Abstract: An improved annular burnable poison pellet of aluminum oxide-boron carbide (Al.sub.2 O.sub.3 --B.sub.4 C) adapted for positioning in the annular space of concentrically disposed zircaloy tubes. Each tubular pellet is fabricated from Al.sub.2 O.sub.3 powders of moderate sintering activity which serves as a matrix for B.sub.4 C medium size particle distrbution. Special pellet moisture controls are incorporated in the pellet for moisture stability and the pellet is sintered in the temperature range of 1630.degree.-1650.degree. C. This method of fabrication produces a pellet about 2 inch long with a wall thickness of about 0.020 inch to 0.040 inch. Fabricating each pellet to about 70% theoretical density gives an optimum compromise between fabricability, microstructure, strength and moisture absorption.

Abstract: A nuclear reactor fuel assembly spacer grid. The grid straps form an egg crate configuration creating standard cells to enclose the fuel rods. The standard cells have at least one of their straps with an integral spring portion extending into the standard cell and pushing against the fuel rod. A distinct backup spring is positioned transverse to and behind each of the spring portions of the straps and is positioned so as not to touch the fuel rods. The straps are made of a material having a low neutron capture cross-section while the backup spring is made of a material having good radiation stress relaxation properties.

Abstract: A burnable poison rod for use in a nuclear reactor fuel assembly which includes concentrically disposed rods having an annular space therebetween which extends the full length of the rods. The inner rod is hollow to permit circulation of coolant therethrough. Annular burnable poison pellets are positioned in the annular space which is closed at both ends by plugs. A spring clip is located in the plenum space above the pellet stack in the rods. The spring clip is of cylindrical configuration having a gap in the material which provides two ends adapted to be squeezed toward each other. A cross section of the clip shows that its ends contain alternating flat and round edges, the round edges conforming to the outer rod inner surface to provide a retentive force which is releasably applied to the pellet stack as it grows during operation in a reactor.

Abstract: A composite nozzle for a fuel assembly adapted for installation on the upper or lower end thereof and which is constructed from two components. The first component includes a casting weldment or forging designed to carry handling loads, support fuel assembly weight and flow loads, and interface with structural members of both the fuel assembly and reactor internal structures. The second component of the nozzle consists of a thin stamped bore machine flow plate adapted for attachment to the casting body. The plate is designed to prevent fuel rods from being ejected from the core and provide orifices for coolant flow to a predetermined value and pressure drop which is consistent with the flow at other locations in the core.