NEUTRON LIFE CYCLE
Reactor Theory (Nuclear Parameters)
Neutron Life Cycle of a Fast Reactor
The neutron life cycle in a fast reactor is markedly different than that for a thermal reactor. In
a 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, many
factors that are taken into account by the thermal reactor neutron life cycle are irrelevant to the
fast reactor neutron life cycle. The resonance escape probability is not significant because very
few neutrons exist at energies where resonance absorption is significant.
non-leakage probability does not exist because the reactor is designed to avoid the thermalization
of neutrons. A separate term to deal with fast fission is not necessary because all fission is fast
fission and is handled by the reproduction factor.
The thermal utilization factor is modified to describe the utilization of fast neutrons instead of
thermal neutrons. The reproduction factor is similarly modified to account for fast fission
instead of thermal fission.
The important information in this chapter is summarized on the following pages.