Nuclear Engineering Commons^™

Optimization Of Scintillator Based Radiation Portal Monitors, Matthew J. Urffer

Doctoral Dissertations

Alternative neutron detection technologies are needed to replace the current He- 3 based Radiation Portal Monitors (RPM) which are employed to detect special nuclear material that may be entering the United States illicitly. Replacement technologies must fulfill the following criteria established by the Department of Homeland Security (DHS): 1) a neutron detection efficiency, 2) a gamma insensitivity, and 3) the performance of the detector should not suffer in the presence of a strong gamma field. Polymeric films containing Li-6 ranging from 15 to 300 microns have the ability to fulfill these criteria if suitably utilized. For a typical detector material …

System Studies Of Fission-Fusion Hybrid Molten Salt Reactors, Robert D. Woolley

Doctoral Dissertations

This work proposes and evaluates a Fission-Fusion Hybrid Molten Salt Reactor (FFHMSR), combining two subsystems, a deuterium + tritium (DT) fusion reactor surrounded by a neutron-absorbing Fusion Blanket (FB) and a critical Molten Salt fission Reactor (MSR). The molten salt, which contains dissolved actinides, circulates at a high rate between them.

As envisioned the MSR exhibits the large Conversion Ratio of graphite moderated reactors having small fissile and large fertile inventories. DT fusion neutrons irradiating actinides in the molten salt release additional neutrons which increase isotope conversion and fission. Actinide fuel is continually added while fission products are continually removed …

Monte Carlo And Depletion Reactor Analysis For High-Performance Computing Applications, Brenden Thomas Mervin

Doctoral Dissertations

This dissertation discusses the research and development for a coupled neutron trans- port/isotopic depletion capability for use in high-preformance computing applications. Accurate neutronics modeling and simulation for \real" reactor problems has been a long sought after goal in the computational community. A complementary \stretch goal" to this is the ability to perform full-core depletion analysis and spent fuel isotopic characterization. This dissertation thus presents the research and development of a coupled Monte Carlo transport/isotopic depletion implementation with the Exnihilo framework geared for high-performance computing architectures to enable neutronics analysis for full-core reactor problems.

An in-depth case study of the current …

Development Of A Monitoring Framework For The Detection Of Diversion Of Intermediate Products In A Generic Natural Uranium Conversion Plant, Jennifer L. Ladd-Lively

Doctoral Dissertations

The objective of this work is the development of an on-line monitoring and data analysis framework that could detect the diversion of intermediate products such as uranium dioxide, uranium tetrafluoride, and uranium hexafluoride in a natural uranium conversion plant (NUCP) using a multivariate statistical approach. This was an initial effort to determine the feasibility of this approach for safeguards applications. This study was limited to a 100 metric ton of uranium (MTU) per year NUCP using the wet solvent extraction method for the purification of uranium ore concentrate. A key component in the multivariate statistical methodology was the Principal Component …

A Context For Assessing The Efficacy Of A Radiological/Nuclear Materials Interdiction Mission At Border Crossings, James Dale White

Doctoral Dissertations

There is no widely accepted contextual framework for planning, designing, and evaluating systems of protocols and equipment for detecting, intercepting, and deterring transport of high consequence radiological and nuclear threats. The author posits a candidate framework for design and application of a security system for detection and interdiction of these threats at an international border crossing. The author then examines the efficacy of this framework. Results indicate that the use of rarely considered criteria provide a promising framework for a broad community of stakeholders to use in planning, design and application of security system upgrades for high consequence threats in …

Investigation Of Time And Position Resolved Alpha Transducers For Multi-Modal Imaging With A D-T Neutron Generator, Joshua William Cates

