Patent GB-940586-A (GB)
Title: Improvements in or relating to nuclear reactor control devices
Inventor: WHITE WILLIAM PAUL
IPC: G21C7/11
Filed: 1961-05-17
Abstract: 940,586. Reactor control rods. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. May 4, 1962 [May 17, 1961], No. 18056/61. Heading G6C. A control element for insertion in a vertical channel of a core of a nuclear reactor comprises discrete bodies of neutron absorbing material linked to form a freely flexible chain held in a compact form but which is releasable to fall under gravity to a dispersed position of increased neutron absorption capacity. In the shut-down control element shown in Fig. 1, a tubular container 4 houses a number of flat annular plates 5 of boron steel loosely hinged together by small rings 6 encircling two pins 7, each pin 7 being located in a hole 8 and traversing a slot 9 (Fig. 2) in one of the plates 5. In this way the plates 5 are retainable in a compact form with one plate 5 flat upon another, being held thus by a retaining rod 15 which passes through a central hole 16 formed by the individual apertures of the plates 5. A coil spring 17 in compression is positioned between the lowermost plate 5 and a horizontal plate 18 welded to the lower end of the rod 15, a horizontal ceramic tube 12 passing through a hole 14 in the upper end of the rod 15. The ends of the tube 12 rest in brackets 13 secured to an annular plate 10 to which the uppermost plate 5 is hinged and which is welded to a tube 11 connected at the top to the container 4 and a cap 19, the latter having a downwardly projecting annular flange 23. A cylindrical bellows 24 is sealed at its upper end to the flange 23 and at its lower end to a flange 25 on an annular plate 26. The plate 26 carries two porous plugs 27 and a tube 28 extending into the recess formed by the flange 23. Coolant gas in the channel 2 can pass into the bellows 24 by way of ports 31 and 29 in the container 4 and tube 11, respectively, the plugs 27, ports 30 in the tube 28 and the open upper end of the tube 28. The bellows 24 is not effected by slow changes of coolant pressure in the channel 2 but should a sudden drop in pressure occur, a significant pressure differential will exist across the bellows 24 due to the restriction of gas flow provided by the plugs 27, the bellows 24 expanding and exerting a thrust on the rod 15 causing the tube 12 to fracture. The spring 17 then ejects the rod 15 to the bottom of the container 4 and the plates 5 fall under gravity to a dispersed position providing an increased neutron absorption capacity, the position of the lowermost plate 5 being indicated in broken outline in Fig. 1. The cap 19 has an upstanding part 21 with a conical recess 22 while the container 4 has a conical end cap 32, thus enabling a number of the elements to be stacked one upon another in the channel 2. The plates 5 are made of boron steel, the plugs 27 of sintered stainless steel powder and the other components (apart from the ceramic tube 12) of stainless steel. Instead of the plates 5, the linked bodies may be in the form of hollow cones interconnected with non-pivotal links such as flexible wires, the cones nesting together in the compact position.