PURPOSE: To increase joint strength by welding and fixing cylindrical reinforcing members to the top and bottom ends of at least a part of intersected parts of straps in such a manner that the central line thereof and the intersected point of straps coincide.

CONSTITUTION: The reinforcing members 11 and 12 are welded and fixed to the front face side and rear face side in the intersected parts of the straps positioned near the inside pipe of a control rod. The members 11, 12 are formed by cutting metallic pipes consisting of the material such as zircalloy similar to the outside diameter at which the members do not come into contact with the fuel rods to be inserted into the grid spaces and to the thickness approximately equal to the thickness of the straps 10. The intersected parts of the straps are reinforced by the members 11, 12 respectively welded at 4 points on one side and, therefore, the joint strength of such supporting grid is increased and the buckling, etc., of the straps 10 during use are decreased.