control based on the two-point kinetics reactor model is presented. The sliding mode method exhibits acceptable tracking performance in the presence of parametric uncertainty only at the expense of high gains and control chattering. Therefore, parameter uncertainties match envisaged by designing adaptive Algorithm for both the control and observer and high chattering authority is inhibited. The adaptation laws to online parameter adaptation and observer gains adaptation are generated using the Lyapunov approach. Also, the stability analysis is given by means of Lyapunov approach, thus the system is guaranteed to be stable within a large range. Simulation results are presented to demonstrate the effectiveness of the proposed controller for the load-following operation, in terms of the robustness and stability. Also, results show that the xenon oscillations kept bounded in the given region and the adaptive parameters are bounded during load following operation and observer follows the actual system variables accurately in the presence of the parameters uncertainties and external disturbances. © 2018 Elsevier Ltd
Publication Date: 2017
Annals of Nuclear Energy (03064549)103pp. 251-264
Control of the nuclear reactors during load-following operation is the most important problem in nuclear power plants due to safety reasons. In the nuclear reactor, imbalance of axial power distribution induces xenon oscillations. These fluctuations must be maintained bounded within allowable limits. Otherwise, the nuclear power plant could become unstable. Therefore, bounded these oscillations is considered to be a restriction for the load following operation. In this paper, for the first time, in order to ensure these oscillations are kept bounded within allowable limits during load-following operation, an adaptive robust control based on the multipoint kinetics reactor model is presented for P.W.R nuclear reactors. The reactor core is simulated based on the multi-point nuclear reactor model (neutronic and thermal-hydraulic) and three delayed neutrons groups. The adaptation laws for updating the reactor parameters are generated using the Lyapunov approach. The stability analysis is given by means Lyapunov approach, then the control system is guaranteed to be stable within a large range. Simulation results are presented to demonstrate the effectiveness of the proposed adaptive control in terms of performance, robustness and stability and show that the adaptive parameters are bounded and stable in the presence of the parameters uncertainties and disturbances. © 2017 Elsevier Ltd
Jabbari, I.,
Shahriari m., ,
Aghamiri s.m.r., ,
Monadi, S. Publication Date: 2012
Journal of Radioanalytical and Nuclear Chemistry (15882780)291(3)pp. 831-837
The energy deposition mesh tally option of MCNPX Monte Carlo code is very useful for 3-Dimentional (3D) dose calculations. In this study, the 3D dose calculation was done for CT-based Monte Carlo treatment planning in which the energy deposition mesh tally were superimposed on merged voxel model. The results were compared with those of obtained from the common energy deposition (*F8) tally method for all cells of non-merged voxel model. The results of these two tallies and their respective computational times are compared, and the advantages of the proposed method are discussed. For this purpose, a graphical user interface (GUI) application was developed for reading CT slice data of patient, creating voxelized model of patient, optionally merging adjacent cells with the same material to reduce the total number of cells, reading beam configuration from commercial treatment planning system transferred in DICOM-RT format, and showing the isodose distribution on the CT images. To compare the results of Monte Carlo calculated and TiGRT planning system (LinaTech LLC. USA), treatment head of the Siemens ONCOR Impression accelerator was also simulated and the phase-space data on the scoring plane just above the Y-jaws was created and used. The results for a real prostate intensity-modulated radiation therapy (IMRT) plan showed that the proposed method was fivefold faster while the precision was almost the same. © 2011 Akadémiai Kiadó, Budapest, Hungary.
Publication Date: 2012
Communications in Nonlinear Science and Numerical Simulation (10075704)17(1)pp. 414-425
This paper presents a new algorithm for designing dynamic sliding-mode controllers. The proposed controller is based on dynamic sliding manifolds to circumvent the difficulties associated with the conventional sliding mode controllers in the face of non-minimum phase systems. Unlike previous works, a proper and easy to implement algorithm is presented for designing the dynamic sliding manifold which facilitates the design of the controller. The output tracking problem in nonlinear non-minimum phase systems with matched and unmatched disturbances and matched nonlinearities is addressed. Then, the performance of the dynamic sliding mode controller is significantly improved by combining the given dynamic sliding manifold with online parameter adaptation. Simulations results are presented to demonstrate the effectiveness of the proposed sliding mode controller in terms of performance, robustness and stability. © 2011 Elsevier B.V.
