Predicting the amount of solar radiation that reaches the earth’s surface is critical to understanding the performance of solar power systems, and cloud cover has a particularly strong impact on both the amount and direction of this radiation. Due to its variable nature, solar power is typically thought of as able to provide electricity only as a supplement to traditional power sources. However, by incorporating energy storage into solar facility design, it is possible to mitigate the variations in power production due to changes in sunlight. A key question then is how much energy storage would be required to account for daily solar irradiance variations and allow a solar power facility to produce electricity at least 80% of the year, comparable to traditional coal and natural gas plants. I have developed a simple algorithm for computing the intensity and angular distribution of light transmitted through, and reflected from, clouds. This result allows for accurate determination of variations in irradiance values across the globe. I have also created a model for the energy produced from a 100MW(e) solar power facility coupled to a large-scale thermal energy storage system. I used daily solar irradiance values to determine the array size needed at every location on the planet, and compared the power output at every location when both 1200MWh(e) and 1800MWh(e) of storage were incorporated into the plant design. I then computed the fraction of the year that power was produced at the rated capacity and the amount of time before the facility energy requirements are recouped. My analysis shows that more than 69% of the global land mass has sufficient solar resources provide continuous electricity output more than 80% of the time, and 27% of the land mass can do this more than 90% of time. In these locations the energy payback time ranges from 1.75 to 10 years. / text

The implementation of a general-purpose tetrahedral mesh phantom geometry library for the Monte Carlo radiation transport code EGSnrc is described. Recently, tetrahedral mesh geometries have been proposed as standard reference phantoms to advance the state of the art over rectilinear voxel phantoms. Prior to this work, EGSnrc already supported voxelized geometries, but not tetrahedral meshes. Other major radiation transport codes such as MCNP6, Geant4, and PHITS, are also capable of simulating the interaction of ionizing radiation with tetrahedral mesh phantoms. Tetrahedral mesh phantoms have a number of advantages over voxel phantoms including improved modelling fidelity and locally varying element resolution. In addition, CAD geometries can be converted into meshes, which can then be directly used in simulations. In this work, an EGSnrc tetrahedral mesh geometry library called EGS_Mesh is implemented. The implementation uses fast computational geometry algorithms from the literature and is accelerated using an octree spatial partitioning scheme. For a preliminary verification, results obtained using EGS_Mesh are compared to classical EGSnrc geometries and theoretical results (including a Fano test) and found to match within 0.1%. To demonstrate the capability of EGS_Mesh to simulate transport in complex mesh phantoms from the literature, results using the ICRP 145 reference human phantoms are compared to published results obtained using Geant4. The comparison has found agreement mostly within 5% of the Geant4 results, but with some differences up to 10%.

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Se presenta el trabajo realizado sobre el paquete de Subrrutinas Penélope. Este código permite la simulación MC del transporte de fotones y electrones en la materia con geometrías complejas. Los aspectos considerados son:A) mejora del algoritmo de SCATTERING de la radiación primaria y de los algoritmos que dan cuenta de las secundarias.B) simplificación del algoritmo de SCATTERING mixto par electrones empleado anteriormente. C) incorporación de secciones eficaces diferenciales. D) un paquete de subrutinas geométricas, pengeom, ha sido desarrollado. Permite geometría combinatoria con superficies cuadricas.e) presentación de un marco teórico para aplicar técnicas de reducción de varianza.F) comparación con resultados experimentales y presentación de 4 aplicaciones reales que emplean pengeom y reducción de varianza. En su estado actual Penélope permite que usuarios externos no especializados puedan abordar problemas en el campo de la ingeniería de radiaciones, de la física médica, etc.

Calculating or predicting the total in-core nuclear heating is a difficult tast. Full-core models can be constructed in a Monte Carlo code, such as MCNP6 or TRIPOLI4, and will allow an analyst to calculate the prompt-gamma heating at any given in-core location; however, such codes are generally unable to track the activated or fission-product isotopes and therefore the delayed-gamma sources can't be included in such a model. Some analysts have coupled Monte Carlo transport codes to burnup codes in an effort to include delayed-gamma sources, but the solutions tend to be reactor specific, time-independent and a lot of work. New ideas are required to calculate the total time-dependent in-core nuclear heating. Within this report, two new models have been derived: the nuclear heating equation, and the coupled neutron and nuclear heating point kinetics (NHPK) equations. These models can be used to calculate the time and position-dependent in-core heating. The nuclear heating equations are generalized expressions of the nuclear heating in a volume of interest, within an arbitrary geometry; these equations use Monte Carlo tallies as coefficients and treat the geometry's scalar neutron flux within as the independent variable. The NHPK model describes the nuclear heating in a volume of interest, within a critical assembly by coupling nuclear heating to the famous neutron point kinetics equations. A SCK-CEN gamma thermometer (GT) was commissioned in a materials testing reactor (MTR), the McMaster Nuclear Reactor (MNR), to measure the dynamic in-core nuclear heating in two locations. The nuclear heating equation was used to calculate self-heating of the SCK-CEN GT by neutron capture reactions. This calculation used CapGam and IAEA PGAA prompt-gamma emission data; delayed-particle emission data from NuDat 2.6 was also employed. Analysis of the GT's signal resulted in a quantitative description of the dynamic delayed-gamma heating in MNR, and provided the coefficients for the NHPK model. The NHPK model is capable of reproducing the measured time-dependent nuclear heating, and therefore should also be capable of predicting in-core nuclear heating as a function of reactor power. / Dissertation / Doctor of Philosophy (PhD)

