Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2008. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 73-76). / This work explores the effects of low-dose-rate radiation on both the AA8 (wild-type CHO cells) and EM9 (XRCC1 null CHO mutants) cell lines. In particular, this study performed clonogenic survival and growth assays to determine the radiations/ effect on the cells proliferative capacity. It was hypothesized that the XRCC1 null mutants would show greater radiosensitivity during continuous low-dose-rate radiation since the inability to rapidly respond to DNA damage would result in the gradual accumulation of cytotoxic double strand DNA breaks and/or chromosome exchanges/aberrations. The cells were irradiated for 7 days with photons from unencapsulated 241Am plate sources for chronic, low-dose-rate studies, at dose-rates between 1.99 ± .610 x 10-3 cGy/h and 1.23 ± .0325 cGy/h, and irradiated with a Phillips RT250 X-ray machine at 250 kVp and 2.5 Gy/min to doses between 0.02-10 Gy for acute studies. There were significant differences in the growth rates of the unirradiated controls and the irradiated flasks at all dose-rates for both AA8s and EM9s (except for the EM9 9.08 ± .390 x 10-3 cGy/h flask where p<.10). There were also suggestive (p<.20) differences in the clonogenic survival for both cell lines compared to controls with significant (p<.05) differences observed in the EM9 irradiated population at dose-rates of: 6.89 ± .315 x 10-3 cGy/h, 3.30 + .80 x 10-3 cGy/h, and 1.99 + .61 x 10-3 cGy/h. Moreover, there are suggestive (p<.15) trends indicating that XRCC1 deficient cells are more susceptible to chronic low-dose-rate radiation (dose-rates compared were between 1.99 ± .61 x 10-3 cGy/hand 9.08 + .39 x 10-3 cGy/h) as compared with acute exposures at the same dose. / (cont.) Despite some procedural differences with other published works, these results may be evidence of the "inverse dose-rate" effect noted by other authors. / b y Dwight McCoy Chambers. / S.M.

Thesis: Ph. D. in Computational Nuclear Science and Engineering, 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 269-274). / The development of high fidelity multi-group neutron transport-based simulation tools for full core Light Water Reactor (LWR) analysis has been a long-standing goal of the reactor physics community. While direct transport simulations have previously been far too computationally expensive, advances in computer hardware have allowed large scale simulations to become feasible. Therefore, many have focused on developing full core neutron transport solvers that do not incorporate the approximations and assumptions of traditional nodal diffusion solvers. Due to the computational expense of direct full core 3D deterministic neutron transport methods, many have focused on 2D/1D methods which solve 3D problems as a coupled system of radial and axial transport problems. However, the coupling of radial and axial problems also introduces approximations. Instead, the work in this thesis focuses on explicitly solving the 3D deterministic neutron transport equations with the Method of Characteristics (MOC). MOC has been widely used for 2D lattice physics calculations due to its ability to accurately and efficiently simulate reactor physics problems with explicit geometric detail. The work in this thesis strives to overcome the significant computational cost of solving the 3D MOC equations by implementing efficient track generation, axially extruded ray tracing, Coarse Mesh Finite Difference (CMFD) acceleration, linear track-based source approximations, and scalable domain decomposition. Transport-corrected cross-sections are used to account for anisotropic without needing to store angular-dependent sources. Additionally, significant attention has been given to complications that arise in full core simulations with transport-corrected cross-sections. The convergence behavior of transport methods is analyzed, leading to a new strategy for stabilizing the source iteration scheme for neutron transport simulations. The methods are incorporated into the OpenMOC reactor physics code and simulation results are presented for the full core BEAVRS LWR benchmark. Parameter refinement studies and comparisons with reference OpenMC Monte Carlo solutions show that converged full core 3D MOC simulations are feasible on modern supercomputers for the first time. / by Geoffrey Alexander Gunow. / Ph. D. in Computational Nuclear Science and Engineering

