Patent ID: 6335956
Filing Date: 2002-01-01
Classification: G21C,Y02E

Abstract:
A fuel assembly comprising:a plurality of fuel rods including a plurality of short-length fuel rods shorter in length than others of said fuel rods and a plurality of long-length fuel rods, said long-length fuel rods having burnable poison rods with burnable poison and fissionable material and fissionable material rods with no burnable poison and fissionable material, said plurality of fuel rods being arranged in a square grid pattern of 9-columns/9-rows or more; and at least one neutron moderator rod; wherein each of said short-length fuel rods is arranged at a position other than in 3-columns/3-rows regions at four corner portions in such a manner as not to be simultaneously adjacent to said at least one neutron moderator rod and others of said short-length fuel rods in the four directions of front and rear and right and left; said burnable poison rods are arranged at positions excluding the outermost periphery; the number of those, of said burnable poison rods, containing burnable poison in a region upward from upper ends of said short-length fuel rods and adjacent to said short-length fuel rods in said four directions of front and rear and right and left is one-half or less the total number of said burnable poison rods; and at a transverse cross-section of the region upward from upper ends of said short-length fuel rods, the amount of burnable poison contained in a polygonal region, whose vertexes are located at centers of those of said short-length fuel rods arranged at the outermost layer is smaller than the amount of burnable poison outside said polygonal region; wherein fuel rods being adjacent to said short-length fuel rods in said four directions of front and rear and right and left and being arranged at the outermost periphery are adjacent to one of said burnable poison rods in said four directions of front and rear and right and left.