Advances In Neutron Imaging For The 21st Century PDF Download

The growing demand for electrical power presents one of the major challenges for the well-being of future generations. For the foreseeable future, it seems highly unlikely that the projected energy needs can be met by fossil and/or alternative energy sources alone; therefore, nuclear power will continue to play a significant role in power generation. Neutrons can be used to study a wide range of problems related to these efforts, providing a unique probe ranging from crystal chemistry of nuclear fuels to engineering diffraction of structural materials used in nuclear reactors. Traditionally, most experimental investigations with neutrons invoke diffraction techniques. However, recent advances in neutron detection resulted in new capabilities of material characterization using neutron imaging, which provides unparalleled opportunities particularly for nuclear materials, where heavy elements (e.g., uranium) need to be imaged together with light elements (e.g., hydrogen, oxygen). The inherent energy sorting of the neutrons at pulsed sources permits performing isotope-specific studies through selected settings of the contrast to a particular isotope (via neutron resonances). Moreover, the application of state-of-the-art tomographic reconstruction algorithms allows reconstructing, in 3D, the spatial distribution in cm-sized samples of quantities derived from these effects, in particular element or isotope distributions. None of this is currently possible with X-ray or reactor neutron radiography, and at present this technique is only possible at pulsed neutron sources at Los Alamos Neutron Science Center (LANSCE), Spallation Neutron Source at Oak-Ridge National Laboratory, ISIS in the United Kingdom, and at the Japan Proton Accelerator Research Complex (J-PARC) in Japan, of which only the J-PARC facility has a dedicated beam line for this technique. In this dissertation, I present the results of spatially-resolved neutron imaging and diffraction experiments (including texture measurements) on non-irradiated nuclear fuels. Furthermore, I present absolute isotopic areal density measurements with a two-dimensional detector and a pixel size of 55[mu]m using the time-structured LANSCE neutron beam applied to some nuclear-engineering application for the first time. More specifically, I introduce a novel, energy-resolved neutron imaging technique that utilizes the physical properties of neutron cross sections by analyzing nuclear resonances with the SAMMY code, which was developed by Oak Ridge National Laboratory for the analysis of cross section data in the resolved and unresolved resonance regions. To the best of my knowledge, this work presents the first applications beyond demonstration experiments of absorption based energy-resolved neutron imaging by applying this technique to characterize the isotope distributions in nuclear fuel and study the diffusion of ions dissolved in aquaeous solution into cement. My dissertation emphasizes the benefits of neutron radiography as a non-destructive characterization method to guide future experiments on post-irradiated nuclear fuels, enabling the quantification of isotope concentrations for a variety of imaging problems.