CONTROL ROD DRIVING MECHANISM

PURPOSE:To obtain a shortened control rod driving mechanism driving part by providing a stroke operation mechanism equipped with a ball screw for stroke operation, etc., a control rod driving shaft and a ratch shaft which are put in a penetration state so that they move up and down relatively, and a latch mechanism. CONSTITUTION:For up-down driving as normal driving, the rotation of a stroke motor 4 is transmitted from a ball screw nut 2 to the ball screw 1 with a spline and then transmitted to a scramming mechanism 11 through the latch mechanism 16. The mechanism 11 consisting of a magnet 25 and a link mechanism 26 energizes the magnet 25 in normal operation to close the mechanism 26 and the up-down driving of the mechanism 16 is transmitted to a driving shaft 19 and the latch shaft 20 as it is. For scramming, the magnet 25 in the mechanism 11 is demagnetized to release the mechanism 26 and the driving shaft 19, etc., is fallen integrally with a control rod 22 which is positioned below it. When fuel is replaced, the latch shaft 20 is pressed up to disconnect the control rod 22 and driving shaft 19 from each other and then the mechanism 16 is lifted. A latch motor 9 is operated after the control rod 22 and driving shaft 19 are disconnected to make a driving shaft lock mechanism 12 operate an armature 27, thereby preventing the driving shaft 19 from falling.