Grid with mixing fins for a nuclear fuel assembly

In a nuclear fuel assembly having fuel elements, a spacing grid with mixing fins comprising two intersecting sets each consisting of a plurality of metal plates defining pockets distributed at the nodal points of a square network, the improvement wherein said plates comprise solely half-fins each relating to a single pocket of the grid, disposed in opposed pairs at the angles of the pockets, the half-fins of one pocket being placed at 90.degree. from the half-fins of adjacent pockets, and wherein hydraulic cells are each defined by the fuel elements occupying four adjacent pockets and each cell has only a single half-fin, orthogonal to the half-fins placed in the nearest hydraulic cells.