The disposal of solidified radioactive wastes requires physical, chemical, and radiological characterization to ensure safety. Two quantities important to physical characterization include compressive strength and leach resistance. It is desirable to monitor strength development on-line in processing whenever possible. Therefore, the ability of nondestructive evaluation techniques to predict the long term compressive strength of waste forms during their processing was theoretically and experimentally evaluated. It was determined that the compressive strength of the mixture could be predicted through analysis of both rheological behavior and maturity development. Ultrasonic methods were shown to be less effective. Leach testing requires destructive analysis. The ability of neutron activation analysis to increase the detection limit of leached cobalt from cement waste forms containing EDTA was experimentally examined. A detection limit approaching 53 parts per billion was found. EDTA concentration had a measurable effect on the cobalt release due to cobalt chelation and matrix degradation.

This thesis compares a new dynamic moving boundary thermal hydraulics fuel pin model (FUELPIN) to a known thermal hydraulics code (COBRA) for the following relationships: (1) Minimum Departure from Nucleate Boiling Ratio (MDNBR) versus time for transient conditions in a Pressurized Water Reactor (PWR) channel, and (2) Position of Minimum DNBR versus time for transient conditions. Relationships between MDNBR and position of MDNBR versus time were analyzed by comparing: (1) output of COBRA, a steady state thermal hydraulics model, with inputs from a PWR simulation code (CEPAC-L), (2) output of CEPAC-L linked FUELPIN. CEPAC-L computer model was shown to be a good simulation of a PWR during steady state conditions and a loss of all primary coolant flow casualty by comparison with an accepted PWR simulation code (CEPAC). FUELPIN was shown to predict larger thermal margins than COBRA for loss of all primary coolant flow transients in PWRs.

Collimator and shield configurations for two high-purity germanium detectors were designed for use during a loss of coolant accident at a boiling water reactor. The detectors will return information concerning stack releases to operators within a 15 minute time frame. Operating parameters for the stack monitors are defined by the United States Nuclear Regulatory Commission (USNRC) and a 24 hour source term generated by ORIGEN2. A lead collimator 0.4 cm in diameter, 20 cm in length for the high range detector and 2 cm in diameter, 20 cm in length for the low range detector was shown through a Monte Carlo code, MCNP4 to prevent high range detector saturation and provide enough low range detector response so good statistical data on stack releases result. A lead shield 20 cm thick was shown through MCNP4 to reduce the background radiation interference for both detectors to levels such that the detection of isotopes within the stack effluent is possible as required by the USNRC.

In this paper, the problem of designing an advanced sensor validation system (SVS) which is robust and fault-tolerant under faulty conditions is considered. Associative memories, which provide robust pattern recognition are investigated as an information processing technology that can be applied to sensor validation. Studies of Binary Associative Memories (BAM) and Continuous Associative Memories (CAM) yield many results including (1) the stability condition of exemplars and spurious memories in BAMs, (2) the formula of choosing diagonal weights and bias that eliminates spurious memories most effectively in BAMs, (3) the convergence theory of CAMs that have asymmetric weight matrix with non-zero diagonal elements and non-monotonically increasing activation functions, (4) the energy function that explores the convergence behavior of CAMs, and (5) the hybrid learning algorithm that reduces spurious memories effectively in CAMs. The concept of performability is introduced to the evaluation of SVS. A set of important performability variables is introduced. Stochastic Activity Networks are used as a modeling tool to evaluate the performability of SVS. An illustration example, the evaluation of the pressurizer SVS of a PWR, is provided.

A computer code that utilizes the consistent energy dependent P1 equations and the multigroup diffusion equations was developed to calculate the cold neutron flux that could be generated if a cold neutron source was built at the University of Arizona TRIGA reactor. The cold neutron current at the surface of the cold neutron source and the energy deposition in the cold neutron source due to neutron-proton interactions were also calculated. The computer code models the cold neutron source as a spherically shaped hydrogen medium embedded in the center of a cylindrical shaped homogenous TRIGA core. The outputs of the computer code were compared for various cold neutron source dimensions.

