Patent Number: 
Section: claims

1. A spacer for nuclear fuel rods of a nuclear fuel assembly comprising: a plurality of sets of two horizontally extending parallel grid strips, a first of the two horizontally extending parallel grid strips being substantially flat and a second of the two horizontally extending parallel grid strips having undulations along its length to form both a vertical flow channel between the first of the two horizontally extending parallel grid strips and the second of the two horizontally extending parallel grid strips and a nozzle connected to the vertical flow channel, the nozzle positioned to produce a swirling motion of coolant and to have non-opposing flow paths in flow channels, the plurality of sets of two horizontally extending parallel grid strips arranged to intersect one another to form a lattice of polygonal shaped cells through which nuclear fuel rods extend and which support the fuel rods positioned asymmetrically within the cells. 2. A nuclear fuel assembly for pressurized water reactors, the assembly having a plurality of elongated fuel rods supported between a lower tie plate positioned toward the bottom of the assembly and an upper tie plate positioned toward the top of the assembly; at least one spacer for positioning and retaining the fuel rods, the spacer comprising: a plurality of sets of two horizontally extending parallel grid strips, a first of the two horizontally extending parallel grid strips being substantially flat and a second of the two horizontally extending parallel grid strips having undulations along its length to form both a vertical flow channel between the first of the two horizontally extending parallel grid strips and the second of the two horizontally extending parallel grid strips and a nozzle connected to the vertical flow channel, the nozzle positioned to produce a swirling motion of coolant and to have non-opposing flow paths in flow channels, the plurality of sets of two horizontally extending parallel grid strips arranged to intersect one another to form a lattice of polygonal shaped cells through which nuclear fuel rods extend and which support the fuel rods positioned asymmetrically within the cells.