Rack and pinion mechanism for moving a unit absorbing neutrons in a nuclear reactor

DETAILED DESCRIPTION The object of the invention is therefore a rack and pinion mechanism for moving a unit absorbing neutrons, movable vertically in a nuclear reactor for controlling the power and for emergency shutdown of the reactor, comprising a vertical control shaft whose lower part is connected to the absorbent unit and whose upper part has a rack disposed in the longitudinal direction of the shaft and a pinion driven in rotation by a motor apparatus, in engagement with the rack so as to move the control shaft and the absorbent unit in both directions, this mechanism having to allow precise movements of the control rods and the halting of these rods in well defined positions and the falling of the rods for emergency shutdown of the reactor controlled by a simple apparatus preventing disengagement of the rack and pinion.
To this end, the pinion permanently in engagement with the rack is mounted to rotate on a shaft connected to the motor apparatus for setting the pinion in rotation and disposed perpendicularly to the control shaft, and a clutch device solid with the shaft in rotation is mounted to move in translation on this shaft between a disengagement position in which the pinion and the clutch device are brought into contact and connected by a mechanical means allowing the rotary movement of the shaft to be transmitted to the pinion, the translatory movement of the clutch device in the axial direction of the shaft being controlled by a push-rod connected to an actuating member with vertical movement which is maneuverable from the upper part of the apparatus.
For a full understanding of the invention, an embodiment of the rack and pinion mechanism according to the invention will now be described by way of example, with reference to the attached drawings.