¯effeffprompttermdelayedterm¯effREACTOR KINETICSDOE-HDBK-1019/2-93Reactor Theory (Reactor Operations)NP-04Rev. 0Page 14Figure 2 Reactor Power Response to Positive Reactivity AdditionReturning now to Equation (4-7) for reactor period.If the positive reactivity added is less than the value of , the emission of prompt fissionneutrons alone is not sufficient to overcome losses to non-fission absorption and leakage. Ifdelayed neutrons were not being produced, the neutron population would decrease as long asthe reactivity of the core has a value less than the effective delayed neutron fraction. Thepositive reactivity insertion is followed immediately by a small immediate power increase calledthe prompt jump. This power increase occurs because the rate of production of prompt neutronschanges abruptly as the reactivity is added. Recall from an earlier module that the generationtime for prompt neutrons is on the order of 10 seconds. The effect can be seen in Figure 2.-13After the prompt jump, the rate of change of power cannot increase any more rapidly than thebuilt-in time delay the precursor half-lives allow. Therefore, the power rise is controllable, andthe reactor can be operated safely.
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