Patent ID: 8571162

Claim:
A control rod drive mechanism which controls a reactivity of a reactor core by inserting or drawing a control rod into or out of the reactor core of a reactor pressure vessel, the control rod drive mechanism comprising: a cylindrical guide tube fixed to a bottom portion of the reactor pressure vessel, said cylindrical guide tube extending in a vertical direction and having a latch hole; a hollow piston coupled to the control rod, said hollow piston freely moving up and down within the guide tube, wherein said hollow piston moves up via application of high-pressure water for a scram, at a time of occurrence of the scram; a latch provided in the hollow piston so as to freely swing, said latch freely engaging with and disengaging from the latch hole of the guide tube; a spring coupled between the hollow piston and the latch, said spring applying a spring force in a direction to the side of the guide tube to the latch so as to lock the latch to the latch hole of the guide tube; an elevating member freely moving up and down within the guide tube, said elevating member freely coming into contact with a lower surface of the hollow piston, and having a latch guide; and a drive portion driving so as to move up and down the elevating member; wherein the latch provided in the hollow piston includes a guide surface coming into contact with the latch guide of the elevating member, the latch is configured to be rotated against a spring force of the spring by the contact of the latch guide with the guide surface, thereby being detached from the latch hole of the guide tube, and wherein, the latch guide includes a guide roller coming into contact with the guide surface of the latch.