Publication Date: 2020
IEEE Transactions on Image Processing (1057-7149)29pp. 5832-5847
The recent application of Fourier Based Iterative Reconstruction Method (FIRM) has made it possible to achieve high-quality 2D images from a fan beam Computed Tomography (CT) scan with a limited number of projections in a fast manner. The proposed methodology in this article is designed to provide 3D Radon space in linogram fashion to facilitate the use of FIRM with cone beam projections (CBP) for the reconstruction of 3D images in a sparse view angles Cone Beam CT (CBCT). For this reason, in the first phase, the 3D Radon space is generated using CBP data after discretization and optimization of the famous Grangeat's formula. The method used in this process involves fast Pseudo Polar Fourier transform (PPFT) based on 2D and 3D Discrete Radon Transformation (DRT) algorithms with no wraparound effects. In the second phase, we describe reconstruction of the objects with available Radon values, using direct inverse of 3D PPFT. The method presented in this section eliminates noises caused by interpolation from polar to Cartesian space and exhibits no thorn, V-shaped and wrinkle artifacts. This method reduces the complexity to O(n3 log n) for images of size {{\mathrm {n}}\times {\mathrm {n}} \times {\mathrm {n}}}. The Cone to Radon conversion (Cone2Radon) Toolbox in the first phase and MATLAB/Python toolbox in the second phase were tested on three digital phantoms and experiments demonstrate fast and accurate cone beam image reconstruction due to proposed modifications in all three stages of Grangeat's method. © 1992-2012 IEEE.
Publication Date: 2018
Progress in Nuclear Energy (01491970)106pp. 44-50
In this study, the core behavior following the reactor vessel lower head rupture together with the moderator system failure in a tank type heavy water research reactor, IHWRR, is analyzed through the MELCOR code. The focus is on the safety assessment of the reactor core for Design Extension Conditions and overall assessment of safety features of the reactor for any residual risk posed by severe accidents. The inherent features of IHWRR provide a broad spectrum of scenarios where the fuel does not melt, even if primary and moderator cooling are lost. Accordingly, coincident with vessel rupture, three different scenarios are considered for moderator failure: i) loss of moderator forced circulation, calandria tube rupture in ii) the upper and iii) the lower parts of the core. The obtained results showed that the vessel rupture that coincides with the tube rupture in the lower part of the core leads to the oxidation of entire Zr cladding and failure of the calandria tubes without core melt or hydrogen explosion in the containment. © 2018
Publication Date: 2020
Nuclear Engineering and Technology (17385733)(8)pp. 1603-1610
Due to ever-growing advancements in computers and relatively easy access to them, many efforts have been made to develop high-fidelity, high-performance, multi-physics tools, which play a crucial role in the design and operation of nuclear reactors. For this purpose in this study, the neutronic Monte Carlo and thermal-hydraulic sub-channel codes entitled MCNP and COBRA-EN, respectively, were applied for external coupling with each other. The coupled code was validated by code-to-code comparison with the internal couplings between MCNP5 and SUBCHANFLOW as well as MCNP6 and CTF. The simulation results of all code systems were in good agreement with each other. Then, as the second problem, the core of the VVER-1000 v446 reactor was simulated by the MCNP4C/COBRA-EN coupled code to measure the capability of the developed code to calculate the neutronic and thermohydraulic parameters of real and industrial cases. The simulation results of VVER-1000 core were compared with FSAR and another numerical solution of this benchmark. The obtained results showed that the ability of the MCNP4C/COBRA-EN code for estimating the neutronic and thermohydraulic parameters was very satisfactory. © 2020
Publication Date: 2025
Nuclear Engineering and Design (00295493)437
This study evaluates and examines the thermal–mechanical behavior of a NuScale reactor core which utilizes TVS-2 M hexagonal fuel assemblies. The efficiency of the fuel rods is validated using the FRAPCON code. Initially, the reactor's core is modeled with the MCNP code to locate the control banks. The design phase ensures the capability to shut down the reactor in two scenarios. In the Hot Zero Power (HZP) scenario, MCNP simulation reveals a sub-critical state with a multiplication factor of 0.94481 ± 0.00023. In the Cold Zero Power (CZP) scenario, the multiplication factor of 0.9935 ± 0.00023 confirms the adequacy of control assemblies. Subsequently, a thermal–mechanical analysis is conducted on the fuel rod over 1330 days, confirming its acceptable design and operational effectiveness in the core. Also, one of the parameters that can be examined during reactor control and load-following operations is Axial Offset (AO). Therefore, the study investigates the impact of AO on fuel rod's thermal–mechanical changes. The MCNP code was used to simulate control rod inputs and obtain power distribution data for each AO deviation. Based on assessments regarding the association between AO and the thermal–mechanical characteristics of fuel, it has been determined that the impact of power distribution increases significantly over time, particularly