Página 3 dos resultados de 452 itens digitais encontrados em 0.031 segundos

Monte Carlo model of a low-energy neutron interrogation system for detecting fissile material

Johnson, Erik D., Ph. D. Massachusetts Institute of Technology
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 101 p.
Português
Relevância na Pesquisa
1291.15305%
(cont.) Further MCNP simulations of the neutron source impinging on cargo containers suggest that this technique can respond, as expected, qualitatively differently to containers containing SNM from containers that do not. Containers that contain small amounts of fissile isotopes as in the case of a few grams of uranium-235 in a kilogram of depleted uranium will also respond to this method but much more weakly. The system as proposed is viable and further simulation and experimental work will elucidate the behavior of this system under a wide range of cargo environments.; The undeniable threat of nuclear terrorism presents an opportunity for innovation in developing active interrogation technology. The proposed system aims to detect the smuggling of special nuclear material (SNM) in maritime containers. Identifying the importation of SNM will be instrumental in protecting the American public from a nuclear terrorist attack made possible by the construction of a weapon with fissile material from abroad. The proposed system uses a directionally-biased beam of low-energy neutrons (60 - 100 keV) generated from a 7Li(p,n)7Be reaction run near threshold. These neutrons are directed towards a cargo container of unknown composition. If SNM is present in the container and the neutrons can reach it...

Development of a low enrichment uranium core for the MIT reactor

Newton, Thomas Henderson
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 312 p.
Português
Relevância na Pesquisa
1288.607%
An investigation has been made into converting the MIT research reactor from using high enrichment uranium (HEU) to low enrichment uranium (LEU) with a newly developed fuel material. The LEU fuel introduces negative reactivity due to absorptions in 238U, which need to be compensated by higher initial content of 235U. Given that the new fuel density is much higher than the HEU density fuel, it is possible to obtain the necessary 235U content in the same core volume. A design of the MIT Nuclear Reactor is made using high density monolithic uranium-molybdenum fuel in an attempt to eliminate the reductions in neutron flux available to experiments due to the conversion to LEU fuel, as well as increasing the flexibility for meeting the needs of in-core experiments. The optimum configuration of fuel plates was made by varying the plate number and thicknesses and using a full-core model of the MITR for the Monte-Carlo transport code MCNP to determine the effect on flux and reactivity. In addition, the use of different moderator and fuel dummy materials as well as fixed absorbers was evaluated to optimize the neutron fluxes, reactivity and neutron spectrum available for experiments. The optimum reactor design consisted of the use of half-sized fuel elements made up of nine U-7Mo LEU fuel plates of 0.55 mm thickness with 0.25 mm finned aluminum cladding. This design also utilized solid beryllium dummies with boron fixed absorbers or solid lead dummies...

Quantum information processing in multi-spin systems

Cappellaro, Paola
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 142 p.
Português
Relevância na Pesquisa
1291.1137%
Coherence and entanglement in multi-spin systems are valuable resources for quantum information processing. In this thesis, I explore the manipulation of quantum information in complex multi-spin systems, with particular reference to Nuclear Magnetic Resonance implementations. In systems with a few spins, such as molecules in the liquid phase, the use of multi-spin coherent states provides a hedge against the noise, via the encoding of information in logical degrees of freedom distributed over several spins. Manipulating multi-spin coherent states also increases the complexity of quantum operations required in a quantum processor. Here I present schemes to mitigate this problem, both in the state initialization, with particular attention to bulk ensemble quantum information processing, and in the coherent control and gate implementations. In the many-body limit provided by nuclear spins in single crystals, the limitations in the available control increase the complexity of manipulating the system; also, the equations of motion are no longer exactly solvable even in the closed-system limit. Entanglement and multi-spin coherences are essential for extending the control and the accessible information on the system. I employ entanglement in a large ensemble of spins in order to obtain an amplification of the small perturbation created by a single spin on the spin ensemble...

