Thesis (Nucl.E)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1984. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Includes bibliographics references. / by José Félix Pérez Méndez-Castrillón. / Nucl.E

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2004. / Includes bibliographical references (p. 129-137). / Performance assessments (PAs) are important sources of information for societal decisions in high-level radioactive waste (HLW) management, particularly in evaluating safety cases for proposed HLW repository development. Assessing risk from geologic repositories for HLW poses a significant challenge due to the uncertainties in modeling complex systems of such large temporal and spatial scales. Because of the extensive uncertainties, a typical safety case for a proposed HLW repository is comprised of PA results coupled with various defense-in-depth elements, such as the multi-barrier requirement for repository design, and insights from supplementary analyses. This thesis proposes an additional supplementary analysis, the Strategic Partitioning of Assumption Ranges and Consequences (SPARC), that could be used: (1) in a safety case to help build confidence in a repository system, (2) to provide risk information for decisions on how to allocate resources for future research, and (3) to provide risk information for stakeholder deliberation. / (cont.) The SPARC method extracts risk information from existing PAs and supporting databases by uncovering what sets of model parameter values taken together could result in a substantially-increased-dose (SID) from the repository, and displays the results in SPARC trees. The SPARC method is applied to the proposed Yucca Mountain HLW repository (YMR), as a demonstrative example. The YMR is a particularly interesting example since there have been many public disagreements about it from the inception of the project. This thesis demonstrates how risk information could be extracted from existing PAs for the YMR, with particular attention to addressing the concerns raised by stakeholders. Preliminary application of the SPARC method to the YMR shows that it yields interesting insights into 'savior' attributes of the repository, i.e., those parameter assumption ranges that, if true, are projected to prevent SIDs to different dose receptors (at 10-km or 20-km from the repository, for different future time periods) with very high probability. The thesis also explores how the SPARC method could contribute to other confidence-building exercises, such as assessing repository barrier capability and prioritizing future research efforts. / by Suchandra Tina Ghosh. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2004. / Includes bibliographical references (leaves 101-103). / If a liquid is cooled sufficiently below the melting point, it becomes metastable with respect to the crystalline state. However, if nucleation is suppressed, one can supercools the liquid without resulting in crystallization. The characteristic time for structural relaxation increases rapidly and at a certain point, it becomes comparable to the duration of experiment time scale. At this point, the liquid is being arrested structurally. We define this structurally arrested matter a glass. Dynamically, a glass transition can be viewed as a transition from ergodic to nonergodic state of matters. In a hard-sphere system, mode coupling theory (MCT) predicts occurrence of a glass transition when the volume fraction exceeds a certain value due to the excluded volume effect. However, Recent MCT calculations for a hard-sphere system with a short-range attraction show that one may observe a new type of structurally arrested state originating from clustering effect, called the "attractive glass", as a result of the attractive interaction. This is in addition to the well-known glass-forming mechanism due to the cage effect in the hard sphere system, called the repulsive glass. / (cont.) The calculations also indicate that, if the range of attraction is sufficiently short compared to the diameter of the hard sphere, within a certain interval of the volume fraction and the effective temperature, the two glass-forming mechanisms can compete with each other. For example, by varying the effective temperature at appropriate volume fractions, one may observe respectively, the glass-to-liquid-to-glass re-entrance or the glass-to-glass transitions. Here we present experimental evidence for both transitions, obtained from small-angle neutron scattering (SANS) and photon correlation spectroscopy measurements taken from dense L64 copolymer micellar solutions in heavy water. We show, a sharp transition between the two types of glass can be triggered by varying the temperature in the predicted volume fraction range. In particular, according to MCT, there is an end point (called A3 singularity) of this glass-to-glass transition line, beyond which the long-time dynamics of the two glasses become identical. Our findings confirm this theoretical prediction. / (cont.) Surprisingly, although the Debye-Waller factors, the long-time limit of the