Neutron spectra and flux calculation in thermalizing regions in LMRs
Abstract
This study addresses the problem of the neutron flux calculation in thermalizing regions in LMRs. Space dependent group constants have been developed for the thermal range to treat the highly non-separable space/energy dependent flux distribution that characterizes the transition of fast neutron spectra into partially thermalized spectra. An improved multigroup diffusion approach was developed to calculate space dependent spectra and group constants near transitory region in the thermal range. The new method is based on the zero dimensional spectral equation using so called 'Heavy Gas Model' for scattering. The absorption cross section includes thermal resonances near and below 1 eV. The space dependent spectral weighting is introduced to thermal group constants by relating the parametric solution of the zero dimensional spectral equation to the group fluxes obtained from the results of one-dimensional diffusion calculations. The space dependent thermal group constant generation method was implemented in a standard multigroup diffusion theory code, executed iteratively. This procedure was applied to compact LMR designs having thermalizing reflectors to investigate the effect of global parameters such as the effect of the size of thermalizing reflector on the space dependence of local reaction rates and to improve the calculations around the transitory region.
Degree
Ph.D.
Advisors
Ott, Purdue University.
Subject Area
Nuclear physics
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