Abstract: A top nozzle is for a fuel assembly of a nuclear reactor. The top nozzle includes a plate portion having a first plurality of apertures structured to receive guide thimbles of the fuel assembly and second and third pluralities of apertures which comprise first and second coolant holes structured to provide passage of a coolant fluid therethrough. The first and second coolant holes have different first and second cross-sectional shapes, respectively. The top nozzle and plate portion preferably comprise a single-piece casting in which numerous features, such as the first and second holes are as-cast, thus reducing production costs. The coolant holes preferably comprise a one-eighth-symmetric coolant hole pattern. The as-cast nature of the coolant holes permits the ligaments between coolant holes to be reduced in thickness, thereby increasing coolant flowthrough area and minimizing the pressure drop across the nozzle.

Abstract: A nuclear fuel assembly having a parallel array of elongated fuel elements supported between an upper and lower nozzle. Main support grids are substantially evenly spaced along the elongated dimension of the assembly to maintain the spacing between fuel elements. A plurality of auxiliary vibration-resistant grids respectively positioned between the main support grids in the middle third elongated dimension of the fuel elements, that are smaller in height and provide a larger fuel element contact area than the main support grids.