Abstract: A nuclear reactor core assembly includes a support plate having a plurality of inlets for channeling water to a core lattice fixedly joined thereto. The lattice includes a plurality of flow channels, each including a respective separately removable fuel bundle. In a preferred embodiment, the core lattice includes a plurality of flow dividers joined together for allowing unrestrained expansion and contraction thereof, and which prevent crossflow of water therebetween.

Abstract: Fresh fuel bundles are inserted into core locations with small coolant flow orifices, while mid-life fuel bundles are inserted into core locatiosn with large coolant flow locations. Thus, fissile fuel production is promoted at the expense of fissioning early in a bundle lifetime, increasing the effective quantity of fuel available for energy production. Moreover, fissioning is promoted at the expense of conversion later in the bundle lifetime to enhance reactivity of the remaining fissile material and to minimize the further production of fissile fuel. The net result is longer fuel lifetimes and reduced radioactive waste.

Abstract: Fuel assemblies of a boiling-water nuclear reactor are inverted during refueling methods. Assemblies burned in a first orientation are subjected to greater burnup near their bottoms and greater conversion of fertile fuel to fissile fuel near their tops. Inverting the assemblies promotes burnup of the actinide products from the conversion of the last cycle. Thus, the procedure greater energy production efficiency and reduced actinide radioactive waste are achieved. One inverted fuel assemblies can be removed for disposal. Alternatively, they can be reinverted to burnup actinide fissile fuel generated at the bottom (while it was downstream of the top) during the second operating cycle. Further inversions are provided for, but the major gains occur during the first and second inversions.