NEUTRON LIFE CYCLEDOE-HDBK-1019/2-93Reactor Theory (Nuclear Parameters)NeutronLifeCycleof a FastReactorThe neutron life cycle in a fast reactor is markedly different than that for a thermal reactor. Ina fast reactor, care is taken during the reactor design to minimize thermalization of neutrons.Virtually all fissions taking place in a fast reactor are caused by fast neutrons. Due to this, manyfactors that are taken into account by the thermal reactor neutron life cycle are irrelevant to thefast reactor neutron life cycle. The resonance escape probability is not significant because veryfew neutrons exist at energies where resonance absorption is significant. The thermalnon-leakage probability does not exist because the reactor is designed to avoid the thermalizationof neutrons. A separate term to deal with fast fission is not necessary because all fission is fastfission and is handled by the reproduction factor.The thermal utilization factor is modified to describe the utilization of fast neutrons instead ofthermal neutrons. The reproduction factor is similarly modified to account for fast fissioninstead of thermal fission.SummaryThe important information in this chapter is summarized on the following pages.NP-03Rev. 0Page 14
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