Surface imaging for patient setup and monitoring for breast radiotherapy

Book, Lynn Novella
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 67 p.
Português
Relevância na Pesquisa
1386.2834%
Approximately one in eight women will get breast cancer at some point in their lives. A promising new treatment is partial breast irradiation, in which multiple radiation beams cross at the tumor site within the patient. This method of radiotherapy treats only a portion of the breast for a relatively small number of treatments with a high dose per treatment. This method requires much higher accuracy of patient alignment as the tumor site must be correct targeted. This study examined the possibility of using the VisionRT (London, UK) software and cameras for surface visualization to align patients for this treatment. A portable, single pod, the "Mini Cam" was found to be able to generate images for translations less than 2.5-5.5 cm, depending on the direction of translation. Calibration was a key aspect to ensuring accurate results. Eight patients were studied for deformation, breathing motion and day to day alignment. Surface images were taken at several points during regular treatment. Deformation was found to be small and never exceeded and average value of 2 mm. No correlation was found between the amount of deformation and the breast size or planning treatment volume. The average peak-to-peak breathing motion was 0.99-2.16 mm. Variability was discovered in the gating function of the VisionRT software. Aligning patients based on the first treatment session was found to be more accurate than aligning to a CT image taken weeks earlier.; by Lynn Novella Book.; Thesis (S.M.)--Massachusetts Institute of Technology...

Analysis of in-core experiment activities for the MIT Research Reactor using the ORIGEN computer code

Helvenston, Edward M. (Edward March)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 158 leaves
Português
Relevância na Pesquisa
1290.0853%
The objective of this study is to devise a method for utilizing the ORIGEN-S computer code to calculate the activation products generated in in-core experimental assemblies at the MIT Research Reactor (MITR-II). ORIGEN-S is a nuclear depletion and decay analysis code. It accounts for all types of nuclear reactions and eliminates the need for selection of the dominant reactions that will occur in a given experiment, as must be done with the existing activity calculation method. It is expected that the new approach will be easy to use, and will produce radioactivity estimations that are generally more accurate than those produced by the existing method. The ORIGEN-S method has been developed and tested for four experiments that have been or are scheduled to be irradiated in the MITR. These experiments are the Advanced Cladding Irradiation (ACI), High Temperature Irradiation Facility (HTIF), Electric Power Research Institute Electro-Chemical Potential (EPRI ECP) loop, and Annular Fuel Test Rig (AFTR). The method has also been used to perform activation analyses for ten individual elements (plus U-235 and U-238) that are commonly found in MITR in-core experiment (ICE) assemblies. The ORIGEN-S analyses for the ACI, HTIF, and EPRI ECP experiments produced results that were relatively similar to the results produced by previous analyses that utilized the current method of activation estimation. This is because the thermal neutron capture reactions...

Off-resonance and detuned surface coils for B₁ inhomogeneity in 7-Tesla MRI

Zakszewski, Elizabeth K
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 33, [1] p.
Português
Relevância na Pesquisa
1386.2834%
A problem with high-field MRI is the lack of B1 homogeneity, particularly signal cancellation in the outer parts of the head. Here we attempt to correct this by adding surface coils. To adjust the mutual coupling, we vary the resonance properties of the added coil. A new agar-based head phantom was built, and two surface coils were built and tuned. The surface coils were placed in various configurations against the phantom to modify the B1 field with their presence, while images were taken using a 16-rung birdcage coil to transmit and receive. Trials were taken with various spacings between the surface coil and the phantom, while the resonance of the surface coil was either shifted in frequency by changing the voltage across a varactor diode, or detuned using a resonant detuning circuit. It was discovered that with a 1 cm spacing and a surface coil tuned just above resonance, SNR near the surface coil could be improved by upwards of 400%, with the trade-off of a reduced signal in other areas on the periphery of the head. Other configurations could achieve better B1 homogeneity at the expense of reduced SNR throughout the head. Future studies will explore the possibility of using more than one surface coil to improve SNR in more places on the periphery of the head.; by Elizabeth K. Zakszewski.; Thesis (S.B.)--Massachusetts Institute of Technology...

Determination of the proper operating range for the CAFCA IIB fuel cycle model

Warburton, Jamie (Jamie L.)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 75 p.
Português
Relevância na Pesquisa
1291.1137%
The fuel cycle simulation tool, CAFCA II was previously modified to produce the most recent version, CAFCA IIB. The code tracks the mass distribution of transuranics in the fuel cycle in one model and also projects costs for various fuel cycle schemes. The mass distribution model also shows the schedule for deployment of recycling plants. All of these models are dependent on user inputs, some of which specify advanced technology type and capacity, plant lifetime and recycling facility capacity. The behavior of CAFCA IIB resulting from the most recent modifications are investigated through extensive modeling of various nuclear fuel cycles. By re-modeling nuclear fuel cycle schemes in CAFCA IIB that were modeled in CAFCA II, the two results can be compared and conclusions can be drawn as to an discrepancies between the two. Specifically, the results representing TRU mass balance accumulation in the system, spent fuel separation plant construction and fertile free fuel spent fuel reprocessing plant construction are compared. Thus, these new runs will substantiate the accuracy of past work and expand the number of reactor options that have been evaluated by CAFCA IIB. Additionally, the new data help pinpoint the operating range for CAFCA IIB in which the code is accurate. Overall...

