LOWER TIE-PLATE LATTICE AS UNITARY BODY IN NUCLEAR FUEL ASSEMBLY, FUEL-ROD SUPPORTING STRUCTURE IN NUCLEAR FUEL ASSEMBLY AND NUCLEAR FUEL BUNDLE AND SUPPORTING DEVICE THEREOF

PURPOSE: To provide an integral lower tie plate, by which passage of broken pieces mixed in a moderator flow passing through a grid is restricted and a pressure loss can be minimized at the same time, in a nuclear fuel assembly. CONSTITUTION: An integral lower tie plate grid 16 is provided with a lower part, 26, which supports a fuel rod, and an upper part 28. The lower tie plate grid 16 extends upward from the grid lower part 26 and comprises a plurality of cylindrical boss parts 36 which are arranged in a square matrix shape so as to support a lower end plug of the fuel rod. A plurality of web parts 38 extending upward from the grid lower part 26 connect the boss parts 36 mutually along the side of the square matrix. The grid lower part 26 includes a plurality of openings, which are connected to flow spaces formed by means of the projection parts of the boss and the web parts 38 in the respective square matrix in the grid upper part 28. The opening, in which roundness of a certain radius is provided in the lower adjacent part while a side wall spreading toward the downstream of a throat area is provided, dividedly forms a venturi.