Patent GB-1142000-A (GB)
Title: Device for controlling a control rod in a nuclear reactor
Inventor: OLSSON CURT SIGVARD
IPC: G21C7/16
Filed: 1966-03-15
Abstract: 1,142,000. Controlling reactors. ATOMENERGI A.B. 15 March, 1966 [25 March, 1965], No. 11406/66. Heading G6C. A device for positioning a control rod 25 of a nuclear reactor comprises a slide 23 for driving the rod 25, a cylinder 5 in which the slide 23 is axially displaceable between an outer position and an inner position, a first sealing means 21 between the slide 23 and the cylinder 5, dividing the latter into an inner chamber subject to reactor pressure and an outer chamber 39 for a control fluid for the axial displacement of the slide 23, a pressure generating means connected to the outer chamber 39 for generating the pressure necessary for the axial displacement of the slide 23, a second sealing means 19 between the slide 23 and the cylinder 5, which together with the first sealing means 21 defines a space 29 connected to a pressure container 33 for control fluid, and means for maintaining the pressure in the container 33 at a value closely corresponding to the reactor pressure. The latter means comprises a dP- cell (differential pressure cell) 64 connected on one side to the upper gas-filled part of the container 33 and on the other side to the interior of the reactor tank 1. The outer chamber 39 is connected to the container 33 by means of a conduit 37 in which a pump 43 and a solenoid valve 45 are arranged. In parallel with the valve 45 is a by-pass conduit 47 including a solenoid valve 49 and in parallel with both the pump 43 and the valve 45 is a by-pass conduit 51 including a solenoid valve 53. In operation, the valves 47, 53 are closed and the valve 45 is adapted to the desired position of the control rod 25. If the latter is to be raised, valve 49 is opened and, if it is to be lowered, valve 53 is opened. As the pressure in the control system is based on the reactor pressure and is varied synchronously therewith by means of the dP-cell 64, the positioning of the control rod 25 is wholly independent of the reactor pressure due to which, at otherwise constant conditions, the position of the control rod 25 remains unchanged. A second pressure container 71 intended for emergency conditions is connected to the outer space 39 by means of a conduit 73 in which a solenoid valve 74 is arranged. The upper gas-filled part of the container 71 is connected in a similar manner to that of container 33 through a dP-cell 83 to the interior of the reactor tank 1. In connection with the cylinder 5 there is a locking device 85 positioned in a casing 87 arranged in the cylinder wall and comprising an intermediate member 93 journalled at one end to a locking arm 91 and at the other end to a magnetic core 95 with a coil spring 97 mounted between the core 95 and the end of the casing 87. A coil 99 supplied with electric current surrounds the casing 87. The dP-cell 83 is adjusted such that the pressure in the container 71 exceeds the reactor pressure by a predetermined amount. In an emergency, e.g. mains failure, the valve 74 is opened and the excess pressure in the container 71 rapidly inserts the control rod 25 into the reactor core. A mains failure will result in the locking device 85 being released and the locking arm 91 moved out into an operable position by the action of the spring 97, due to which the slide 23 is locked in its inner position.