towards the end of the operational period. Afterward, based on FRAPCON results, an artificial neural network (ANN) estimator is developed to predict thermal–mechanical parameters at the beginning of the cycle (BOC). The ANN proves to be a powerful method for estimation. By employing the ANN estimator and exploring different cost functions based on thermal–mechanical parameters, the optimal AO is determined using a genetic algorithm, which enhances the reactor's performance, particularly in load-following operations. The attained optimal AO value for various cost functions are as follows: −0.10316, −0.19635, and −0.25817. This approach allows for the selection of the most efficient AO, leading to improved performance of the NuScale reactor core loaded with TVS-2 M hexagonal fuel assemblies. Indeed, optimization of AO is very important and useful for load-following operation. © 2025 Elsevier B.V.
Publication Date: 2025
Nuclear Engineering and Design (00295493)433
This study investigates the application of Artificial Intelligence in nuclear reactors, focusing on the impact of Accident Tolerant Fuel (ATF) composition and geometry on Small Modular Reactors (SMRs) parameters. Leveraging Artificial Neural Networks (ANNs) and Adaptive Neuro-Fuzzy Inference Systems (ANFIS), the research comprehensively examines the effects of cladding material (FeCrAl) modifications and burnable absorber concentration variations on key characteristics of the NuScale reactor. Neutronic calculations were meticulously conducted using MCNP6, a state-of-the-art Monte Carlo particle transport code, to assess reactivity, radial power peaking factor, feedback coefficients, and delayed neutron fraction. The results demonstrate that cladding thickness, chromium content, aluminum content, and gadolinia concentration significantly influence neutronic parameters. Furthermore, the study reveals intricate relationships between these parameters and reactor performance, providing valuable insights for reactor design and optimization. In addition to the aforementioned case studies and simulations, ANNs, and ANFIS were developed to predict key neutronic and safety parameters in the NuScale SMR loaded with ATF. The models, trained on extensive neutronic data, accurately predicted these parameters. The model's inputs included gadolinium concentration, cladding material weight percentage, and cladding thickness, while outputs encompassed excess reactivity, hot full power reactivity, effective delayed neutron fraction, radial power peaking factor, and fuel and coolant reactivity feedback coefficients. Both ANN and ANFIS models demonstrated exceptional accuracy and generalizability, offering a valuable tool for predicting the influence of ATF variations on reactor behavior. However, the ANN model consistently outperformed the ANFIS model, exhibiting lower prediction errors and demonstrating superior suitability for the intended application. © 2025 Elsevier B.V.
Publication Date: 2022
International Journal of Energy Research (1099114X)46(7)pp. 8838-8871
The reactor design includes optimizing parameters such as fuel composition. In this research, the issue of fuel composition optimization in a Small Modular Nuclear Reactor (SMR) is investigated. Indeed, considering the importance of fuel management optimization at the core of a nuclear reactor as a fundamental issue, this study analyzes gadolinium concentration effects on the neutronic and thermal hydraulic parameters in the NuScale reactor. In addition, optimizing the gadolinium concentration in fuel composition has been done via a genetic algorithm (GA) as a Machine Learning method. At first, the core of the NuScale reactor was modeled using neutronic codes (WIMS & CITATION). Then, the core of this reactor was simulated in different concentrations of natural gadolinium with 141 different concentration combinations in fuel assemblies through the mentioned neutronic codes. Furthermore, the neutronic parameters, including excess reactivity, radial and axial power peaking factors (PPFradial, PPFaxial) related to each design, were calculated. Thermal-hydraulic modeling of the hot channel for each design created was performed using ANSYS FLUENT code, and thermal-hydraulic parameters including heat transfer coefficient, MDNBR, pressure drop, Vout-Vin, and Vmax/Vavg, have been obtained. An artificial neural network (ANN) was trained using the obtained data. Finally, optimal gadolinium concentrations in fuels were determined using the ANN by implementing the GA. In the core of the conventional NuScale reactor, there are assemblies with 2%, 6%, and 8% gadolinium concentrations. Via optimization algorithm, in this paper, two sets of optimal gadolinium concentrations have been presented using different appropriate cost functions. First cost function proposed the optimal concentrations as 1.4256%, 4.2606%, and 5.4968%, while, based on the second one, 1.4502%, 4.2552%, and 5.5296% are optimal concentrations. Finally, the reactor core containing the optimal fuel composition has been redesigned and compared with the conventional NuScale reactor core. Most of the neutron and thermal-hydraulic parameters significantly improved over the NuScale reactor's optimally designed core. This optimization leads to better fuel management and safety in the optimized core than in the core of the NuScale reactor and can also economically increase power plant efficiency. © 2022 John Wiley & Sons Ltd.
