Doctoral Dissertations

Date of Award

12-2012

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Nuclear Engineering

Major Professor

G. Ivan Maldonado

Committee Members

Lawrence Heilbronn, Howard Hall, Robert Grzywacz

Abstract

The Radiochemical Engineering Development Center at Oak Ridge National Laboratory is the world's leader in production of californium-252. This and other heavy actinides are produced by irradiation of mixed curium/americium targets in the High Flux Isotope Reactor. Due to the strong dependence of isotopic cross sections upon incoming neutron energy, the efficiency with which an isotope is transmuted is highly dependent upon the neutron flux energy spectrum and intensities. There are certain energy ranges in which the rate of fissions in feedstock materials can be minimized relative to the rate of (n,γ) absorptions. This work shows that by perturbing the flux spectrum, it is possible to alter the net consumption of curium feedstock, as well as the yields of key isotopes for the heavy element research program, such as 249Bk and 252Cf. This flux spectrum perturbation is accomplished by means of focused resonance shielding through the use of filter materials. This work further shows that these perturbations can alter the target yields in a significant way, increasing the amount of 252Cf produced per unit curium consumption. All materials with isotopes containing appropriate energy level resonances are examined and extensive data has been obtained on the filtering effects of these materials. Neural networks and genetic algorithms are used to develop an optimization framework for evaluating the performance of filter materials. This algorithm allows for customized optimization and selection of filter materials depending upon the need of the user and the campaign conditions.

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