Nuclear fuel assemblies include fuel elements that are sintered or cast into billets and co-extruded into a spiral, multi-lobed shape. The fuel kernel may be a metal alloy of metal fuel material and a metal-non-fuel material, or ceramic fuel in a metal non-fuel matrix. The fuel elements may use more highly enriched fissile material while maintaining safe operating temperatures. Such fuel elements according to one or more embodiments may provide more power at a safer, lower temperature than possible with conventional uranium oxide fuel rods. The fuel assembly may also include a plurality of conventional UO2 fuel rods, which may help the fuel assembly to conform to the space requirements of conventional nuclear reactors.

A nuclear reactor is constructed in sub-modules and super modules which are manufactured, packaged, and shipped to a construction site. At least some of the modules are packaged in suitable shielding containers or portions of containers, which may be steel. The modules are assembled on-site, and some of the modules remain within their respective shipping containers after assembly. One or more of the shipping containers may be used as concrete forms to support the pouring of concrete in between selected modules. The concrete may be used for structural support, shielding, or both.

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.

Nuclear fuel assemblies include fuel elements that are sintered or cast into billets and co-extruded into a spiral, multi-lobed shape. The fuel kernel may be a metal alloy of metal fuel material and a metal-non-fuel material, or ceramic fuel in a metal non-fuel matrix. The fuel elements may use more highly enriched fissile material while maintaining safe operating temperatures. Such fuel elements according to one or more embodiments may provide more power at a safer, lower temperature than possible with conventional uranium oxide fuel rods. The fuel assembly may also include a plurality of conventional UO.sub.2 fuel rods, which may help the fuel assembly to conform to the space requirements of conventional nuclear reactors.

Nuclear fuel assemblies include fuel elements that are sintered or cast into billets and co-extruded into a spiral, multi-lobed shape. The fuel kernel may be a metal alloy of metal fuel material and a metal-non-fuel material, or ceramic fuel in a metal non-fuel matrix. The fuel elements may use more highly enriched fissile material while maintaining safe operating temperatures. Such fuel elements according to one or more embodiments may provide more power at a safer, lower temperature than possible with conventional uranium oxide fuel rods. The fuel assembly may also include a plurality of conventional UO.sub.2 fuel rods, which may help the fuel assembly to conform to the space requirements of conventional nuclear reactors.

Fuel pellets and fuel pellet arrangements include thermally-conductive inserts within a fuel. The inserts have at least one portion of a thermally-conductive material, such as radially-extending fins. The inserts are configured to dissipate heat during use of the fuel pellets, while minimizing the amount of the total volume of the fuel pellet that is occupied by non-fissile material. The inclusion of heat-dissipating inserts enables the fuel pellets to exhibit improved thermal performance over the lifetime of the fuel, including a relatively low peak temperature and relatively low integrated average temperatures, while the minimal volume of the inserts avoids significantly decreasing the percent of enrichment achievable.

Fuel pellets and fuel pellet arrangements include thermally-conductive inserts within a fuel. The inserts have at least one portion of a thermally-conductive material, such as radially-extending fins. The inserts are configured to dissipate heat during use of the fuel pellets, while minimizing the amount of the total volume of the fuel pellet that is occupied by non-fissile material. The inclusion of heat-dissipating inserts enables the fuel pellets to exhibit improved thermal performance over the lifetime of the fuel, including a relatively low peak temperature and relatively low integrated average temperatures, while the minimal volume of the inserts avoids significantly decreasing the percent of enrichment achievable.

Disclosed embodiments include fuel assemblies, fuel element, cladding material, methods of making a fuel element, and methods of using same.

Engineered surfaces, such as surfaces having nano- and/or micro-scale features, may provide an enhanced flow boiling Critical Heat Flux (CHF) at ambient or higher pressures, which may enhance cooling. Enhancing flow boiling CHF may be desirable for nuclear reactors, where heat is generated by a heater such as a nuclear reactor core. Enhanced flow boiling CHF may provide larger safety margins and/or better economics of nuclear reactors, for example, because reactor power rating may be increased as cooling is enhanced.