Browsing by Subject "Flux"
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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 Estimation and Fate of New Production in the Marine Environment(2014-06-03) McInnes, Allison SkinnerThe fate of carbon in the ocean determines both the amount of CO_(2) that can be sequestered and the amount of sustainable biomass. Compartmentalization into new and regenerated production allows a first order estimate of carbon available to the local community versus the amount exported. The goal of this project was to study sources and sinks of production in order to test the general hypothesis that new production is underestimated in the marine environment. Specifically we looked at pulsed new nutrients and the effect on the ecosystem, the effect of currents on our measurements and estimates of export (equivalent to new production), and finally development of a new method which will allow in situ determination of new production in the majority of the global ocean. Specifically, the role of a Pacific herring spawn was investigated as an important stimulant to ecosystem wide carbon and nitrogen cycling in Simpson Bay, Alaska. A consistent pattern was observed each year: a large bloom in June corresponded to the timing of the herring spawn and low nutrients, low phytoplankton diversity, and high POC concentrations; elucidating a previously unidentified pulse of new nutrients to the system. Estimates of carbon export are affected by the physical environment. The model presented and validated herein is used to improve our understanding of C export by including the effect of horizontal transport. We show that measurements of export to shallow water traps are less impacted by currents than deep traps. Spatial extent of variable primary production necessary to affect deep water traps is greater, as such, over half of the traps analyzed in this study are affected by up-current productivity regimes. A method to simultaneously quantify the C and N fixing community in the same sample was developed, eliminating many assumptions introduced when using different techniques and incubations. Cultured and environmental samples were successfully hybridized using TSA-FISH. Strong correlations between positively tagged community abundance and ^(14)C/^(15)N measurements are presented. The findings of this work support the general hypothesis that new production is under-accounted for in marine systems.Item Fluence based neutron balance approach using spatial flux calculations(2015-08) Bagdatlioglu, Cem; Schneider, Erich A.; Wilson, Paul P. H.This thesis describes the addition of spatially dependent power sharing to a methodology for calculating the input and output isotopics and burnup of nuclear reactors within a nuclear fuel cycle simulator. This methodology carries out neutron balance and depletion calculations by using pre-calculated fluence-based libraries. These libraries track the transmutation and neutron economy evolution of unit masses of isotopes available in input fuel. The current work generalizes the method to simulate reactors that contain more than one type of fuel in their core, for instance breeders with a driver-blanket configuration. To achieve this, spatial flux calculations are used to determine the fluence-dependent relative average flux inside macroscopic spatial regions. These fluxes are then used to determine the relative average power of macroscopic spatial regions as well as to more accurately calculate region-specific transmutation rates. The paper presents several cases where the fluence based approach alone would not have been sufficient to determine results.