Patent Number: 048045160
Section: claims

1. In a nuclear reactor having a vessel for containment of a moderating and cooling pressurized water, a core in said vessel, arranged to be upwardly traversed by said water and comprising a plurality of mutually adjacent upstanding nuclear fuel assemblies, a nuclear fuel assembly comprising: 2. A nuclear fuel assembly according to claim 1, wherein the upper grids of the upper set of grids are provided with flow mixing fins, the lower grids of the lower set of grids are devoid of fins, and said nuclear fuel assembly further comprises a top grid located between the upper set of grids and the upper end piece of the nuclear fuel assembly and devoid of fins. 3. A nuclear fuel assembly according to claim 1, wherein the first predetermined distance between the upper grids has a value within the range of 15 to 30 cm. 4. A nuclear fuel assembly according to claim 1, wherein the upper grids comprise a peripheral belt and at least two series of parallel plates, the plates of one serie being of an angle with the plates of the other so that the series define passage cells for the fuel elements, said parallel plates being distributed in at least two beds spaced in the longitudinal direction of the assembly, and being provided with fins having different orientations.