Method of monitoring the power distribution in a reactor

Purpose: To rapidly and accurately obtain the present power distribution in the nuclear reactor corresponding to the monitor demand generated at an optional point even when the plant operation status is changed. Method: When a monitor demand signal for the reactor power distribution is generated, a monitor control section actuates a three dimensional nuclear thermo-hydrodynamic model by a calculation start signal. The control section is also adapted to put the three dimensional nuclear thermo-hydrodynamic model section into a predetermined value preparing mode in the case of receiving a plant state change detection signal from a plant status change detection section. The model section receives the monitor result for the power distribution in the previous time stored in a memory section as an initial value and determines the present power distribution by the repeating matrix calculation using the initial value and the plant data. (Yoshino, Y.)