Publication Date: 2014
Radiation Physics and Chemistry (18790895)101pp. 59-65
This paper offers a comprehensive investigation of image quality parameters for a small plasma focus as a pulsed hard x-ray source for radiography applications. A set of images were captured from some metal objects and electronic circuits using a low energy plasma focus at different voltages of capacitor bank and different pressures of argon gas. The x-ray source focal spot of this device was obtained to be about 0.6. mm using the penumbra imaging method. The image quality was studied by several parameters such as image contrast, line spread function (LSF) and modulation transfer function (MTF). Results showed that the contrast changes by variations in gas pressure. The best contrast was obtained at a pressure of 0.5. mbar and 3.75. kJ stored energy. The results of x-ray dose from the device showed that about 0.6. mGy is sufficient to obtain acceptable images on the film. The measurements of LSF and MTF parameters were carried out by means of a thin stainless steel wire 0.8. mm in diameter and the cut-off frequency was obtained to be about 1.5. cycles/mm. © 2014 Elsevier Ltd.
Publication Date: 2014
Radiation Protection Dosimetry (17423406)162(1-2)pp. 120-124
Renal angiography is one of the medical imaging methods in which patient and physician receive high equivalent doses due to long duration of fluoroscopy. In this research, equivalent doses of some radiosensitive tissues of patient (adult and child) and physician during renal angiography have been calculated by using adult and child Oak Ridge National Laboratory phantoms and Monte Carlo method (MCNPX). The results showed, in angiography of right kidney in a child and adult patient, that gall bladder with the amounts of 2.32 and 0.35 mSv, respectively, has received the most equivalent dose. About the physician, left hand, left eye and thymus absorbed the most amounts of doses, means 0.020 mSv. In addition, equivalent doses of the physician's lens eye, thyroid and knees were 0.023, 0.007 and 7.9E24 mSv, respectively. Although these values are less than the reported thresholds by ICRP 103, it should be noted that these amounts are related to one examination. © The Author 2014.