abstract: As photons, electrons, and neutrons traverse a medium, they impart their energy in ways that are analytically difficult to describe. Monte Carlo methods provide valuable insight into understanding this behavior, especially when the radiation source or environment is too complex to simplify. This research investigates simulating various radiation sources using the Monte Carlo N-Particle (MCNP) transport code, characterizing their impact on various materials, and comparing the simulation results to general theory and measurements. A total of five sources were of interest: two photon sources of different incident particle energies (3.83 eV and 1.25 MeV), two electron sources also of different energies (30 keV and 100 keV), and a californium-252 (Cf-252) spontaneous fission neutron source. Lateral and vertical programmable metallization cells (PMCs) were developed by other researchers for exposure to these photon and electron sources, so simplified PMC models were implemented in MCNP to estimate the doses and fluences. Dose rates measured around the neutron source and the predicted maximum activity of activation foils exposed to the neutrons were determined using MCNP and compared to experimental results obtained from gamma-ray spectroscopy. The analytical fluence calculations for the photon and electron cases agreed with MCNP results, and differences are due to MCNP considering particle movements that hand calculations do not. Doses for the photon cases agreed between the analytical and simulated results, while the electron cases differed by a factor of up to 4.8. Physical dose rate measurements taken from the neutron source agreed with MCNP within the 10% tolerance of the measurement device. The activity results had a percent error of up to 50%, which suggests a need to further evaluate the spectroscopy setup. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2014

We use cosmological hydrodynamic simulations to study the impact of out-flows and radiative feedback on high-redshift galaxies. For outflows, we consider simulations that assume (i) no winds, (ii) a .constant-wind. model in which the mass-loading factor and outflow speed are constant, and (iii) "momentum driven" winds in which both parameters vary smoothly with mass. In order to treat radiative feedback, we develop a moment-based radiative transfer technique that operates in both post-processing and coupled radiative hydrodynamic modes. We first ask how outflows impact the broadband spectral energy distributions (SEDs) of six observed reionization-epoch galaxies. Simulations reproduce five regardless of the outflow prescription, while the sixth suggests an unusually bursty star formation history. We conclude that (i) simulations broadly account for available constraints on reionization-epoch galaxies, (ii) individual SEDs do not constrain outflows, and (iii) SED comparisons efficiently isolate objects that challenge simulations. We next study how outflows impact the galaxy mass metallicity relation (MZR). Momentum-driven outflows uniquely reproduce observations at z = 2. In this scenario, galaxies obey two equilibria: (i) The rate at which a galaxy processes gas into stars and outflows tracks its inflow rate; and (ii) The gas enrichment rate owing to star formation balances the dilution rate owing to inflows. Combining these conditions indicates that the MZR is dominated by the (instantaneous) variation of outflows with mass, with more-massive galaxies driving less gas into outflows per unit stellar mass formed. Turning to radiative feedback, we use post-processing simulations to study the topology of reionization. Reionization begins in overdensities and then .leaks. directly into voids, with filaments reionizing last owing to their high density and low emissivity. This result conflicts with previous findings that voids ionize last. We argue that it owes to the uniqely-biased emissivity field produced by our star formation prescriptions, which have previously been shown to reproduce numerous post-reionization constraints. Finally, preliminary results from coupled radiative hydrodynamic simulations indicate that reionization suppresses the star formation rate density by at most 10.20% by z = 5. This is much less than previous estimates, which we attribute to our unique reionization topology although confirmation will have to await more detailed modeling.

