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 control rod position detector including a permanent magnet that is attached on a control rod inserted in a reactor pressure vessel, where the permanent magnet is capable of moving together with the control rod, and a plurality of reed switch mechanisms that are arranged in the reactor pressure vessel at regular intervals in an insertion direction of the control rod. Each of the reed switch mechanisms is provided with a pair of reed switches that are placed so as to overlap with each other in the insertion direction of the control rod. The pair of reed switches are connected to a common wiring. The common wiring is connected to a detector that detects a position of the control rod based on signals from the reed switches.

Abstract: The object of the present invention is to provide a control rod position detector that is capable of avoiding and preventing a situation which makes impossible a detection of a position of a control rod inserted in a reactor pressure vessel. A control rod position detector of the present invention includes: a permanent magnet 10 that is attached on a control rod 4 inserted in a reactor pressure vessel 1, the permanent magnet 10 being capable of moving together with the control rod 4; and a plurality of reed switch mechanisms 31 that are arranged in the reactor pressure vessel 1 at regular intervals in an insertion direction of the control rod 4, the reed switch mechanisms 31 being operated by a magnetic flux of the permanent magnet 10. Each of the reed switch mechanisms 31 is provided with a pair of reed switches 13 and 14 that are placed so as to overlap with each other in the insertion direction of the control rod 4. The pair of reed switches 13 and 14 are connected to a common wiring 11.