An advanced initial core fuel configuration is for improving the fuel management efficiency and thus economics for a nuclear reactor. The advanced initial core fuel configuration includes a plurality of fuel assemblies having different average enrichments of uranium 235 and arranging the fuel assemblies in an initial core configuration structured to emulate a known equilibrium reload cycle core at least in terms of spatial reactivity distribution. The resulting average enrichment within the initial core ranges from below about 1.0 percent weight of uranium 235 to about 5.0 percent weight of uranium 235. An advanced lattice design is also disclosed.

Fuel elements having distinct zones or concentration gradients of fuel material along the axial direction, the radial direction, or both the axial and radial direction. An additive manufacturing process may be used to produce the fuel elements. The additive manufacturing process may facilitate production of the distinct zone or concentration gradient arrangement of the fuel elements, and may further allow both fuel and non-fuel material to be incorporated into any of the zones or within the gradients.

Thorium-based fuel bundles according to one or more embodiments of the present invention are used in existing PHWR reactors (e.g., Indian 220 MWe PHWR, Indian 540 MWe PHWR, Indian 700 MWe PHWR, CANDU 300/600/900) in place of conventional uranium-based fuel bundles, with little or no modifications to the reactor. The fuel composition of such bundles is 60+ wt % thorium, with the balance of fuel provided by low-enriched uranium (LEU), which has been enriched to, according to one or more embodiments, 13-19.95% .sup.235U. According to various embodiments, the use of such thorium-based fuel bundles provides (1) 100% of the nominal power over the entire life cycle of the core, (2) high burnup, and (3) non-proliferative spent fuel bundles having a total isotopic uranium concentration of less than 12 wt %. Reprocessing of spent fuel bundles is also avoided.

In a fuel assembly, a plurality of fuel rods are arranged in an array of 10 rows and 10 columns in the cross section of the fuel assembly. A flow resistance member is disposed in a central portion in the cross section at upper end portions of partial length fuel rods which are a part of the fuel rods. In the flow resistance member, resistance members are each disposed between ferrules arranged in an array of 6 rows and 6 columns in the diagonal direction of the flow resistance member. Resistance members are each disposed between the ferrules in a peripheral portion of the flow resistance member. By disposing the resistance members, the pressure loss in an inner region in the cross section of the fuel assembly is increased, and the flow rate of a gas-liquid two-phase flow in an outer region surrounding the inner region is increased.

A fuel assembly includes a plurality of elongated fuel elements. Each of the plurality of fuel elements has a spirally twisted, multi-lobed profile that defines a plurality of spiral ribs. Each of the plurality of fuel elements has a fuel kernel that includes fuel material disposed in a matrix of metal non-fuel material. The fuel material includes fissile material. A cladding surrounds the fuel kernel. A moderator: fuel ratio in a region of the fuel elements is 2.4 or less. The moderator: fuel ratio is an area ratio within a cross-section that is perpendicular to longitudinal axes of the plurality of fuel elements and extends through the plurality of fuel elements. The area ratio is a ratio of: (1) a total area available for moderator flow for the plurality of fuel elements to (2) a total area of the fuel kernels of the plurality of fuel elements.