Evaluation of human error probabilities for post-initiating events

Dawson, Phillip Eng
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 85 leaves
Português
Relevância na Pesquisa
1291.0117%
The United States Nuclear Regulatory Commission is responsible for the safe operation of the United States nuclear power plant fleet, and human reliability analysis forms an important portion of the probabilistic risk assessment that demonstrates the safety of sites. Treatment of post-initiating event human error probabilities by three human reliability analysis methods are compared to determine the strengths and weaknesses of the methodologies and to identify how they may be best used. A Technique for Human Event Analysis (ATHEANA) has a unique approach because it searches and screens for deviation scenarios in addition to the nominal failure cases that most methodologies concentrate on. The quantification method of ATHEANA also differs from most methods because the quantification is dependent on expert elicitation to produce data instead of relying on a database or set of nominal values. The Standardized Plant Analysis Risk Human Reliability Analysis (SPAR-H) method uses eight performance shaping factors to modify nominal values in order to represent the quantification of the specifics of a situation. The Electric Power Research Institute Human Reliability Analysis Calculator is a software package that uses a combination of five methods to calculate human error probabilities. Each model is explained before comparing aspects such as the scope...

Optimized core design of a supercritical carbon dioxide-cooled fast reactor

Handwerk, Christopher S. (Christopher Stanley), 1974-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 367 p.
Português
Relevância na Pesquisa
1288.71875%
Spurred by the renewed interest in nuclear power, Gas-cooled Fast Reactors (GFRs) have received increasing attention in the past decade. Motivated by the goals of the Generation-IV International Forum (GIF), a GFR cooled by supercritical carbon dioxide (S-CO2), fueled with Light Water Reactor spent fuel transuranics, and directly coupled with a Brayton cycle is under investigation as part of a larger research effort at MIT. While the original GFR chosen by the GIF is a 600MWth version using Helium as a coolant, the work presented here is for a 2400 MWt, core using S-CO2 as a coolant, which has comparable thermal efficiency (-45%) at much lower temperatures (650TC v. 8500C) A reactor core for use in this direct cycle S-CO2 GFR has been designed which satisfies established neutronic and thermal-hydraulic steady state design criteria, while concurrently supporting the Gen-IV criteria of sustainability, safety, proliferation, and economics. Use of innovative Tube-in-Duct (TID) fuel has been central to accomplishing this objective, as it provides a higher fuel volume fraction and lower fuel temperatures and pressure drop when compared to traditional pin-type fuel. Further, this large fuel volume fraction allows for a large enough heavy metal loading for a sustainable core lifetime without the need for external blankets...

Disruption mitigation and real-time detection of locked modes

Angelini, Sarah Martha
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 58 p.
Português
Relevância na Pesquisa
1386.1317%
Disruptions are one of the largest problems facing tokamaks. In a large-scale experiment such as ITER, disruptions may cause crippling damage and severe setbacks in experimentation. One method for disruption mitigation involves the use of a gas jet which has been tested on both stable plasmas and vertical displacement events (VDEs) on Alcator C-Mod. In both cases, the jet was successful in mitigating disruption effects. The gas jet has not yet been tested on other types of disruptions. Locked-mode disruptions are easily created in C-Mod and could be used to test the effectiveness of the gas jet as a mitigation method if the jet could be fired early enough. It has been empirically observed that the electron cyclotron emissions (ECE) signal displays a flattening of the normally-present sawteeth before the current quench occurs in certain locked-mode disruptions. A procedure has been written which detects the ECE sawtooth suppression by calculating changes in the standard deviation of the signal over a moving time-window. This procedure has been programmed into the digital plasma control system (DPCS) for real-time testing. The procedure successfully located the locked modes present during a run.; by Sarah Martha Angelini.; Thesis (S.M.)--Massachusetts Institute of Technology...

