¯ ¯ eff ¯ eff eff prompt term delayed term ¯ eff Reactor Theory (Reactor Operations) DOE-HDBK-1019/2-93 REACTOR KINETICS Rev. 0 NP-04 Page 21 Summary The important information in this chapter is summarized below.   Reactor Kinetics Summary Reactor period is the time required for reactor power to change by a factor of e (2.718). Doubling time is the time required for reactor power to double. Reactor startup rate is the number of factors of ten that reactor power changes in one minute. The delayed neutron fraction (   ) is the fraction of all fission neutrons that are born as delayed neutrons for a particular type of fuel (that is, uranium-235 and plutonium-239). The average delayed neutron fraction (    ) is the weighted average of the total delayed neutron fractions of the different types of fuel used in a particular reactor. The effective delayed neutron fraction ( ) is the average delayed neutron fraction multiplied by an Importance Factor which accounts for the fact that delayed neutrons are born at lower average energies than fast neutrons. The reactor period equation is stated below. where: =  reactor period * =  prompt generation lifetime =  effective delayed neutron fraction =  reactivity =  effective delayed neutron precursor decay constant eff =  rate of change of reactivity