A nuclear fuel assembly having varying spacing between fuel rods is provided. The nuclear fuel assembly includes a bundle of fuel rods. The fuel rods are arranged in a first lattice with a non-uniform pitch between the fuel rods in the lowermost section of the fuel assembly and in a second lattice with a uniform pitch between the fuel rods in the uppermost section of the fuel assembly.

A nuclear fuel assembly having varying spacing between fuel rods is provided. The nuclear fuel assembly includes a bundle of fuel rods. The fuel rods are arranged in a first lattice with a non-uniform pitch between the fuel rods in the lowermost section of the fuel assembly and in a second lattice with a uniform pitch between the fuel rods in the uppermost section of the fuel assembly.

A method is provided for operating a nuclear reactor. The method includes operating the nuclear reactor for at least one plutonium equilibrium cycle during which the core contains plutonium-equilibrium nuclear fuel assemblies; subsequently, operating the reactor for transition cycles, at least some of the plutonium-equilibrium nuclear fuel assemblies being progressively replaced with transition nuclear fuel assemblies and then with uranium-equilibrium nuclear fuel assemblies; and then operating the nuclear reactor for at least one uranium equilibrium cycle.

A method is provided for operating a nuclear reactor. The method includes operating the nuclear reactor for at least one plutonium equilibrium cycle during which the core contains plutonium-equilibrium nuclear fuel assemblies; subsequently, operating the reactor for transition cycles, at least some of the plutonium-equilibrium nuclear fuel assemblies being progressively replaced with transition nuclear fuel assemblies and then with uranium-equilibrium nuclear fuel assemblies; and then operating the nuclear reactor for at least one uranium equilibrium cycle.

Disclosed is a nuclear fuel assembly suitable for a small modular reactor (SMR), wherein the nuclear fuel assembly includes a spacer grid having 1717 lattice cells, a plurality of fuel rods, each arranged within an associated lattice cell of the spacer grid, guide tubes, each arranged and fixed within an associated lattice cell of the spacer grid, and a top nozzle and a bottom nozzle fixed to an upper end and a lower end of each guide tube, respectively, wherein, with respect to a center cell of the spacer grid, each of eight guide tubes is arranged in an associated one of principal axis directions Ixx and Iyy, each of four guide tubes in an associated one of on-diagonal directions Ixy, and each of 16 guide tubes in an associated one of off-diagonal directions Ixxy and Ixyy.

Disclosed is a nuclear fuel assembly suitable for a small modular reactor (SMR), wherein the nuclear fuel assembly includes a spacer grid having 1717 lattice cells, a plurality of fuel rods, each arranged within an associated lattice cell of the spacer grid, guide tubes, each arranged and fixed within an associated lattice cell of the spacer grid, and a top nozzle and a bottom nozzle fixed to an upper end and a lower end of each guide tube, respectively, wherein, with respect to a center cell of the spacer grid, each of eight guide tubes is arranged in an associated one of principal axis directions Ixx and Iyy, each of four guide tubes in an associated one of on-diagonal directions Ixy, and each of 16 guide tubes in an associated one of off-diagonal directions Ixxy and Ixyy.

A nuclear reactor is designed to allow efficient packing of components within the reactor vessel, such as by offsetting the core, and/or vertically stacking components. The in-vessel storage system can be separate from the support cylinder and these components can be fabricated and shipped separately and coupled together at the construction site. Furthermore, the in-vessel storage system can be located adjacent to the core rather than being located circumferentially around it, and may also be located beneath the heat exchanger to further improve packing of components within the vessel. Through these, and other changes, the delicate components can be manufactured in a manufacturing facility, assembled, and shipped by commercial transportation options without exceeding the shipping envelope.

A nuclear reactor is designed to allow efficient packing of components within the reactor vessel, such as by offsetting the core, and/or vertically stacking components. The in-vessel storage system can be separate from the support cylinder and these components can be fabricated and shipped separately and coupled together at the construction site. Furthermore, the in-vessel storage system can be located adjacent to the core rather than being located circumferentially around it, and may also be located beneath the heat exchanger to further improve packing of components within the vessel. Through these, and other changes, the delicate components can be manufactured in a manufacturing facility, assembled, and shipped by commercial transportation options without exceeding the shipping envelope.

A nuclear fuel assembly is constructed with fuel assembly components that are wire wrapped and positioned in hexagonal rings within a fuel assembly duct. The fuel assembly components positioned in an outermost ring of the fuel assembly are wire wrapped with a pitch that is shorter than fuel assembly components positioned at an interior ring of the fuel assembly. The shorter pitch at the outer ring of the fuel assembly increases pressure drop of a coolant fluid at the edge and corner subchannels and thereby reduces the temperature gradient across the fuel assembly, which provides a higher output temperature of the nuclear reactor without substantially increasing peak temperature of the fuel cladding.

A nuclear fuel assembly is constructed with fuel assembly components that are wire wrapped and positioned in hexagonal rings within a fuel assembly duct. The fuel assembly components positioned in an outermost ring of the fuel assembly are wire wrapped with a pitch that is shorter than fuel assembly components positioned at an interior ring of the fuel assembly. The shorter pitch at the outer ring of the fuel assembly increases pressure drop of a coolant fluid at the edge and corner subchannels and thereby reduces the temperature gradient across the fuel assembly, which provides a higher output temperature of the nuclear reactor without substantially increasing peak temperature of the fuel cladding.