Patent GB-1088123-A (GB)
Title: Nuclear reactor control mechanisms
Inventor: CHALLENDER RONALD SCOTT
IPC: G21C7/14
Filed: 1964-12-30
Abstract: 1,088,123. Controlling reactors. UNITED KINGDOM ATOMIC ENERGY AUTHORITY Dec. 13, 1965 [Dec. 30, 1964], No. 52914/64. Heading G6C A nuclear reactor control mechanism, for normal control movement of a control-rod relative to a reactor core and releasable to allow for rapid movement of the rod in a direction to reduce reactivity of the core, comprises a drive member engaging, on one side of a gland, a driven member which extends through the gland, first means for restraining the driven member against rotation during normal control movement, a releasable mechanical coupling between the driven member and a control rod carrier on the other side of the gland, and second means for effecting limited rotation of the driven member to release the coupling so as to allow for rapid movement of the carrier in the direction to reduce reactivity of the core. In the embodiment described, the drive member which is in the form of a screw member 42 rotatably housed in a main control mechanism body 41 engages the driven member which is in the form of a nut 36. The screw member 42 is rotated by way of a gear-box and a drive motor (not shown) at the upper end of the main body 41. The nut 36 has an integral extension tube 37 which extends down through a gland inside the reactor pressure vessel (the reactor being a pressurized water reactor) to a releasable mechanical coupling formed by a hammerhead consisting of rollers mounted on the ends of a shaft. The hammerhead is adapted to be inserted through a diametral slot in the enlarged end of a tubular member connected to the control rod carrier and rotated through 90 degrees to engage the underside of flanges defining the diametral slot. The enlarged end of the tubular member serves as a damping piston, being movable axially in a coaxial damping tube. The nut 36 has a key 43 engaging a longitudinal keyway 44 in a rotatably mounted restraint tube 45 coaxially disposed in the main body 41 around the nut extension tube 37. In the annulus between the restraint tube 45 and the main body 41 is an annular piston 46 and a helical spring 47 extending between a flange on the lower end of the main body 41 and the underside of the piston 46. On its upperside, the piston 46 carries by way of a connecting sleeve 48 a transverse restraint shaft 49. The inner end of the shaft, 49 has a roller 50 which engages a helical cam slot 51 in the outer surface of the restraint tube 45, whilst the outer end of the shaft 49 has a roller 52 which engages a longitudinal cam slot 53 in the inner wall of the main body 41. During assembly, pressurized fluid is supplied by way of an inlet 54 to the interior of the main body 41 to move the annular piston 46 to its lower limit of travel and compress the helical spring 47. This movement rotates the restraint tube 45 due to the engagement of the restraint shaft 49 in the cam-slots 51, 53 which are designed to give 90 degrees of rotation over the length of travel of the piston 46. Since the nut 36 is keyed to the restraint tube 45, the nut 36 and extension tube 37 are also rotated through 90 degrees, and similarly the hammerhead is rotated through 90 degrees to engage the coupling as described above. For emergency control, the fluid pressure above the piston 46 is reduced and the helical spring 47 rapidly moves the piston 46 to its upper limit of travel, thus releasing the coupling. The control rod carrier is then free for rapid downward movement under the action of gravity and a normally compressed main-spring.