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. In one implementation, the fuel ducts have a first hollow structure having a first cross-sectional geometry and a second hollow structure positioned within the first hollow structure, the second hollow structure having a second cross-sectional geometry different from the first cross-sectional geometry.

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. In one implementation, the fuel ducts have a first hollow structure having a first cross-sectional geometry and a second hollow structure positioned within the first hollow structure, the second hollow structure having a second cross-sectional geometry different from the first cross-sectional geometry.

An assembly to be inserted into a nuclear reactor, such as a liquid sodium-cooled fast neutron reactor SFR, includes an assembly hollow body, of elongate shape along a longitudinal axis X. The wall of the hollow body includes at least one open-ended opening. The assembly also includes an assembly element inserted at least in part into the hollow body. The assembly element includes at least one flexible blade of which the free end is shaped into a clip-fastening hook collaborating in clip-fastening with the open-ended opening from inside the hollow body, so as to connect the assembly element to the hollow body. The assembly also includes at least one removable structure for locking the flexible blade clip-fastened into the open-ended opening. The removable locking structure makes it possible to prevent the flexible blade from flexing and thus lock the connection between the assembly element and the hollow body.

A method of operating a nuclear fission reactor, the reactor comprising a reactor core, and a coolant tank containing coolant, the reactor core comprising an array of fuel assemblies arranged in generally parallel rows, each fuel assembly comprising one or more fuel tubes containing fissile fuel. For each row of the array, one or more spent fuel assemblies are removed from the array at a second end of the row, fuel assemblies are moved along the row from a first end to the second end; and one or more fuel assemblies are introduced to the array at the first end of the row. Each fuel assembly remains within a single row while the fuel assembly is within the array. At least the fuel-filled portions of the fuel tubes of each fuel assembly are immersed in the coolant while the fuel assembly is within the array.

There are provided a continuous fiber-reinforced silicon carbide member and the like which allow sufficient improvement in a mechanical property and environmental resistance. The continuous fiber-reinforced silicon carbide member of an embodiment is a tubular shape and has a first composite material layer and a second composite material layer. In the first composite material layer, continuous fibers of silicon carbide are combined with a matrix of silicon carbide. In the second composite material layer, continuous fibers of carbon are combined with a matrix of silicon carbide. Then, the first composite material layer and the second composite material layer are stacked.

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.

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.

A fuel assembly for a pressure-tube nuclear reactor includes a fuel channel assembly. The fuel channel assembly has an outer conduit and an inner conduit received within the outer conduit. The conduits define an annular fuel bundle chamber for receiving a flow of a coolant in one direction. The inner conduit includes a central flow passage for receiving a flow of the coolant in an opposite direction. A fuel bundle positioned within the fuel bundle chamber consists of fuel elements arranged to form an inner ring surrounding the inner conduit, and an outer ring surrounding the inner ring. The coolant may be light water, and geometries of the fuel assembly may be selected so moderation by the volume of coolant promotes generally uniform power distribution in the fuel elements.

A fuel assembly for a pressure-tube nuclear reactor includes a fuel channel assembly. The fuel channel assembly has an outer conduit and an inner conduit received within the outer conduit. The conduits define an annular fuel bundle chamber for receiving a flow of a coolant in one direction. The inner conduit includes a central flow passage for receiving a flow of the coolant in an opposite direction. A fuel bundle positioned within the fuel bundle chamber consists of fuel elements arranged to form an inner ring surrounding the inner conduit, and an outer ring surrounding the inner ring. The coolant may be light water, and geometries of the fuel assembly may be selected so moderation by the volume of coolant promotes generally uniform power distribution in the fuel elements.

A fuel core for a nuclear reactor in one embodiment includes an upper internals unit and a lower internals unit comprising nuclear fuel assemblies. The assembled fuel core includes an upper core plate, a lower core plate, and a plurality of channel boxes extending therebetween. Each channel box comprises a plurality of outer walls and inner walls collectively defining a longitudinally-extending interior channels or cells having a transverse cross sectional area configured for holding no more than a single nuclear fuel assembly in some embodiments. A cylindrical reflector circumferentially surrounds channel boxes and is engaged at opposing ends by the upper and lower core plates. Adjacent cells within each channel box are formed on opposite sides of inner walls such that the cells are separated from each other by the inner walls alone without any water gaps therebetween which benefits neutronics for some small modular reactor designs.