IBR-2 dynamics with power shedding

Calculations have shown that in the presence of power shedding the reactivity depends strongly on the moment of shedding relative to the start of the reactor cycle, the stopping time of the reactor after power shedding, and the number of sheddings. It is shown that reactivity effects due to power shedding continue to act for 2 days after shedding, after which these effects can be neglected. The total change of the reactivity after power shedding can range from 0.12 to –0.05%Δk/k. A region of negative reactivity forms in most practical cases after power shedding. The depth of this region can reach –0.05%Δk/k, and the duration varies from several hours to several tens of hours. Knowledge of the reactivity after power shedding makes it possible to determine more accurately the consequences of different emergency situations and to predict the critical state of the reactor when the reactor is once again brought up to power.