GB1195834A - Improvements relating to Control Systems for Nuclear Reactors - Google Patents

Abstract

1,195,834. Controlling reactors. A. REYROLLE & CO. Ltd. 28 Sept., 1967 [29 June, 1966], No. 29214/66. Heading G6C. A driving system for inserting a control-rod 10 vertically upwards from below into a control channel 12 of a reactor core 11 comprises a drive-rod 14 secured to the control-rod 10 and carrying a rack 17 in mesh with which is a pinion 18 whose shaft 19 is coupled via a magnetic clutch 20 with an electric motor/brake unit 21 by which the control-rod 10 can be raised and lowered slowly or held stationary in a selected position when required during normal service, with the clutch 20 energized. The driverod 14 is engaged by rollers 15 orientated in several planes to guide the rod 14 throughout the full distance of its travel. In the event of an emergency requiring the rapid shut-down of the reactor, the clutch 20 is disengaged to allow a gravity-operated emergency actuator mechanism to take charge and insert the control rod 10 very rapidly into the reactor core. This mechanism comprises a driving mass 25 coupled by a flexible chain 26 and pulley system 28 to a bracket 29 at the lower end of a tail-rod 16 attached to the bottom end of the drive-rod 14. One end of the chain 26 is secured to a fixed anchorage 30, from which the chain passes down, around a first pulley 28 pivotally mounted on top of the mass 25, up and around a second pulley 28 pivotally mounted on the fixed anchorage 30, and down again to the tail-rod bracket 29 to which the other end of the chain is attached. The velocity ratio of the chain and pulley system 26, 28 is in excess of unity and this, together with the weight of the mass 25, is chosen to give an upward acceleration of the control-rod 10 in excess of 1 g., e.g. 1.5 g., when the clutch 20 is released and the mass 25 descends under gravity. A stop 31 is provided to limit the downward movement of the mass 25. A suitable shock-absorbing or damping device is provided to arrest the motion of the mass 25 and/or the control-rod assembly 10, 14, 16 at the end of the travel. One or more pneumatic cylinders may be provided for this purpose, acting on the tail-rod 16. In addition, the driving mass 25 may be constructed of several portions which telescope successively one within another as they successively engage the stop 31. In a modified construction, the motor/brake unit is coupled through the clutch 20 to the pulley 28 mounted on the fixed anchorage 30. The pulley is formed as a sprocket whose teeth are in engagement with the chain 26. In a second embodiment (Fig. 2, not shown), the motor/brake unit is mounted below the control-rod assembly and drives a winch drum round which is wound a flexible chain or cable whose upper end is connected to the lower end of the tail-rod.