¯¯eff¯effeffprompttermdelayedterm¯effReactor Theory (Reactor Operations)DOE-HDBK-1019/2-93REACTOR KINETICSRev. 0NP-04Page 21SummaryThe important information in this chapter is summarized below.Reactor Kinetics SummaryReactor 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 inone minute.The delayed neutron fraction ( ) is the fraction of all fission neutrons that areborn as delayed neutrons for a particular type of fuel (that is, uranium-235 andplutonium-239).The average delayed neutron fraction ( ) is the weighted average of the totaldelayed neutron fractions of the different types of fuel used in a particular reactor.The effective delayed neutron fraction () is the average delayed neutronfraction multiplied by an Importance Factor which accounts for the fact thatdelayed 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 constanteff= rate of change of reactivity
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