Sharif Digital Repository

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... 

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... 

In every nuclear reactor core, there are neutron flux fluctuations around the mean value. The neutron noise is the deviation between the time-dependent neutron flux and its expected value, assuming that all process is stationary and ergodic in time. These fluctuations can be caused by the stochastic nature of neutron interactions or mechanical oscillations in the reactor cores. In a reactor working at a high-power level, mechanical fluctuations are the major cause of the fluctuations measured by the detectors. These mechanical vibrations include control rod or fuel rod vibrations, changes in the incoming coolant speed, or changes in the coolant temperature. These perturbations are seen as... 

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... 

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.... 

Our main goal in this project is to calculate the cell survival fraction (SF) in unhealthy tissue after carbon ion beams are emitted and hit the target tissue. At present, in the stages of carbon therapy, it usually takes a long time to make the necessary calculations for that particular person, and this makes the treatment process progress slowly, but in this project, we intend to address this problem with Eliminating the use of neural network. The main reason is the use of carbon ions to increase efficiency in the treatment of tumors and deep cancerous tissues. To do this project, we first convert the carbon ion energy to the dose absorbed at the desired point. For this phase of the... 

In radiation therapy, different radiation were used to cancer treatment. The use of hadrons is more common than gamma rays for cancer treatment. Hadron therapy is appropriate to treat cancers that are close to organs at risk and can be severely damaged by X-rays during treatment. The survival fraction of cells was irradiated is important during treatment. In this study, using Geant code, simulation of choroidal melanoma tumor in the phantom of the eye was performed. The linear energy transfer and dose data of proton beam radiation were calculated, in addition, the cell survival fraction were calculated using Survival codeand the Geant simulation data such as number of inputs and dose with... 

Gamma ray spectroscopy has a special place in the industrial applications of nuclear radiation. Currently, the most common device for gamma ray detection and spectroscopy is the sodium iodide scintillation detector. Long life and high efficiency and reasonable price of these detectors are the reasons for the development of the use of these detectors in industries and laboratories. But these detectors in the classification of energy sensitive detectors are considered as detectors with low resolution. The presence of broad peaks in the gamma ray spectrum of this detector increases the possibility of interference of peaks related to different energies and makes it difficult to identify the... 

The present M.Sc. thesis consists of two sections including the static calculation and neutron noise calculation in rectangular and hexagonal geometries. The multi-group, two dimensional neutron diffusion equations and corresponding adjoint equations are solved in the static calculation. The spatial discretization of equations is based on Average Current Nodal Expansion Method (ACNEM). Size of nodes is the same size of the fuel assemblies in modeling both of rectangular and hexagonal geometries. The results are benchmarked against the valid results for BIBLIS-2D and IAEA-2D benchmark problems. In the second section, neutron noise calculations are performed for two types of noise sources,... 

One of the ways to enhance the safety and economic performance of nuclear power plants, is to choose an appropriate policy for arrange the reactor fuel assembly in the beginning of each cycle. There are variety of ways to optimize the layout of the fuel in the reactor core, but to achieve more than one goal, choosing multi-objective method can be used.One of the intelligent optimization methods is the genetic algorithms that emulate nature of biological processes and can be used to optimize two or more of the target.The goals of this research is to increase the neutron multiplication factor is to make maximum use of the fuel in the reactor and maintain the radial power peaking factor for... 

In this project we studied Soft and Hard x-ray emissions from Sharif University of Technology’s Plasma Focus (SUT-PF) device filled with Argon gas. SUT-PF is a Mather type plasma focus device ( ). Our expriments have been done in various charging voltages ( ) and various filling pressures. Using different diagnostics X-ray’s intensity in each working condition (voltage and pressure) has been measured and finally these data analysed to find optimum conditions for maximum x-ray production in this device. Used diagnostics was: Rogowski coil, photodiodes combination with ultra thin metal foils, type Plastic scintillation detectors, and pinhole camera. In each shot, time resolved Rogowski coil,... 

Many advanced process plants and machines are extremely complex, and always depend on automatic control for satisfactory operation. In order to achieve and maintain system stability and assure satisfactory and safe operation, there is increasing demand for dynamic systems to continue acceptable operation following failures. Therefore failures detection has always been an important aspect of fault tolerant control design. In nuclear power plant, for example, tens of alarms can occur in a few second after a fault. Fault detection might be of utmost importance due to safety, political and other reasons. There are many methods to detect fault on the system. In this project approach based on... 

In this thesis, TTL-1 thermo hydraulic test loop which was constructed in the Nuclear Science and Technology Research Institute (NSTRI) has been modified. These modifications include changing core section from one fuel rod to a fuel assembly with triangular arrangement, adding a pressurizer on the hot leg of loop, an accumulator, LOCA valve and installation of new sensors for upgrading of data acquisition system and modification of loop piping design. By these modifications, we will able to study different accidents such as LOHA, LOFA and LOCA and validate nuclear thermo hydraulic codes. Moreover, this new thermo hydraulic test loop (TTL-2) has been modeled by RELAP5/MOD3.2 in order to... 

In this thesis a digital electronic readout system is designed and constructed for MWPC detector. This detector is aimed to be used in ILSF synchrotron. The detector readout system is based on delay line and position of incoming photon can be underestood from delay of cathode signals arrivals. The detector has two dimentional position detecting system and the instruments used in every dimention are identical. Every dimention has a start and stop signal, the time difference between these two signals can be detected by time to amplitude converter or time to digital converter. In this thesis time to digital converter has been used and the time diference of start and stop signals arrivals is... 

Validation of dosimetry accuracy in the context of advanced methods for radiotherapy, including proton therapy for ensure the accuracy of treatment plan is nessecory. One of the reasons for using MC code is the modeling of PT systems and the support of more accurate computation of dose distribution in clinical tarin. The purpose of this project is to validate the modeling of a spot scanning proton therapy system using a GATE MC code. In this study, the dose distribution calculated in the calibration process of the device and syno TPS is used as a criterion and the dose distribution obtained from the GATE MC code is calculated and validated with it. For this purpose, a water phantom was used... 

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... 

Design and construction process of special kind of sputter ion pump is described briefly in this paper. In order to investigate the optimization of effective parameters in choosing and designing ILSF ion pumps, this pump has been designed and manufactured. By optimizing some parameters such as dimension and shape of penning cells, anode voltage, magnetic field and internal structure of pump, it is possible to significantly decrease the cost of construction and operation of synchrotron vacuum system. By using the results of simulations and calculations of electromagnetic field, plasma simulation or glow discharge, titanium sputtering, etc., critical parameters in design of internal structure... 

In this study, the reconstruction of the neutron noise source in the core of the VVER-1000 reactor was carried out using fuzzy neural network and parallel processing of parallel process circuit design. The noise of power reactors is derived from neutron fluctuations. Which are affected by fluctuations in reactor characteristics. These oscillations can be caused by the displacement of the elements forming the core or due to changes in temperature or density and so on. It is clear that any change in the elements of a reactor will make itself a change in the corresponding to cross-section of material. These changes called as pertubation. In this project, by using neuro-fuzzy network...