Mathematical methods have been developed to perform arms-control-treaty verification tasks for enhanced information security. The purpose of these methods is to verify and classify inspected items while shielding the monitoring party from confidential aspects of the objects that the host country does not wish to reveal. Advanced medical-imaging methods used for detection and classification tasks have been adapted for list-mode processing, useful for discriminating projection data without aggregating sensitive information. These models make decisions off of varying amounts of stored information, and their task performance scales with that information. Development has focused on the Bayesian ideal observer, which assumes com- plete probabilistic knowledge of the detector data, and Hotelling observer, which assumes a multivariate Gaussian distribution on the detector data. The models can effectively discriminate sources in the presence of nuisance parameters. The chan- nelized Hotelling observer has proven particularly useful in that quality performance can be achieved while reducing the size of the projection data set. The inclusion of additional penalty terms into the channelizing-matrix optimization offers a great benefit for treaty-verification tasks. Penalty terms can be used to generate non- sensitive channels or to penalize the model's ability to discriminate objects based on confidential information. The end result is a mathematical model that could be shared openly with the monitor. Similarly, observers based on the likelihood probabilities have been developed to perform null-hypothesis tasks. To test these models, neutron and gamma-ray data was simulated with the GEANT4 toolkit. Tasks were performed on various uranium and plutonium in- spection objects. A fast-neutron coded-aperture detector was simulated to image the particles.

A instalação do IPEN para pesquisas em BNCT (Terapia por Captura de Nêutrons em Boro) utiliza o canal de irradiação número 3 do reator IEA-R1, no qual tem-se um campo misto de radiação nêutrons e gama. As pesquisas em andamento necessitam que o campo de radiação, na posição de irradiação de amostra, tenha na composição os nêutrons térmicos maximizados e os componentes de nêutrons epitérmicos, rápidos e radiação gama minimizados. Este trabalho foi desenvolvido com o objetivo de avaliar se o campo de radiação atual na instalação é adequado aos trabalhos em BNCT. Para cumprir com este objetivo, uma metodologia para dosimetria de nêutrons térmicos e radiação gama em campos mistos de altas doses, que não era disponível no IPEN, foi implantada no Centro de Engenharia Nuclear do IPEN, utilizando dosímetros termoluminescentes TLDs 400, 600 e 700. Para as medidas de fluxo de nêutrons térmicos e epitérmicos foram utilizados detetores de ativação de ouro aplicando a técnica de razão de cádmio. Um simulador antropomórfico cilíndrico composto de discos de acrílico foi desenvolvido e testado na instalação e para obter valores teóricos do fluxo de nêutrons e a dose ao longo do simulador antropomórfico foi utilizado o código computacional DOT 3.5. Na posição correspondente a aproximadamente metade do comprimento do cilindro do simulador antropomórfico, foram obtidos os seguintes valores: fluxo de nêutrons térmicos (2,52 ± 0,06).108n/cm2s, epitérmicos (6,17 ± 0,26).107n/cm2s, dose absorvida devido a nêutrons térmicos de (4,2 ± 1,8)Gy e devido a radiação gama (10,1 ± 1,3)Gy. Os valores obtidos mostram que os fluxos de nêutrons térmicos e epitérmicos são adequados para os estudos em BNCT, porém, a dose devido a radiação gama está elevada, indicando que a instalação deve ser aprimorada. / IPEN facility for researches in BNCT (Boron Neutron Capture Therapy) uses IEA-R1 reactor\'s irradiation channel number 3, where there is a mixed radiation field neutrons and gamma. The researches in progress require the radiation fields, in the position of the irradiation of sample, to have in its composition maximized thermal neutrons component and minimized, fast and epithermal neutron flux and gamma radiation. This work was developed with the objective of evaluating whether the present radiation field in the facility is suitable for BNCT researches. In order to achieve this objective, a methodology for the dosimetry of thermal neutrons and gamma radiation in mixed fields of high doses, which was not available in IPEN, was implemented in the Center of Nuclear Engineering of IPEN, by using thermoluminescent dosimeters TLDs 400, 600 and 700. For the measurements of thermal and epithermal neutron flux, activation detectors of gold were used applying the cadmium ratio technique. A cylindrical phantom composed by acrylic discs was developed and tested in the facility and the DOT 3.5. computational code was used in order to obtain theoretical values of neutron flux and the dose along phantom. In the position corresponding to about half the length of the cylinder of the phantom, the following values were obtained: thermal neutron flux (2,52 ± 0,06).108n/cm2s, epithermal neutron flux (6,17 ± 0,26).107.106n/cm2s, absorbed dose due to thermal neutrons (4,2 ± 1,8)Gy and (10,1 ± 1,3)Gy due to gamma radiation. The obtained values show that the fluxes of thermal and epithermal neutrons flux are appropriate for studies in BNCT, however, the dose due to gamma radiation is high, indicating that the facility should be improved.