Feedwater flow rate control device in nuclear reactor

This invention concerns a control device used in a feedwater control system of BWR nuclear power plant and suitable to optimum control for the reactor water level upon transient state such as insertion of a control rod. Reduction in the reactor water level upon insertion of the control rod is due to the decrease in the voids caused by the reduction of the reactor power. Taking notice on the fact that the reduction occurs only temporary, it is possible to suppress the subsequent water level increase without changing the reduciton amount of the reactor water level by increasing the mismatching gain in the temporary state. That is, it can be attained by inputting a control rod insertion signal indicating the change of the status on the side of the reactor into a flow rate control device of a nuclear reactor feedwater and changing the mismatch gain with the signal. According to the present invention, since the main target for the feedwater flow rate control upon insertion of the control rod can be transferred from the water level control to the deviation between the flow rate of the main streams and the flow rate of feedwater, it is possible to suppress the water level increase upon settling of the transient phonomenon. (I.S.)