Power control method and device for natural convection type reactor

Purpose: To increase the control range for the reactor core flow rate to cope with the load fluctuations in the natural convection type nuclear reactors. Method: In a downward coolant flowing channel formed between a reactor container and a surrounding shroud, for returning the coolants discharged from the reactor core again to the reactor core, the coolant level is controlled to below the coolant level in the shroud based on a reactor power demand signal, to thereby control the reactor power to a predetermined level. Further, by disposing coolant supply means to the inside of the reactor container and control means for controlling the coolant flow rate dependent on the pressure of the coolants together, the object can be attained. That is, the liquid level at the outside of the shroud is controlled to below the inside thereby enabling to increase the control range for the reactor core flow rate and, in addition, reactor power control capable of coping with the load change is enabled by such reactor core flow rate control. (Horiuchi, T.)