Browsing by Subject "Nuclear forensics"
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Item A comparison of nuclide production and depletion using MCNPX and ORIGEN-ARP reactor models and a sensitivity study of reactor design parameters using MCNPX for nuclear forensics purposes(2010-05) Chambers, Angela Sue; Biegalski, Steven R.; Charlton, William S.; Foltz Biegalski, Kendra M.; Landsberger, Sheldon; Schneider, Erich A.The Oak Ridge Isotope Generation and Depletion – Automatic Rapid Proccessing (ORIGEN-ARP) deterministic code has been extensively utilized for determining nuclide concentrations at various specific burnup values for a variety of nuclear reactor designs. Given nuclide concentrations or ratios, such calculations can be used in nuclear forensics and nuclear non-proliferation applications to reverse-calculate the type of reactor and specific burnup of the fuel from which the nuclides originated. Recently, Los Alamos National Laboratory has released a version of its probabilistic radiation transport code, MCNPX 2.6.0, which incorporates a fuel burnup feature which can also determine, via the probabilistic Monte Carlo method, nuclide concentrations as a function of fuel burnup. This dissertation compares the concentrations of 46 nuclides significant to nuclear forensics analyses for different reactor types using results from the ORIGEN-ARP and the MCNPX 2.6.0 codes. Three reactor types were chosen: the Westinghouse 17x17 Pressurized Water Reactor (PWR), the GE 8x8-4 Boiling Water Reactor (BWR), and the Canadian Deuterium Uranium, CANDU-37, reactor. Additionally, a sensitivity study of the different reactor parameters within the MCNPX Westinghouse 17x17 PWR model was performed. This study analyzed the different nuclide concentrations resulting from minor perturbations of the following parameters: assembly rod pitch, initial moderator boron concentration, fuel pin cladding thickness, moderator density, and fuel temperature.Item Determination of fission product yields of 235U using gamma ray spectroscopy(2012-12) Lu, Christopher Hing; Biegalski, Steven R.; Landsberger, SheldonIt is important to have a method of experimentally calculating fission product yields. Statistical calculations and simulations produce very large uncertainties. Experimental calculations, depending on the methods used, tend to produce lower uncertainties. This work set up a method to calculate fission product yields using gamma ray spectroscopy. In order to produce a method that was theoretically sound, a simulation was set up using OrigenArp to calculate theoretical concentrations of fission products from the irradiation of natural uranium. From these concentrations, the fission product yields were calculated to verify that they would agree with expected values. Moving forward in the work, the total flux at the point of irradiation, in the pneumatic transfer system, was calculated and determined to be 3.9070E+11 ± 6.9570E+10 n/cm^2/s at 100 kW. Once the flux was calculated, the method for calculating fission product yields was implemented and yields were calculated for 10 fission products. The yields calculated were in very good agreement (within 10.04%) with expected values taken from the ENDF-349 library. This method has strong potential in nuclear forensics as it can provide a means for developing a library of experimentally-determined fission product yields, as well as rapid post-nuclear detonation analysis.Item Development of PYRAMDS (Python for Radioisotope Analysis and Multi-Detector Suppression) code used in fission product detection limit improvements with the DGF Pixie-4 digital spectrometer(2011-05) Weaver, Christopher Jordan; Biegalski, Steven R.; Landsberger, Sheldon; Keillor, Martin E.; Schneider, Erich A.; Foltz Biegalski, Kendra M.The work presented here develops a gamma-ray spectral construction and analysis software tool that was used to analyze multi-detector data collected using a digital spectrometer with list mode capabilities. The tool was used to parse the output from three detectors and generate new spectra that the user chooses from post-processing suppression routines, such as simulated anticoincidence and coincidence spectra. Part of this research was also to characterize the improvements in the detection limits and the various detector efficiencies from this method as opposed to creating these spectra using traditional electronic gating systems. A focus is placed on the detection capability improvements for nuclear forensics purposes, particularly the identification and quantification of fission product samples, and structuring the code framework for handling these types of time-dependent samples while increasing the versatility of the detector system. Improvements to the minimum detectable activity for a series of fission products was accomplished through post-processing suppression methods and multi-dimensional spectral data structures are now achievable.Item Multispectral gamma-ray