Doctoral Dissertations

Deuterium-Tritium (D-T) neutron generators have been used as an active interrogation source for associated particle imaging (API) techniques. The D-T reaction yields a 14.1 MeV neutron and a 3.5 MeV alpha (or assoicated) particle, projected nearly back-to-back. The kinetics of the reaction allow the direction and initial time of the neutron to be determined utilizing position sensitive detectors for both the alpha and neutron. This information facilitates multi-modal fast neutron imaging of inspection objects and closed containers to infer the geometry within them and the presence of special nuclear material (SNM). Since position and time of interaction of the alpha …

Semi-Implicit Direct Kinetics Methodology For Deterministic, Time-Dependent, Three-Dimensional, And Fine-Energy Neutron Transport Solutions, James Ernest Banfield

Doctoral Dissertations

Using a semi-implicit direct kinetics (SIDK) method that is developed in this dissertation, a finer neutron energy discretization and improved fidelity for transient radiation transport calculations are facilitated to reduce uncertainties and conservatisms in transient power and temperature predictions. These capabilities are implemented within a parallel computational solver framework, which is able to represent an arbitrary number of neutron energy groups, angles, and spatial discretizations, while internally coupled to an unstructured finite element multi-physics code for temperature and displacement calculations. This capability is demonstrated on a three-dimensional control rod ejection simulation run in parallel utilizing forty-four neutron energy groups.

An …

Studies Of Reaction Processes For Voloxidation Methods, Jared Allen Johnson

Doctoral Dissertations

Various facets of the voloxidation process and processes that have been derived from the voloxidation process have been investigated since its development over four decades ago. Despite the numerous studies performed, gaps remain in understanding of particular fundamental aspects of the reaction processes. In this work, several of these specific aspects of the oxidation processes for standard voloxidation and NO₂ [nitrogen dioxide] voloxidation are studied experimentally and modeled.

In the case of standard voloxidation, the oxidation rates of simulant UO_­2 [uranium dioxide] pressurized water reactor pellets in oxygen-rich environments were studied with an emphasis on the controlling phenomena …

Sensitivity And Uncertainty Analysis Of A Fixed Source Criticality Accident Alarm System Benchmark Experiment, Kevin Howard Reynolds

Doctoral Dissertations

The Department of Energy (DOE) Nuclear Criticality Safety Program (NCSP) funded the development of a criticality accident alarm system (CAAS) benchmark to be published by the International Criticality Safety Benchmark Evaluation Project (ICSBEP) in the International Handbook of Evaluated Criticality Safety Benchmark Experiments (handbook). While there are shielding related benchmark evaluations published in the handbook, the effort in this dissertation concerns a first of its kind experiment that has been conceived from the ground up as a pulsed critical fixed source benchmark.

The experiment was designed in conjunction with the French government and conducted at their SILENE reactor facility at …

Enrichment Determination Of Uranium Metal In Shielded Configurations Without Calibration Standards, Jason Michael Crye

Doctoral Dissertations

The determination of the enrichment of uranium is required in many safeguards and security applications. Typical methods to determine the enrichment rely on detecting the 186 keV gamma ray emitted by uranium-235. In some applications the uranium is surrounded by external shields, and removal of the shields is undesirable. In these situations, methods relying on the detection of 186 keV gamma rays fail because these gamma rays are shielded easily.

This research presents a novel method to estimate the enrichment of uranium metal when heavily shielded by high-Z materials. The method uses fast neutron tomography to estimate the geometry …

Design, Development And Characterization Of A Novel Neutron And X-Ray Combined Computed Tomography System, Vaibhav Sinha

Doctoral Dissertations

"Visualizing the three dimensional structure of objects (e.g. nuclear fuel, nuclear materials, explosives and bio materials) and phenomena (e.g. particle tracking) can be very important in nondestructive testing applications. Computed tomography systems are indispensable tools for these types of applications because they provide a versatile non-destructive technique for analysis. A novel neutron and X-ray combined computed tomography (NXCT) system has been designed and developed at the Missouri University of Science & Technology. The neutron and X-ray combined computed tomography system holds much promise for non-destructive material detection and analysis where multiple materials having similar atomic number and differing thermal cross …