Control rod drives

Purpose: To enable to accurately detect the falling position of control rods, even upon reactor scram in control rod drive mechanisms for use in LMFBR type reactors. Constitution: An accelerating tube for falling control rods under acceleration upon scram is divided into two upper and lower portions. When a control rod is disconnected, it is inserted integrally with both of the upper and lower accelerating tubes. The upper accelerating tube is deccelerated by an upper deccelerating mechanism comprising a dash pot and a ram in the course of the falling and detached from the lower accelerating tube. The lower accelerating tube continues to fall integrally with the control rod even after detaching from the upper accelerating tube and deccelerated to stop by a lower deccelerating mechanism after a permanent magnet assembled to the upper portion of the lower accelerating tube has passed a switch disposed to the inside of a upper guide tube at a position capable of confirming the insertion of the control rod into the reactor core. At this instance, the switch is actuated to generate a pulse signal. The signal can be detected by a detection device to confirm the position of the control rod. (Horiuchi, T.)