Partial grid for a nuclear reactor fuel assembly

In a nuclear reactor fuel assembly including a plurality of elongated fuel rods disposed in a generally parallel array, a number of longitudinally extending control rod guide thimbles strategically arranged within said fuel rod array and a plurality of transversely extending fuel rod support grids axially spaced along and mounted to said guide thimbles, said support grids supporting and encompassing all of said fuel rods in said fuel assembly, the improvement which comprises:

• at least two partial grid structures extending transversely across and each encompassing less than all of said fuel rods, said partial grid structures being so mounted on selected ones of said guide thimbles such that an inner border of one of said grid structures is disposed in abutting engagement with an inner border of the other one of said grid structures, each of said grid structures including a plurality of interleaved straps arranged in an egg-crate configuration in defiing a plurality of cell openings for receiving therethrough respective ones of a group of fuel rods defined by a predetermined number of said plurality of fuel rods being less than the total number thereof in said fuel assembly.

In a nuclear reactor fuel assembly including a plurality of elongated fuel rods disposed in a generally parallel array wherein each fuel rod in a first group of fuel rods defined by a predetermined number of said plurality of fuel rods being less than the total number thereof has a first diameter and each fuel rod in a second group of fuel rods defined by a predetermined number of said plurality of fuel rods being less than the total number thereof has a second diameter greater than said first diameter, a grid assembly comprising:

• (a) a first grid structure encompassing less than all of said fuel rods in said fuel assembly and including a plurality of interleaved straps arranged in an egg-crate configuration in defining a plurality of cell openings for receiving therethrough respective ones of said fuel rods in said first fuel rod group;
• and
• (b) a second grid structure encompassing less than all of said fuel rods in said fuel assembly and including a plurality of interleaved straps arranged in an egg-crate configuration in defining a plurality of cell openings for receiving therethrough respective ones of said fuel rods in said second fuel rod group.

In a nuclear reactor fuel assembly including a plurality of elongated fuel rods disposed in a generally parallel array, a number of longitudinally extending control rod guide thimbles strategically arranged within said fuel rod array and a plurality of transversely extending fuel rod support grids axially spaced along and mounted to said guide thimbles, said support grids supporting and encompassing all of said fuel rods in said fuel assembly, the improvement which comprises:

• at least one partial grid structure extending transversely across and encompassing less than all of said fuel rods, said partial grid structure being mounted on selected ones of said guide thimbles and including a plurality of interleaved straps arranged in an egg-crate configuration in defining a plurality of cell openings for receiving therethrough respective ones of a group of fuel rods defined by a predetermined number of said plurality of fuel rods being less than the total number thereof in said fuel assembly.