Reactor feedwater control system in BWR type reactor

The control device of the present invention is adapted to always conduct stable and highly reliable control by minimizing the fluctuation of the reactor water level even upon occurrence of remarkable external disturbances such as abrupt change of the reactor power. That is, a water level deviation feedwater controller is operated so as to control the feedwater flowrate depending on the magnitude of a water level deviation signal indicating the difference between an actual water level and an aimed water level. A mismatching feedwater controller is operated so as to control the feedwater flowrate in accordance with a magnitude of a mismatch signal for advancing and delay compensation for the difference of the reactor main steam flowrate. The controllers are optimally set to each of the signals. This can minimize the interference between the water level fluctuation due to the swelling caused by the abrupt change of the reactor core flowrate and the water level fluctuation caused by the mismatching between the main steam flowrate and the feedwater flowrate. Accordingly, the fluctuation of the reactor water level can be minimized even if a significant external disturbance such as abrupt change of the reactor power should occur. (I.S.)