<p> Traditional parametric Common Cause Failure (CCF) models quantify the soft dependencies between component failures through the use of empirical ratio relationships. Furthermore CCF modeling has been essentially restricted to identical components in redundant formations. While this has been advantageous in allowing the prediction of system reliability with little or no data, it has been prohibitive in other applications such as modeling the characteristics of a system design or including the characteristics of failure when assessing the risk significance of a failure or degraded performance event (known as an event assessment). </p><p> This dissertation extends the traditional definition of CCF to model soft dependencies between like and non-like components. It does this through the explicit modeling of soft dependencies between systems (coupling factors) such as sharing a maintenance team or sharing a manufacturer. By modeling the soft dependencies explicitly these relationships can be individually quantified based on the specific design of the system and allows for more accurate event assessment given knowledge of the failure cause. </p><p> Since the most data informed model in use is the Alpha Factor Model (AFM), it has been used as the baseline for the proposed solutions. This dissertation analyzes the US Nuclear Regulatory Commission's Common Cause Failure Database event data to determine the suitability of the data and failure taxonomy for use in the proposed cause-based models. Recognizing that CCF events are characterized by full or partial presence of "root cause" and "coupling factor" a refined failure taxonomy is proposed which provides a direct link between the failure cause category and the coupling factors. </p><p> This dissertation proposes two CCF models (a) Partial Alpha Factor Model (PAFM) that accounts for the relevant coupling factors based on system design and provide event assessment with knowledge of the failure cause, and (b)General Dependency Model (GDM),which uses Bayesian Network to model the soft dependencies between components. This is done through the introduction of three parameters for each failure cause that relate to component fragility, failure cause rate, and failure cause propagation probability.</p>

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007. / Source: Dissertation Abstracts International, Volume: 68-07, Section: B, page: 4797. Adviser: James F. Stubbins. Includes bibliographical references (leaves 164-171) Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2008. / Source: Dissertation Abstracts International, Volume: 69-05, Section: B, page: 3243. Adviser: James F. Stubbins. Includes bibliographical references (leaves 230-240) Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2008. / Source: Dissertation Abstracts International, Volume: 69-11, Section: B, page: 7075. Adviser: Robert S. Averback. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.

<p>This thesis presents the design and simulation of a multi-channel integrated circuit (IC) that will be used in nuclear physics experiments. The chip is being designed as a companion chip for another IC used in particle identification called PSD8C. The IC described in this thesis is used to create precise timing pulses for starting time-to-voltage converters (TVCs) and gated integrators on the PSD8C. These timing pulses are created using a technique called Constant Fraction Discrimination (CFD). Each of the sixteen channels in the IC contains a Nowlin circuit, leading-edge discriminator, zero-cross discriminator, and a one-shot circuit to generate the output. The IC will support input pulse amplitudes between 15 mV and 1.5 V (both positive and negative), and input pulse rise times between 2 nsec and 192 nsec. The IC will feature a programmable output pulse width between 50 nsec and 500 nsec. The IC will have an average power dissipation of 220 mW and occupy an area of 2.4 x 3.5 mm. The variation (due to process and mismatch) in the trailing edge of the output timing pulse will be less than 5 nsec (for pulse width of 50 nsec). The assosciated jitter the output timing pulse is ?20 psec (for the 50 nsec pulse width mode). Most importantly the output pulse firing time variation will be independent of the input amplitude, having a time walk of only 500 psec or less (for input pulse rise time constants of 2 nsec). The IC has been named CFD16C and the design presented is implemented in a 0.35 micron NWELL process.

<p> Nuclear fuels with similar aggregate material composition, but with different millimeter and micrometer spatial configurations of the component materials can have very different safety and performance characteristics. This research focuses on modeling and attempting to engineer heterogeneous combinations of nuclear fuels to improve negative prompt temperature feedback in response to reactivity insertion accidents.</p><p> Improvements in negative prompt temperature feedback are proposed by developing a tailored thermal resistance in the nuclear fuel. In the event of a large reactivity insertion, the thermal resistance allows for a faster negative Doppler feedback by temporarily trapping heat in material zones with strong absorption resonances.</p><p> A multi-physics simulation framework was created that could model large reactivity insertions. The framework was then used to model a comparison of a heterogeneous fuel with a tailored thermal resistance and a homogeneous fuel without the tailored thermal resistance. The results from the analysis confirmed the fundamental premise of prompt temperature feedback and provide insights into the neutron spectrum dynamics throughout the transient process. </p><p> A trade study was conducted on infinite lattice fuels to help map a design space to study and improve prompt temperature feedback with many results. A multi-scale fuel pin analysis was also completed to study more realistic geometries.</p><p> The results of this research could someday allow for novel nuclear fuels that would behave differently than current fuels. The idea of having a thermal barrier coating in the fuel is contrary to most current thinking. Inherent resistance to reactivity insertion accidents could enable certain reactor types once considered vulnerable to reactivity insertion accidents to be reevaluated in light of improved negative prompt temperature feedback.</p><p>

Abstract not available.

