Patent Number: 039363490
Section: summary

BACKGROUND OF THE INVENTION This invention relates to nuclear reactors of the kind having a core composed of closely packed parallel fuel elements which are provided with bearing pads at selected levels whereby the elements are firmly positioned against one another to prevent them rattling. Such a nuclear reactor core is disclosed in U.S. Pat. No. 3,383,287 and the fuel elements in that reactor core are arranged in groups in each of which each element is supported in such a manner as to tend to tilt the element towards the centre of the respective group whereby the elements of each group are urged laterally into firm engagement either with one another or with a structural member around which the group may be arranged. Thus the elements of each group are jammed together, and, where desirable, about a central post on which the surrounding elements lean. SUMMARY OF THE INVENTION According to the present invention, in a nuclear reactor core comprising 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 are 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 have interlocking bearing pads intermediate their ends whereby relative lateral movement of two adjacent fuel elements is resisted. By reducing sideways slip of fuel elements the stability of of the reactor core is improved during refuelling operations. The invention also resides in a nuclear reactor fuel element for a nuclear reactor core in accordance with the preceding paragraph, the fuel element comprising a cluster of parallel fuel pins enclosed by a peripheral wrapper of hexagonal cross-section, the bearing pads being in the form of spline-like ribs extending parallel to the longitudinal axis of the fuel element and interlockable with complementary ribs of pads on adjacent fuel elements in the group. The invention is applicable to a nuclear reactor core wherein the components, which comprise fuel elements and control rods, are generally arranged in modules each module comprising a cluster of four components at least three of which are fuel elements, one fuel element being rigidly supported whilst the remaining components are resiliently tilted towards the centre of the cluster to lean on the rigidly supported element. The invention is also applicable to a nuclear reactor core wherein the fuel elements are arranged in modules, each module comprising a cluster of six fuel elements, each resiliently tilted towards a central void to form a circular arch. The modules may include additional fuel elements disposed outside the cluster and resiliently tilted towards the central void. The central void may be used to accommodate a control rod. By using a module arrangement of fuel elements wherein one element serves to support the remaining elements and control rods of the cluster, or wherein the elements lean on each other in a circular arch, the need for structural members to form leaning posts in the manner described in U.S. Pat. No. 3,383,287 is avoided. Such structural members are subject to irradiation embrittlement which could lead to failure within the core.