Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2008. / "September 2007." / Includes bibliographical references (leaves 99-100). / Three ionization chambers with different geometries have been constructed and filled with dielectric liquids for detection of fast neutrons. The three dielectric liquids studied were Tetramethylsilane (TMS), Tetramethylpentane (TMP), and Isooctane, which each have intrinsic properties that make them attractive for fast neutron detection. Their electronic properties are similar to those of condensed noble gases, but they don't require cryogenic temperatures to maintain liquid phase. However, like condensed noble gases, they do require a high level of purity. A stainless steel purification system was constructed to purify the liquids and the purity was monitored by an ionization chamber with a 241Am source inside. The three liquid detectors were exposed to 250keV x-rays from an orthovoltage x-ray tube and neutrons (1.4-12MeV) from a 1-Ci 239Pu-Be source. Experimental data show that an ionization chamber filled with dielectric liquid is capable of detecting fast neutrons in pulse mode. While chamber 1, chamber 2, and chamber 3 (filled with TMS) did not respond to the Pu-Be source, chamber 3 (filled with TMP and Isooctane) successfully detected the presence of neutrons. Data also show that the chambers could not detect gamma rays from 1[mu]Ci Co-60 and Cs-137 check sources. In addition, the chambers could detect 250 keV x-rays in current mode, but not pulse mode. These results present positive implications for the gamma-blindness of the dielectric liquids studied. / by Erin M. Boyd. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2008. / Cataloged from PDF version of thesis. / Includes bibliographical references. / This thesis contributes to the Flexible Conversion Ratio Fast Reactor Systems Evaluation Project, a part of the Nuclear Cycle Technology and Policy Program funded by the Department of Energy through the Nuclear Energy Research Initiative. The goal of this project is to develop conceptual designs of fast flexible conversion ratio reactors using lead and liquid salt coolants and compare the results with the gas cooled fast reactor developed in an MIT NERI project and the sodium cooled reactor under development at ANL. This thesis is the summary of the design and analysis of the lead-cooled reactor portion of the project. Core designs that fit in the same reactor plant were executed for two limiting conversion ratios: (1) near zero to transmute legacy waste and (2) near unity to operate in a sustainable closed cycle. To reap the benefits of economy of scale, a large power rating of 2400MWt was set as the target thermal power for both reactor designs. In addition, the achievement of inherent reactor shutdown in unprotected accidents (without scram) was set as a desirable goal. The core employs transuranic metallic fuel. The large pool vessel contains four intermediate heat exchangers (IHX) that couple the primary system to an efficient and compact supercritical CO2 power conversion system. To prevent CO2 from entering the core in case of intermediate heat exchanger tube rupture, a dual-free level design for the primary vessel is adopted. Ultimate decay heat removal is accomplished by passive means through an enhanced reactor vessel auxiliary cooling system (RVACS) complemented by a passive secondary cooling system (PSACS). / (cont.) The transient simulation of station blackout (SBO) using the RELAP5-3D/ATHENA code shows that inherent shutdown without scram can be accommodated within the cladding temperature limit by the enhanced RVACS and PSACS by removing a fraction of decay power with the PSACS. The PSACS was designed such that the balance between two limiting cases was achieved: (1) peak cladding temperature limit is satisfied during unprotected station blackout with a minimum (two) number of PSACS trains operated, and (2) the minimum coolant temperature is kept above the freezing point with a maximum (four) number of PSACS trains operated. The PSACS design satisfies the conditions of both unity and zero conversion ratio cores. The other SBO accident conditions are bounded by the above cases. In addition, two other transients are considered: loss-of-flow accident (LOFA) and inadvertent reactivity insertion transient (UTOP). Both reactors show good performance during these additional transients. / by Anna S. Nikiforova. / S.M.