Master of Science / Department of Mechanical and Nuclear Engineering / William L. Dunn / Two types of high efficiency neutron detector arrays (HENDAs), a 32-channel planar device and two trenched devices, were constructed at Kansas State University (KSU) and characterized. These HENDAs are prototypes for a detector that will be developed for the Spallation Neutron Source (SNS), which is located at Oak Ridge National Laboratory (ORNL). The general design objectives of a proposal from the KSU Semiconductor Materials and Radiological Technologies (SMART) Lab to the National Science Foundation, which led to a grant that funded this research, were reached. A spatial resolution for the HENDA prototypes of approximately 120 μm was achieved. The prototypes had relatively fast response times of approximately 1.2 μs, with rise times of 300 ns for the planar device and 200 ns for the 100-μm deep trenched device. The thermal neutron counting efficiency of one of the trenched devices was measured to be about 12%. It is expected that the goal of a 50% efficient HENDA is attainable by making trenches contained within the trenched device deeper and by stacking modules in a sandwich design. The pulse heights produced by the HENDA prototypes were approximately 0.5 volt with noise levels of 13 mvolt, resulting in a signal to noise ratio of almost 40:1. The response of HENDA, when placed in the neutron beam from the tangential beam port of the KSU TRIGA Mark II was proportional to the reactor power from 2 kW to 512 kW. At 512 kW, the neutron flux is φ = 1.08x10[superscript]7 cm[superscript]-2 s[superscript]-1, and therefore HENDA can operate with negligible dead time at neutron fluxes beyond 107 cm-2 s-1. From the experimental results, HENDA is a valuable linear array detector and can be applied to experiments that are designed to study material properties and structures through methods such as neutron diffraction and imaging.

Master of Science / Department of Mechanical and Nuclear Engineering / William L. Dunn / Improvised explosives devices (IEDs) are the cause of many casualties worldwide. Current methods for detecting IEDs are insufficient. A signature-based scanning technique based upon the fact that explosives consist primarily of hydrogen, oxygen, nitrogen, and carbon is examined as a possible rapid, standoff method for detecting IEDs. Devices employing this method rely on a template-matching technique in which the detector responses acquired through neutron and photon interrogation are compared to responses from a known explosive. A figure-of-merit is calculated to determine how well the template and the unknown match. This thesis explores the feasibility of employing the neutron interrogation aspect of this method.

<p> Developing new multifunctional materials in recent years for nuclear systems has become increasingly critical owing to the high demand on better shielding in extreme environments. The purpose of this research was to design, manufacture, and evaluate the feasibility of utilizing novel light weight close-cell composite metallic foam (CMF) and open-cell Al foam with fillers as radiation shields at nuclear facilities to attenuate the background of ionization radiations to a minimum level for creating a safer workplace, meeting regulatory requirements and maintaining high quality performance. </p><p> Steel-steel composite metal foams (S-S CMFs) and Aluminum-steel composite metal foams (Al-S CMFs) with various sphere sizes and matrix materials were manufactured and investigated for nuclear and radiation environments applications. 316L stainless steel, highspeed T15 steel and aluminum materials were used as the matrix material together with 2, 4 and 5.2 mm steel hollow spheres to manufacture various types of composite metal foams (CMFs). High-speed T15 steel is selected due to its high tungsten and vanadium concentration (both high-Z elements) to further improve the shielding efficiency of CMFs. This new type of S-S CMF is called High-Z steel-steel composite metal foam (HZ S-S CMF). Open-cell Al foams with fillers were obtained by infiltrating original empty pores with variety of hydrogen-rich compounds: petroleum wax, borated polyethylene, water, and borated water. </p><p> All the foams were investigated for their radiation shielding efficiency in terms of X ray, gamma ray and neutron. X-ray transmission measurements were carried out on a highresolution microcomputed tomography (microCT) system. Gamma-emitting sources: 3.0mCi ⁶⁰Co, 1.8mCi ¹³⁷Cs , 13.5mCi ¹²⁴Am, and 5.0mCi ¹³³Ba were used for gamma-ray attenuation analysis. The evaluations of neutron transmission measurements were conducted at the Neutron Powder Diffractometer beam facility at North Carolina State University. The experimental results were verified theoretically through XCOM and Monte Carlo Z-particle Transport Code (MCNP). </p><p> A mechanical investigation was performed by the means of quasi-static compressive testing. Thermal characterizations were carried out through effective thermal conductivity and thermal expansion analyses in terms of high temperature guarded-comparativelongitudinal heat flow technique and thermomechanical analyzer (TMA), respectively. The experimental results were compared with analytical results obtained from respectively Brailsford and Major&rsquo;s model and modified Turner&rsquo;s model for verification. Flame test was performed in accordance with United States Nuclear Regulatory Commission (USNRC) standard. CMF sample and a 304L stainless steel control sample were subjected to a fully engulfing fire with an average flame temperature of 800&deg;C for a period of 30 minutes. Finite Element Analysis was conducted to secure the credibility of the experimental results. </p><p> This research indicates the potential of utilizing the lightweight close-cell CMFs and open-cell Al foam with fillers as shielding material replacing current heavy structures with additional advantage of high-energy absorption and excellent thermal characteristics.</p>