Thermal hydraulics analysis of the MIT research reactor in support of a low enrichment uranium (LEU) core conversion

Ko, Yu-Chih, Ph. D. Massachusetts Institute of Technology
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 145 leaves
Português
Relevância na Pesquisa
1288.607%
The MIT research reactor (MITR) is converting from the existing high enrichment uranium (HEU) core to a low enrichment uranium (LEU) core using a high-density monolithic UMo fuel. The design of an optimum LEU core for the MIT reactor is evolving. The objectives of this study are to benchmark the in-house computer code for the MITR, and to perform the thermal hydraulic analyses in support of the LEU design studies. The in-house multi-channel thermal-hydraulics code, MULCH-II, was developed specifically for the MITR. This code was validated against PLTEMP for steady-state analysis, and RELAP5 and temperature measurements for the loss of primary flow transient. Various fuel configurations are evaluated as part of the LEU core design optimization study. The criteria adopted for the LEU thermal hydraulics analysis for this study are the limiting safety system settings (LSSS), to prevent onset of nucleate boiling during steady-state operation, and to avoid a clad temperature excursion during the loss of flow transient. The benchmark analysis results showed that the MULCH-II code is in good agreement with other computer codes and experimental data, and hence it is used as the main tool for this study. In ranking the LEU core design options...

Feasibility and economics of existing PWR transition to a higher power core using annular fuel

Beccherle, Julien
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 135 p.
Português
Relevância na Pesquisa
1386.3389%
The internally and externally cooled annular fuel is a new type of fuel for PWRs that enables an increase in core power density by 50% within the same or better safety margins as the traditional solid fuel. Each annular fuel assembly of the same side dimensions as the solid fuel has 160 annular fuel rods arranged in a 13x13 array. Even at the much higher power density, the fuel exhibits substantially lower temperatures and a MDNBR margin comparable to that of the traditional solid fuel at nominal (100%) power. The major motivation for such an up-rate is reduction of electricity generation cost. Indeed, the capital cost per kWh(e) of the construction is smaller than the standard construction of a new reactor with solid fuel. Elaborating on previous work, we study the economic payoff of such an up-rate of an existing PWR given the expected cost of equipment and also cost of money using different assumptions. Especially, the fate of the already bought solid fuel is investigated. It is demonstrated that the highest return on investment is obtained by gradually loading annular fuel in the reactor core such that right before shutting the reactor down for the up-rate construction, two batches in the core are of annular fuel. This option implies running a core with a mixture of both annular fuel and solid fuel assemblies. In order to prove the technical feasibility of such an option...

Assessment of high-burnup LWR fuel response to reactivity-initiated accidents; Assessment of high-burnup Light Water Reactor fuel response to reactivity-initiated accidents

Liu, Wenfeng, Ph.D. Massachusetts Institute of Technology
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 273 p.
Português
Relevância na Pesquisa
1288.8965%
The economic advantages of longer fuel cycle, improved fuel utilization and reduced spent fuel storage have been driving the nuclear industry to pursue higher discharge burnup of Light Water Reactor (LWR) fuel. A design basis accident, the Reactivity Initiated Accident (RIA), became a concern for further increase of burnup as simulated RIA tests revealed lower enthalpy threshold for fuel failure associated with fuel dispersal, which may compromise the core coolability and/or cause radiological release should this happened in LWRs. Valuable information on the behavior of high burnup fuel during RIA are provided by the simulation tests. However atypical design and operating conditions in simulated tests limited the application of experimental data directly to evaluate the failure potential of LWR fuels. To better interpret the experimental results and improve the capability of the fuel performance codes to predict high burnup fuel behavior, this thesis developed mechanistic models of high burnup fuel during an RIA and implemented models in a transient fuel performance code FRAPTRAN 1.3. Fission gas release (FGR) and swelling were systematically modeled to quantify gaseous loading effects. The grain boundary fission gas inventory is simulated prior to the transient using a diffusion model in FRAPCON 3.3 code. The restructuring of high burnup fuel in rim region is described in terms of porosity...