Ayoubi, S.,
Mohammadi, A.,
Abdi, M.R.,
Abbaszadeh afshar, F.,
Wang, L.,
Zeraatpisheh, M. Publication Date: 2022
Agronomy (20734395)12(2)
This study was executed to explore soil redistribution and soil quality changes induced by land degradation and then rehabilitation by orchard plantation in different slope positions in a semi-arid region in central Iran. A total of 72 surface soil samples (0–30 cm) were collected from three land uses (natural rangelands, dryland farming, and apple orchards) in four slope positions (shoulder, backslope, footslope, and toeslope). The soil physicochemical properties and magnetic parameters were measured, and soil redistribution was determined in the selected soil samples using the137Cs technique. The results showed that rangeland degradation and, subsequently, rainfed cultivation, led to a significant decline in the soil quality indicators, such as soil organic matter (SOM), total nitrogen (TN), available potassium (Kava), and available phosphorous (Pava), thus incurring further soil loss, as determined by the137Cs technique. Conversely, the conversion and rehabilitation of drylands to apple orchards cultivated on the contour terraces improved soil quality significantly and decreased soil loss (p < 0.05) and soil quality grade (p < 0.01). Additionally, the findings indicated that slope positions relative to land use change had a reasonable impact on the variability of soil properties and soil loss and deposition. The results of137Cs analysis showed that the drylands had the highest soil loss (185.3 t ha−1 yr−1) and maximum sedimentation (182. 5 t ha−1 yr−1) in the shoulder and footslope positions, respectively. The random forest model applied between137Cs inventory and soil properties indicated that calcium carbonate equivalent (CCE), TN, Pava, Kava, and bulk density (ρb) could explain 75% of the total variability in137Cs inventory with high R2 (0.94) and low RMSE (111.29). Magnetic measurements have shown great potential as a cost-effective and fast method for assessing soil redistribution in hilly regions, as confirmed by the findings of the137Cs analysis, which agreed well with the magnetic susceptibility at low frequency (χlf). Overall, the results confirmed that restoring abandoned dryland by orchard cultivation may improve soil quality and diminish soil loss in the semi-arid region of Iran. However, further research is required to assess other aspects of the ecosystem affected by this restoration. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
Publication Date: 2019
Annals of Nuclear Energy (03064549)133pp. 623-636
Increasing efficiency and improving energy consumption in the nuclear power plants have always been of interest for researchers. So, they try to improve the heat transfer in the applied systems. Hence, extensive research has been performed to apply an alternative fluid which has more suitable thermal properties instead of the conventional fluids such as water. One of these efforts is application of nanoparticles in a coolant fluid. The most important advantage of the nanoparticles is increase of the thermal conductivity and heat transfer coefficient. Considering the importance of the nanofluids effect as a coolant in the nuclear reactors on the reactor dynamic parameters, in this paper, for the first time, fuel and coolant temperature reactivity coefficients which have important contribution in the dynamic analysis and safety requirements of the nuclear reactors, are calculated in a VVER-1000 Nuclear Reactor with nanofluid as a coolant. In this study, using different volumetric percentages and sizes of Al2O3 (Alumina) nanoparticle, the important and fundamental parameters of the VVER-1000 reactor, including dynamic reactor parameters such as temperature reactivity coefficients are calculated. For this purpose, at the first, the equivalent cell of the fuel rod and the surrounding coolant nanofluid are simulated in the hexagonal fuel cell of the VVER-1000 reactor. Then, the thermal hydraulic calculations are carried out at different concentrations and sizes of the nanoparticle and their effects on the heat transfer parameters such as the heat transfer coefficient, temperature of coolant and fuel are assessed. Also, using the neutron calculating codes, the reactor core is simulated and the effect of coolant and fuel temperature changes on the effective multiplication factor is calculated and analyzed. Through the thermal hydraulic and neutronics calculations, the fuel and coolant temperature reactivity coefficients are calculated and analyzes versus variation of the concentration and size. © 2019 Elsevier Ltd
Publication Date: 2015
Nuclear Engineering and Technology (2234358X)47(7)pp. 814-826
The most important advantage of nanoparticles is the increased thermal conductivity coefficient and convection heat transfer coefficient so that, as a result of using a 1.5% volume concentration of nanoparticles, the thermal conductivity coefficient would increase by about twice. In this paper, the effects of a nanofluid (TiO2/water) on heat transfer characteristics such as the thermal conductivity coefficient, heat transfer coefficient, fuel clad, and fuel center temperatures in a VVER-1000 nuclear reactor are investigated. To this end, the cell equivalent of a fuel rod and its surrounding coolant fluid were obtained in the hexagonal fuel assembly of a VVER-1000 reactor. Then, a fuel rod was simulated in the hot channel using Computational Fluid Dynamics (CFD) simulation codes and thermohydraulic calculations (maximum fuel temperature, fluid outlet, Minimum Departure from Nucleate Boiling Ratio (MDNBR), etc.) were performed and compared with a VVER-1000 reactor without nanoparticles. One of the most important results of the analysis was that heat transfer and the thermal conductivity coefficient increased, and usage of the nanofluid reduced MDNBR. © 2015.
