Patent Number: 048448621
Section: claims

1. A spacing grid assembly for a nuclear fuel assembly, comprising: a plurality of plates disposed in two directions at least for defining cells having a predetermined mutual spacing and formed with windows distributed at even intervals corresponding to the mutual spacing of said cells, and  a plurality of hairpin springs each consisting of a metal strip bent to form two mutually confronting legs welded together through said windows,  wherein the cross-section of one of said legs of each of said hairpin springs in a direction perpendicular to said legs of the respective one of the hairpin springs has a U shape in a zone bearing on the other leg of the hairpin spring through a respective one of said windows and said U has a width slightly greater than the width of the other leg in the same zone so as to receive said other leg. 2. The spring as claimed in claim 1, wherein the U has a lateral size which corresponds to the width of the windows to be received therein. 3. The spacing grid as claimed in claim 1, wherein said springs are of a material retaining resiliency after irradiation and said plates are of an alloy having a low neutron capture cross-section as compared with said material. 4. The spacing grid as claimed in claim 1, wherein said other leg has a locally decreased width in said zone, so that the lateral size of the U corresponds to that of the remainder of the spring. 5. A hairpin spring for use in holding a fuel rod in position in a fuel assembly grid, consisting of an elongated metal strip having a 180.degree. bend to form two mutually confronting legs each having a zone of limited extent in the direction of elongation which bears on a mating zone of the other, said zones being arranged to be welded together locally and wherein one of said legs only has a U shape in its said zone and said U shape has a width slightly greater than the width of the other leg in the respective zone so as to receive said other leg in flat contact abutment. 6. The spring as claimed in claim 5, wherein the U has a widening shape for self-centering of the other leg. 7. A hairpin spring for use in holding a fuel rod in position in a fuel assembly grid, consisting of a metal strip bent to form two mutually confronting legs arranged to be welded together locally, wherein one of said legs has two lateral appendices bent substantially at 90.degree. which impart to said one of the legs a U shape, at least in a zone which bears on the other leg and said U shape has a width slightly greater than the width of the other leg in the same zone so as to receive said other leg. 8. The spring as claimed in claim 7, wherein the appendices of the U close up slightly so that the other leg can snap therebetween. 9. The spring as claimed in claim 7, wherein said other leg has portions for progressive merging of a current part and the portion of reduced width retained by the U.