Feasibility analysis of scanning 100% of maritime cargo containers for fissile material

Foley, William E., III
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 61 leaves
Português
Relevância na Pesquisa
1289.9995%
On August 3, 2007, President George W. Bush signed into law H.R. 1: Implementing Recommendations of the 9/11 Commission Act of 2007. The law mandates that 100% of air and maritime cargo must be scanned prior to entering the United States, and has been deemed unfeasible by many opponents. The analysis contained in this thesis shows that it is much more feasible for a major port to absorb the huge initial investments and operating costs than a smaller port. A port shipping 750,000 TEUs annually would charge a tax of $49.48 for ten years to recover their initial investment, while a port shipping 150,000 TEUs annually would need to charge $123.52 annually. This number rises exponentially as volume shipped drops. Furthermore, a port that is willing to invest in the developing technologies will be able to handle scanning of 100% of maritime cargo with minimal delays. Using current technology would result in delays of over 80,000 hours annually. However, investing in four next generation scanning machines would result in delays of only 560 hours annually. Finally, there exists a variety of political and logistical barriers that must be overcome. I recommend that in all circumstances, the United States retain control and oversight of all scanning operations in order to maintain quality control and throughput times. When weighed against the potential destruction of nuclear terrorism...

Micronuclei induction in AG01522 cells is independent of temperature and linear energy transfer

Buchanan, Carrie C
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 46 p.
Português
Relevância na Pesquisa
1386.3389%
The bystander effect describes radiation-induced biological effects in nonirradiated cells that have received signals from irradiated cells. In a co-culture experiment, the bystander signaling is proposed to occur via the medium. Using a co-culture setup, the work in this thesis investigates the effects of temperature as an experimental parameter and linear energy transfer (LET) dependence on the bystander effect. Using the micronucleus assay and primary human AG01522 fibroblast cells co-cultured as both the target and bystander cells, the incidence of micronuclei in both X-ray irradiated and alpha particle irradiated bystander experiments were ~2 fold over control averages. In the temperature experiment, there were no significant differences between bystander cells co-cultured with cold (4°C) target cells and those co-cultured with warm control target cells. These results have shown, for AG01522 fibroblasts, that the bystander effect is independent of temperature and LET.; by Carrie C. Buchanan.; Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2008.; Includes bibliographical references (p. 42-44).

Benchmarking of the MIT High Temperature Gas-cooled Reactor TRISO-coated particle fuel performance model; Benchmarking of the Massachusetts Institute of Technology HTGR TRISO-coated particle fuel performance model

Stawicki, Michael A
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 133 p.
Português
Relevância na Pesquisa
1288.696%
MIT has developed a Coated Particle Fuel Performance Model to study the behavior of TRISO nuclear fuels. The code, TIMCOAT, is designed to assess the mechanical and chemical condition of populations of coated particles and to determine the failure probability of each of the structural coating layers. With this, the code determines the overall particle failure rate. TIMCOAT represents a significant advancement over earlier codes as it includes a pyrocarbon crack induced particle failure mechanism, which applies probabilistic fracture mechanics. As part of the International Atomic Energy Agency (IAEA) Coordinated Research Program (CRP) on coated particle fuel technology, a code benchmark has been developed by the Idaho National Laboratory (INL). The benchmark includes simple analytic studies and more complex simulations of TRISO particles from past and future experiments. For each study a large variety of particle parameters are specified. This thesis reports TIMCOAT's results from the benchmark study. As this was a blind benchmark, no other results are available for comparison. However, TIMCOAT is able to independently calculate several of the parameters specified by the benchmark, and comparisons are made between results obtained using IAEA parameters and TIMCOAT calculated parameters. The material properties which describe the effects of irradiation on pyrolytic carbon are the focus of the comparison. The rates of irradiation induced creep and swelling calculated by TIMCOAT and the rates provided in the benchmark differed by a factor of two to four in some cases and led to differences in particle failure rate by several orders of magnitude. In addition...

On the evaluation of human error probabilities for post-initiating events

Presley, Mary R
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 115 p.
Português
Relevância na Pesquisa
1288.8544%
Quantification of human error probabilities (HEPs) for the purpose of human reliability assessment (HRA) is very complex. Because of this complexity, the state of the art includes a variety of HRA models, each with its own objectives, scope and quantification method. In addition to varying methods of quantification, each model is replete with its own terminology and categorizations, therefore making comparison across models exceedingly difficult. This paper demonstrates the capabilities and limitations of two prominent HRA models: the Electric Power Research Institute (EPRI) HRA Calculator (using the HRC/ORE and Cause Based Decision Tree methods), used widely in industry, and A Technique for Human Error Analysis (ATHEANA), developed by the US Nuclear Regulatory Commission. This demonstration includes a brief description of the two models, a comparison of what they incorporate in HEP quantification, a "translation" of terminologies, and examples of their capabilities via the Halden Task Complexity experiments. Possible ways to incorporate learning from simulator experiments, such as those at Halden, to improve the quantification methods are also addressed. The primary difference between ATHEANA and the EPRI HRA Calculator is in their objectives. EPRI's objective is to provide a method that is not overly resource intensive and can be used by a PRA analyst without significant HRA experience. Consequently...

