A separating and coupling system of a nuclear fuel assembly top nozzle. The system includes a top nozzle; a flow channel plate provided at a lower portion of the top nozzle and allowing coolant to pass therethrough; a guide hole provided in the flow channel plate; a lock insert in a hollow shape including an insertion part configured to be inserted into the guide hole; and a separation member configured to separate the lock insert from the guide hole. The circumference of the insertion part is variable in size, thereby being capable of being inserted into and separated from the guide hole. Accordingly, disassembly and reassembly of the top nozzle of the nuclear fuel assembly and the lock insert are simplified, thereby simplifying the process and reducing the number of processes. The system is effective for maintenance and repair of the nuclear fuel assembly.

A separating and coupling system of a nuclear fuel assembly top nozzle. The system includes a top nozzle; a flow channel plate provided at a lower portion of the top nozzle and allowing coolant to pass therethrough; a guide hole provided in the flow channel plate; a lock insert in a hollow shape including an insertion part configured to be inserted into the guide hole; and a separation member configured to separate the lock insert from the guide hole. The circumference of the insertion part is variable in size, thereby being capable of being inserted into and separated from the guide hole. Accordingly, disassembly and reassembly of the top nozzle of the nuclear fuel assembly and the lock insert are simplified, thereby simplifying the process and reducing the number of processes. The system is effective for maintenance and repair of the nuclear fuel assembly.

A spring apparatus in accordance with the disclosed and claimed concept is usable in a nuclear installation. In one embodiment, the spring apparatus includes a plurality of springs that are in a compressed state and that are compressively engaged with an upper core plate of a nuclear reactor when the reactor is in a cold condition. However, when the reactor is in a hot condition, a spring of the plurality of springs is in a free state wherein a free end of the spring is in an uncompressed state and is disengaged from the upper core plate. In another embodiment, the spring apparatus employs a support apparatus that is also in accordance with the disclosed and claimed concept and that includes one or more bumpers that engage the springs of a spring pack from the underside.

An improved retention system for retaining fuel rods in a fuel assembly is disclosed. The retention system includes a plurality of first engagement surfaces on the bottom nozzle of a fuel assembly. There is at least one engagement surface for each fuel rod. A second engagement surface is formed on the bottom end plug of each fuel rod. The first and second engagement surfaces are configured for engagement with each other for axially and laterally retaining each fuel rod within the fuel assembly. Debris deflectors may also be provided to deflect debris from coolant channels surrounding the fuel rods.

A nuclear reactor is configured with an intermediate coolant loop for transferring thermal energy from the reactor core for a useful purpose. The intermediate coolant loop includes a bypass flowpath with an air heat exchanger for dumping reactor heat during startup and/or shutdown. A fluidic diode along the bypass flowpath asymmetrically restricts flow across the bypass flowpath, inhibiting flow in a first flow direction during a full power operating condition and allowing a relatively uninhibited flow in a second direction during a startup and/or shut down low power operating condition.

An improved retention system for retaining fuel rods in a fuel assembly is disclosed. The retention system includes a plurality of first engagement surfaces on the bottom nozzle of a fuel assembly. There is at least one engagement surface for each fuel rod. A second engagement surface is formed on the bottom end plug of each fuel rod. The first and second engagement surfaces are configured for engagement with each other for axially and laterally retaining each fuel rod within the fuel assembly. Debris deflectors may also be provided to deflect debris from coolant channels surrounding the fuel rods.

Embodiments of a bottom nozzle of a nuclear fuel assembly provided with flow holes by utilizing a layered aircraft airfoil structure are provided. The bottom nozzle not only increases efficiency of filtering foreign substances by minimizing a size of the flow holes by constituting a shape of flow holes into cross stripes but also prevents coolant water flow velocity drop through prevention of coolant water pressure drop by constituting a lateral sectional shape of the grid frames constituting the cross stripes into an aircraft airfoil type.

The present invention relates to a top nozzle and a nuclear reactor in which an in-core instrument, which is supposed to be inserted through a top head of a nuclear reactor, is inserted through a guide pin for an upper core plate. In a nuclear reactor including guide pins for aligning a top nozzle for a nuclear fuel assembly with an upper core plate of a nuclear reactor, a guide hole (210) is axially formed through the guide pins (200) and in-core instruments (10) are inserted through the guide holes (210).

A core plate assembly for a boiling water reactor, and a method of performing work thereon are disclosed. The core plate assembly comprises a core plate having through-going apertures, and a beam structure comprising parallel first beams and parallel second beams being perpendicular to the first beams. The beams enclose a plurality of rectangular areas each enclosing four of the through-going apertures. Control rod guide tubes are aligned with a respective one of the through-going apertures. A transition pieces is received in a respective one of the control rod guide tubes, and has four passages for communicating with a respective fuel assembly. Each passage permits a coolant flow into the respective fuel assembly. A flow inlet is provided for the coolant into each passage. At least one of the flow inlets has a cross-sectional shape deviating from a circular shape.

A core plate assembly for a boiling water reactor, and a method of performing work thereon are disclosed. The core plate assembly comprises a core plate having through-going apertures, and a beam structure comprising parallel first beams and parallel second beams being perpendicular to the first beams. The beams enclose a plurality of rectangular areas each enclosing four of the through-going apertures. Control rod guide tubes are aligned with a respective one of the through-going apertures. A transition pieces is received in a respective one of the control rod guide tubes, and has four passages for communicating with a respective fuel assembly. Each passage permits a coolant flow into the respective fuel assembly. A flow inlet is provided for the coolant into each passage. At least one of the flow inlets has a cross-sectional shape deviating from a circular shape.