Sharif Digital Repository

This thesis has been done with the goal of comprehensive neutronic calculation of a small size High Temperature Gas Cooled Reactor and HTTR was selected as a reference reactor for simulations. Calculations are divided into four parts of zero and full power stochastic calculations, deterministic calculations and noise analysis. In zero power calculations, an algorithm is proposed for modeling random arrangement of TRISO particles in the fuel compacts of HTTR. The effect of this arrangement on criticality calculations, i.e. effective multiplication factor and critical position of control rods, is then compared with regular arrangement. In the second part, full power calculations with the use... 

In this research work an analytical instrument has been developed for assessment of energy technologies, R&D resource allocation and technology development. Development of new technologies has been considered according to the specific conditions of developing countries. The analytical instrument includes two models interlinked with each other: energy technology assessment and optimal control of innovation activities. Energy technology assessment and prioritization of new energy technologies are provided by the model of the energy supply system that contains a detailed representation of current and emerging technologies characterized in terms of their technical indices. The results of this... 

In this thesis, we consider the simulation and active control of a centrifugal compressor in during surge occurrence. Surge, as an aerodynamic instability in compressors, causes to severe decrease of efficiency and loss of energy and with stabilizing the compressor in this condition, efficiency and system reliability increase. Nowadays, anti surge systems are used for surge avoidance in different industrials. They recycle the compressed gas from compressor down-stream to up-stream in instability condition and cause to exit the operation point from unstable zone. In this thesis, at first compression system is modeled based on Greitzer model and governing equation of compressor shaft in surge... 

Because of the Complexity in Calculating the Probability of Failure of the System, This Computation is Done by the Software Have Been Developed for this Purpose. Of Course, When We Use Them, We See That Each of Them Have Their Advantages and Disadvantages. One of the disadvantages that have been tried to be resolved over time, the type of programming and algorithm for calculation of it is the fault tree Because new techniques like modularization which have been designed in recent years, a significant improvement in accuracy and speed performance computing applications that use this method have been obtained.In This Thesis Has Developed Software That is Able to Calculate the Probability of... 

In the present work storage of hydrogen molecules in hybrid nanostructures has been evaluated. Hybrid nanostructures consist of carbon structure bases which have been doped by metal atoms. Carbon structures used in this thesis include graphene and metal organic frameworks (MOFs). Carbon structures have superior properties such as very low density, while metal atoms are considered to enhance the interactions and increase the hydrogen storage capacity. In the first step of the work, Monte Carlo method was applied to model the system. To develop the Monte Carlo method for hydrogen adsorption on graphene sheets, Feynman-Hibbs corrections were added to Lennard-Jones potential. However in the next... 

In this study the modeling of low pressure injection system to remove heat from the reactor core of Bushehr nuclear power plant(BNPP) after it has been paid off. After a full assessment of the primary circuit and the Bushehr nuclear power plant emergency cooling system, all the information needed to model the primary circuit and the low pressure injection system and the plant were collected in the available evidence. Then, according to the code, a code RELAP5 standards for light-water reactors(LWR) in steady state and transient parameters termohydraulic is a component of the hydrodynamic and thermal structures suitable for modeling of low-pressure injection system and primary circuit... 

Due to inherent dangerous on human and environment safety in the nuclear power plant has significant importance. In order to ensure the safety of the plant and proper functioning ofits various components,before its operational exploitation, a series of commissioning tests should be conducted according to international standards for nuclear power plants. In addition, safety of the plant can be guaranteed bymodeling of transient states and possible scenarios of accident in different situations.In this research,by gathering geometric data and information about the facilities installed in the plant, modeling of Commissioning test of Bushehr Nuclear Power Plant (BNPP) and its associated accident... 

The event of the loss of off-site power (loop) is one of the nuclear power plant accidents which, if occurred, in worst case , the main generator will be stopped after a short time after beginning of the accident and AC feed of the power plant loads such as safety systems and main pumps of primary circuit will be interrupted . In order to control the event, it is necessary to start the emergency diesel generators, at least for one of safety channels. If the diesel generators are not started or not loaded, the accident will advance, and it will be changed to station black-out (SBO). If the SBO occurs, due to non operation of residual heat removal systems (RHR), it may be result to melt the... 

Gaseous uranium hexa fluoride is the basic component for almost all industrial enrichment methods. In this work different UF6 production methods are described and fluorination of green salt powder in a flying bed reactor is selected and simulated. At the present time one flying bed reactor is producing UF6 in Esfahan UCF facilities which its specifications and characteristics are used for the present project. In this research, a multi stage method is used and some new options are added to simulation in each step. First, gas mixing without the presence of solid particles is simulated and its results are discussed qualitatively and some suggestions are expressed to obtain better results. After... 

In this survey the TTL-1 thermal hydraulic test loop in Nuclear Science and Technology Research Institute (NSTRI) has been modified to study thermal hydraulic phenomenon in research reactor thermal condition. These modifications include: replacing the test section containing a single heating rod by a group of 31 rods in a triangular array, relocating the pressurizer from the cold leg to the hot leg and improving piping of the test loop. In order to measure the time dependant flowrate of the coolant, a rotameter flowmeter is added. Three level meter measure the water level in pressurizer, test section and the primary loop drain tank and a 3-phase AC inverter controls the rotational speed of... 

