¯effReactor Theory (Reactor Operations)DOE-HDBK-1019/2-93REACTOR KINETICSRev. 0NP-04Page 15Figure 3 Reactor Power Response to Negative Reactivity AdditionConversely, in the case where negative reactivity is added to the core there will be a promptdrop in reactor power. The prompt drop is the small immediate decrease in reactor powercaused by the negative reactivity addition. The prompt drop is illustrated in Figure 3. After theprompt drop, the rate of change of power slows and approaches the rate determined by thedelayed term of Equation (4-7).PromptCriticalityIt can be readily seen from Equation (4-7) that if the amount of positive reactivity added equalsthe value of , the reactor period equation becomes the following.