Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2008. / Includes bibliographical references (leaf 23). / Error correction codes are necessary for the development of reliable quantum computers. Such codes can prevent the lost of information from decoherence caused by external perturbations. This thesis evaluates a five qubit code for correcting second order bit-flip errors. The code consists of encoding, decoherence, decoding, and error correction steps. This work analyzes the proposed code using geometric algebra methods and examines the state of the system after each step in the process. / by Sarah Sheldon. / S.B.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2009. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 72-74). / Stress Corrosion Cracking (SCC) is a failure mechanism that results from the combination of tensile stress, corrosive environment and material susceptibility; it is frequently an intergranular attack. Material-environment combinations for SCC readily exist in nuclear power plants, and are critical for to the longevity of the reactor components. Inconel 690 (alloy 690 UNS N06690) is an alloy that has been put into service in the nuclear industry over the past 20 years due to its relatively good resistance to SCC. A new generation of nuclear plants is likely to be built in the US and the life of existing and new nuclear plants are expected to extend to 60-80 years. The study of alloy 690, as well as other structural metals, is important in order to understand, predict, and avert costly and dangerous failures that could occur due to SCC later in the life of the plants. The microstructure of an alloy has an important effect on its corrosion and SCC behavior. In particular, high energy grain boundary structures in austenitic Ni-base alloys and stainless steels have been shown to have greater SCC susceptibility. This thesis studies the fundamental structural and chemical properties of grain boundaries in alloy 690, to better understand the SCC resistances and susceptibilities of different grain boundary structures. In order to investigate the grain boundaries based on their structure, an integrated approach was developed to allow for site-specific chemical and mechanical characterization. / (cont.) The chemical analysis, which was the focus of this thesis, was accomplished using a Transmission Electron Microscope (TEM) for imaging and a Scanning Transmission Electron Microscope (STEM) with Energy Dispersive X-ray Spectroscopy (EDS) for elemental analysis. TEM samples from selected grain boundaries were prepared in a site-specific manner using a Focused Ion Beam (FIB). The mechanical analysis of the grain boundaries was accomplished through nanoindentation by a collaborator in the same research group. To identify grain boundaries of interest, for TEM sample creation by FIB or nanoindentation, the surface crystallographic structure was mapped using Orientation Image Microscopy (OIM). Microindents on the surface were utilized as fiduciary markers in the navigation of the surface. The three structures examined were low 1, low angle, and high angle grain boundaries. Boundaries were characterized in a: 1) solution annealed state, 2) Thermomechanically Processed (TMP) state consisting of a 5% compression followed by annealing at 10000 C with a water quench, 3) TMP state consisting of a 5% compression followed by annealing at 9500 C with a furnace cooling. Chemical composition differences, major element segregation or precipitation, were not found at grain boundaries in the solution annealed material or the TMP material that was water quenched. Cr-carbide precipitation was observed at the grain boundaries in the furnace cooled samples. The structural character and distribution of the carbides was dependent on structure of the host grain boundary. / (cont.) Low E grain boundaries exhibited a thin band of Cr-carbide on the boundary that was approximately 50 nm thick. On low angle grain boundaries, coarsened Cr-carbides were observed in semi-continuous form; with an average size of 230 nm. On high angle grain boundaries, further coarsening of the carbides resulted in a discontinuous distribution with an average precipitate size of 430 nm. Cr depletion occurred in the vicinity of the carbides; depletion was the most severe on high angle grain boundaries, down to 20wt-%. The suspected cause of the varying degree of coarsening of the Cr-carbides was the differences in diffusivity that control the kinetics of precipitation at the grain boundary. The "mean field" model for the coarsening of a distribution of carbides was used for quantitatively comparing the diffusivity of Cr at the high and low angle grain boundaries. The result indicated that diffusivity of Cr at high angle grain boundaries was an order of magnitude higher than at low angle grain boundaries, at the temperature of Cr-carbide formation 600-950' C. High angle grain boundaries have been shown to be the most susceptible to corrosion and SCC previously. The results of this work suggest that the higher diffusivity of Cr at the high angle boundaries of alloy 690 could contribute to SCC susceptibility through two mechanisms: 1) The coarser carbides, formed because of higher diffusivity, can more easily initiate microcracks if they are present. 2) The higher diffusivity leads to greater Cr redistribution, which could leave the boundary in a chemical state more prone to corrosion. / by Joseph William Fricano. / S.M.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 37). / Using recently collected data which was measured with state-of-the-art techniques, models for nucleation site density, bubble departure diameter, and nucleation frequency were compared against the acquired data. The particular focus of this work is on the ebullition cycle and associated bubble nucleation frequency, looking at the models proposed by M.Z. Podowski. In my analysis, I took the average values for the growth and dwell times directly from the data, rather than from the models for those parameters. The results of those investigations showed that the basic principles approach for considering the parameters of the ebullition cycle held up pretty well with the experimental data, with Ti(t), the temperature curve during the ebullition cycle, corresponding remarkably well with the data curves. However, one parameter which was always overvalued was T(0*) - the predicted temperature of the start of the dwell phase. It was generally 1-2 degrees Celsius higher than the experimental value. For a fully rigorous analysis of the ebullition models in future works, it is recommended that all parameters be predicted rather than pulled from the data, particularly of the growth and dwell times. / by Matthew Miguel Virgen. / S.B.