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2013. / "June 2013." Cataloged from PDF version of thesis. / Includes bibliographical references (page 14). / A Monte Carlo algorithm for solving simple linear systems using a random walk is demonstrated and analyzed. The described algorithm solves for each element in the solution vector independently. Furthermore, it is demonstrated that this algorithm is easily parallelized. To reduce error, each processor can compute data for an independent element of the solution, or part of the data for a given element for the solution, allowing for larger samples to decrease stochastic error. In addition to parallelization, it is also shown that a probabilistic chain termination can decrease the runtime of the algorithm while maintaining accuracy. Thirdly, a tighter lower bound for the required number of chains given a desired error is determined. / by Cyrus Vafadari. / S.B.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 143-154). / Recent advances in high temperature superconductors (HTS) have opened up a new parameter space for the design of tokamak fusion pilot plants. While previously the maximum on-axis field in a superconducting tokamak was limited to ~6 T, HTS allows tokamaks to be designed with much higher on-axis fields, leading to smaller reactor designs. For these designs, it is critical to determine the lifetime of modern HTS technology in an environment relevant to compact, high-field fusion reactors as well as develop strategies to mitigate this damage. While some studies have been undertaken to assess the lifetime of coated conductors in a fast neutron environment, facilities do not exist to perform cryogenic neutron irradiations at the present. In addition, reactor studies are costly and activate the samples, requiring long cooldown times and specialized analysis facilities to handle radioactive material. In order to complement reactor irradiation studies of HTS and determine whether elevated temperature irradiation has an effect on Jc degradation, REBCO coated conductors were irradiated with a 1.2 MeV proton beam at 80 K, 323 K, and 423 K. Proton irradiation at cryogenic temperatures was found to substantially reduce the amount of Jc degradation in the REBCO samples irradiated to high fluences, a result of great importance to superconducting REBCO magnets in fusion applications where the radiation will occur at T < 80 K. An analysis of temperature, field, and angle dependencies of Jc was performed to investigate the microstructural mechanisms behind the Jc degradation at different temperatures. The key mechanism driving the differences in Jc degradation was found to be radiation-enhanced diffusion at higher temperatures, leading to grain boundary widening between superconducting crystals which in turn blocked supercurrent transport through the conductor. Molecular dynamics simulations suggest that the same mechanism (enhanced diffusion to grain boundaries) also applies to neutron irradiations. This motivates a re-evaluation of previous REBCO neutron irradiation studies at temperatures between 323 K and 383 K, specifically with regards to predictions about REBCO lifetimes in a fusion environment. The work in this thesis suggests that at cryogenic temperatures, the Jc degradation observed in these studies could be substantially less than previously reported. / by Brandon Nils Sorbom / Ph. D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2008. / Includes bibliographical references (leaves 58-61). / 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, this law is feasible for any port that is able to make the initial investment. A nuclear weapon would be destructive to both the U.S. and the country of origin, which should convince anyone that the benefits outweigh the costs. / by William E. Foley, III. / S.B.

Thesis: S.M., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 89-90). / Experimental quantification of PWR fuel reactivity burnup decrement biases and uncertainties using in-core flux map data from operating power reactors has previously been conducted employing analytical methods to systematically determine experimental fuel reactivities that best match measured fission rate distributions. This optimal core reactivity distribution that best matches the measured fission rate distribution is assumed to be associated with the true fuel reactivity distribution. Some parties have questioned whether fortuitous cancellation of errors between various approximations inherent in the 3D nodal diffusion core analysis models might have caused reactivity decrement biases and uncertainties to be unrealistically small. In this study, the BEAVRS benchmark is modeled with both 2D, full-core, multi-group transport calculations and 2D and 3D nodal diffusion calculations. The calculated reaction rates are compared with measured in-core detector reaction rates supplied in the benchmark. These models are used in conjunction with analytical methods to obtain fuel reactivity biases and uncertainties. Results demonstrate that fuel batch reactivities inferred from flux map data using full-core transport calculations are nearly identical to those inferred using nodal diffusion calculations. Consequently, nodal methods do not contribute significantly to reactivity decrement biases. Fuel reactivity biases and uncertainties inferred from 3D nodal diffusion calculations remain valid. / by Geoffrey Alexander Gunow. / S.M.

Thesis: S.M., 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. / Page 99 blank. Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references (pages 93-98). / Future multilateral nuclear arms reduction efforts will require technologies for the verification of treaty compliance. In particular, warheads slated for dismantlement will need to be verified for authenticity without revealing any sensitive weapons design information to international inspectors. Recent efforts have investigated physical cryptographic verification protocols that attempt to solve this treaty verification problem by using physics processes rather than electronics to encrypt sensitive information. The physical cryptographic protocol simulated in this thesis exploits the isotope-specific nature of nuclear resonance fluorescence (NRF) measurements to provide a strong indicator of the authenticity of a warhead. To protect against sensitive information leakage, the NRF signal from the warhead is convoluted with that of an encrypting foil containing the same isotopes as the warhead but in unknown amounts. The convoluted spectrum from a candidate warhead is then statistically compared against that from an authenticated template warhead to determine whether the candidate itself is authentic. This work presents the initial Geant4 Monte Carlo simulations of the physical cryptographic warhead verification protocol. Using a 2.7 MeV endpoint bremsstrahlung beam, a template warhead is interrogated. Several hoax geometries are also compared against the template to show the protocol's robustness against cheating. Isotopic hoaxes in which weapons-grade plutonium is replaced with reactor-grade plutonium or depleted uranium are shown to be detectable in realistic measurement times. An optimized geometric hoax that mimics the areal densities and attenuations of the authentic template warhead along one axis can also be detected with a second measurement under a different projection. Results of the simulations as well as future research objectives will be presented and discussed. / by Jayson Robert Vavrek. / S.M.

