GB1340782A - Nuclear fuel rdo assemblies - Google Patents

Abstract

1340782 Fuel elements BABCOCK & WILCOX 13 Jan 1971 [14 Jan 1970] 1769/71 Heading G6C A nuclear fuel assembly comprises an array of spaced, parallel fuel rods 11 and end grids 14, 16 to which are secured the respective ends of longitudinally extending control rod guide tubes 12, the upper grid 16 being formed with T- shaped slots 24 accommodating the fuel rod heads 23 and the lower grid 14 being formed with recesses 41 for pin terminations 25 at the other ends of the fuel rods 11. Each of the grids 14, 16 is formed of vertical strips 18, 19 intersecting at right angles in "egg crate" manner, and at each desired location in a grid for a guide tube 12 the adjacent strips 18, 19 are welded to a vertically extending fitting 20 which receives an end length of the guide tube 12. The extremity of the guide tube 12 projecting beyond the fitting 20 is threaded and engaged by a nut 21. Each fuel rod 11 terminates at its upper end in a stem 22 surmounted by a head 23 which is accommodated in a slot 24 sufficiently closed below the head 23 to allow the fuel rod to be supported by its head from the upper grid 16. Each fuel rod terminates at its lower end in a pin 25 accommodated in the lower grid 14 in a recess 41. The recess 41 allows free downward movement of the rod lower end relative to the grid 14 under the influence of differential expansion in reactor operation. After the removal of the fuel assembly from the reactor core, it can be dismantled by removal of the nuts 21 at the upper grid 16, whereupon the grid 16 together with the fuel rods is moved away from the lower grid 14 until the grid 16 is clear of the guide tubes 12, the grid 16 then. being removed by displacing it laterally in a direction parallel to the alignments of the grid slots 24 at right angles to the planes of the slots. The fuel rods 11 can then be removed lengthwise from the remaining components of the assembly. In a modification, the heads of the fuel rods are at their lower ends and it is the lower grid which is formed with aligned slots accommodating the fuel rod heads. In this case, the fuel rods are supported for individual upward expansions. This arrangement suffers from the drawback, however, that in normal handling of the fuel assembly the weight of the fuel rods is borne by the control rod guide tubes.