Reactor shut-down device

Purpose: To shorten the armature disconnecting time by the provision of a permanent magnet to an armature to thereby reduce the decay time for secondary current in the polarity switching of the scram magnet upon reactor scram. Constitution: An outside extension tube is mounted at its upper end with a scram magnet and an internal extension tube is provided at its upper end with an armature. The armature is incorporated in its inside with a permanent magnet secured at its upper surface with a hard rubber for improving the close contaction at the lower surface of the scram magnet, and mounted at its lower surface with a cushion for absorbing the falling shocks upon disconnection. While the scram magnet attracts the armature to hold the control rods in normal operation, the magnet changes its polarity upon scram thereby repulsing the permanent magnet, releasing the armature rapidly, falling the internal extension tube, lowering the finger rod, disengaging the ratch finger and rapidly disconnecting the control rod, to enable rapid and safe reactor stop. (Kawakami, Y.)