Thesis: S.B., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2017. / DISCLAIMER NOTICE: The pagination in this thesis reflects how it was delivered to the Institute Archives and Special Collections. Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references (pages 46-48). / The mechanism by which tellurium causes intergranular corrosion (IGC) of structural alloys in molten salt reactors is currently poorly understood. Limited corrosion testing has been performed on a few select alloys in simulated reactor conditions. In this thesis, the results of performing 50 h, 100 h, and 150 h corrosion tests on alloys Hastelloy N, Nickel-201, Incoloy 8ooH, and 316L Stainless Steel are presented. Upon inspection of the corroded surfaces of each alloy after its immersion in molten LiF-NaF-KF (FLiNaK) salt at 700 °C using scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS), a consistent corrosion rate could not be determined for any of the alloys, nor could confident identification of telluride compounds within the corrosion layer or grain boundaries of any alloy be made. However, the results did appear to confirm the importance of using a low oxygen environment and avoidance of galvanic corrosion during testing. Furthermore, preliminary results from EDS analysis of one alloy sample implied that, with improved count rates taken during the elemental identification process, tellurium may be more clearly revealed in the corrosion layers and grain boundaries of the alloys tested. / by Natasha Skowronski. / S.B.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, February 2007. / Includes bibliographical references (p. 53). / (cont.) Investigated in this thesis are the excitation and observation of Langmuir wave turbulence caused by the parametric decay instability (PDI) in high-frequency space plasma heating experiments conducted at the NSF/DoD High Frequency Active Auroral Research Program (HAARP) facility in Gakona, Alaska during the spring and summer of 2006. The PDI is the decay of an electromagnetic (EM) wave into an electron plasma wave (i.e., Langmuir wave) and an ion acoustic wave. When the excited Langmuir wave parametrically decays into another Langmuir and ion acoustic wave pair, a cascade of Langmuir waves can occur provided that the instability threshold is satisfied. According to recently advanced theory by Kuo and Lee [2005], there are two possible methods of cascade: non-resonant and resonant. While the non-resonant cascade proceeds at the location of excitation, the resonant process occurs at lower altitudes to minimize losses that the non-resonant process incurs by remaining at the excitation altitude. Such losses are caused by the frequency mismatch effect, as the decay ion acoustic wave frequency becomes much less than that of the normal ion acoustic waves. In their downward propagation the Langmuir waves in the resonant cascade suffer from propagation losses, however these losses are less than those associated with the non-resonant process. The resonant process is therefore expected to have a lower threshold. Theoretical claims and calculations are compared to observations made at Arecibo, Puerto Rico and Tromso, Norway. Claims are also are supported by incoherent backscatter radar observations made at the HAARP facility in Gakona. / by Daniel L. Rokusek. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2008. / "June 2008." / Includes bibliographical references. / The supercritical carbon dioxide (S-CO₂) cycle is a promising advanced power conversion cycle which couples nicely to many Generation IV nuclear reactors. This work investigates the power conversion system design and proposes several "Third Generation" plant layouts for power ratings ranging between 20 and 1200 MWe for the recompression cycle. A 20 MWe simple cycle layout was also developed. The cycle designs are characterized by a dispersed component layout in which a single shaft turbomachinery train is coupled to parallel arrays of multiple printed circuit heat exchanger modules. This configuration has arrangement benefits in terms of modularity, inspectability, repairability and replaceability. Compared to the prior second generation dispersed layouts, its lower ductwork pressure drop confers approximately 2% higher thermal efficiency. Two alternative S-CO₂ cycle designs for medium power applications were developed using an in-house optimization computer code and Solid Edge software. The first design is a recompression cycle derived from the 300 MWe design developed at MIT for Generation IV reactors. The design employs one turbine, two compressors (main and recompression) working in parallel and two recuperators (high and low temperature) and maximizes cycle efficiency while striving for a small plant footprint. The second design is a simple S-CO₂ power cycle, which has only one turbine, one compressor, and one recuperator. The main focus of the simple S-CO₂ design is cycle compactness and simplicity while achieving still attractive efficiency. Extensive sensitivity studies were performed for both the medium power recompression and simple S-CO₂ cycles to reveal areas for performance improvement, or performance degradation. Cycle efficiency is most sensitive to turbine inlet temperature. / (cont.) Peak cycle pressure is also an important parameter affecting cycle efficiency, although to a smaller extent than turbine inlet temperature. Higher pressure gives higher efficiency, but this gradually saturates around 28 MPa. Other sensitivity studies included turbomachinery performance, cooling water temperature, and heat exchanger fouling and plugging The reference parameters chosen are a 650°C turbine inlet temperature and 20 MPa peak cycle pressure (compressor outlet) because they reach a high thermodynamic efficiency (~/~47-48%) while staying within materials limitations. In order to couple the cycle to many of the Generation IV nuclear reactors a second reference case was chosen with a turbine inlet temperature of 550°C and a peak cycle pressure of 20 MPa. / by Jonathan Paul Gibbs. / S.M.