Abstract: 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.

Abstract: 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.

Abstract: A nuclear reactor instrumentation system including a plurality of incore nuclear instrumentation assemblies arranged in a gap between a number of fuel assemblies charged in a reactor core. The incore nuclear instrumentation assemblies each include a fixed type neutron detector having a plurality of fixed type neutron detectors dispersively arranged in a core axial direction and a fixed type gamma thermometer assembly having a plurality of fixed type gamma ray heat detectors arranged at least in a same core axial direction as the fixed type neutron detectors. A power range detector signal processing device operatively connected to the fixed type neutron detector assemblies through signal cables. A gamma thermometer signal processing device is operatively connected to the fixed type gamma thermometer assembly of the incore nuclear instrumentation assembly through a signal cable.

Abstract: A reactor nuclear instrumentation system comprises: a plurality of incore nuclear instrumentation assemblies arranged in a gap between a number of fuel assemblies charged in a reactor core, the incore nuclear instrumentation assemblies each including a fixed type neutron detector assembly comprising a plurality of fixed type neutron detectors dispersively arranged in a core axial direction and a fixed type gamma thermometer assembly comprising a plurality of fixed type &ggr;-ray heat detectors arranged at least in a same core axial direction as the fixed type neutron detectors; a power range detector signal processing device operatively connected to the fixed type neutron detector assemblies through signal cables; and a gamma thermometer signal processing device operatively connected to the fixed type gamma thermometer assembly of the incore nuclear instrumentation assembly through a signal cable.

Abstract: A nuclear reactor instrumentation system including a plurality of in core nuclear instrumentation assemblies arranged in a gap between a number of fuel assemblies charged in a reactor core. The income nuclear instrumentation assemblies each include a fixed type neutron detector assembly having a plurality of fixed type neutron detectors dispersively arranged in a core axial direction and a fixed type gamma thermometer assembly having a plurality of fixed type gamma ray heat detectors arranged at least in a same core axial direction as the fixed type neutron detectors. A power range detector signal processing device is operatively connected to the fixed type neutron detector assemblies through signal cables. A gamma thermometer signal processing device is operatively connected to the fixed type gamma thermometer assembly of the in core nuclear instrumentation assembly through a signal cable.

Abstract: A fuel assembly for a nuclear reactor includes a number of fuel rods filled with a fuel material. A plurality of fuel rods have a partial effective fuel area filled with a fuel material and has a portion in which enrichment of a fissile nuclide is significantly reduced or the fissile nuclide does not exist at all on an axial level including a reactor shut-down zone at which subcriticality becomes small during a reactor operation period. The other fuel rods are filled with the fuel material throughout the entire axial length thereof. The first mentioned fuel rod may be provided with a partially interposed zone or may be constructed by a fuel rod having a length shorter than that of the other fuel rod. The tube means may be arranged in the fuel assembly so as to pass the moderator therethrough.

Abstract: A fuel assembly for a nuclear reactor comprising a number of fuel rods arranged in a regular fashion in a channel box which is surrounded by water gap in a reactor core. Some of fuel rods disposed at portions facing the water gap through which no control blade is inserted or drawn out, have atomic number densities of fissionable material contained in the fuel rods. The atomic number density of each of these fuel rods is made smaller than that of the fuel rod disposed in the fuel assembly at portions other than the portions referred to above.