Patent GB-1117237-A (GB)
Title: Improvements in or relating to nuclear reactor fuel assemblies
Inventor: SEDDON THOMAS
IPC: G21C3/34
Filed: 1964-10-30
Abstract: 1,117,237. Fuel elements. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. 22 Oct., 1965 [30 Oct., 1964], No. 44459/64. Heading G6C. A spacer grid for a clustertype fuel element comprises a surround defining the boundary of the grid, at least two sets of wires or rods secured to and traversing the surround so that each set crosses another set and with it defines cells for accommodating fuel rods, and a closed loop carried by the wires or rods at each position where one crosses another, each loop being capable of limited movement relative to the wires or rods which carry it and serving, in association with adjacent loops, for contacting and locating a fuel rod in each of the cells. As shown in Fig. 1, the surround is constituted by a framework 2 of strip material bent into a square shape in plan view with its ends butt-welded together. The framework 2 has the wires or rods 6 secured to it by ferrules 5 screwed on to the ends of the wires or rods, the ferrules 5 being accommodated in apertures 4 in inwardly recessed portions 3 of the framework 2 and having heads 16 of larger diameter than the apertures 4. Each head 16 has a lateral groove by means of which it can be engaged and turned, whereby the grip of the closed loops 7 on the fuel rods 9 can be varied. The loops 7 which are circular in plan are bent in end view so that they can be threaded on to the wires or rods 6 at the crossing points. Dimples 10 are provided in the framework 2 between adjacent recesses 3 to contact the fuel rods 9 in the outer cells 8 (except the " corner " cells). The spacer grid is positioned within the outer casing 11 of the fuel element by dimples 12 provided in the framework 2 below that portion in which the recesses 3 and apertures 4 are provided. The framework 2 is slitted between the dimples 12 and the apertures 3 to allow the upper part of the framework 2 to bend inwardly on applying tension to the wires or rods 6 without affecting the lower part of the framework 2 and thereby its location, via the dimples 12, in the casing 11. The spacer grid may be longitudinally located in the casing 11 by means of the " corner " fuel rods 9 which are made up from sections corresponding in length to the longitudinal spacing between spacer grids. One section 14 as shown in Fig. 4, terminates above the spacer grid and has an end cap 15 provided with a screw-threaded spigot 17 engaging a screw-threaded aperture 18 in an end cap 19 of another section 20 below the spacer grid. The end cap 19 has a recess 21 in which is accommodated a ring 22 carried in arcuate portions 23 of a generally triangular corner cell assembly 24 secured along two of its sides to the framework 2 by spot welding or brazing. A shim 26 is provided between abutting faces of the end caps 15, 19 and serves also to retain the ring 22 in the recess 21. A locking pin 27 is employed to prevent unscrewing of the spigot 17 from the aperture 18. An alternative means for longitudinal location of each spacer grid resides in omitting the framework 2 and mounting the ferrules 5 directly in apertures in the casing 11, in which case the corner cell assemblies 24 need only locate with and not be connected to corner fuel rods, which are of full assembly length and not divided. As a further alternative, the wires or rods 6 can be adjusted to tighten the hold of the loop 7 on the fuel rods 9 sufficiently to locate the spacer grid longitudinally, in which all the fuel rods may be of full assembly length and not divided.