Patent GB-1444011-A (GB)
Title: Nuclear reactors
IPC: G21C1/00
Filed: 1973-01-05
Abstract: 1444011 Reactors UNITED KINGDOM ATOMIC ENERGY AUTHORITY 18 Dec 1973 [5 Jan 1973] 858/73 Heading G6C A nuclear reactor core comprises an array of closely packed components which include fuel elements, the components being arranged with their longitudinal axes generally vertical in groups, at least some of the components in each of several groups being supported in such manner as to tend to tilt the components towards the centre of the respective group whereby the components of each group are urged laterally into abutment with one another, and the fuel elements having interlocking bearing pads intermediate their ends whereby relative lateral movement of two adjacent fuel elements is resisted. In a fast breeder reactor core (Fig. 1, not shown), there are central and intermediate zones having Pu-enriched fuel elements and an outer breeder zone. Except at the periphery of the latter zone, the components are arranged in modules each comprising a cluster of four components of which at least three are fuel elements. One of the fuel elements (component "Z" in Fig. 2) of each module is rigidly supported in upright position whilst the remaining fuel elements (components "X" and "Y") are tilted towards the rigidly supported fuel element. Either of the components "X" can be a control rod or shut down rod guide tube, in which ease it is either free standing or leaning on the fuel elements but does not have interlocking bearing pads. The fuel elements comprise assemblies of fuel pins (not shown) housed in wrappers 5. Bearing pads 11 are located intermediate the ends of each fuel element (Figs. 3 and 6), one pad on each side of the fuel element wrapper 5 and each pad comprising one full width and one half width rib 11a. As a fuel element is loaded into the reactor core, a circular taper 9 at the lower end of the wrapper 5 contacts a side of a hexagonal taper 8 at the upper end of an adjacent installed fuel element so that the fuel element being lowered is displaced sideways into its correct azimuthal position relative to the centre of the cluster of components. On further lowering of the fuel element, its corner splines 10 abut the hexagonal tapers 8 of adjacent fuel elements causing rotation of the element such that its wrapper 5 will pass between the pads 11 on adjacent elements. When the fuel element is lowered sufficiently to engage the lower ends of its ribs 11a with the upper ends of the ribs 11a of adjacent elements, taper lead-in surfaces 11b of the ribs assist in radial and fine rotational adjustment of the fuel element, and taper lead-in surfaces 11c assist in radial alignment, to engage the ribs accurately so that the fuel element can then be fully lowered and spiked into the diagrid. Those fuel elements which are arranged to tilt have resilient spikes 6 at the lower ends of their wrappers 5. A second construction of reactor core (Figs. 7 and 8, not shown) is generally similar to the above-described except that fuel elements only are arranged in clusters of six, each resiliently tilted towards a central void to form a circular arch. This void can be occupied by a free standing control rod or shut down rod guide tube.