Grid having mixing fins for a nuclear fuel assembly

A nuclear fuel assembly having a bundle of mutually parallel fuel elements and a support structure including guide tubes and a plurality of grids, wherein each one of only some of said grids comprise at least two sets of crossed plates fixed together at their cross-points and defining cells distributed in a regular array, some for receiving fuel rods and the others for receiving guide tubes, the plates being provided with coolant stirring fins extending the plates downstream and disposed to deflect the coolant transversely to its general flow direction, each plate being provided with abutment means projecting inwardly from each of the sides of those cells which are to receive fuel rods, thereby defining a passage that is larger than the size of the rods but small enough to prevent a rod contained in the cell coming into contact with the fins, wherein said abutment means comprise, in each plate separating two cells other than peripheral which receives a rod, two portions of said plate that are cut out and deformed into two scoops, and that are mutually offset in the coolant flow direction, said scoops projecting in mutually opposite directions and tending to cause coolant to pass from one cell to another across said plate.

A mixing grid for a nuclear fuel assembly, said mixing grid comprising two sets of crossed plates fixed together at their cross-points and defining cells distributed in a regular array, some of said cells for receiving fuel rods and the others for receiving guide tubes, wherein said plates are formed with coolant mixing fins extending the plates on their downstream side and angularly disposed with respect to said plates to deflect coolant transversely to its general flow direction along the fuel rods;

• wherein each of said plates further comprises abutment means projecting inwardly from each of the sides of those cells which are to receive fuel rods by such amounts that they define in each said cell a passage that is larger than the size of the rod but small enough to prevent the rod contained in the cell from coming into contact with the respective fins;
• and wherein said abutment means comprise, in each portion of one of said plates which separates two cells which each receives one fuel rod, except peripheral cells, two cut out portions of said plate mutually offset in the coolant flow direction, projecting in mutually opposite directions and forming scoops having mutually confronting openings separated by a slot formed in the plate transversely to the general coolant flow direction.