IBR-2 reactor physical start-up. The power pulse shape measurements

The power pulse shape measurements were performed during the IBR-2 physical start-up experiments. The pulse duration dependence upon some features of core environment and reactor operation regime were investigated. Both the individual pulse shape of the current from the neutron detector and averaged pulse shape received by means of time analyzer were measured. For the pulse criticality conditions pulse duration THETA depends on a composition of the core environment and varies whithin the 150-200 μs range. The most effect on THETA is due to a water moderator positioned behind the moving reflector (deltaTHETA=30 μs), and the beryllium block of the supplementary moving reflector (deltaTHETA=40 μs). The experimental shape of the pulse and theoretical one, based on the one-point kinetics, are in good agreement. The factors which allow one to decrease the pulse duration up to 130 μs are shown