Thesis: S.B., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2017. / 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 57-58). / Neutron diffraction is a technique that allows scientists to measure the arrangement and motions of atoms in a crystalline lattice by observing neutrons scattering at angles that are characteristic of the interatomic distances of the crystal. This is useful for studying the response of crystals to stress, irradiation, or for observing their phases. This thesis implements and analyzes a technique known as polychromatic neutron powder diffraction, which has the potential to be used by an instrument to make many simultaneous neutron diffraction measurements. In this experiment, powder diffraction patterns were measured with a diffractometer in polychromatic mode, using both angle-dispersive and wavelength-dispersive scans of a silicon powder. The intensity and resolution of the Bragg peaks with the instrument in this configuration were compared to Bragg peaks measured by the same instrument in a monochromatic configuration. The intensity of the polychromatic mode was only comparable to the monochromatic mode with looser collimation, which had the consequence of increasing the widths of the measured peaks. This resulted in a polychromatic signal intensity that was greater than the monochromatic signal intensity, and a Bragg peak that was wider than the monochromatic Bragg peak. The effects of the collimators and the sample to detector distances were quantified in experiment and in ray-tracing simulations. While both the monochromatic and the polychromatic configurations had similar counting rates in this experiment, they were both limited by the high background due to the open-beam geometry. A successful implementation of a polychromatic instrument would require substantial filtering and shielding to overcome this effect. / by Jonathan T. Morrell. / S.B.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 102-104). / The primary product of this thesis is a faster running computer code to model air ingress events in high temperature gas reactors as a potential subroutine for nodal codes such as MELCOR to model air ingress events. Because of limitations found in FLUENT, and the limitations of the data set, a simple model of the effects of graphite oxidation reactions and structures was built in MATLAB code and is described. This code is based on the fundamental understanding of the physical phenomena at work along with common assumptions. The code is subject to typical instabilities inherent in the physical phenomena as well as uncertainties introduced in the numerical methods themselves. Sample results of the code are presented, which show remarkable similarities to the NACOK data considering the simplistic formulas used. The code structure is described in detail. A simplistic MELCOR model is described, which was built to inform the structure of the code, although the source code for MELCOR was not provided to allow integration of the code into MELCOR. As part of the code development process, the previous MIT work to model air ingress experiments were reviewed to understand the reasons for the portions of apparently non-physical results obtained through past FLUENT models. In addition, a 2-D FLUENT model was created to perform transient analysis which was previously limited to steady state conditions due to the longer computational time required for the 3-D modeling. This model was also created in an effort to compare the results of the previous models using porous media assumptions versus explicitly modeled geometry. Finally, the 2-D model showed valuable steady state results in a much shorter time period than the 3-D model. / by Caroline A. Cochran. / S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2018. / 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 155-160). / This thesis presents an in-depth thermal-fluid analysis of direct absorption molten salt solar receivers. In this receiver concept, an open tank of semi-transparent liquid is directly irradiated with concentrated sunlight, where it is absorbed volumetrically and produces internal heat generation. The intensity distribution of the internal heating depends on the optical properties of the absorber liquid and the dimensions of the receiver. This heating results in a combination of thermal stratification and radiation-induced natural convection in the receiver, which govern the general thermal-fluid behavior and performance of the system. Direct absorption requires molten salts to be contained in open tanks directly exposed to the environment; consequently, the liquid absorber experiences thermal losses to the environment which reduces absorption efficiency and produces large temperature gradients immediately below the exposed liquid surface. The thesis presents an apparatus that allows for the precise measurement of light attenuation in high temperature, nearly transparent liquids. The apparatus is used to measure and characterize the absorption properties of the 40 wt. % KNO₃:60 wt. % NaNO₃ binary nitrate and the 50 wt. % KCl:50 wt. % NaCl binary chloride molten salt mixtures. The analytical model of the thermal stratification, radiation-induced convection, and radiative cooling effects highlights the key parameters and conditions for optimizing the thermal-fluid performance of the receiver. Computational fluid dynamics and heat transfer modeling of the CSPonD Demonstration prototype of a direct absorption molten salt solar receiver provide further insight into its performance. The findings from the analytical and computational analyses give motivation to create a new cover design for open tanks of molten salts consisting of floating hollow fused silica spheres. The cover concept is demonstrated experimentally and the analysis shows the cover's ability to reduce thermal losses by 50%. / by Mélanie Tétreault-Friend. / Ph. D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2008. / Includes bibliographical references (leaves 97-103). / Nanofluids are engineered colloidal dispersions of nanoparticles (1-100nm) in common fluids (water, refrigerants, or ethanol...). Materials used for nanoparticles include chemically stable metals (e.g., gold, silver, copper), metal oxides (e.g., alumina, zirconia, silica, titania) and carbon in various forms (e.g., diamond, graphite, carbon nanotubes). The attractive properties of nanofluids include higher thermal conductivity, heat transfer coefficients (HTC) and boiling critical heat flux (CHF) than that of the respective base fluid. Nanofluids have been found to exhibit a very significant enhancement up to 200% of the boiling CHF at low nanoparticle concentrations. In this study, nanofluids were investigated as an agent to modify a heater surface to enhance Critical Heat Flux (CHF). First, the CHF of diamond, Zinc Oxide and Alumina water-based nanofluids at low volume concentration (<1 vol%) were measured to determine if nanofluid enhances CHF as seen in literature. Subsequently, the heaters are coated with nanoparticles via nucleate boiling of nanofluids. The CHF of water was measured using these nanoparticle precoated heaters to determine the magnitude of the CHF enhancement. Characterization of the heaters after CHF experiments using SEM, confocal, and contact angle were conducted to explain possible mechanisms for the observed enhancement. The coating thickness of the nanoparticle deposition on a wire heater as a function of boiling time was also investigated. Finally, theoretical analyses of the maximum CHF and HTC enhancement in term of wettability were performed and compared with the experimental data. The CHF of nanofluids was as much as 85% higher than that of water, while the nanoparticle pre-coated surfaces yielded up to 35% CHF enhancement compared to bare heaters. / (cont.) Surface characterization of the heaters after CHF experiments showed a change in morphology due to the nanoparticles deposition. The coating thickness of nanoparticle was found to deposit rather quickly on the wire surface. Within five minutes of boiling, the coating thickness of more than 1 pm was achieved. Existing CHF correlations overestimated the experimental data. / by Bao H. Truong. / S.M.