Experimental and numerical characterization of ion-cyclotron heated protons on the Alcator C-Mod tokamak

Tang, Vincent, 1978-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 187 p.
Português
Relevância na Pesquisa
1386.2158%
Energetic minority protons with -100 keV effective temperature are routinely created in Alcator C-Mod plasmas with the application of ICRF. A new multi-channel Compact Neutral Particle Analyzer is used to make measurements of these distributions in Alcator C-Mod's unique and reactor-relevant operating space via an active charge-exchange technique (CX). Using a detailed model that accounts for beam, halo, and impurity CX, core proton temperatures of 430-120 keV are directly measured for the first time in lower density (neo0 0.8 - 1.5 x 1020/m3) Alcator C-Mod plasmas using only 0.5 MW of ICRF power. The model found that the minority proton temperatures are peaked spatially away from r/a=O, even for an on-axis resonance. Additionally, noticeable phase-space anisotropy is seen as expected for ICRF heating. The measured effective temperatures scale approximately with the Stix parameter. The CNPA measurements are also compared with several leading simulation packages. Preliminary comparisons with results from the AORSA/CQL3D Full-wave/Fokker-Planck (FW/FP) code using a new synthetic diagnostic show good agreement and demonstrate that these complex codes are required to simulate Alcator C-Mod's energetic minority populations with accuracy. These FW/FP analyses represent the first comparison between predictions of such detailed codes and extensive minority ion experimental measurements.; by Vincent Tang.; Thesis (Ph. D.)--Massachusetts Institute of Technology...

Innovative fuel designs for high power density pressurized water reactor

Feng, Dandong, Ph. D. Massachusetts Institute of Technology
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 259 p.
Português
Relevância na Pesquisa
1288.7735%
One of the ways to lower the cost of nuclear energy is to increase the power density of the reactor core. Features of fuel design that enhance the potential for high power density are derived based on characteristics of the pressurized water reactor (PWR) and its related design limits. Those features include: large fuel surface to volume ratio, small fuel thickness, large fuel rod stiffness, low core pressure drop and an open fuel lattice design. Three types of fuel designs are evaluated from the thermal-hydraulic point of view: conventional solid cylindrical fuel rods, internally and externally cooled annular fuel rods, and spiral cross-geometry fuel rods, with the major effort allocated to analyzing the annular fuel. Limits of acceptable power density in solid cylindrical fuel rods are obtained by examining the effects of changing the core operation parameters, fuel rod diameter and rod array size. It is shown that the solid cylindrical geometry does not meet all the desired features for high power density well, and its potential for achieving high power density is limited to 20% of current PWR power density, unless the vibration problems at the coolant higher velocity are overcome. The internally and externally cooled annular fuel potential for achieving high power density is explored...

Characterization of fissile material using low energy neutron interrogation

Padilla, Eduardo A
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 76 p.
Português
Relevância na Pesquisa
1292.5921%
The glaring need to develop methods for detecting and interdicting illicit nuclear trafficking has resulted in the exploration of various methods for active neutron interrogation, specifically for the presence of special nuclear material (SNM) in cargo containers. The proposed system aims to defeat the ability of terrorists to import SNM into the United States via maritime shipping, thus greatly reducing the possibility of a successful nuclear terrorist attack. The proposed system uses 60-100 keV neutrons, produced by the 7Li(p,n)7Be reaction in a linear accelerator and kinematically beamed into various targets. In the event that fissile material is present, highly energetic neutrons will be emitted from the fissioning of a nucleus and some of these neutrons will eventually radiate from the container. Inevitably, high energy photons will also radiate from the target due to the interactions of neutrons and host materials. Utilizing a neutron detection system that is able to discriminate low energy neutrons, high energy gamma rays and the high energy neutrons from fission enables the detection of fissile material in various containers. An increase in discriminated high energy neutron events during active neutron interrogation selectively indicates the presence of SNM...