AdvisorHetrick, David L.
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PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractSolutions of fissile materials are often encountered during spent-fuel reprocessing. In order to estimate the hazards from accidental criticalities in these solutions, models have been developed to understand better the dynamics involved. Accurate representation of reactivity feedback mechanisms are a crucial part of such models. Reactivity feedback from uniform volumetric solution expansion is studied. For faster transients, density redistribution may also occur due to a variation of nuclear energy as a function of position in the assembly. Neutronic spectral temperature reactivity effects are studied using two methods: cross section corrections via a Maxwellian flux weighting and creation of temperature dependent cross sections from ENDF/B-VI data. The volumetric and temperature reactivity feedback coefficients are determined for the CRAC, KEWB-5, SILENE, and SHEBA solution assemblies. Spectral temperature coefficients are also calculated for poisoned, unpoisoned, and reflected plutonium solutions. Feedback coefficients are seen to be functions of geometry and isotopic contents of the assemblies. Results for plutonium solutions agree with British calculations reported in 1991, confirming the possibility of autocatalytic excursions in large, dilute solutions.