analysis using clover detectors with application to uranium fission product analysis(2013-05) Horne, Steven Michael; Landsberger, Sheldon; Jackman, Kevin RichardA high-efficiency gamma-ray counting system has been built at Los Alamos National Laboratory for use in analyzing nuclear forensics samples. This system consists of two clover high-purity germanium detectors and is surrounded by a thallium-doped sodium iodide annulus. Special precautions have been taken to ensure the system has a low background. The system is connected to XIA Pixie-4 fast digitizers and collects data in list-mode. This work is split into two main parts. The first part describes the proper steps and techniques to initialize the settings of a detector system connected to fast digitizers in order to optimize the system for resolution and throughput. The various counting modes for this particular system are described in detail, including the benefits and drawbacks of each mode. Steps are then shown to characterize the system by obtaining efficiency curves for various counting modes and sample geometries. Because of the close counting geometry involved with this system, true-coincidence summing factors must be calculated, and are done so in part by measuring the peak-to-total ratios of the system in its various counting modes across a wide energy range. The dead-time for the system can be complicated due to the multiple inputs of the system. Techniques for calculating the dead-time of multiple-detector systems are discussed. The second part of this work shows the system's usefulness in analyzing nuclear forensics samples, specifically irradiated enriched uranium. Three fission product parent-daughter pairs of different lifetimes are analyzed over a course of six months. The activities of each nuclide are calculated at each time step. Age dating techniques using the parent-daughter pairs are discussed, as well as the detection limits of each nuclide for a range of sample ages. Finally, avenues for further research are presented, as well as potential sources of error or uncertainty for this work.Item The simultaneous quantification of fissile U and Pu nuclides using delayed neutron activation analysis(2013-05) Kapsimalis, Roger James, 1985-; Landsberger, SheldonThe ability to quickly and accurately quantify fissile constituents in bulk materials remains essential to many aspects of nuclear forensics and for safeguarding nuclear materials and operations. This often entails the analysis of trace quantities of nuclear debris or effluents, and typically requires bulk sample digestion followed by actinide separation and mass spectrometry. Because destructive methods are time and labor intensive, efforts have been made to develop alternative nondestructive methods for this type of analysis. This work, performed at Oak Ridge National Laboratory at the High Flux Isotope Reactor (HFIR), seeks to utilize delayed neutron activation analysis on samples of interest containing multiple fissile constituents. Based on the variances in the fission product yields of individual fissile nuclides, this work utilizes methods of linear regression to derive a technique that allows for such analysis, forgoing chemical separation and using only a single irradiation and counting step.Item Trace Fission Product Ratios for Nuclear Forensics Attribution of Weapons-Grade Plutonium from Fast Breeder Reactor Blankets(2014-08-13) Osborn, JeremyA nuclear terrorist attack is one of the most serious threats to the national security of the United States, and in the wake of an attack, attribution of responsibility will be of the utmost importance. Plutonium, a by-product in spent nuclear reactor fuel, can be used in a nuclear weapon when obtained from reactor fuel discharged at a low burnup (1 MWd/kg). Characteristics of plutonium reprocessed from reactor fuel depend on factors such as the reactor type (thermal or fast reactor), fuel burnup, production history and the plutonium separation process used. Detailed understanding of the plutonium isotopic composition and fission product contaminant concentrations in separated plutonium would aid nuclear forensics activities aimed at source attribution in the case of interdicted smuggled plutonium, bolstering nuclear deterrence. The study presented here shows that trace fission product to plutonium ratios are amenable for nuclear forensics attribution. Through computational reactor core physics simulations, results are obtained for weapons-grade plutonium produced in a Fast Breeder Reactor (FBR). These fission product to plutonium ratios for the FBR are further compared with results reported elsewhere for a thermal Pressurized Heavy Water Reactor. This comparison of isotopic ratios results in substantial differences between fast and thermal neutron reactor systems, leading to the determination that a suite of selected isotopic ratios can attribute separated weapons-grade plutonium to a fast or thermal neutron source reactor system.