Patent Number: 
Section: claims

1. A spacer grid provided in a lower end of a nuclear fuel assembly, the spacer grid comprising:a plurality of grid strips assembled in a lattice pattern; anda plurality of grid cells formed by the plurality of grid strips,wherein a section of each of the grid strips, corresponding to each grid cell of the plurality of grid cells, includesa first set of holes disposed in a top portion of the section, formed in a planar surface of the section and including two or more holes arranged in a lateral direction perpendicular to a fuel rod, said two or more holes of the first set of holes having a circular shape and a same size with each other and clearly open to an adjacent grid cell,a dimple supporting the fuel rod and having slits formed in the lateral direction and arc-shape portions protruding inwards or outwards between the slits, the dimple being disposed below the first set of holes,a second set of holes disposed below the dimple and formed in a planar surface of the section, the second set of holes including two or more holes arranged in the lateral direction along the slits of the dimple and clearly open to an adjacent grid cell, said two or more holes of the second set of holes having a circular shape and having a same size with each other, anda filtering part disposed below the second set of holes for filtering out foreign substances and having slits formed in the lateral direction and arc-shape portions protruding inwards or outwards between the slits of the filtering part,wherein the first set of holes, the dimple, the second set of holes and the filtering part are arranged in this order from the top portion to a bottom portion of the section,wherein the first and second set of holes are respectively formed separately from the slits surrounding the dimple and the filtering part, andwherein the first and second set of holes cause a damping effect, by reducing a pressure difference between opposite sides of the holes and by generating friction between cut edges of the holes and a coolant, when the coolant is drawn into the fuel assembly. 2. The spacer grid as set forth in claim 1, further comprisinga third set of holes disposed below the filtering part and formed in a planar surface of the section, the third set of holes including two or more holes arranged in the lateral direction along the slits of the filtering part and clearly open to an adjacent grid cell, said two or more holes of the third set of holes having a circular shape and having a same size with each other.