Top nozzle adapter plate with fuel rod capture grid having pressure drop

Abstract

A top nozzle adapter plate for use in a fuel assembly of a nuclear reactor includes an upper structural component and a lower functional component supported from the upper component. The fuel assembly has elongated structural members and fuel rods disposed in a predetermined array. The upper structural component of the adapter plate includes spaced and interconnected hubs and ligaments arranged to define substantial open areas for coolant flow therethrough while providing a rigid framework capable of transmitting lifting loads imposed by the fuel assembly. The hubs are connected to the elongated structural members of the fuel assembly. The lower functional component of the adapter plate includes a grid composed of a plurality of spaced and interleaved straps which cross one another to form intersections aligned with individual fuel rods in the array thereof for restraining movement of fuel rods upward from the fuel assembly while defining open channels through the grid for allowing passage of coolant flow therethrough. The grid also contains void areas through which extend the hubs of the upper component. The lower component also includes coolant flow directing means being operable to establish a predetermined desired pressure drop across the top nozzle of the fuel assembly. In one form, the coolant flow directing means is a plurality of tabs connected to the grid straps and extending outwardly therefrom. The tabs are adjustable into various desired positional relationships with respect to the grid channels for controlling coolant flow therethrough. In a modified form, the coolant flow directing means is in the form of a thin flat plate having holes of predetermined desired sizes and shapes formed therein. The plate extends along the interleaved straps of the grid with its holes generally aligned with the open channels of the grid.