Thesis (M.S.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 77-83). Also available on the World Wide Web.

Oregon State University is home to a TRIGA® Mark II reactor. In October of 2008, the reactor began operating on low enriched uranium fuel. A model of the facility exists in MCNP, a Monte Carlo code that can be used for criticality calculations. Until now, a bias in the calculation of the neutron multiplication factor has been carried forward from outdated core models. This work involves updating various aspects of the model, including the geometry of the facility as well as materials and their properties, in order to arrive at a more accurate representation of the facility as it is today. The individual effect that each change has on the results of MCNP calculations of the core is documented. Following the updates to the model, the model can emulate records that describe the startup of the reactor in October of 2008. The results of these calculations can be compared to actual data in order to establish a foundation for benchmarking the model and characterizing the reactor core. The deviation between calculated and expected results can be used to determine a single reactivity bias in the model. The bias determined as a result of this work can be applied to future calculations using the model developed as a part of this work. / Graduation date: 2013

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

In this work, Neutron Depth Profiling (NDP) analysis capability has been added to the Oregon State University TRIGA�� Reactor Prompt Gamma Neutron Activation Analysis Facility (PGNAA). This system has been implemented with an advanced digital spectroscopy system and is capable of rise time pulse shape analysis as well as coincidence measurements from multiple detectors. The digital spectroscopy system utilizes a high-speed multichannel digitizer with speeds up to 200 Megasamples/second (MS/s) with advanced hardware trigger and time stamping capabilities. These additions allow the facility to conduct simultaneous NDP and PGNAA combined measurements, which also enables cross calibration. The digital pulse processing is implemented with software programmed rise time pulse shape analysis capabilities for the analysis of the detector responses on a pulse-by-pulse basis to distinguish between different interactions in the detector. The advanced trigger capabilities of the digitizer were configured to accurately measure and correct for dead time effects from pulse pile up and preamplifier decay time. / Graduation date: 2013

In 2008, the Oregon State TRIGA�� Reactor (OSTR) was converted from highly-enriched uranium (HEU) fuel lifetime improvement plan (FLIP) fuel to low-enriched uranium (LEU) fuel. This effort was driven and supported by the Department of Energy's (DoE's) Reduced Enrichment for Research and Test Reactors (RERTR) program. The basis behind the RERTR program's ongoing conversion effort is to reduce the nuclear proliferation risk of civilian research and test reactors. The original intent of the HEU FLIP fuel was to provide fuel to research reactors that could be utilized for many years before a necessary refueling cycle. As a research reactor, the OSTR provides irradiation facilities for a variety of applications, such as: activation analysis, fission-track dating, commercial isotope production, neutron radiography, prompt gamma characterization, and many others. In order to accurately perform these research functions, several studies have been conducted on the HEU FLIP fuel core to characterize the neutron spectra in various experimental facilities of the OSTR. As useful as these analyses were, they are no longer valid due to the change in fuel composition and the resulting alteration of core performance characteristics. The purpose of this study is to characterize the neutron spectra in various experimental facilities within the new LEU core so as to provide data that is representative of the OSTR's current state. / Graduation date: 2013

Experiments were performed at the Nuclear Engineering Teaching Laboratory (NETL) in 2005 and 2006 in which a 20 MeV linear electron accelerator operating as a photoneutron source was coupled to the TRIGA (Training, Research, Isotope production, General Atomics) Mark II research reactor at the University of Texas at Austin (UT) to simulate the operation and characteristics of a full-scale accelerator driven subcritical system (ADSS). The experimental program provided a relatively low-cost substitute for the higher power and complexity of internationally proposed systems utilizing proton accelerators and spallation neutron sources for an advanced ADSS that may be used for the burning of high-level radioactive waste. Various instrumentation methods that permitted ADSS neutron flux monitoring in high gamma radiation fields were successfully explored and the data was used to evaluate the Stochastic Pulsed Feynman method for reactivity monitoring. / text