Neutronic modeling and design optimization of additively manufactured control elements for the high flux isotope reactor
Burns, Joseph Raymond
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One of the key challenges to the advancement of nuclear power technology nationally and globally is the substantial upfront capital investment required for the construction of new nuclear power plants. A research effort has been launched at the Oak Ridge National Laboratory to investigate the potential for advanced manufacturing methods to fabricate nuclear reactor components with reduced cost, time, and labor by demonstrating production of control elements (CEs) for the High Flux Isotope Reactor (HFIR) using ultrasonic additive manufacturing (UAM). At this scale, this practice offers particular potential for reducing costs associated with continuous maintenance of reactor components, considering the regular intervals of replacement of the HFIR CEs. UAM yields a unique CE design with lumped neutron absorber regions, in contrast to typical CEs with uniformly distributed absorbers, thereby necessitating an analysis of the neutronic impact of this design change. This dissertation takes on the computational modeling of additively manufactured CEs in HFIR to assess their neutronic and operational feasibility. The impact of the additively manufactured CE design on the HFIR core physics is investigated, and the performance of the new CEs (characterized by reactivity worth and core power shaping) is compared with that of the original homogeneous CEs. It is found that while some limited changes in the HFIR core physics behavior are introduced by the additively manufactured CEs, they consistently exhibit performance that is comparable to the original CE design with no prohibitive impact to reactor safety. It is therefore concluded that the additively manufactured CEs are feasible for use in the operation of HFIR. Finally, the additively manufactured CE design is optimized by taking advantage of new design variables introduced by UAM fabrication that were not applicable to the original CE design. The additively manufactured CEs are designed to minimize their impact on the HFIR core physics so as to provide a seamless transition between CE designs and avoid reevaluation of compliance with the well-established HFIR safety margins. This work provides a first look at the neutronic characteristics of in-core nuclear reactor components fabricated with additive manufacturing, and it is hoped that these promising results will encourage future consideration of applications of advanced manufacturing methods elsewhere in the nuclear industry to realize economic improvements.