Reactor Theory (Reactor Operations)DOE-HDBK-1019/2-93SUBCRITICAL MULTIPLICATIONExample:Calculate the subcritical multiplication factors for the following values of k_{eff}.1)k_{eff} = 0.62)k_{eff} = 0.986Solution:1)M 11 k_{eff}11 0.62.52)M 11 k_{eff}11 0.98671.4The example above illustrates that the subcritical multiplication factor will increase as positivereactivity is added to a shutdown reactor, increasing the value of k_{eff}. If the source strength ofthis reactor were 1000 neutrons/sec, the neutron level would increase from 2500 neutrons/secondat a k_{eff} of 0.6 to a neutron level of 71,400 neutrons/sec at a k_{eff} of 0.986.EffectofReactivityChangesonSubcriticalMultiplicationIn a subcritical reactor, the neutron level is related to the source strength by Equation (4-2).(4-2)N (S) (M)where:N=neutron levelS=neutron source strengthM=subcritical multiplication factorRev. 0NP-04Page 3

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