PRESSURIZED WATER REACTOR

PURPOSE:To enable output control without causing the distortion of an output distribution by dividing a control rod assembly for output control into plural groups and inserting and extracting the assembly into and from a reactor core so that some of them overlap one another. CONSTITUTION:A control rod assembly 2 whose neutron absorbing ability is axially uniform and the control rod assembly 3 for output control whose neutron absorbing ability is small at the lower part and large at the upper part are arranged in the reactor core 1, the assembly 2 is divided into control group banks A, B, C, and D and stop group banks SA, SB, and SC, and the assembly 3 is divided into control rod assembly groups G1 and G2 for output control. Then the assembly group G1 and G2 are inserted into and extracted from the reactor core 1 so that some of them overlap one another; and the neutron absorb ing ability of overlap parts is larger than that of nonoverlapping lower parts and smaller than that of nonoverlapping upper parts. Consequently, the output control and output distribution control are excellently performed.