A spacer grid of a nuclear fuel assembly having a simple shape structure is proposed. The spacer grid includes square grid cells having respective inner walls and constituting a square lattice structure. Each of the grid cells includes a plurality of springs for elastically supporting a fuel rod. Each of the plurality of the springs has a fixed end along a vertical direction on each of the inner walls and a free end curvedly provided in a horizontal direction from the fixed end. The grid cells also include a plurality of flow channels each provided in the vertical direction to each of the grid cells and a plurality of mixing vanes each protrudingly provided in a downstream direction of cooling water flow at end parts of each of the grid cells.

A fuel rod support insert for a nuclear fuel assembly spacer grid, a spacer grid and a nuclear fuel assembly are provided. The support insert is for a nuclear fuel assembly spacer grid comprising interlaced straps defining a lattice of cells for receiving fuel rods, the insert being adapted to be secured to the straps for extending in at least one cell. The insert extends along an axis intended to be parallel to that of a cell and comprises two axially spaced end portions for connecting the insert to the straps and at least one elongated blade-like spring extending axially between the end portions for supporting a fuel rod. The spring has a non-rectilinear cross-section in each plane perpendicular to the insert axis.