Sharif Digital Repository

This study consists of two parts: steady state calculations and neutron noise calculations in the frequency domain for two rectangular and hexagonal geometries. In the steady state calculation, the neutron diffusion and its adjoint equations are approximated by two-dimensional coordinates in two-group energy and are solved using the average current nodal expansion method. Then, by considering the node size in the dimensions of a fuel assembly, different orders of flux expansion are investigated. For verification purposes, the calculations have been performed by power iteration method for two test problems of BIBLIS-2D and IAEA-2D. For rectangular geometry with increasing flux expansion order... 

The safety and optimal performance of nuclear reactors require online monitoring in the core. One of the most important requirements of core monitoring is the knowledge at all time of the neutron flux distribution in the core. The present M.Sc thesis describes a method which avoids the solution of time dependent neutron diffusion equation and uses online readings of the fixed in-core neutron detectors to reconstruct the three-dimensional (3D) neutron flux distribution. The essential idea of nodal synthesis method is separation of time and space dependence of the neutron flux distribution. The time dependent section of the flux distribution is determined by neutron detector readings and space... 

In this study, epoxy resin has been modified by nano-clay additives using direct mixing method and epoxy-clay nanocomposites were designed and produced with optimized percentage of clay content. By adding the powder of born carbide and lead oxide in nanocomposites new compounds are obtained. The results are used for protection against neutron and gamma rays, respectively. After preparation of epoxy-clay-born carbide and epoxy- clay-lead oxide nanocomposite the effects of irradiation and carbon fiber on mechanical and thermal properties of nanocomposites were examined. The Nanocomposites were exposed to Electron Beam Irradiation (EBI) in 100 and 500 kGy doses to investigate the effect of... 

Ahwaz is typical of a polluted city. It ranks in the third place after Tehran and Esfahan and with the onslaught Of the dust storms it has acquired the dubious distinction of 1st polluted city in the world. The pollution status of this city was investigated from May 2012 to May 2013. 110 air filters were collected during this period. The air filters were analysed with AAS and INAA techniques. with the use of AAS we measured the concentration of Cd, Cu, Fe, Mg, Mn, Ni and Pb elements. For the use of INAA method on the air filters we used two reactors of MNSR at Esfahan and the 5MW research reactor of Tehran. We managed to measure twenty five elements of Al , As , Br , Ca , Ce , Cl , Co , Cr ,... 

Localization of a neutron point source using a designed computer program namely “MCMC-MATURE” is performed. The computer program analyses several detector responses in some certain media by Markov Chain Monte Carlo (MCMC) method and a new iteration algorithm. Identification of the possible regions of source position would be found by analyzing the initial fluxes generated by mesh tally of MCNPX computer code. The designed computer program is capable to generate the flux between detectors. “Regular-Sequential”, “Irregular-Sequential” and “Non-Sequential” are three methods used for sampling the generated random number in two dimensions. Each sample multiplied by a sampling function and lead to... 

To study the structure of materials, among materials containing hydrogen, an instrument called the "small-angle neutron scattering instrument" is used. Having a monochromatic neutron beam is the most basic component of this instrument. This beam is often produced using a device called the "neutron velocity selector". The neutron velocity selector is a rotating mechanical piece that allows for passage of neutrons at a certain speed, according to its rotational speed. In fact, this device produces a monochromatic neutron beam with continuous flux. Until now, it has been designed and manufactured in a variety of models, which are generally divided into two groups of multi-disc and multi-blade... 

The core behaviour of a nuclear reactor might be fluctuated (deviations from the normal operating conditions) in operating conditions due to various reasons. Control rod vibrations and the alterations of coolant temperature and velocity could be the main reasons for the fluctuations. These fluctuations lead to neutronic flux noise and subsequently power noise. The main objective of the current thesis was to study the thermal-hydraulic noise of the PWRs in two-phase with the emphasis on VVER-1000, which is similar to the Bushehr-1 nuclear reactor. By considering the possibility of existing two-phase flow (maximum allowable quality is about 14%) in hot channel of the PWRs, thermal-hydraulic... 

Discovery of the effect of a massive object on the light path, reaching its exact formalism through general relativity and utilizing this phenomenon as a natural lens, opened a new window in astronomical research. Gravitational lensing occurs in three different ways; strong lensing, weak lensing, and microlensing which we focus on the third one. Gravitational microlensing is useful in studying dark matter candidates, discovering exoplanets, finding the surface properties of stars, and calculating the mass distribution of galactic objects. From a typical microlensing event, Einstein crossing time is obtained which is the time scale of source star passing by the lens. This is the only... 

In this study, the emission and detection of secondary particles such as gamma and neutron along the beam path was investigated to evaluate proton range during treatment. Simulations and detections were performed by Geant4 toolkit that was developed base on Monte Carlo method. First, a mono-energetic proton beams irradiated a homogeneous water phantom. Then the factors influencing the accuracy of beam range estimation have been investigated and finally proton beam range was evaluated by simulation the human eye phantom. According to the results, the accuracy of range verification by prompt gamma is very high, about 1 mm. In phantoms with more oxygen in their composition, the percentage of... 

Scintillation detectors are categorized as low energy resolution detectors in the classification of energy-sensitive detectors. The presence of broad peaks in the gamma-ray spectra of these detectors increases the overlapping probability of photopeaks of different isotopes and makes it extremely difficult to identify the spectra. The common method for identifying and quantifying of elements in a sample using nuclear spectroscopy is to use photopeak counts obtained with high-energy resolution detectors such as semiconductor detectors. To deal with the low energy resolution of scintillation detectors in quantitative analysis, the whole information of gamma-ray spectra is used instead of using... 

