Abstract: A core of a fast reactor having arranged therein at least one gas expansion module each of which being a hollow tubular structure with one end closed and the other end opened, the core including at least one neutron absorber that absorbs neutron, or, at least one neutron moderator that slows down neutron, arranged so as to adjoin the outer face, in the radial direction of the core, of the gas expansion module.

Abstract: There is provided a core of a fast reactor capable of achieving a sodium-cooled metal fuel fast reactor with high adaptability to a molten salt heat storage system, by flattening the output distribution and raising the coolant outlet temperature while suppressing deterioration of the core characteristic. A core of a fast factor is a fuel assembly obtained by densely disposing fuel rods within a wrapper tube, the fuel rod storing, within a cladding tube, hollow fuel in which Pu-enrichment is made to be a predetermined value within a range of 11 to 13 wt %. In the core of a fast factor, a first fuel assembly including a fuel rod with a large hollow diameter of the hollow fuel is loaded on the center side of the core, and a second fuel assembly including a fuel rod with a hollow diameter smaller than the hollow diameter of the hollow fuel of the first fuel assembly is loaded on the circumferential side of the core.

Abstract: A fast reactor core includes a sodium plenum installed above the fuel. The sodium plenum is capable of reducing a void reactivity. During operation, a tip of a primary control rod is inserted in a core fuel region, and a tip of a backup control rod is arranged near an upper end of the sodium plenum.

Abstract: The invention provides a core of a fast reactor including a sodium plenum installed above a core fuel, which is capable of reliably reducing a void reactivity, and an operation method thereof. The core of a fast reactor including the sodium plenum installed above the core fuel is characterized in that a tip of a primary control rod is inserted into a core fuel region, and a tip of a backup control rod is arranged above an upper end of the core fuel region for operation.