coherent intermediate scattering functions, of these two glasses obtained from PCS measurements indeed become identical at the pre- dicted volume fraction, they exhibit distinctly different intermediate time relaxation. Furthermore, our SANS results on the local structure obtained from volume fractions beyond the end point are characterized by the the same features as the repulsive glass obtained before the end point. A complete phase diagram giving the boundaries of the structural arrest transitions for L64 micellar system is given. Furthermore, SANS experiment shows that, in the region of disordered micellar liquid phase, as the hydrostatic pressure increases, the effective micellar interaction potential changes in response to the pressure perturbation, resulting in a significant increase in the low-k part of the SANS intensity distribution, characterizing the formation of fractal clusters. In addition to the formation of fractal clusters, starting from a structurally arrested state, the applied pressure induces the matrix to evolve from an initial attractive glass state through an intermediate state and ends up in a final liquid state. / (cont.) Inspired by the random phase approximation, an additional structure factor term derived from fractal clusters is added to the adhesive hard sphere structure factor to approximate the variation of the effective interaction potential. Based on this idea, a model for the scattering intensity distribution is developed which successfully explains the measured SANS intensity distributions. One of the great challenges in soft matter sciences is to understanding the structurally arrested state of matter. Although it still remains as an open question, it is well-acknowledged that the understanding of the interaction potential is of fundamental importance. Due to the fact that colloidal particles can be produced with well-defined chemical and physical properties such as shape, size and most importantly, the tunable interaction potential. Combining with theoretical predictions, they serves as convenient model systems to provide key information about the relationship between the rich phase behaviors and various interaction potential, such as van der Waals forces, short-range attraction et al. / (cont.) The experimental studies of kinetic glass transition in a micellar system presented in this thesis may provide useful in- formation to further experimental investigations and theoretical calculations on this rapidly expanding field of research. / by Wei-Ren Chen. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2005. / "September 2005." / Includes bibliographical references (leaves 194-197). / The goal of this work is to develop a charged-particle microbeam for use in radiobiological research at the MIT Laboratory for Accelerator Beam Applications (LABA). The purpose of this device is to precisely explore the radiation response of biological systems on a cellular and subcellular level, particularly in the area of temporal and spatial effects of radiation on in vitro systems. An accelerator-based 750 keV proton source was characterized and integrated into a laboratory-scale device that includes a deflection/gating system, single-particle detection system, imaging and positioning system, and a collimation system with two designed modes: a "charged-particle microslit" for delivering a -3 micron by 1 mm dose profile; and a pinhole aperture for delivering a -3 micron diameter pattern of radiation. The entire device measures less than 4 m, requires minimal radiation shielding, and utilizes a dedicated ion source. The charged particle microslit has been fully characterized and used to deliver a radiation pattern to a series of mammalian fibroblast cell monolayers that have subsequently been assayed for direct and indirect chemical effects of radiation, double-stranded DNA damage, and DNA repair protein localization. These studies will contribute to the understanding of the radiation-induced bystander effect, which is generally defined as the induction of biological effects in cells that are not directly traversed by ionizing radiation. / (cont.) Analysis of the range of assays performed on the microbeam-irradiated cells demonstrates that even though the physical radiation dose is confined to a subnuclear width (< 5 microns), in many cases the biological effects of the radiation extend for many cell widths (> 40 microns) and show dependence on the initial radiation dose delivered to the directly irradiated cells. As an experimental system, the LABA Microbeam was designed to be practically turn-key, and most applications require only one operator to perform. The LABA Microbeam represents a significant step towards a cost-effective and easily operated charged-particle microbeam appropriate for use as a standard laboratory research tool. Further work remains in automation of the microbeam subsystems and optimization/characterization of the pinhole-aperture collimator, as well as expanding the scope of the radiobiological assays performed using the charged-particle microslit. / by Michael R. Folkert. / Ph.D.