Thesis: S.M., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2017. / 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 161-166). / Concerns of climate change and sustainable energy policy are driving the deployment of wind and solar energy towards the goal of reducing fossil fuel emissions. In liberalized (deregulated) markets, the large-scale deployment of wind or solar energy results in electricity price collapse at times of high wind or solar output to below the price of fossil fuels. This revenue collapse limits economic large-scale use of wind and solar and reduces the revenue for nuclear plants. The current electrical energy storage options are too expensive to be deployed in sufficient quantity to prevent the price collapse. A less expensive approach to energy storage is required to enable a low carbon-energy grid. This thesis explores the potential of a new energy storage technology to address the challenges of a low-carbon energy grid: FIrebrick Resistance-heated Energy Storage (FIRES). FIRES is a storage technology that takes in surplus electricity, stores the energy as high temperature sensible heat (1200°C-1700°C) in a firebrick storage medium, and outputs the stored heat as hot air when the energy is desired. The stream of hot air can be used to (1) provide heat to high temperature industries in place of natural gas, or (2) be added to a power cycle to produce electricity when it is in demand. FIRES heat storage is nearly two orders of magnitude less expensive than the current energy storage options (on the order of dollars per kilowatt-hour capital cost). Cheap electricity transferred to the heating market by FIRES reduces heating costs and carbon emissions by offering industries cheaper energy than that of the competing fossil fuel, while ensuring revenue to the solar, wind and nuclear power plants. FIRES has "unlimited" storage capacity. If the firebrick is fully charged, FIRES electric resistance heaters will provide hot air to furnaces as long as electric prices are less than fossil-fuel prices. In the long term, FIRES stored heat may be used for peak electricity production in advanced nuclear plants with air-Brayton power cycles, with roundtrip storage efficiencies (electricity-to-heat-to-electricity) near 70%, in class with that of existing electrical energy storage options. Conceptual designs of FIRES heat storage on the megawatt-hour scale were found to be chargeable and dischargeable over periods of several hours or several days as needed. FIRES technology is ready for applications under 1200°C using existing technologies; research is required for higher temperature and high pressure (Brayton power cycle) applications. The applications, conceptual designs, system modeling and preliminary performance and economic evaluations are detailed in the following study. / by Daniel Christopher Stack. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2007. / Includes bibliographical references (p. 53-56). / Selective vascular irradiation enables the critical examination of the vasculature and its role in the onset of late radiation effects. It is a novel approach to expose the endothelial cells to much higher levels of ionizing radiation relative to normal cells by utilizing the boron neutron capture reaction. When boron-containing compounds are restricted to the lumen of the blood vessel, the resulting high-LET alpha and lithium particles cannot deposit their energy in the normal cells beyond the vasculature after the target is exposed to thermal neutrons. This allows for a 2- to 3-fold increase in the calculated dose to the endothelial cells. However, this technique has been criticized because there is no direct evidence that the endothelial cells receive an absorbed dose from the selective vascular irradiation. The objective of this work is to provide corroborating experimental evidence that selective vascular irradiation physically damages the endothelial cells. An established assay utilizing blood-brain barrier disruption was adopted to quantify the radiation damage to the endothelial cells in female BALB/C mice, 8-12 weeks of age. A dye that attaches to the plasma proteins in the blood and that is ordinarily kept out of the brain by the blood-brain barrier is injected into the blood supply before the irradiation, and following irradiation, damage to the vasculature will result in disruption of the blood-brain barrier that allows blood stained with the dye to enter the brain. After sacrificing, the blood in the vessel lumen is cleared by performing a trans-cardiac perfusion, and the brain is homogenized and prepared for analysis. The absorbance of the resulting supernatant of each brain sample is measured with a spectrophotometer at the optimal wavelength of the dye. / (cont.) The absorbance is related to the quantity of blood that leaked through the blood-brain barrier, which is also related to the damage caused to the vasculature from exposure to ionizing radiation. Increased leakage through the blood-brain barrier was observed for those mice exposed to selective vascular irradiation, indicating a direct relationship between the leakage through the blood-brain barrier and the 10B concentration in the blood. The most significant increase in the leakage through the blood-brain barrier (p<0.002) was observed at the highest lOB concentration in the blood (161 ppm). The compound biological effectiveness (CBE) for sulfhydryl borane (BSH) was calculated to be 0.28, which is consistent with the published value of the CBE for BSH in the rat spinal cord. This suggests that the assumptions used for calculating the absorbed doses for selective vascular irradiation are reasonable and approximate to what the endothelial cells receive. / by Rebecca L. Raabe. