Reactor stability monitoring device

Purpose: To operate nuclear reactors without degrading the stability by comparing the distortion of the actually measured axial power distribution with the allowable value thereof. Constitution: In BWR type reactors, nuclear or thermohydrodynamic unstability tends to be induced when the coolants are at the low flow rate and reactor power is high. In the stability monitoring device for the reactor according to the present invention, the axial power distribution of the reactor core is also taken into consideration in addition to the conventional reactor flow rate and the reactor power as the parameter for giving undesired effect on the stability of the reactor. That is, the stability monitoring device monitors the reactor core axial power distribution and compares the distortion of the reactor core axial power distribution with the allowable value of the distortion for the axial power distribution set on the reactor core flow rate or reactor power as the parameter. Then, the operation of the control rod drive system and the recirculation flow rate control circuit are controlled based on the result of the comparison. Accordingly, the operation range of the reactor can be widened to increase the operation margin and improve the operationability. (Kamimura, M.)