Investigation of stochastic radiation transport methods in random heterogeneous mixtures

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Title: Investigation of stochastic radiation transport methods in random heterogeneous mixtures
Author: Reinert, Dustin Ray, 1982-
Abstract: Among the most formidable challenges facing our world is the need for safe , clean , affordable energy sources . Growing concerns over global warming induced climate change and the rising costs of fossil fuels threaten conventional means of electricity production and are driving the current nuclear renaissance . One concept at the forefront of international development efforts is the High Temperature Gas -Cooled Reactor (HTGR ) . With numerous passive safety features and a meltdown -proof design capable of attaining high thermodynamic efficiencies for electricity generation as well as high temperatures useful for the burgeoning hydrogen economy , the HTGR is an extremely promising technology . Unfortunately , the fundamental understanding of neutron behavior within HTGR fuels lags far behind that of more conventional watercooled reactors . HTGRs utilize a unique heterogeneous fuel element design consisting of thousands of tiny fissile fuel kernels randomly mixed with a non -fissile graphite matrix . Monte Carlo neutron transport simulations of the HTGR fuel element geometry in its full complexity are infeasible and this has motivated the development of more approximate computational techniques . A series of MATLAB codes was written to perform Monte Carlo simulations within HTGR fuel pebbles to establish a comprehensive understanding of the parameters under which the accuracy of the approximate techniques diminishes . This research identified the accuracy of the chord length sampling method to be a function of the matrix scattering optical thickness , the kernel optical thickness , and the kernel packing density . Two new Monte Carlo methods designed to focus the computational effort upon the parameter conditions shown to contribute most strongly to the overall computational error were implemented and evaluated . An extended memory chord length sampling routine that recalls a neutron’s prior material traversals was demonstrated to be effective in fixed source calculations containing densely packed , optically thick kernels . A hybrid continuous energy Monte Carlo algorithm that combines homogeneous and explicit geometry models according to the energy dependent optical thickness was also developed . This resonance switch approach exhibited a remarkably high degree of accuracy in performing criticality calculations . The versatility of this hybrid modeling approach makes it an attractive acceleration strategy for a vast array of Monte Carlo radiation transport applications .
URI: http : / /hdl .handle .net /2152 /3924
Date: 2008-08-29

Citation

Investigation of stochastic radiation transport methods in random heterogeneous mixtures. Doctoral dissertation, The University of Texas at Austin. Available electronically from http : / /hdl .handle .net /2152 /3924 .

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