Reactor Theory (Reactor Operations)DOE-HDBK-1019/2-93SUBCRITICAL MULTIPLICATIONExample:Calculate the subcritical multiplication factors for the following values of keff.1)keff = 0.62)keff = 0.986Solution:1)M 11 keff11 0.62.52)M 11 keff11 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 keff. If the source strength ofthis reactor were 1000 neutrons/sec, the neutron level would increase from 2500 neutrons/secondat a keff of 0.6 to a neutron level of 71,400 neutrons/sec at a keff 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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