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 33-34). / .The Treaty on the Non-Proliferation of Nuclear Weapons creates a loophole that allows a non-nuclear-weapon country to avoid international safeguards governing fissile materials if it claims that the materials will be used for naval nuclear propulsion purposes. The United States ability to negotiate a closing of this loophole is hampered by the fact that its entire nuclear fleet is powered by highly enriched uranium (HEU). In 1995, the U.S. Navy issued a report indicating that converting the nuclear reactors on its submarines and carriers from the use of HEU to the use of low enriched uranium (LEU) would create numerous problems. However, since that time significant technological advances in LEU fuel systems and naval propulsion strongly indicate that the issue of LEU conversion should be re-examined. This paper suggests that a high-level independent commission should be appointed and directed to thoroughly study the pros and cons of LEU conversion and to make recommendations to decision makers regarding what path should be followed. / by Cameron McCord. / S.B.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 29-30). / Computed tomography (CT) is a prominent procedure in the US with larger radiation doses than traditional radiology. CT is a powerful tool in the diagnosis of a wide variety of conditions and its use has grown quickly because of its power. CT contributes a significant portion of annual per capita dose in the US. The risk of this additional dose is poorly understood. The risks of low doses of radiation are estimated through models, primarily the linear no-threshold (LNT) model. Epidemiological evidence from atomic bomb survivors provides some understanding of the risk of low doses of radiation, but not on the order of doses from typical CT procedures. This paper explores the evidence of the risk of low doses of radiation and discusses some of the models proposed. Recommendations for improving these models are made including experimental and epidemiological studies. Recommendations for reducing radiation exposure through the intelligent use of CT are also presented including: using CT only when it produces a clear clinical benefit, reducing dose per scan, and tracking total patient dose. Finally, a case is made that a thorough understanding of the risk versus dose relationship at doses relevant to CT is not necessary to use CT appropriately. The culture of evidence-based medicine will achieve this result without conscious efforts to reduce patient radiation exposure. / by Gary Eastwick. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Spontaneous electromagnetic fields can be important to the dynamic evolution of a plasma by directing heat flow as well as providing additional pressures on the conducting fluids through the Lorentz force. Electromagnetic fields are predicted to affect fluid behavior during the core-collapse of supernovae through generation of fields due to hydrodynamic instabilities. In the coronae of stars, self-generated magnetic fields lead to filamentary structure in the hot plasma. Recent experiments by Gregori et al. investigated sources of protogalactic magnetic fields generated by laser-produced shock waves. In inertial confinement fusion experiments, self-generated electromagnetic fields can also play a role and have recently become of great interest to the community. Present day laser facilities provide a unique opportunity to study spontaneous field-generation in these extreme environments under controlled conditions. Instability-induced electromagnetic fields were investigated using a novel monoenergetic-proton radiography system. Fusion protons generated by an 'exploding-pusher' implosion were used to probe laser-irradiated plastic foils with various preimposed surface perturbations. Imaging protons are sensitive to electromagnetic fields and density modulations in the plasma through the Lorentz force and Coulomb collisions, respectively. Corresponding x-ray radiographs of these targets provided mass density distributions and Coulomb effects on protons were assessed using a Monte Carlo code written using the Geant4 framework. Proton fluence distributions were recorded on CR-39 detectors and Fourier analyzed to infer path-integrated field strengths. Rayleigh-Taylor (RT) growth of preimposed surface perturbations generated magnetic fields by the RT-induced Biermann battery and were measured for the first time. Good data were obtained during linear growth and when compared to ideal calculations, demonstrated that field diffusion near the source played an important role. At later times in the plasma evolution, 3-D cellular structures were observed for all foil types. These features were found to be analogous to previously observed filamentary field structures by Séguin et al. in laser-driven spherical targets. Face-on images of these field structures provided good data to quantitatively analyze the size of these features, not previously attainable due to the complexity of the 3-D spherical data. Work presented here demonstrates that these field structures are likely caused by the magnetothermal instability in the underdense corona. / by Mario J.-E. Manuel. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2016. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references (pages 203-212). / Computational methods for on-the-fly representation and processing of nuclear data within Monte Carlo neutron transport simulations of intermediate and fast spectrum systems are developed and implemented in a continuous-energy Monte Carlo code. First, a capability to compute temperature-dependent unresolved resonance region (URR) cross sections directly from zero-temperature average resonance parameters is presented. The use of this capability in benchmarking both evaluated and processed URR data is demonstrated. Results of this benchmarking lead to a partial resolution of a longstanding discrepancy between experiment and calculation results for a well-known fast critical assembly. Next, an on-the-fly probability table interpolation scheme for computing temperature-dependent URR cross sections is developed and used in analyses which show that interpolation on a relatively coarse temperature