Publication Date: 2018
Iranian Journal of Medical Physics (17357241)15(3)pp. 169-175
Introduction: Crosstalk is a leakage of X-ray or light produced in a matrix of X-ray detectors or array of photodiodes in one element to other elements affecting on image contrast and spatial resolution. In this study, we assessed X-ray crosstalk in a computed tomography (CT) scanner with small detector elements to estimate the effect of various parameters such as X-ray tube voltage, detector element sizes, scintillator material, impurities in the scintillator material, and the material of detector separators on X-ray crosstalk. Materials and Methods: This study was performed using Monte Carlo simulation. In the first step, X-ray tube and its energy spectrum at the energies of 80, 100, 120, and 140 keV were simulated and validated by using SpekCalc and t-test. Then, other important parts of CT scanner, namely filters, detectors, and grids were simulated. X-ray crosstalk between CT detectors was calculated in air and in the presence of water phantom (as a simulator of human body) to compare the effect of scattered photons. Finally, the influence of some important parameters on X-ray crosstalk was evaluated. Results: In CT scanner with small elements, when using phantom, crosstalk increases by 16-50%. Using the lowest possible energies of X-ray, decreases the crosstalk up to 43% of its initial amount. Furthermore coating a 10 or 20 μm layer of tungsten or lead on the detector separators, decreases the X-ray crosstalk significantly. Conclusion: Choosing the proper high voltage, detectors' material and its dimensions, scintillator impurities and septa material can decrease X-ray crosstalk. © 2018, Mashhad University of Medical Sciences.
Karimi, A.H.,
Das, I.J.,
Chegeni, N.,
Jabbari, I.,
Jafari, F.,
Geraily, G. Publication Date: 2024
Scientific Reports (20452322)14(1)
Grid therapy recently has been picking momentum due to favorable outcomes in bulky tumors. This is being termed as Spatially Fractionated Radiation Therapy (SFRT) and lattice therapy. SFRT can be performed with specially designed blocks made with brass or cerrobend with repeated holes or using multi-leaf collimators where dosimetry is uncertain. The dosimetric challenge in grid therapy is the mystery behind the lower percentage depth dose (PDD) in grid fields. The knowledge about the beam quality, indexed by TPR20/10 (Tissue Phantom Ratio), is also necessary for absolute dosimetry of grid fields. Since the grid may change the quality of the primary photons, a new kq,q should be evaluated for absolute dosimetry of grid fields. A Monte Carlo (MC) approach is provided to resolving the dosimetric issues. Using 6 MV beam from a linear accelerator, MC simulation was performed using MCNPX code. Additionally, a commercial grid therapy device was used to simulate the grid fields. Beam parameters were validated with MC model for output factor, depth of maximum dose, PDDs, dose profiles, and TPR20/10. The electron and photon spectra were also compared between open and grid fields. The dmax is the same for open and grid fields. The PDD with grid is lower (~ 10%) than the open field. The difference in TPR20/10 of open and grid fields is observable (~ 5%). Accordingly, TPR20/10 is still a good index for the beam quality in grid fields and consequently choose the correct kq,q in measurements. The output factors for grid fields are 0.2 lower compared to open fields. The lower depth dose with grid therapy is due to lower depth fluence with scatter radiation but it does not impact the dosimetry as the calibration parameters are insensitive to the effective beam energies. Thus, standard dosimetry in open beam based on international protocol could be used. © The Author(s) 2024.
Publication Date: 2008
Annals of Nuclear Energy (03064549)35(12)pp. 2313-2320
This paper describes the application of a multilayer cellular neural network (CNN) to model and solve the time dependent one-speed neutron transport equation in slab geometry. We use a neutron angular flux in terms of the Chebyshev polynomials (TN) of the first kind and then we attempt to implement the equations in an equivalent electrical circuit. We apply this equivalent circuit to analyze the TN moments equation in a uniform finite slab using Marshak type vacuum boundary condition. The validity of the CNN results is evaluated with numerical solution of the steady state TN moments equations by MATLAB. Steady state, as well as transient simulations, shows a very good comparison between the two methods. We used our CNN model to simulate space-time response of total flux and its moments for various c (where c is the mean number of secondary neutrons per collision). The complete algorithm could be implemented using very large-scale integrated circuit (VLSI) circuitry. The efficiency of the calculation method makes it useful for neutron transport calculations. © 2008 Elsevier Ltd. All rights reserved.
