GB1127390A - Control rod driving systems for nuclear reactors - Google Patents

Abstract

1,127,390. Controlling reactors. NUCLEAR POWER GROUP Ltd. 11 May, 1967 [24 May, 1966], No. 23134/66. Heading G6C. [Also in Division H2] A control rod driving system includes means for determining and comparing automatically and continuously, during control rod movement within the reactor, the position of each control rod in a group in relation to the other rods of the group, or the position of each group of control rods in relation to the other groups, which means are also adapted to arrest movement of one or more control rods or groups of rods automatically when it or they become displaced relative in advance of one or more other rods in the group or one or more other groups, in excess of a predetermined amount. By way of example, a plurality of 3-phase induction motors la, 1b, 1c, each connected to a power supply 2 at mains frequency, drive pulleys 3a, 3b, 3c through electromagnetic clutches and reduction gearing 4a, 4b, 4c, in the manner described in Specification 967,513. The drive to each pulley is through a worm and wheel so that if the clutch is energized but the power supply to the motor is cut off, the rod is held in position and does not fall into the reactor. It can only fall into the reactor under its own weight in an emergency condition when the clutch is de-energized. The control rods A, B, C are supported from their pulleys by flexible members, such as cables 6a, 6b, 6c. Control rod position sensing devices 7a, 7b, 7c operate in conjunction with the cables and feed signals representative of the positions of the rods to an automatic control device or computer 8. This continuously compares the positions of the rods and should the position of one differ from that of one or more of the others by more than a predetermined amount, feeds a signal to the corresponding control contact 9a, 9b or 9c to cut off the power supply to the motor concerned. The positions of the rods vary in practice because of varying amounts of slip in the motors. If as in the case shown, the rod B has reached a position in advance of a defined limit band between line XX and line YY, the device 8 operates contact 9b to cut off the power supply to motor 1b and the rod B comes to rest until the limit band moving upwards at the speed of the slowest rod is in a position where rod B again lies within the limit band, at which point the device 8 closes contact 9b and the power supply is restored to motor 1b. The contacts 9a, 9b, 9c are operated on a fail-safe basis so that should the signals from the device 8 be cut off, the supply to the motors 1a, 1b 1c is cut off and the rods come to rest. An overriding switch 10 enables manual control to be substituted for automatic control.