mesh (>100 K) can be used to reproduce results obtained with cross sections generated at an exact temperature. This enables the simulation of systems having detailed temperature distributions using probability table data which require significantly less memory than data generated on a fine temperature mesh. Additional methods for use in the investigation of two common approximations that are made in representing URR cross section data are developed. Namely, a multi-level URR cross section calculation capability is used to show that level-level interference effects in elastic scattering cross sections are negligible in many cases of interest. A capability to generate resonance structure in competitive reaction cross sections is used to show that neglecting cross section structure for reactions other than elastic scattering, capture, and fission can lead to non-negligible, unconservative biases (>100 pcm) in criticality safety calculations. The principal underlying assumption of the probability table method is also tested by comparing the results it yields with results that are averaged over many independent simulations, each using a single, independent realization of URR resonance parameters. Unknown URR resonance structure is observed to induce an uncertainty on the multiplication factor for intermediate and fast spectrum systems that is nearly an order of magnitude greater than that which is purely stochastic. This significantly increases the uncertainty to which results of simulations of those systems should be stated. Finally, a procedure for consistent, on-the-fly sampling of temperature-dependent neutron reaction kernels which requires no additional secondary distribution data is presented. It is used to show that Doppler effects may have only a small impact on elastic scattering secondary angular distributions at typical power reactor operating temperatures but can be appreciable at astrophysical temperatures. / by Jonathan A. Walsh. / Ph. D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2012. / "June 2012." Cataloged from PDF version of thesis. / Includes bibliographical references (p. 42). / Monte Carlo computationals methods are widely used in academia to analyze nuclear systems design and operation because of their high accuracy and the relative ease of use in comparison to deterministic methods. However, current Monte Carlo codes require an extensive knowledge of the physics of a problem as well as the computational methods being used in order to ensure accuracy. This investigation aims to provide better on-the-fly diagnostics for convergence using Shannon entropy and statistical checks for tally undersampling in order to reduce the burden on the code user, hopfully increasing the use and accuracy of Monte Carlo codes. These methods were tested by simulating the OECD/NEA benchmark #1 problem in MCNP. It was found that Shannon entropy does accurately predict the number of batches required for a source distribution to converge, though only when when the Shannon entropy mesh was the size of the tally mesh. The investigation of undersampling showed evidence of methods to predict undersampling on-the-fly using Shannon entropy as well as laying out where future work should lead. / by Ruaridh Macdonald. / S.B.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2008. / "June 2008." / Includes bibliographical references (leaves 51-53). / Since Enrico Fermi first discovered that neutrons could split atoms in 1934, peaceful and militaristic uses of nuclear energy have become prevalent in our society. Two case studies, Three Mile Island and the Nevada Test Site, allow for the examination of radiation injury liability in the context of existing radiation compensation systems. The Price-Anderson Nuclear Industries Indemnity Act, which governs civilian nuclear use, and the Radiation Exposure Compensation Act, which governs compensation for military nuclear weapons tests, are compared to determine the most efficient compensation system. Issues such as determining compensable diseases, establishing rigid criteria, and a heavy burden of proof define the efficiency of each system. A compensation system combining elements of the existing civilian and military compensation systems is proposed, which can be applied to future nuclear ventures such as the Yucca Mountain Repository. / by Jeccisa Flores. / S.B.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2007. / "June 2007." / Includes bibliographical references (p. 37-43). / Lymphatic vessels play a crucial role in both the pathophysiology of tumors and in the spread cancer cells to lymph nodes. The effects of radiation on these vessels, however, are largely unknown. Here, we seek to describe the effects of ionizing radiation on normal and tumor-associated lymphatic vessels in vitro and in vivo. Clonogenic assays were employed to study the radiation dose response of lymphatic endothelial cells. Putative lymphatic endothelial cell mitogens and antiproliferative agents, including vascular endothelial growth factor-A (VEGF-A), VEGF-C and AZD2171, a tyrosine kinase inhibitor of the VEGF receptors, were tested as radiation sensitizers and protectors. Our results indicate that VEGF-A and VEGF-C are radiosensitizers while AZD2171 did not modulate the radioresponse. In vivo, normal lymphatics were studied with the experimental group receiving a single fraction of 8 Gy and the control group receiving no radiation. We observed no difference in the average lymphatic vessel diameter between these two groups over the course of 6 months. VEGF-C overexpressing tumor-associated lymphatic vessels were studied in vivo with four treatment groups: control animals (no irradiation), 8 Gy two weeks prior to implantation, 8 Gy at the time of implantation and 16 Gy given in two fractions before implantation (two weeks prior to and at the time of implantation). The average lymphatic vessel diameter and frequency of lymph node metastasis in these four groups indicates that the ability of radiation to prevent VEGF-C driven lymph node metastases is time-dependent; radiation must be delivered in close proximity to VEGF-C overexpressing tumor cell implantation to impact nodal metastases. This suggests that VEGF-C may be a functional lymphatic vessel radiosensitizer in vivo. / (cont.) However, reductions in lymphatic hyperplasia, as measured by lymphatic vessel diameter, did not explain the observed differential effects of radiation timing on lymph node metastasis rate. / by Jennifer D. Lobo. / S.B.