Energy industries in many countries have initiated the process of privatization. Restructuring of energy systems is usually started with dividing the vertically integrated national systems into regional companies. Due to the geographical dimension of energy systems and natural monopoly in many activities, the process of privatization has started with segmentation of the vertically integrated national systems into regional companies. Thus, regional independent companies are formed that include a collection of producers and consumers of energy in their geographic area. These regional companies are economic entities who are pursuing a policy of maximize profit. On the other hand, exchange of... 

HTGRs are considered as 4th generation reactors & have major characteristics such as inherent safety & high temperature applications. In this thesis, HTTR reactor has been selected as a reference reactor &studied at cold zero power (CZP) & hot full power (HFP) states with probabilistic MCNPX 2.6.0 code. At CZP state, radial & axial flux distribution, control rod criticality height with & without considering nitrogen as impurity in fuel blocks, effective multiplication factor at experimental criticality height & finally effective delayed neutron fraction (βeff) have been evaluated. Moreover, at HFP state, prompt neutron life time (λ), effective multiplication factor versus time curve for... 

Load following operations on PWRs that Adjusted based on demand of network electricity, in fact is not easy, because of the complex conditions of the reactor heart.One of the reasons for the complexity when changing the reactor power level is the production of Xe in the heart and its associated oscillations, which also cause oscillations in the power distribution.Many studies have been performed on the control of xe oscillations based on solving complex mathematical problems and neutron diffusion equations. But what is the research method of choice is the simple and practical TRIAX method. In this method by Convergence control of elliptic trajectory related to three axial offset (Axial... 

The capability of Bushehr nuclear power plant spray system to reduce fission product and control a specified severe accident has been investigated in this study. In order to evaluate spray system in one of the worst cases for containment, we have chosen Large Break Loss of Coolant Accident (LB-LOCA) without access to active part of ECCS system. We have only simulated containment, so the leakage of various materials from core and primary circuit of nuclear power plant are considered as the boundary conditions for simulation. Following the Fukushima accident in 2011, many nuclear safety legislative groups concentrated on using mobile equipment which is essential for nuclear power plants these... 

A prismatic high temperature gas-cooled reactor (HTGR), which is a graphite moderated, helium-cooled reactor, is a promising candidate for next generation nuclear power plant in that it enables applications, such as hydrogen production or process heat for petrochemical by supplying heat with core outlet temperatures as high as 1000°C. A Thermal Hydraulic Analysis Code (THAC) for gas-cooled reactors has been developed. THAC implicitly solves heat transfer equation of fuel, graphite block and helium. Three types of fuel pins were considered; solid fuel pin, fuel pins with inside holes and annular fuels with coolant flow from its inside and outside surfaces. THAC predicts axial and radial... 

High temperature gas cooled reactors (HTGR) are one of the most promising reactors in the new generation of world commercial reactors. They are divided into two main categories: Prismatic gas cooled reactors and pebble bed gas cooled reactors. These reactors have many advantages, such as inherent safety, high thermodynamic efficiency and the possibility of producing hydrogen. One of the most important challenges in developing these reactors is providing appropriate codes in design and simulating their performance. Two codes have been developed in this thesis. The first, THFAM, is a steady state thermal hydraulic code which helps in analyzing a fuel assembly. The second, named THCM is... 

In a nuclear power plant, transients are initiated for various reasons such as equipment failure or external disturbances. A transient should be identified as quickly as possible so that countermeasures can be taken to reduce its negative consequences. Due to the large number of parameters that can be monitored in nuclear power plants, the time limit for interpreting the information, and the stressful conditions of the incident, it will be very difficult to detect transients by the plant operators. Therefore, the development of operator support tools to identify transients is of great importance in the safe operation of nuclear power plants. Various studies have shown that data-driven... 

Compressors are one of the most important components of gas turbines and turbomachinery processes. Thus some precise and quick tools are needed for design and analysis purposes. Despite of vast development of Computational Fluid Dynamics (CFD) tools, Through-Flow Streamline Curvature Methods (SCM) has retained their position. 2D and quasi-3D forms of SCM in combination with CFD results nowadays make more than 80% of turbomachinery design process of axial and radial compressors and turbines. In this thesis, the basics of developing a tool for axial-flow compressor analysis are introduced. As will be seen, this analysis tool can be used for design purposes too. The method that is chosen for... 

The main purpose of this work is investigation of coolability of a boiling debris bed. The main governing equations are derived using volume averaging technique. From this technique some specific interfacial areas between phases are appeared and proper relations for modeling these areas are proposed. Using these specific areas, a modification for the Tung/Dhir model in the annular flow regime is proposed. The proposed modification is validated and the agreements with experimental data are good. Finally, governing equations and relations are implemented in the THERMOUS program to model two-phase flow in the debris bed in the axisymmetric cylindrical coordinate. Two typical configurations... 

Uptake characteristics of alginate microcapsules containing D2EHPA/TOPO for adsorption of uranium from industrial effluent were examined using batch, stirred and column method .stable alginate microcapsules in dried form was developed by immobilizing of D2EHPA/TOPO in porous matrix of calcium alginate. Characteristics of microcapsules were carrying out by destructive chemical analysis, BET, SEM and TG .the synthesized microcapsules showed a good column properties and high selectivity and reusability. In addition, isotherm adsorption of calcium alginate and microcapsules were fitted with frendlich's equation .the microcapsules also demonstrated that, the uptake percentage was constantly high...