Patent Number: 
Section: claims

1. A grid for a nuclear fuel rod assembly, the grid comprising:a plurality of perpendicularly flat plates, the flat plates forming substantially square cells;a plurality of deflectors formed integrally with the flat plates, wherein each deflector is oriented at an angle to a longitudinal axis of the grid, and wherein each cell has at least two opposing deflectors;each cell having an insertable spacer having a substantially octagonal shape that is [s]ymmetric about a center axis of the cell, the insertable spacer having a constant height along its perimeter, and a uniform cross-section along its height, the insertable spacer having a closed contour in a cross-sectional view, the 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 for fixing a corresponding fuel rod and which is flat prior to insertion of the fuel rods,wherein opposite longitudinal surfaces of the insertable spacer are parallel to each other. 2. The spacing grid of claim 1, wherein a length of each cell is between 28 and 34 mm. 3. The spacing grid of claim 1, wherein a length of the spacer is between 0.3 and 0.9 of a length of each cell. 4. The spacing grid of claim 1, wherein the spacer is formed as a unitary element. 5. The spacing grid of claim 1, wherein the spacer has no openings along its body. 6. The grid of claim 1, wherein each concave surface has a flat portion in contact with a corresponding flat plate. 7. The grid of claim 1, wherein the insertable spacers are formed as tubular elements with a substantially octagonal cross-section.