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 145-146). / Fuel swelling and fission gas generation for fast reactor fuels are of high importance since they are among the main limiting factors in the development of metallic fast reactor fuel. Five new fission gas and swelling modules for the fast reactor metallic fuel code FEAST-METAL were developed. This increases the number of degrees of freedom in the code and enhances the science -based modeling options for fuel swelling. All of the modules developed were benchmarked against data from EBRII. Particularly, the code was benchmarked against U-19Pu-lOZr fuel and was applied to U-6Zr fuel. The modifications made still kept the overall GRSIS algorithm present in the code. The GRSIS model tracks "closed" and "open" bubbles. The new modifications increased the number of closed bubble groups used in the algorithm, inserted a model that changed the bubble groups from being based on constant volumes to ones with constant numbers of atoms, added phase dependence and reexamined closed bubble spacing through the implementation of a Monte-Carlo algorithm to calculate the effective distance between the nearest bubbles. All model options added to the code predicted the swelling, fission gas release and cladding strain effectively for the benchmark cases. However, significant differences in the results were fotind when the codes were applied to long-term U-6Zr fuel. The differences in the results cannot be resolved without more data on fuel behavior under irradiation; particularly, breeder fuel (blanket) data is needed to develop effective benchmarks. Until more data becomes available, it is advisable to use the original two group constant volume version of the code and the phase dependent version of the code and compare the results. The latter offers a much more scientifically based version of the code. Sensitivity analysis to the number of bubble groups indicate limited benefit may be obtained by using more than 2 bubble sizes. Additionally, care should be taken to ensure that the axial nodding of the fuel be such that the axial mesh length is smaller than 10% of the fuel length. Furthermore, if the FEAST code is to be used in a coupled fashion with the coolant sub-channel analysis code COBRA, the accuracy of the results depend on the model used for fuel swelling. / by Nathan Christopher Andrews. / S.M.

Thesis: S.M., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2017. / 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 187-197). / The Fluoride Salt-Cooled High-Temperature Reactor (FHR) is an advanced reactor concept, that uses molten-salt coolant and solid-uranium fuel composed of graphite and silicon carbide-encapsulated tri-structural isotropic (TRISO) particles. The primary coolant salt is known as flibe (7Li2BeF4), which was chosen for its desirable thermal-hydraulic and neutronic properties. Under irradiation, coolant salts containing lithium capture neutrons generating tritium in quantities that are several orders of magnitude larger than the amounts generated by existing light water reactors. Adsorption technology is proposed, using chemically compatible carbon materials for the capture and control of tritium in the FHR. Various nanoporous activated carbon, graphene and nuclear graphite materials have been characterized. This includes the determination of BET surface area, total pore volume, average pore size, and pore size distribution by performing low-temperature gas adsorption experiments and applying microscopic thermodynamic theory. In addition, morphological analysis was conducted with scanning electron microscopy. Hydrogen was used as a surrogate. Its chemisorption on these materials have been measured and modeled at the reactor conditions of 700°C and pressures under 4 kPa. Models suggest that the total measured solubility of hydrogen includes a combination of dissociative and molecular adsorption. Carbon materials containing larger volumetric fractions of micropores (width < 2 nm) generally exhibited a higher hydrogen capacity. Further, the presence of micropores was associated with a relatively weak and reversible form of hydrogen chemisorption. At 500 Pa, microporous carbon materials captured 50 times more hydrogen than graphite, which was previously known to be the largest hydrogen sink at reactor conditions. The coupled effects of generation, chemical speciation, adsorption and diffusion of tritium in the FHR system were simulated over 200 full-power days. It was found that an adsorption column using high-performance carbon-based catalyst adsorbed substantial amounts of tritium and reduced the peak release rate from 2400 Ci/day to 40 Ci/day for the 236 MWt FHR. Further, the total tritium inventory in the system decreased by more than 70%, from 68,400 Ci to 19,400 Ci. This demonstrates that adsorption technology can greatly reduce the risk of radiological release during normal operation and reactor transient events. / by Stephen Tsz Tang Lam. / S.M.