Three-dimensional (3D) nuclear organization is the study of the spatial distribution of nuclear contents and components. Aspects of nuclear organization that are examined in this thesis were chromosome territories, chromosomal sub-regions and telomeres. We began by examining nuclear disorganization in a transgenic mouse model. Fast-onset PCTs, compared to slow-onset PCTs and wild-type mice, had higher numbers of telomeres and telomeric aggregates per cell, more short telomeres, an altered distribution of telomeres throughout the nucleus, and a larger nuclear volume (P < 0.0001). We further examined this in a human context, looking for changes in nuclear organization in MYCN amplified compared to non-amplified neuroblastomas. Using dual-colored FISH and MYCN immunofluorescence on 16 neuroblastoma tissue samples, the unbalanced gain of 17q was found to be associated with high MYCN expression, no gain of 17q to be associated with medium MYCN expression, and numerical gain of chromosome 17 to be associated with low expression (P < 0.0001). The nuclear location of 17q also correlated with chromosome 17 copy number status. Telomere Q-FISH on 74 neuroblastoma tissue samples identified three tumor subgroups based on the measured telomere parameters, which represented unique levels of telomere dysfunction and genomic instability. Subgroups with higher levels of telomere dysfunction had more telomeres and telomeric aggregates per cell, and greater percentages of short and long telomeres (P < 0.0001); these subgroups also were associated with poor prognostic clinical features (P < 0.001). This thesis illustrates the significance of multiple parameters of 3D nuclear organization in both PCT and neuroblastoma. The changes observed in the nuclear architecture of these cancers reflect increased telomere-mediated genomic instability that is driven by MYC and MYCN. Furthermore, the differences between aggressive and less-aggressive forms of the tumors suggest 3D nuclear organization could be used as a novel biomarker in cancer. / May 2017

This thesis summarizes and analyzes the key factors in the cooperative U.S-Russian effort, pre-and post-9/11, to prevent nuclear proliferation. Especially highlighted are pertinent efforts to prevent terrorist organizations from obtaining nuclear weapons or nuclear weapons capabilities. This thesis catalogues both, Russian and the U.S. successes and failures to prevent nuclear proliferation through administration policies, as well as, the various cooperative threat reduction measures employed in coordination with the nations that once composed the former Soviet Union. Finally, this thesis offers a prediction of what the near future will hold for threat reduction and arms elimination programs.

<p> Conventional ceramic oxide nuclear fuels are limited in their thermal and life-cycle properties. The desire to operate at higher burnups as is required by current utility economics has proven a formidable challenge for oxide fuel designs. Metallic formulations have superior thermal performance but are plagued by volumetric swelling due to fission gas buildup. In this study, we consider a number of specific microstructure configurations that have been experimentally shown to exhibit considerable resistance to porosity loss. Specifically, a void sizing that is bimodally distributed was shown to resist early pore loss and could provide collection sites for fission gas buildup. We employ the phase field model of Cahn and Hilliard, solved via the finite element method using the open source Multi-User Object Oriented Simulation Environment (MOOSE) developed by INL.</p>

<p> The interaction of tritium with aluminum, copper, stainless steel, and gold plated substrates was studied using a low-pressure, argon plasma, as well as thermal desorption spectroscopy. These experimental methods allowed the influence of modifying metal surfaces on the absorption and adsorption of tritium to be measured. Stainless steel surfaces were modified by mechanical polishing, electropolishing, selective oxidation pre-treatments, and gold plating. The only surface modification performed on aluminum and copper samples was gold plating.</p><p> Use of the low-pressure plasma constitutes a novel approach to studying tritium migration and to measuring the quantity of adsorbed tritium. The migration of tritium was inferred from experiments, where a metal sample was exposed to a pulsed plasma. In such a method, tritium migration to the surface in between each pulse influences the quantity of tritium removed during subsequent plasma pulses. The results of these measurements indicated that the mechanism for tritium migration to the surface was limited by diffusion out of the underlying metal lattice. The measured rate of tritium migration to the surface does not appear to depend strongly on the metal type or surface modification. </p><p> Thermal desorption experiments were used to measure the influence of modifying metal surfaces on the total absorption of tritium. Thermal desorption involves heating samples to high temperatures for protracted periods of time, in order to remove all tritium contained within the metal lattice. These measurements indicated that modifying a metal surface significantly influences the total absorption of tritium during room temperature (25&deg;C) exposures. </p><p> Finally, a quantitative tritium migration model (QTRIMM) was developed in this work to describe the transport of the isotope through metal lattices. Additionally, QTRIMM includes a condition that relates the tritium concentrations adsorbed to the surface to the concentrations within the metal lattice. This model represents a major step forward in describing the migration of tritium through metal substrates, as many previous transport models have not included a condition for tritium adsorption. As demonstrated in this study, QTRIMM describes the measured data reasonably well.</p>

Source: Dissertation Abstracts International, Volume: 40-07, Section: B, page: 3236. / Thesis (Ph.D.)--The Florida State University, 1979.