Patent GB-1248737-A (GB)
Title: Nuclear reactor fuel element clusters and assemblies
Inventor: LEWIS ROBERT ALEC
IPC: G21C3/344
Filed: 1968-03-01
Abstract: 1,248,737. Fuel elements. UNITED KING- DOM ATOMIC ENERGY AUTHORITY. 20 Feb., 1969 [1 March, 1968], No. 10181/68. Heading G6C. A fuel element assembly comprises a plurality of fuel element clusters interconnected end-toend by releasable telescopic couplings so that they are movable into and out of end abutment, each coupling comprising a resiliently deformable latch member extending coaxially from one end of a cluster and a non-deformable latch member secured to an adjacent end of an endwise adjacent cluster, the latch members having annular lips for interengagement when the clusters are telescoped apart, each fuel element cluster having a central perforated tube adapted at each end for demountable connection with the central perforated tube of an end-wise adajcent cluster to form a continuous duct extending along the central axis of the fuel element assembly. As shown in Fig. 1, each cluster 2 comprises a group of parallel, spaced fuel elements 3 supported between grid plates 9, 11. The clusters 2 are interconnected by a telescopic releasable coupling 4 arranged so that when the clusters are suspended for removal from the tube 1 they become spaced from each other. Spacing enables manipulation equipment to engage and release the coupling 4 so that the clusters can be positionally interchanged. Three of the fuel elements 3 of each cluster have sheaths of greater wall thickness than the remaining elements, the thicker sheaths serving as struts to support operational compressive loads on the assembly. Fourteen cellular bracing grids 12 are equally spaced between the grid plates 9, 11. The six inner fuel elements 3b are shorter than the remainder and supported from a stool 13 inside the lower end of the cluster, the upper ends of these elements being slidably guided by the uppermost grid 12. The stool 13 houses a spring collet 17 consisting of a thin wall tube which is slit longitudinally from the lower end to define six spring fingers 18. The lower ends of the fingers 18 have shoulders 20 with recessed rear faces 22 forming a hooked lip. The upper grid 9 of each cluster 2 has a boss 23 with a central aperture 23a. The collet 17 of the upper cluster 2 engages the boss 23 of the lower cluster telescopically to enable the clusters to move into and out of end abutment. The upper grid aperture 23a is bounded by a lip 25 on the lower side, which lip is complementary to the recessed surfaces 22 of the collet fingers so that on suspending the upper cluster the lip 25 engages with the recessed surfaces 22 to lock the coupling against release. When the fuel element assembly is removed from the reactor and supported horizontally in a manipulating device the clusters can be moved together sufficiently to release locking engagement of the lips 25 and recessed surfaces 22. The tube 1 has a tapered transition piece 28 welded to its lower end, as shown in Fig. 2. A support stool 31 for the stacked clusters 2 is carried by the transition piece 28 and comprises an annular plate 32 and a tube 33 interconnected by six webs 34. The webs 34 abut the converging inner walls of the transition piece 28. The tube 33 has an upstanding cylindrical plug 35. The fuel elements 3 are arranged about a central perforated tube 8 in each of the clusters, and during insertion of the lower cluster its tube 8 is guided by a bell mouth 26 to ensleeve the plug 35. The tubes 8 of the clusters together provide a sparge tube for conducting and spraying an emergency supply of water on to the fuel elements which is brought into use in an emergency in which the normal supply of coolant is cut off.