Thesis (Nucl.E. and S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1998. / Includes bibliographical references. / The steady improvement of US Nuclear Utility generation capability observed over the past two decades has recently halted and somewhat degraded. For the industry to resume its upward trend in performance a detailed examination must be performed of current performance and new methods developed to continue the improvement. A detailed study of Boiling Water Reactor, Class IV (BWR/4) performance over the past five years was conducted to gain insight to the nature of lost generation capability and develop a methodology to improve capability. Extensive electronic NRC records were used in conjunction with detailed power plant records and engineering experience at PECO Energy's Limerick Generating Station and Peach Bottom Atomic Power Station for this research. Administrative or regulatory shutdowns within the study dominated the lost generation capability and detracted from the goal of analyzing equipment reliability. Nine of two hundred thirty five shutdowns were therefore limited to maximum impact of 30 days lost generation. Balance of Plant system failures were found to initiate 69% of the occurrences of lost generation capability and account for 59% of the capability loss. The failures of these systems were found to be infrequent events which correlated poorly to the aggregate industry experience. Approximately fifty percent of the forced outages were the result of equipment related failures such as weak design or worn parts with the remaining fifty percent the result of human related failures. Only 19% of the failures were noted to be the result of component age related failures while 31% of the failures were related to poor equipment design. The time frame of forced outages with in operating cycles was additionally reviewed. Failures were found to be more frequent in the early phase of the operating cycle following start up from a refueling and approximately 400 to 550 days after start up. The impact of these failures was not great enough to affect the steady state cumulative capability factor of the aggregate BWR/4 utility achieved after one year of operation. Individual utility sites were found to have opposing strong and weak periods of performance within their operating cycles. The loss of generation capacity taken for planned maintenance outages and on line maintenance for minor equipment problems was not found to have a significant impact on aggregate BWR/4 performance. For plants not involve in lengthy shutdowns, the strongest impacts on cumulative capacity were forced outages, initial start up and coast down. The unpredictable and design nature of system failures necessitates a structured effort to improve the combined performance of all systems at a utility. Balance of Plant systems were found to all have a 25% probability of causing a single forced outage lasting slightly less than 5 days in length. The infrequent nature of significant failures necessitates a broad based communication between utilities to maintain an adequate level of awareness of system vulnerabilities and possible improvements. Two specific sites examined had opposing and repeatable strong and weak cycle performance traits. The unique nature of site performance demonstrates the impact that improved communications between utilities could have on transferring strengths and diminishing weaknesses thus improving overall utility performance. / by David Lester Brodeur. / Nucl.E.and S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2001. / Includes bibliographical references (p. 246-250). / To address the proliferation risk of separated plutonium, a technical and institutional design of an international plutonium storage system (IPSS) is presented. The IPSS is evaluated from two perspectives: its ability to address the proliferation risk of excess civilian inventories, and its ability to reduce the threat from excess Russian military plutonium. A systems dynamic model of global plutonium inventories projects a capacity requirement for an IPSS of 450 to 600 MT. A conceptual design of a representative 100 MT storage facility was shown to meet criticality safety requirements for a range of operational and accident scenarios. From an institutional perspective, a hybrid organizational structure drawing on rganizational features of the United Nations Security Council and the International Atomic Energy Agency is proposed as a model for system participation and governance. For political and nonproliferation reasons, a multiple-site arrangement for the IPSS is recommended. The following locations are identified as potential IPSS sites: Savannah River (U.S.), Mayak (Russia), La Hague (France), and Rokkasho (Japan). A set of rules governing material ownership and release conditions is also proposed. Intrinsic barriers to the proliferation of plutonium of the type envisioned by the "spent fuel standard" will not be achieved for many years. In the meantime, primary reliance must be placed on extrinsic barriers. / (cont.) The effectiveness of an IPSS would derive mainly from the extrinsic (institutional) barriers to proliferation it would provide. An IPSS would significantly enhance the proliferation resistance of global plutonium inventories. Several hurdles to IPSS implementation are identified, and a proposal for implementing the IPSS in Russia is described. The total life-cycle cost of an IPSS is estimated at $9 billion (in 2000 dollars). The cost to the U.S. of addressing the excess military plutonium problem with an IPSS strategy is estimated at $2.9 billion, or $4.2 billion if the U.S. covers Russian costs as well. Several financing options are identified. A lifetime-levelized plutonium storage fee of ~$900/kg-year would be sufficient to recover the full life-cycle cost of the IPSS. / by Eugene Bae. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1999. / Includes bibliographical references (leaf 46). / The Modular Pebble Bed High Temperature Gas Reactor (MPBR) being designed by the Massachusetts Institute of Technology and the Idaho National Engineering and Environmental Laboratory operates with an online refueling system. This leads to an increased risk of proliferation because the fuel pebbles can be diverted while the plant is operating. In order to show that the MPBR dose not pose a proliferation risk the fuel content was determined for different burnups up to 94 MWD/kg. This data shows that the fuel is very poor nuclear weapon material. Safeguard systems were also designed in agreement with the International Atomic Energy Agency's standards to prevent diversion of significant quantities of fissile material. / by Jennifer Marie Anderson. / S.B.

Thesis (Nucl. E.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1990. / Includes bibliographical references (p. 145-147). / by William Andrew Stewart. / Nucl.E.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1987. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Bibliography: v.3, leaves 516-522. / by Michael G. Izenson. / Ph.D.

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1986. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Bibliography: leaves 227-233. / by Kosuke Kato. / Sc.D.