Abstract: Modular neutron reflector assemblies removably insertable into the irregular space in a nuclear reactor between a generally cylindrical array of square fuel assemblies comprising the core and the cylindrical core barrel surrounding the core, include an elongated enclosure having a strongback adjacent the core barrel and flat plates adjacent the fuel assemblies. The strongback is thicker than the steel plates by an amount which results in the strongback and plates reaching approximately the same temperature to minimize thermal stresses despite the 8 to 20 times greater nuclear heating at the core side of the enclosure as opposed to that at the core barrel side. The enclosure is suspended by a single point mounting on the core barrel which permits vertical, radial, and circumferential expansion but a pin depending from the lower end of the enclosure slides in a vertical bore in the reactor lower core support plate to limit lateral movement while allowing unrestrained vertical expansion and contraction.

Abstract: A holddown spring retention assembly for use in a nuclear reactor having a pressure vessel, a core barrel having an upper outwardly extending flange, an inner barrel having an upper outwardly extending flange and an annular holddown spring, the barrels and the spring being installed in the pressure vessel during normal operation, with the inner barrel flange disposed above the core barrel flange and the holddown spring interposed between the core barrel flange and the inner barrel flange, the holddown spring retention assembly is composed of a plurality of assembly units disposed around the periphery of the holddown spring, each unit including a lift lug secured to the outer periphery of the spring and having at least one outwardly radially projecting portion and a hanger secured to the inner barrel flange and having a lower portion suspended below the inner barrel flange and below the radially projecting portion of the lift lug means; the lower portion being arranged to support the radially projecting portio

Abstract: A mechanical drive system (10) for moving alternate nuclear reactor fuel rods (14) within the nuclear reactor core (12) and relative to the remaining stationary nuclear reactor fuel rods (16) so as to axially displace the movable fuel rods (14), and enriched and natural uranium fuel zones defined therein, relative to similarly defined enriched and natural uranium fuel zones within the stationary fuel rods (16) in order to optimize utilization of excess or free neutrons produced within the nuclear reactor core within a fuel cycle. The nuclear reactor fuel rods (14, 16) all have a length which is less than that of standard-sized nuclear reactor fuel rods, and therefore, a plenum chamber (20) is able to be defined between an upper core plate (22) and an auxiliary upper core plate (24).