Farzaneh, A.,
Abdi, M.R.,
Saraee, K.R.E.,
Mostajabodaavati m., M.,
Quaranta a., Publication Date: 2016
Optical Materials (09253467)55pp. 22-26
We report on the synthesis of cesium-iodide nanoparticles using sol-gel technique. The structural properties of CsI nanoparticles were characterized by X-ray diffraction and optical properties were followed by optical absorption and UV-vis fluorescence. Intense photoluminescence is also observed, with some spectral tuning possible with ripening time getting a range of emission photon wavelength approximately from 366 to 350 nm. The size effect on CsI luminescence leads to an increase in scintillation light yield, a redshift of the emission bands of the on-center and off-center self-trapped excitons (STEs) and an increase in the contribution of the off-center STEs to the net intrinsic emission yield. The energy transfer from the matrix to CsI nanoparticles is a key characteristic for scintillation detectors. So the scintillation spectra and decay curve to alpha particles of sample were monitored. © 2016 Elsevier B.V. All rights reserved.
Publication Date: 2017
Journal of Fusion Energy (15729591)36(4-5)pp. 120-126
The present study examined the formation of hot spots in the plasma column of a 3.5 kJ Mather-type plasma focus device. Experiments were performed with air and argon as operating gases at 0.2–1.5 mbar of pressures. X-ray source images were obtained using a pinhole camera with dental X-ray film as X-ray detector. The objective was to investigate the effect of the operating conditions and gas type on formation and characteristics of the hot spots. Results showed that when using air in comparison to argon, the total X-ray emission is increased and therefore, the hot spots are covered by this high intensity emission and would be observed less frequently in the image. Using metal filters to attenuate the low-energy X-rays revealed that the most energetic or the most intense radiation was emitted from the hot spots region. The images of the X-ray source obtained using argon at the middle pressures (0.4–0.6 mbar) showed both the plasma column and the photons emitted from the anode surface. A pressure of 0.8–1.5 mbar using argon was most likely to observe the hot spots. For argon gas, the 0.9 mbar was the pressure in which the hot spots were more frequently observed with high reproducibility of location and number. Measurements revealed that the typical size of a hot spot was 10–300 µm and the distance from the anode surface was 0.5–20 mm. © 2017, Springer Science+Business Media New York.
Ahmadian, S.,
Jabbari, I.,
Bagherimofidi, S.M.,
Rad, H.S. Publication Date: 2021
Magnetic Resonance Materials in Physics, Biology and Medicine (13528661)34(2)pp. 213-228
Objective: Inversion recovery-pointwise encoding time reduction with radial acquisition (IR-PETRA) is an effective magnetic resonance (MR) pulse sequence in generating pseudo-CTs. The hardware-related spatial-distortion (HRSD) in MR images potentially deteriorates the accuracy of pseudo-CTs. Thus, we aimed at characterizing HRSD for IR-PETRA. Materials and methods: gross-HRSDoverall (Euclidean-sum of gross-HRSDi (i = x, y, z)) for IR-PETRA was assessed using a brain-specific phantom for two MR scanners (1.5 T-Aera and 3.0 T-Prisma). Moreover, hardware imperfections were analyzed by determining gradient-nonlinearity spatial-distortion (GNSD) and B0-inhomogeneity spatial-distortion (B0ISD) for magnetization-prepared rapid acquisition gradient-echo (MP-RAGE) which has well-known distortion characteristics. Results: In 3.0 T, maximum of gross-GNSDoverall (Euclidean-sum of gross-GNSDi) and gross-B0ISD for MP-RAGE was 2.77 mm and 0.57 mm, respectively. For this scanner, the mean and maximum of gross-HRSDoverall for IR-PETRA were 0.63 ± 0.38 mm and 1.91 mm, respectively. In 1.5 T, maximum of gross-GNSDoverall and gross-B0ISD for MP-RAGE was 3.41 mm and 0.78 mm, respectively. The mean and maximum of gross-HRSDoverall for IR-PETRA were 1.02 ± 0.50 mm and 3.12 mm, respectively. Discussion: The spatial accuracy of MR images, besides being impacted by hardware performance, scanner capabilities, and imaging parameters, is mainly affected by its imaging strategy and data acquisition scheme. In 3.0 T, even without applying vendor correction algorithms, spatial accuracy of IR-PETRA image is sufficient for generating pseudo-CTs. In 1.5 T, distortion-correction is required to provide this accuracy. © 2020, European Society for Magnetic Resonance in Medicine and Biology (ESMRMB).