Steels as structural materials of pressure vessels of nuclear reactors, in addition to high temperatures and pressures, are exposed to ionizing radiation such as neutrons. The primary effects of damage caused by exposing these solids to radiation are the displacement of atoms from their equilibrium positions and the formation of point defects and damage clusters caused by damage accumulation due to displacement cascades produced by transmitting the energy of the incident particle to an atom by interactions such as elastic and inelastic scatterings neutrons with the nucleus. These microstructural changes cause large structural defects such as swelling, cracking, cracking, creep, reducing... 

Neutron noise equations, which are obtained by assuming small perturbations of macroscopic cross sections around a steady-state neutron field and by subsequently taking the Fourier transform in the frequency domain, have been usually solved by analytical techniques or by resorting to diffusion theory, but in this thesis, in order to increase of accuracy of neutron noise calculation, has been used transport approximation for neutron noise calculation and the Monte Carlo method has been used to solve transport equation of the neutron noise in the frequency domain. Since the transport equation of the neutron noise is a complex equation, a new Monte Carlo technique for treating complex-valued... 

Effective delayed neutrons fraction is one of important reactor dynamic parameters. Prompt neutrons decay constant is one of another reactor dynamic parameters that for its relation with effective delayed neutrons fraction is important. The Feynman- alpha method is one of famous methods in noise analysis. In this method, prompt neutrons decay constant can be obtained by obtaining variance to mean ratio of a detector counts in different time windows and fitting a specific formula to these ratios. In previous applied works, required data of Feynman- alpha method were obtaining mainly by experimental data or Monte Carlo simulations. In experimental way, detectors with high efficiency are needed... 

Neutron Radiography is one of the non-destructive testing methods of materials and due to its special application compared to gamma or X-ray imaging, it is highly regarded and developed in the world. A special application of neutron imaging is the imaging of materials with a low atomic number, even when coated with a material with a high atomic number. Neutron Radiography has different methods for capturing and recording images by neutrons. Among these methods, the following 7 methods can be mentioned: Neutron radiography (film), Track Etch, Digital neutron imaging, Neutron camera (DR System), Image plates (CR System), Flat panel silicon detectors (DR system) and Micro channel plates (DR... 

Generating the experimental spectrum for all gamma-ray elements is difficult and practically impossible in some industrial applications. Furthermore, in many applications such as neutron activation, it is not possible to obtain an experimental spectrum for a single isotope on account of the fact that the gamma-ray spectrum obtained from neutron activation is derived from the gamma-rays of various elements in a sample. Therefore, using computational techniques like Monte Carlo method for calculating the detector response functions seems an appropriate solution. The detector response functions for 3''×3'' NaI detectors have been simulated using MCNPX 2.7 code and Ptrac card in this project.... 

The widespread use of nuclear energy leads to obtain detailed information, such as neutron flux distribution (power) which is very effective in designing and evaluating the reactor safety. The neutron flux (power) reconstruction method uses the homogeneous flux distribution and the heterogeneous form function in a fuel assembly to calculate the heterogeneous power in the fuel rods. Therefore, this method has been widely developed in the last two decades. This study investigates to calculate two-dimensional and two-group neutron flux (power) in the fuel rod for both quadrilateral and hexagonal geometry related to core results by using nodal method. To achieve a more complete program and join... 

The main purpose of this research is to select a suitable solution for regeneration of ion exchange resins of TR system of Bushehr nuclear power plant and also to compare and evaluate the possibility of using industrial cationic resin (Amberlite IR120) instead of nuclear grade cationic resin (Amberlite IRN97).First, different solutions for regeneration of cationic resins were investigated. For this purpose, three strong acids including hydrochloric acid (HCl), sulfuric acid (H2SO4) and nitric acid (HNO3) were selected and each of these acids was tested in two different concentrations and two different linear velocities; Also, to evaluate the appropriate solution for anionic resin... 

Since the beginning of discussion on neutron-gamma discrimination, different methods were suggested for this purpose. In early 2000s, Analogue methods were mainly used to discriminate the spectrum in mixed fields which mostly depends on electronic modules used in the lab setup; Nowadays, with improvements in digital pulse processing techniques, analyzing mixed neutron-gamma fields for pulse discrimination is also available.In this research, the recent MC developed toolkit called GEANT4 is used to simulate the 3-inch BC501A scintillation detector and 500 mCi Am-Be source (that emits neutron and gamma at the same time). For the next step, an experiment with same source and detector was done... 

If nuclear radiation is not weakened and absorbed, it can cause serious damage to human devices or the environment. Dual-purpose dry casks are one of the sources of nuclear radiation production as a place to keep the spent fuel assemblies. One of the ways to protect against them is to use shield. One of the most common of them is composite shield. The composite used in this study has a polymer matrix. The matrix of the used polymer is epoxy resin. In this study, two separate composites have been made to attenuate neutron and gamma radiation. In this thesis, first, by using the MCNPX code, the necessary simulations for the design and construction of composite shields have been carried out.... 

One of the most essential concepts for describing neutron stars is investigating their radial mass distribution or mass-radius relation. The aim of this thesis is to evaluate radial mass distribution of neutron stars in the presence of magnetic fields. To achieve this objective we use the Tolman- Oppenheimer-Volkoff equation of hydrostatic equilibrium for non-rotating cases and the Hartle- Thorne equations for rotating cases. olving these equations depends on determination of equation of state of neutron star in the presence of magnetic fields. For determining the corresponding equation of state, one can use QCD-like non-perturbative models, in particular Nambu-Jona- Lasinio (NJL) model. In...