Method for measuring reactor core flow rate

Difference of the difference present-flow rate characteristics between a test device for the reactor core flow rate in a reactor incorporated with a recycling pump and an actual device is eliminated to improve the measuring accuracy. This can be attained by determining the difference pressure-flow rate characteristics of the recycling pump in the actual device. Heretofore, since the test device could not simulate the actual device completely, this causes the difference of the difference pressure-flow rate characteristics between the test device and the actual device to lower the accuracy of the reactor core flow rate measurement. However, it is no more necessary to consider the error of the difference pressure-flow rate characteristics in the present invention in which the difference pressure-flow rate characteristics are determined in the actual device. Therefore, accuracy of the reactor core flow rate measurement is improved. As a result, the reliability and safety of the plant are improved. (I.S.)