Nuclear fuel assembly with hydraulically balanced mixing vanes

Abstract

A support grid for laterally maintaining the relative position of elongated fuel elements within a fuel assembly for use within a core of a nuclear reactor. The grid is formed in the shape of a lattice with the intersecting lattice members defining a plurality of cells, most of which respectively support the nuclear fuel elements. The remaining cells support nuclear control rod guide tubes and instrumentation thimbles. The cells supporting the nuclear fuel elements are provided with diagonally positioned springs on two, adjacent walls. The springs support the fuel elements against dimples which protrude from the opposite cell walls. The adjacent, diagonal springs in each fuel element cell are inclined in opposite directions. The walls of the cells supporting the control rod guide tubes are embossed along their height at the locations intermediate the intersection between adjoining walls with a concave notch having a curvature which conforms to the outside surface curvature of the control rod guide tubes. The grid is provided with mixing vanes which are positioned in a symmetrical, regional pattern, with the pattern varying between adjacent regions, and configured such that the hydraulic forces across the center of the grid are balanced. The grid is reinforced with welds at the mid point of the intersection of the lattice straps.