Method of controlling FBR type reactor

The present invention concerns a method of controlling an FBR type reactor, which can suppress external disturbances in the exit temperature of an intermediate heat exchanger (IHX) and deviation in the exit steams of a steam generator (SG) from the aimed values resulting upon power change. That is, a plant power demand is given only to a secondary sodium flow rate control system with a slow flow rate changing rate and only the secondary sodium flow rate with slow flow rate changing rate is caused to change preferentially. Then, aimed values of the primary sodium flow rate and the feedwater flow rare with rapid flow rate changing rate are given as a function of the measured value for the secondary sodium flow rate thereby reducing the difference in the flow rate changing rate of the primary sodium flow rate, secondary sodium flow rate and feedwater flow rate. With this control method, since the difference in the flow rate changing rate between the primary and the secondary sides of IHX and SG can be compensated upon power change of the plant, fluctuations at the exit temperature of IHX and SG can be suppressed. Accordingly, the plant's integrity and safety can be improved. (I.S.)