An improved retention and alignment system for nuclear fuel rods includes an upper nozzle plate and a lower nozzle plate, nuclear fuel rods, each having an upper end and a lower end and extending axially between the upper and lower nozzle plates, a first precision magnet incorporated onto the lower end of the fuel rod, and a plurality of second precision magnets incorporated onto the lower nozzle plate in positions confronting the first precision magnets on the fuel rods. Each first precision magnet has at least one of a magnetic north or south polarity and the second precision magnet has at least one of a magnetic south or north polarity opposite the polarity of the confronting first precision magnet to effect magnetic attraction between the confronting first and second precision magnets. Grids between the upper and lower nozzle plates form cells through which the fuel rods pass. Precision magnets of the same polarity may be positioned laterally along the fuel rods and grid walls in positions confronting each other to repel the fuel rods from the grid walls to maintain fuel rod alignment and prevent contact between the fuel rods and the grids.

An improved retention and alignment system for nuclear fuel rods includes an upper nozzle plate and a lower nozzle plate, nuclear fuel rods, each having an upper end and a lower end and extending axially between the upper and lower nozzle plates, a first precision magnet incorporated onto the lower end of the fuel rod, and a plurality of second precision magnets incorporated onto the lower nozzle plate in positions confronting the first precision magnets on the fuel rods. Each first precision magnet has at least one of a magnetic north or south polarity and the second precision magnet has at least one of a magnetic south or north polarity opposite the polarity of the confronting first precision magnet to effect magnetic attraction between the confronting first and second precision magnets. Grids between the upper and lower nozzle plates form cells through which the fuel rods pass. Precision magnets of the same polarity may be positioned laterally along the fuel rods and grid walls in positions confronting each other to repel the fuel rods from the grid walls to maintain fuel rod alignment and prevent contact between the fuel rods and the grids.

Disclosed embodiments include fuel ducts, fuel assemblies, methods of making fuel ducts, methods of making a fuel assembly, and methods of using a fuel assembly. An inner hollow structure has a first geometry and an outer hollow structure has a second geometry different from the first geometry. The first hollow structure is configured to expand in at least one dimension under stress and cause the first hollow structure to contact the second hollow structure. The second hollow structure distributes at least a portion of the stress of the first hollow structure.

Disclosed embodiments include fuel ducts, fuel assemblies, methods of making fuel ducts, methods of making a fuel assembly, and methods of using a fuel assembly. An inner hollow structure has a first geometry and an outer hollow structure has a second geometry different from the first geometry. The first hollow structure is configured to expand in at least one dimension under stress and cause the first hollow structure to contact the second hollow structure. The second hollow structure distributes at least a portion of the stress of the first hollow structure.

Methods of installing an external dashpot tube around a control rod guide tube in a nuclear reactor fuel assembly are disclosed herein. The nuclear reactor fuel assembly may include a top nozzle, a bottom nozzle, and a plurality of grids. The various methods may comprise inserting a guide tube into a skeleton of the nuclear reactor fuel assembly to a lower middle grid, the lower middle grid being second closest grid to the bottom nozzle of the plurality of grids. The various methods may also include installing an external dashpot tube over the guide tube after it has been inserted to the lower middle grid; inserting the guide tube with the installed external dashpot tube to the bottom nozzle; attaching the guide tube to the skeleton; and bulging the guide tube onto the external dashpot tube.

Methods of installing an external dashpot tube around a control rod guide tube in a nuclear reactor fuel assembly are disclosed herein. The nuclear reactor fuel assembly may include a top nozzle, a bottom nozzle, and a plurality of grids. The various methods may comprise inserting a guide tube into a skeleton of the nuclear reactor fuel assembly to a lower middle grid, the lower middle grid being second closest grid to the bottom nozzle of the plurality of grids. The various methods may also include installing an external dashpot tube over the guide tube after it has been inserted to the lower middle grid; inserting the guide tube with the installed external dashpot tube to the bottom nozzle; attaching the guide tube to the skeleton; and bulging the guide tube onto the external dashpot tube.

A nuclear fuel assembly for a boiling water reactor extends along a fuel assembly axis and includes a base including a lower tie plate, a head including an upper tie plate and a lift handle, a bundle of fuel rods extending axially between the lower tie plate and the upper tie plate, and a water channel extending within the bundle of fuel rods with axially connecting the base to the head such that the load of the base is transferred to the head via the water channel. The fuel assembly further comprises a tie rod extending between the base and the head. The tie rod is axially fixed to the base and connected to the head via a connection assembly comprising a stopping member configured to abut an abutting surface of the head for limiting a downward movement of the base relative to the head during lifting of the fuel assembly, in case of a breakage of the water channel.

Carbide-based fuel assembly includes outer structural member of ceramic matrix composite material, the interior surface of which is lined in higher temperature regions with an insulation layer of porous refractory ceramic material. A continuous insulation layer extends the length of the fuel assembly or separate insulation layer sections have a thickness increasing step-wise along the length of the fuel assembly from upper (inlet) section towards bottom (outlet) section. A fuel element positioned inward of the insulation layer and between support meshes has a fuel composition including HALEU and has the form of a plurality of individual elongated fuel bodies or one or more fuel monolith bodies containing coolant flow channels. Fuel assemblies are distributively arranged in a moderator block, with upper end of the outer structural member attached to an inlet for propellant and lower end of the outer structural member operatively interfaced with a nozzle forming a NTP reactor.

In a pressurized water reactor operation method, a fuel assembly including first fuel rods that operates for a preset first operation time and second fuel rods that operates for a second operation time longer than the first operation time is prepared. An operation schedule of a pressurized water reactor is created by mixing the first operation time of the first fuel rods and the second operation time of the second fuel rods. The pressurized water reactor operates by repeating the operation schedule.

In a pressurized water reactor operation method, a fuel assembly including first fuel rods that operates for a preset first operation time and second fuel rods that operates for a second operation time longer than the first operation time is prepared. An operation schedule of a pressurized water reactor is created by mixing the first operation time of the first fuel rods and the second operation time of the second fuel rods. The pressurized water reactor operates by repeating the operation schedule.