TOP-PART INSTALLED CONTROL ROD DRIVING UNIT

PROBLEM TO BE SOLVED: To enhance aseismatic performance by installing a control rod driving unit on a top lid of a reactor pressure vessel to decrease the space in the lower section of the reactor pressure vessel and lower the center of gravity of the reactor. SOLUTION: The control rod driving unit secured to the top lid 22 of the reactor pressure vessel via a housing 23 for the control rod driving unit can vertically move a control rod 42 by moving a ball nut 37 up and down by rotative drive of a motor assembly 30 in the case of normal driving, and controls the output of the reactor by adjustment of insertion/withdrawal of the control rod 42 to/from the reactor core. In the case of a scram, the ball nut 37 is rotated through a guide tube 39 by rotating a scram magnet 50, a hollow piston 40 connected with the control rod 42 with a coupling is separated from the ball nut 37, and the control rod 42 is made to enter the core of the reactor by its self-weight. COPYRIGHT: (C)2006,JPO&NCIPI