Patent ID: 7792236

Claim:
A nuclear fuel rod assembly, comprising: a plurality of fuel rods, arranged vertically and in parallel to each other; a plurality of grids through which the fuel rods pass; the plurality of grids including a bottom grid, a top grid, and at least two intermediate grids between the top grid and the bottom grid; each grid formed of a plurality of perpendicularly flat plates, the flat plates forming substantially square cells; a plurality of deflectors formed integrally only with the flat plates of the intermediate grids, wherein each deflector is oriented at an angle to the vertical, and wherein each cell of the intermediate grid has only two opposing deflectors, wherein the top and bottom grids have no deflectors; each cell of each grid having a single insertable spacer having a substantially octagonal and axially symmetrical shape, the single insertable spacer having a closed contour in a cross-sectional view, the single insertable spacer formed of four convex surfaces and four concave surfaces, the four concave surfaces being in contact with the corresponding flat plates, and the four convex surfaces each having a flat portion that is in contact with the corresponding fuel rod and which is flat prior to insertion of the fuel rods, wherein opposite longitudinal surfaces of the single insertable spacer are parallel to each other, and wherein the single insertable spacer has no openings on its longitudinal surface.