Fuel assembly

A fuel assembly for use in a core of a nuclear power reactor, the assembly comprising:

• a frame comprising a lower nozzle that is shaped and configured to mount to an internal core structure of the nuclear power reactor;
• and
• a plurality of elongated, extruded fuel elements supported by the frame, each of said plurality of fuel elements comprising
• a fuel kernel comprising fuel material disposed in a matrix of metal non-fuel material, the fuel material comprising fissile material, and
• a cladding surrounding the fuel kernel,
• wherein a moderator:
• fuel ratio in a region of the fuel elements is 2.4 or less,
• wherein the moderator:
• fuel ratio is an area ratio within a cross-section that is perpendicular to longitudinal axes of the plurality of fuel elements and extends through the plurality of fuel elements, the area ratio is a ratio is of:
• (1) a total area available for moderator flow for the plurality of fuel elements to (2) a total area of the fuel kernels of the plurality of fuel elements;
• and
• wherein a plurality of said plurality of fuel elements each has a spirally twisted, multi-lobed profile that defines a plurality of spiral ribs.