Double strip mixing grid for nuclear reactor fuel assemblies

Abstract

A double strip mixing grid for nuclear reactor fuel assemblies is disclosed. This grid is fabricated by intersecting at right angles a plurality of double strips, each fabricated by welding two thin sheets together into a single structure with coolant channels. The mixing grid, having the channels, effectively mixes low temperature coolant with high temperature coolant within a fuel assembly, thus improving the thermal efficiency of the fuel assemblies. This mixing grid also effectively prevents the coolant from being partially overheated, thus improving the soundness of nuclear reactors. This mixing grid also has swirling flow blades and/or lateral flow blades to further improve the thermal efficiency of the fuel assembly. This mixing grid elastically supports the fuel rods by the sheets of the double strips, collaterally acting as positioning springs. Each double strip also has a vertical slot at a position around each channel, and so the elastic range of the positioning springs of the grid is preferably enlarged. The slots also enlarge the fuel rod contact area of the grid, thereby effectively protecting the fuel rod from fretting corrosion. In addition, the intersecting strips are welded together at the intersections through a continuous welding process, thus improving the mechanical strength of the grid.