A fuel assembly for a nuclear power boiling water reactor including a fuel channel defining a central fuel channel axis, fuel rods, each having a central fuel rod axis, at least 3 water channels for non-boiling water, each water channel having a central water channel axis and each water channel having a larger cross-sectional area than the cross-sectional area of (the average) fuel rod. The fuel rods include a first group of full length fuel rods and a second group of shorter fuel rods. The fuel assembly comprises 3 or 4 fuel rods which belong to said second group and which are positioned such that the central fuel rod axis of each of these 3 or 4 fuel rods is closer to the central fuel channel axis than any of the water channel axes of the water channels.

A fuel assembly for a nuclear power boiling water reactor including a fuel channel defining a central fuel channel axis, fuel rods, each having a central fuel rod axis, at least 3 water channels for non-boiling water, each water channel having a central water channel axis and each water channel having a larger cross-sectional area than the cross-sectional area of (the average) fuel rod. The fuel rods include a first group of full length fuel rods and a second group of shorter fuel rods. The fuel assembly comprises 3 or 4 fuel rods which belong to said second group and which are positioned such that the central fuel rod axis of each of these 3 or 4 fuel rods is closer to the central fuel channel axis than any of the water channel axes of the water channels.

Light water reactor fuel assemblies each comprises: light water reactor fuel rods that extend longitudinally, contain nuclear fuel materials including enriched uranium, and are arranged parallel to each other; and burnable poison containing fuel rods that extend longitudinally, contain nuclear fuel materials whose main component is uranium that is lower in enrichment than the enriched uranium of the light water reactor fuel rods, and burnable poison, and are arranged in a lattice pattern together with the light water reactor fuel rods. The assemblies are arranged parallel to each other and in a lattice pattern. An initial value of a first enrichment of the enriched uranium is set in such a way that the first enrichment of the enriched uranium at an end of each operation cycle is greater than a predetermined value.

Light water reactor fuel assemblies each comprises: light water reactor fuel rods that extend longitudinally, contain nuclear fuel materials including enriched uranium, and are arranged parallel to each other; and burnable poison containing fuel rods that extend longitudinally, contain nuclear fuel materials whose main component is uranium that is lower in enrichment than the enriched uranium of the light water reactor fuel rods, and burnable poison, and are arranged in a lattice pattern together with the light water reactor fuel rods. The assemblies are arranged parallel to each other and in a lattice pattern. An initial value of a first enrichment of the enriched uranium is set in such a way that the first enrichment of the enriched uranium at an end of each operation cycle is greater than a predetermined value.

A method of producing a light water reactor fuel assembly may include: setting conditions at least concerning an operation cycle period and burnup; setting an initial enrichment of enriched uranium; calculating excess reactivity of a light water reactor core where light water reactor fuel assemblies including the enriched uranium are burned until an end stage of a final operation cycle; determining whether a condition where excess reactivity at an end of a first operation cycle in the burnup calculation step is close to a predetermined positive value is true or not; and returning to the setting of the initial enrichment, when it is determined at the determining that the situation is not true, or deciding an enrichment of the enriched uranium when it is determined that the situation is true.

A method of producing a light water reactor fuel assembly may include: setting conditions at least concerning an operation cycle period and burnup; setting an initial enrichment of enriched uranium; calculating excess reactivity of a light water reactor core where light water reactor fuel assemblies including the enriched uranium are burned until an end stage of a final operation cycle; determining whether a condition where excess reactivity at an end of a first operation cycle in the burnup calculation step is close to a predetermined positive value is true or not; and returning to the setting of the initial enrichment, when it is determined at the determining that the situation is not true, or deciding an enrichment of the enriched uranium when it is determined that the situation is true.

Fuel bundles for nuclear reactors are provided, and can include a fuel element containing U-233, U-235, PU-239, and/or PU-241 fissile material, along with at least two neutron absorbers consisting of Gd, Dy, Hf, Er, and/or Eu, wherein the fissile material(s) and the at least two neutron absorbers are homogeneously mixed in the fuel element. Fuel bundles for nuclear reactors are also provided that include fuel elements having inner elements and outer elements, wherein at least one of the inner elements includes a homogeneous mixture of a fissile material and at least two neutron absorbers. Fuel elements for nuclear reactors are also provided, and can include U-233, U-235, PU-239, and/or PU-241 fissile material, along with at least two neutron absorbers consisting of Gd, Dy, Hf, Er, and/or Eu, wherein the fissile material(s) and the at least two neutron absorbers are homogeneously mixed in the fuel element.

Fuel bundles for nuclear reactors are provided, and can include a fuel element containing U-233, U-235, PU-239, and/or PU-241 fissile material, along with at least two neutron absorbers consisting of Gd, Dy, Hf, Er, and/or Eu, wherein the fissile material(s) and the at least two neutron absorbers are homogeneously mixed in the fuel element. Fuel bundles for nuclear reactors are also provided that include fuel elements having inner elements and outer elements, wherein at least one of the inner elements includes a homogeneous mixture of a fissile material and at least two neutron absorbers. Fuel elements for nuclear reactors are also provided, and can include U-233, U-235, PU-239, and/or PU-241 fissile material, along with at least two neutron absorbers consisting of Gd, Dy, Hf, Er, and/or Eu, wherein the fissile material(s) and the at least two neutron absorbers are homogeneously mixed in the fuel element.

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.

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.