Patent GB-1300759-A (GB)
Title: Improvements in nuclear reactors
Inventor: SUVANTO ANTTI
IPC: G21C19/105
Filed: 1970-04-20
Abstract: 1300759 Reactors ASEA-ATOM AB 20 April 1970 [21 April 1969] 18721/70 Heading G6C A blocking arrangement for preventing an incorrectly orientated fuel assembly from being inserted in a fuel assembly position in a reactor core comprises a handle 124 attached to the upper grid of a fuel rod bundle 19, a central blocking protuberance 120 projecting from one side of the handle and two asymmetrically positioned blocking protuberances 121 projecting from the other side. These protuberances provide a grip on the handle 124 for a manipulating tool 67 (Fig. 13) only if the handle 124, and thus the fuel assembly, is correctly orientated with respect to rotation in relation to the tool 67. The tool 67 comprises a scissor-like gripping member 68 having a single leg 69 and a fork-like leg 70 which are pivoted on a shaft pin 71. The upper ends of the legs are joined by short link arms to an operating rod 73. At their lower ends, the legs 69, 70 have hook means 76, 77 for engagement in lifting holes 129 in a pair of diagonally opposite lifting lugs, these lugs being an extension of the fuel assembly shroud tube 112, also hook means 78, 79 for engaging the handle 124 when the hook means 76, 77 are swung clear of the holes 129 (Fig. 15, not shown) and hook means (80), 81 for engaging the handle 124 when the hook means 76, 77 are engaged in the holes 129 (as shown). The two fork claws of the fork-like leg 70 are joined by the hook means 77, and the shroud tube 112 has two lifting holes 129 corresponding to the hook means 76, 77. When the gripping member 68 and the fuel assembly 19 have a correct orientation with respect to each other, the hook means (80), 81 can pass the blocking protuberances 120, 121 and engagement can take place. Otherwise, the protuberances prevent the hook means (80), 81 from passing the upper surface of the handle 124 and is thus impossible to grip the fuel assembly. In an alternative embodiment, the handle 124 has smooth sides and correct orientation is ensured in this case by providing the gripping member 68 with a hook means 76 and two hook means 77, and by arranging three corresponding lifting holes 129 in the shroud tube 112. When the fuel assembly is hanging from the manipulating tool 67, there is normally a certain clearance between the lower surface of the handle 124 and the upwardly facing shoulders of the hook means (80), 81. This means that these hook means will only lift the handle 124 if, when the fuel assembly is lifted, the shroud tube should get stuck and be extended or even break completely while being pulled. The fuel assemblies 19 are guided at their upper ends by a core grid 15 formed of flat bars placed horizontally but on edge and crossing each other at right angles. Each of the core-grid meshes thus formed takes up four fuel assemblies 19, guide springs 128 of which run against the vertical sides of the bars and also against vertical partitions 56 projecting from the centre of each mesh side. The single leg 69 of the gripping member 68 is provided with a stop in the form of a pin 53 and unless the fuel assembly 19 on being lowered into the reactor core is of the correct orientation, this pin 53 will hit the core grid 15, lowering is interrupted and the gripping member 68 cannot be opened. When the four fuel assemblies which are nearest a control rod have been lifted out of the core, the control rod can be exchanged. The manipulating tool 67 is lowered and grips a handle (Fig. 10, not shown) on the control rod. A boiling light water reactor incorporating the invention is described.